Picture of DIY Solar USB Charger - Altoids

I've been reading a bunch of blogs this fine Earth Day morning and have noticed that most of them are posting little write ups about green solar powered USB gadget chargers. They're all quite nice, but also quite expensive. I don't think I've seen any for less than $60, and I've not seen one that really suits my style.

Instructables has quite a few guides on how to make Solar USB Chargers, including the very well done guide on how to combine a Lady Ada Minty Boost circuit with a solar + lithium ion battery. Great, but a bit expensive to make and not a very simple project for the weekend DIY person.

Well luckily for us I know how to make one for under $20 that is better in nearly every way and also completely fits into an Altoids Tin. Covert style.

*** Update: I've since retired this kit. It's not held up over time very well. I've done an updated version called Solar USB Kit 2.0 and a more rugged version called Lithium Heavy Duty 2.0. If you're looking for something pre made, especially for camping or emergencies, you should try out one of our Folding USB Solar Cells. They're inexpensive and much much more powerful than what you'll find here.

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Step 1: What You Need

Picture of What You Need

USB Charging Circuit
Solar Panel 4V or greater
AA Battery Holder
AA Rechargeable Batteries
1N914 Diode
Altoid Tin (or whatever)

Soldering Iron
Tin Snips
Melt Glue Gun and Glue

Cost is less than $30. I can make one for under $10 when I buy parts in bulk. I have a kit available at my website which has everything you need to make this project. Also, if you're lazy, I do sell made versions in a variety of tin styles.

Nice build. Do you think if you placed a mirror in the lid you could use it to refract more light onto the solar panel?

Have a great day! :-)
JoshuaZimmerman (author)  Just4Fun Media1 month ago

Nah, it would be a super duper tight fit then, and you're better off just angling the panel at 45 degrees.

justForFun's idea [ i think ] was to have direct sun on the panel PLUS reflected light from a mirror to increase output LOL i think you misunderstood the idea trying to be conveyed. JustForFun did not mean for the mirror's light to be the only light applied to the solar panel. personally i thought it was a fantastic idea!!!!!! be well my friends

ThomasW2015 days ago

Could this be done using an 18650 battery? I am thinking this way I could set it in a window to charge all day and get a full charge or 2 to my cell phone off it.

have you thought about using super capacitors? they charge in seconds

JoshuaZimmerman (author)  Di Immortales27 days ago

Super caps are nice, but they hold very very very very very very very little amperage compared to even the cheapest AA. Sure, you could get giant soda bottle sized super caps (and spend hundreds of dollars per cap), but thats a bit above and beyond the scope of this. With current technology it's not financially or practically a good solution.

Azzurro1 month ago

nice and simple, i like it. a question: why don't you add a switch for solar charging? just because when there is no sunlight, the panel will slowly drain the batteries. better to open the circuit when you don't use the panel.

JoshuaZimmerman (author)  Azzurro1 month ago

Thats why there is a diode, to prevent drain. A lot of people add switches to this project, no reason why you couldn't. Just not necessary.

ah well okay a diode is a lot better of course :)
Elmercab2 months ago
I got this circuit board off an LG travel charger . Trying to figure out where I would put the negative and positive wires. I also wanted to add a switch I'm not sure if that would makes things more complicated. Wondering if any of you could help

those looks like a step-down? If they are they will work if you have a big solar panel to step the voltage down to 5vdc. You can get the battery powered usb charge at the Dollarama if you live in Ontario, they are like three bucks!

What the guy above me said. You have a STEP DOWN. You want a STEP UP. Two completely different things.

GaetanoM1 month ago

sorry, where have u find the usb charging circuit

JoshuaZimmerman (author)  GaetanoM1 month ago

My website,

BilalK21 month ago

Does this work with 18650 battery cells?

JoshuaZimmerman (author)  BilalK21 month ago

No, you'd need a charge controller in the mix. At the start of the write up I link to my Lithium Heavy Duty 2.0 project, which uses 18650 lithium battery cells. It's not too much different from this write up.

this instructable was posted in 2011, so this guy made it about 4 years ago.

Edbed1 month ago
These look awesome!
SeanC55 months ago

What was the problem with this kit? what batteries did you use?

JoshuaR8 SeanC55 months ago
aa batteries
SeanC5 JoshuaR85 months ago

Lithium aa?

Those would explode.

Lithium batteries are NOT rechargable. Lithium-Ion batteries are, but with special controlling hardware. He used Nickel Metal Hydride batteries (Ni-Mh), your standard rechargable ones.

use NiCads if you are not concerned about their self-discharge rate, they have a much higher mAh than their cousin NiMh.

JoshuaZimmerman (author)  waterlubber4 months ago

Rechargeable 1.2V AA batteries. Nothing special.

RodneyMori3 months ago

what happens when the battery is fully charged, nothing is connected but the panel is left out in the sun?

given the cell panel's low amperage, it should be safe to leave them in the sun once they are fully charged.

JoshuaZimmerman (author)  RodneyMori2 months ago

Nothing. It just kind of tops off. Thats why we keep the amperage low enough as to not harm the batteries.

SeanC55 months ago

What was the problem with this kit? what batteries did you use?

JoshuaZimmerman (author)  SeanC54 months ago

Not enough battery power, not enough solar power. Newer gadgets require more amperage and 2 AAs just doesn't do it any more.

will energizer rechargeable batteries work they are 1400 mAh

they would work, but it will give your device about a 10-15% charge before they drain.

So if i make this will it charge my galaxy s4? Because other comments arent specific

It would charge it but since the energy density of the two AA batteries aren't that high, it would charge your S4 to about 10-17% before the two AA batteries drain.

every time i plug my phone in it shuts off

whats wrong

Probably you've done something wrong with the connections and either there's a short circuit or the voltage is too high/low. Recehck all the connections and/or use another converter.

Will this work for the converter I took it out of a car charger

Nope, thats a STEP DOWN converter which drops the voltage, you need a STEP UP converter to boost the voltage high.

You COULD use it, but you'd need a super super super large solar panel to do so.

Could I use energizer rechargeable batteries they are 1400 mAh
spatuladle2 months ago

Awesome Instructable! I was wondering if this usb charger would work for this project. Please respond as soon as possible. Thanks!


Ok thanks. I will probably try it since I already have it but if it does not work I will probably buy yours. The website I bought it on I says that output current is 500ma. Also what does mA stand for?

JoshuaZimmerman (author)  spatuladle2 months ago

Yes and no. Yes, it can work. No, it probably won't. In my experiences those board put out too little amperage for most phones (these days) to charge with. Newer phones need AT LEAST 500ma to charge off of, and I think those boards do something around 300mA. My iPhone charges off the circuit I use but it won't charge off one of those boards. Shoot, giant Galaxy Phones want around 1A of power to charge off of and often have issues with the circuit I use. (And to get 1A you're better off with Lithium Batteries.)

I saw the exact same project on Kipkay's channel on YouTube.

Guess who he stole the idea from? Kipkay is notorious for poaching other people's projects off of many a DIY site.

My proof of such poaching? Well... I did post this project TWO FULL YEARS before he posted his video.

JeromeC33 months ago
Hi dude ima buy from ur store, cause im doing a charger for sci fair
Psych.3 months ago

Do you have a schematic I can use?

waterlubber4 months ago

I have a few questions:

-Does your step-up voltage device have a power draw when nothing is plugged in;

- How much voltage/amperage do I need to occasionally top off my phone;

-Should I use three batteries (3.6v) and your step-up device or a similar one to get a longer lasting charge? I understand that having more mAh adds capacity, but will 3 batteries in series also increase it because it has more watt-hours?

-Is there a schematic so I can build one of these step-up things myself?


If I am using a 10V solar panel, Do I need to use a voltage regulator?

Boss_man39176 months ago
Is the duracell battery pack a good circuit you can use
What all are components in dc to usb converter
daddyaggie8 months ago

I just ordered and received the DC to USB from your website. I followed the instructions and can get it to charge, but it keeps disconnecting. The phone says "charging" for a few seconds then stops. I can only get it to charge when I kind of push down on the USB cord. Tried with two of my converters and different cords, same results. Any thoughts?

l3w1sw00d8 months ago

Could I use this as the USB Charging Circuit?

l3w1sw00d8 months ago

Could I use this as the USB Charging Circuit?

TiagoV10 months ago

How do you control the battery charge to it don´t overcharge?

6V 80mA Solar Cell

3 AA Holder

3 Rechargeable AA Batteries @ 2600mAh




Shrink Tubing

Laser Cut Enclosure w/ Screws

There is no component to control it!

JoshuaZimmerman (author)  TiagoV8 months ago

You don't need any battery control for AAs as long as you don't throw a lot of amperage at them. Really, for those kinds of larger projects you'd be using a Lithium Battery or Lead Acid in which case you'd need a controller of some kind. Thats why I love AAs. They're so darn simple.

issa.kawar8 months ago

I decided to build a series circuit with a transformer or resistor, a solar panel(6V), and a USB panel (no batteries) in a small plastic box. Am I going in the right direction?

edrisamiry9 months ago
hi can someone please tell me where can I find USB circuit or how can I make a USB circuit is my email address plzzzzzzzz me great Instructable ;)

HI, great tutorial! I will try it for sure. Solar charger will be great for long trips in mountains or wherever else :) But, is it possible to connect LCD display to show how much power we have got or it will be too difficult?

Thanks in advance for answer :)

I will upload some picture when I did it!

TiagoV10 months ago

How do you control the battery charge to it don´t overcharge?

6V 80mA Solar Cell

3 AA Holder

3 Rechargeable AA Batteries @ 2600mAh




Shrink Tubing

Laser Cut Enclosure w/ Screws

There is no component to control it!

Mr_Rep10 months ago

so...i need to see if this works, since he said that 6v is inneficent. i gutted a cheap cigarette lighter usb charger, and plan on linking up a 4x AA battery holder for power storage. i want to use a 6v .5W solar cell to receive power from the sun. Is this an unsmart way of going about this? if so, any suggestions? also, say i took 4 normal AA's and stuck them in to charge my device. what level charge will i get?

Mr_Rep Mr_Rep10 months ago

also, i am considering using a 7.2 volt Ni-Mh rechargable battery I yanked of a rather large RC helicopter. how well will this handle? more efficent than 2 or 4 AA's?


electro182 years ago
I bought a 5v solar panel and connected a diode to it....... and connected it to my phone. It was charging well so is there any need of the DC-USB converter?
JoshuaZimmerman (author)  electro1812 months ago

I agree. If you want to do direct solar you'd need something akin to 9V at 500mA (or more) and a 5V regulator. The issue is that solar depends on how much sun you're getting. In full sunlight you're probably getting 5V. In anything (and I mean anything) less than 100% full sun you're under 5V. You always want to do 1.5X the solar voltage of what you need, so that even in less sunlight you're getting your minimum.

Would "minty boost" (by adafruit ) serve the purpose ?

Please forgive me, I am NOT trying to be a smart aleck....but to use only a solar panel would be like only eating bologna sandwiches. Your solar panel may not give 5V 100% of the time (e.g. cloudy day, shady area, etc). The IC on the DC-USB converter ensures you will always be pushing 5V. The other items help ensure the quality of the voltage is that of a prime rib. lol
Well, thanks ! but i am not able to find any sort of DC-USB converter ,so is there any way to make it ?
Could you show us how you connected it to your phone?
brburrous made it!1 year ago

Cool looking and easy to make, but not to effective.

JoshuaZimmerman (author)  brburrous12 months ago

Nope, thus why I recommend using lithium batteries if you want to make a daily charger. This is more a "My First Solar Project" or "Student" charger. Cheap, easy to make, and works. Just doesn't work super well due to the AAs and small solar cell.

Animag7711 year ago

I made one very similar to this. I put two 2V solar solar panels connected in series with a diod and attached them to the lid. Wired them to the battery holder and then from there it goes to my 2V-5V DC 1.2A USB converter. The problem I am having is after it charges my phone up about 20% the batteries have dropped down to about 0.7V which is completely un-usable.

What did I do wrong? Why are my batteries losing voltage?

JoshuaZimmerman (author)  Animag77112 months ago

They're losing voltage because you're using up the "power" inside them. Think of Voltage like water pressure and amperage like the amount of water stored up. If you have a big barrel of water and punch a hole in the bottom you get a strong jet stream coming out. As the amount of water inside decreases the amount of pressure also decreases. Same thing with a battery.

This happens with all batteries. Thus why going with Lithium Batteries over AAs is preferable when building a charger.

GrayAlien1 year ago

I might be wrong but if you cut a square into the top of the altoids can you could hot glue the solar panel facing up inside. Then you would not have to worry about dragging along the solar panel. Also, this would place it in a tight package, and make it easier to carry around in your pocket or purse.

JoshuaZimmerman (author)  GrayAlien12 months ago

You most certainly could, but then you'd lose the fun of it being an Altoids tin. (And really, I highly recommend NOT using an Altoids tin.)

Thus why I switched to a wooden box in my 2.0 update. Makes things far easier.

Quick question. I was able to salvage a DC to USB board from a car charger. I actually left the LED on the board for ease of checking if power was flowing or not. I can not seem to get it to light up unless my power source is 9v or greater. In your tutorial your using 2.4 volts of output to charge a device via batteries. I am running a 1watt 6volt panel and it wouldn't light it up either although I was only getting about 3.5 volts due to cloudy weather. Any thoughts?

I tried that at first too... It doesn't work. The USB converting from car chargers are designed to dump 12V DC down to 5V DC, what the op is using is designed to take 2-5V DC and bump it up to 5V DC. You need a different USB converter.

JoshuaZimmerman (author)  Animag77112 months ago

Bingo. It's easier to bump up than bump down.

Merahu1 year ago

The update above says that Joshua Zimmerman has retired this charger as unreliable. I have one, plus one without a USB port, produced by BrownDogGadgets, that I have been using to charge four AA batteries for my camera. Yesterday I picked up the tin with the USB port and the metal was hot at one end of the batteries, very hot. It was in the shade and cool surroundings, not in direct sun. I pulled one battery out and set it aside to cool so I could toss it in the garbage. Then I noticed (smell, not visual) acrid fumes. I was using ordinary rechargables, not lithium batteries. (Rayovac.) Since lithium batteries can burst into flames when exposed to high heat, I would be very cautious about using such products with lithium batteries. Given that mine developed a serious problem without lithium batteries, I will be cautious with any use. I am glad I was present when the problem was developing.

One possible contributing factor may be that I have regularly used this on the dash of my car. They have certainly had a chance to get overheated, and perhaps the wiring or components themselves are capable of melting under those conditions, though they were not in the sun at the time I picked them up and found the one hot. I am very pro solar and very pro do-it-yourself. There is some safety risk here, and I hope it will be further clarified in the future, and fixes presented for safe function in sometimes hot conditions.

Thank you to everyone who advances clean energy such as solar, and to those who improve safety as well.

JoshuaZimmerman (author)  Merahu12 months ago

Two things.

1) Metal tins are bad for electrical projects, exactly what you felt. Shorts causing uncontrolled power usage. Plus you can't fit more than 2AAs and a small solar cell inside.

2) Bigger gadgets mean bigger batteries. In the past three years the size of phone and mp3 player batteries have more than doubled. Using 2 AAs isn't going to cut it. Using a Lithium Battery provides a larger power output in a small size. Plus you can charge up lithium batteries faster than AAs. Much much faster.

In my new USB charger kit I use 3 AAs (which helps out quite a bit) and a wooden box. Since I switched to the wooden box the number of emails from customers (having problems) has dropped dramatically. I love Altoids tins, but they do cause many issues.

mkovtchega1 year ago

Do you think I can replace the Dc to USB thingy with a female end of a USB extension cord?


mmcl265541 year ago

Couldn't you use an LM317 as a current limiter and then higher voltage of 4 or 5 NiMh cells won't matter?

hi i had done everything ou said and even bought the equipment but my phone still cannot charge the red led light is on i am outside with batteries but it still wont work??

You're essentially charging two devices, the external backup battery and your phone, at the same time. This instructable explains what kind of charge controller and power is required to perform this task and give constant phone charge even under non-ideal conditions:

Could you fit a triple AA battery holder in here?

jody341 year ago
Where did you get the USB charging circuit?
You can use a voltage regulator. I made a similar one (currently making the instructable). When charging a device via USB then the voltage will always be 5.0 volts. Check my page.
Hey there! This is an excellent looking project that I plan on completing soon! I do have one question: what is the best way to go about harvesting the usb charging circuit from a usb charger?

Thanks so much!
Rip that puppy open.

Find that that turns 2 or 3 AAs into 5V USB.

(Not a wall one. Bad idea.)
Can I use an AC to USB converter? I ripped apart a kindle charger cord; would this work?
Did you ever find out? I'm wondering the same thing, I have an MP4 charger cord
TheArtVark1 year ago
If I understand correctly, if I leave the batteries in and place it in the sun it will use BOTH the solar panel out and the batteries ate the same time if I want to charge anything, right? No need to take out the batteries? When the it's less sunny the batteries drain faster, when it's scorching the batteries drain slower?

Thanks for the instructions!
The temperature of the air doesn't matter as much as you might think. The panel will output more mA when it is 60 degrees and sunny...compared to 110 degrees and mostly cloudy. But yes, leave the batteries in.
Ah, thanks for your answer. No hassle charging then, just stick it out in the sun. With 'warm' I actually meant 'sunny', but good to know that temperature is not an issue either :-)
No problem...but as another user mentioned I would add a small circuit to prevent overcharging the batteries.
Schmidty162 years ago
I was wondering if I could use another usb connector if so can I fond 1 at RadioShack if so what is it called and if I can where can I find one in stuff ling around my house
This has a "USB Type A" for charging electronic devices, you shouldn't need anything else because it's the industry standard. To use anything else would be over-complicating things or risking damage to your equipment. Your best bet is to buy the kit: and add a solar panel to it.
I don't have access to your store
xJValx2 years ago
is it somehow possible for the charger itself after it is complete, to pull juice out of the phone that its supposed to be charging?
There should be diodes in the device and on the USB-DC converter to prevent that from happening.
Snakera1 year ago
Do you know if this will charge the iphone 5?
The iPhone5 and iPad4 both require more wattage than their predecessors (that's why Apple changed the plug). I'm not exactly sure of the iPhone5 power requirements, but my iPad4 requires 12W of power (12W/5V=2.4A). Thus I cannot charge it in my vehicles, laptop/desktop computers (500mA max), etc. If the components of the USB-DC converter can handle it, then yes. But, you'd have to check the appropriate datasheets. I would send an e-mail to AdaFruit and ask her.
rsantos241 year ago
I have a 6 VSolar panel wired to 2 rechargeable batteries, and the battery wires and solar panel wires are soldered to the USB connector. The USB connector is lit up so there is some power going to it but the device is not charging.
One of the IC's could be bad or there could be a bad solder joint.
rweiss1 year ago
I am wondering, if we're using some internal batteries (ie. AA in your case), that are wired directly to the solar cell, are they at risk of overcharging if the device is left in the sun?
Thanks for the great tutorial.
Electronics should never be "left out" in the sun long enough to overcharge the batteries and you should be able to find a solar panel that will fit in the tin. However..."stuff" happens! So I do plan to incorporate a protection circuit in mine.
cnephew1 year ago
When you say "You can rip one out of a cheap USB charger" what exactly do you mean by that?
Some wall warts and car chargers have a USB connection on them. I assume that is what he's referring to. I'm going to build my own USB-DC converter using AdaFruits Instructable. It calls for a 22uH inductor and I did find a 20uH inductor in a Motorola RAZR charger.
jayc1601 year ago
I tried making with with two recharchable 9v batteries and im not making any headway does it only work with the AA's ? Or do I need to add something in the line to make it work ? im also going to use a plastic pelican case instead of an altoids can just seems a little more rugged.
Pelican cases are awesome! If you are using 9V batteries you need to add a LM7805 circuit or you risk frying your electronics. But you will be wasting a lot of power and therefore, money. To know more, read AdaFruit's Instructable:!---Small-battery-powered-USB-charger/step2/The-Process-Come-up-with-an-idea/
Fashiondez2 years ago
Hey, does anyone know what to do when you hook everything up, and it is working/shows that the Iphone is plugged in, but it doesn't charge it? Should I cut all the wires and re attach them?
Ever solve this? Same problem.
gowtham771 year ago
If I rip out a USB Charging Circuit from a cheap charger would it work. I mean the transformer in the circuit is designed to reduce 230volts into 5 volts required for output. But when the input is just 6 volts would it work
henryd1061 year ago
Just how many devices at once could this support?
RallyDriver2 years ago
Is the USB constantly putting out charge? Because a switch would be needed to turn on and off the output, right?
Schmidty162 years ago
can I find another dc to usb converter that is cheap on RadioShack that will work on my iPod or is there a cheaper 1 that I can find in an old device if there is 1 at RadioShack what would it be called?
Schmidty162 years ago
cool thx I have a few questions
Houghie722 years ago
I have got the USB charging circuit from a USB car charger that turns 12v into 5v. Does this mean in order to charge, I have to have 12v going into the USB charging circuit?
scientist442 years ago
On the brown dog gadgets website I found a 6V solar cell, and a 1.5V cell which would be best? I don't completely understand the voltage situation.
ccc22 years ago
I made this, and I am able to charge my simple keypad phone, but I can't seem to charge my ipod touch. I keep getting the message, "charging not supported with this accessory." I am guessing that this is because my ipod needs more power to be charged, but 'm not sure. Any ideas on how I could fix this?
ttawi2 years ago
Hi~ u said "just connect all the red wires with all the black wires", but u r actually connect the red wires to the red wires. i dont know what to do. i think i should connect the postive wire from the solar panel to the postive wire from battery, right?
yoji2 years ago
hello, i have a question. how can we know if the battery is fully charged? and is it possible that battery may explode due to overcharging? how to prevent it?

lg902212 years ago
i have a question im new to this but i was wondering can you use the usb circuit found in car chargers? because those are 1.99 compared to the 8.99 dc to usb circuits. i know it takes 12v and drops it to 5v volts but if it receives 6v wont it just drop it to 5v? not really into the whole elctronic thing. or where can i buy cheap dc usb
rev5122 years ago
Hey so it started charging for a few seconds and then my phone said something about my phone is not comparable with this accessory and now it won't charge!?!?
Sorry if this has already been asked, but will this one work with an iPhone 4s?
bulletbkr2 years ago
just a note, if you use hot glue to secure and insulate the connections and wires on the back of you solar cells, be sure to put something under them when you put them in the sun to charge. I now have a ruined dashmat in my truck because the hotglue melted into the fibers as I was charging my batteries. Boo for hot glue. I thought it had a much higher melting point than that.
BillMetrey2 years ago
Hello, I tried to access y our website several times with no success. Are you still accepting requests? I would like to buy at least one of your solar chargers. Thank you!

Bill Metrey
kldtia2 years ago
I attempted this project. I have one question I'm charging a samsung Gs2 phone and I pluged it in. It says it's charging but when I look at the phone it seems like my battery is losing charge. What did I do wrong.

budhaztm2 years ago
Would one be able to use lets say a (or a couple) li-po battery for rc airplanes and have a dc-dc converter?
tboultwood12 years ago
Hello there, me and a friend have a project idea. We are planning to use a 12v battery of arrays of AA rechargeable batteries, also using a 12v panel. Will we need protection against overcharge?
Gigean2 years ago
How do I know if I should use a 4V Solar Panel or something else? Also, where would I find a solar panel, a battery holder, and the diode? This may be the first Instructable project I tackle, so sorry for so many questions
jpman2 years ago
f i use one of those Ipod charger usb thingos would it work??? i really dont have money to buy the minty boost usb circuit i have one of this usb charger things for ipods and phones so yea Email me @
kenkenken442 years ago
hi this project is cool so i made 1 with a car charger and it seems to not work any help?
b.t.w im using a 6v solar panel
valiantX2 years ago
In regards to batteries, I think people should try buying some of these new japanese 'water charging', that's right, batteries instead. Excuse my language here, but these batteries can be charged by any form of non-acidic water including urine, sewage water, creek water, your sweat, etc.

Check out the site info right here:

A cheaper site to buy from:
pertamax112 years ago
how much current can be drawn from this dc-usb converter?
agqy28012 years ago
Can rechargeable batteries above 2000mAh - 3000 mAh be used? I managed to find one claiming to be 3500mAh. Plus, the battery claims to be AA Lithium Ion and not NiMh, will that affect anything?
Fashiondez2 years ago
Okay, I finally began putting together the usb solar charger. I got all the supplies from your web, except for the usb circuit board.... I got that out of a cheap usb car charger. Anyways, when I got the solar cells, i wasn't sure what the soldering tabs were and found out the hard way that, without them, it is not really that possible to connect the wires to the glass of the solar cell lol. Anyways, I needed to attach a diode to the positive wire, so i had detached it from the solder tab, and ended up detaching the soldering tab itself (not knowing it was it wasn't in the picture in the instructions and this was my first time). I am wondering if there is any way to recover my supplies now that two of the tabs are gone.
I hooked up two cells in a series and connected it to two AAs and then those to the circuit board, even tho I am not 100% sure that i am hooking them to the correct place, because it does not have a + or -, so I am just trying to use common sense and I picked a place :). Currently the charger is not working, so i am trying to evaluate. Hope this was understandable.
JoshuaZimmerman (author)  Fashiondez2 years ago
Car charger won't work. A car charger takes 12V from your car battery and lowers it to 5.

The circuit I uses takes 2-3V (such as 2 AAs) and boosts it up to 5.

Two completely different circuits.

I emailed you about all this as well, so check your inbox.
Can you email me the circuit diagram of the DC usb charger? Having a bit trouble with it :) .
yes, thank you. I am pretty sure I got all of yours! I had written you via this and e-mail at first. I don't know if i received a reply to my last one though.
paintphone2 years ago
What was your USB charging circuit originally from?
JoshuaZimmerman (author)  paintphone2 years ago
Surplus from a commercial charger.
I would also like a schematic. It looks simple enough to cobble together.
Quite simple.
So give it to us!
johnestan2 years ago
Could you please tell me what the advantage of having a separate battery charging circuit is. Many of the other instructables use lithium batteries and require a LiPo charger circuit. Is this not needed when using NiMh batteries, or are you just saving money. Is it worse for the batteries in the long run?
JoshuaZimmerman (author)  johnestan2 years ago
Lithium batteries need a charge controller because if their very specific power requirements. NiMh batteries do not.

It's a connivence and price thing when you choose batteries. Lithium are better, but are more expensive and are more work to wire up. NiMh are cheap and easy to use, but are not as effective.

skeys22 years ago
I salvaged a USB thingie from a DC-USB and am using that. It looks just like the one you have pictured; however, I can't seem to fing the negative or positive connections. It would be amazing if I got a response... Thanks!!!
JoshuaZimmerman (author)  skeys22 years ago
They should be labeled. Or marked on the board.

Or you could just take a 2AA battery pack and just touch the wires to the board. If it works, you have things right. If not, switch the positive and negative spots and try again. (Guess and check)
Diggyx172 years ago
Will the solar panel charge the batteries when its not in use???
JoshuaZimmerman (author)  Diggyx172 years ago
Thats the idea.
Diggyx172 years ago
I'm not understanding. how do you know if its just charging from the panel and not the batteries? and when you say "test it" do you mean its going to run off the solar panel and not the batteries?
JoshuaZimmerman (author)  Diggyx172 years ago
Well you can take the batteries out of the setup, then plug in a gadget, then stick it in the sun. If your gadget starts to charge, awesome.

Or you can just stick some batteries in and then plug a gadget in.

Though with this small of a solar cell a lot of USB stuff won't charge directly from the solar cell, they need the batteries in there as well to augment things. (Which is why I have more heavy duty versions of this charger setup with more powerful solar cells.)
ctschoepe2 years ago
Will this work with the newer ipods/iphones? I heard some of them require special circuitry. Also, will the AA batteries recharge from the solar panel or no? And more batteries = more current = faster charging, correct?
JoshuaZimmerman (author)  ctschoepe2 years ago
It works with my iPhone 4. The AAs do in fact recharge from the solar cell (thats the point). More batteries would give you a higher capacity and make things charge faster.

Though to be honest the best solution is 3 AAs in a series to give you 3.6V, but then you'd need about 5V coming in to charge.
Acura282 years ago
I just built one of these with your USB Charging Circuit, but it won't charge my iPhone 4s. I'm using 4 AA 1.2V/2500mAh batteries, should I use 2 instead? I am also using a 6V solar panel with 84mA will this work? My last question is in what position should the USB Charging Circuit be when charing? Your USB Charging Circuit has three positions right? Thanks! Can't wait until I can get mine to work!
JoshuaZimmerman (author)  Acura282 years ago
Your setup sounds fine. How are your batteries wired up? (Which could make a huge difference)

The switch should be all the way back. Towards the positive and negative terminals in the "rear" of the board.

When in doubt, try using regular AAs to see if it works. Often the rechargeables will be "low" and thus charging won't happen.

You can email me directly off the site. It's a lot easier to get ahold of me that way.
bruechel873 years ago
I wired up the usb charger to some batteries to see if it would power my droid and two AA's wouldn't do it. I needed four AA's wired in series so 6v maybe a bit less. (I used non-rechargable) My question is does the solar panel need to be wired in and in sunlight as well as the batteries giving off their 2.4v for this to work? Or do I just have a usb charger that needs more juice than the ones you use? Thanks for the help. Also, I desoldered the led but that didn't seem to do anything power wise.
JoshuaZimmerman (author)  bruechel873 years ago
The USB circuit should boost the voltage up to 5V from the 2.4-3V the batteries would give you. No need to add anything else.

I have no idea what to say unless I was to take a look at the charger you used and how it was wired up.
Thanks. I tested it and it wouldn't charge without 5v comming in. If I bought one from your website it would work with 2.4v? Also, do you by chance know how many volts those little garden light solar panels give off.
JoshuaZimmerman (author)  bruechel872 years ago
If you used 4 AAs you'd have 6V. Which defeats the purpose of the boosting circuit entirely. Its designed to work with power between 2- 3V, and boost it up to 5V.

Little garden lights generally, from what I've found, put off between 2 - 3V of power. Which seems about right as they charge up a single AAA battery inside (AA if you're lucky). The big problem with them is their current flow is usually really low.
creatox2 years ago
Saw a couple folks comment that 2 AA batteries wouldnt cut it.. be warned that not all NiMH batteries are created equal. Some of them (particular the R$ variety) are only 1.2 volts.. i found on this build that 4 1.2v AAs in series were needed to power the USB circuit sufficiently to charge any device.
JoshuaZimmerman (author)  creatox2 years ago
Actually all rechargeable AAs are 1.2 - 1.3V.

Wiring up two in a series (like using a 2 AA battery holder would do) will give you enough to work the USB boosting circuit just fine.

You can always wire in 3 or 4 in a series, that works even better. Though 3 would really be all you'd need, a 4th one would be overkill.

Some customers have wired up two of the 2 AA battery packs together, which does a nice job of boosting capacity while also maintaining a higher voltage longer. Though that makes for a tight Altoids tin.
Great project. Do you think that this would work for the dc to usb converter?
JoshuaZimmerman (author)  schoonovermr2 years ago
Yes and No. I've played around with one of those before and it does not work with Apple gear. If you have non-Apple gear it should work fine.

(It is probably the same one I played around with, but I know there are like 3 or 4 variations of it on eBay and I've not tested them all yet.)
rats... do you know of one on ebay (pretty cheap preferably) that would work with apple products?
JoshuaZimmerman (author)  schoonovermr2 years ago
Not off the top of my head. It seems that these days you need to take apart a decent USB charger to find a decent boosting circuit. (Thus why I'm happy I found a surplus supplier to sell me the circuits I use on my website.)
franny23dmt2 years ago
and this sucker .... 11000 mAh battery pack included!!
JoshuaZimmerman (author)  franny23dmt2 years ago
I also like how you just joined instructables and the only two comments you've made are to link to eBay products. This makes me suspect that you're just trying to throw down some old school comment SPAM.
franny23dmt2 years ago
erm , not trying to troll but
JoshuaZimmerman (author)  franny23dmt2 years ago
Yeah, you're pretty much trolling.

This is instructables. For people who want to build their own things. Many projects on instructables you can buy similar things in stores, but people come here to learn and create. Not to find cheap deals.

There are lots of great solar USB chargers on the market. Some are quality and some, like the one you linked to, are cheaply built and function cheaply. I've taken apart enough of them to know that there is a big difference between a $10 charger and a $50 charger.
Tuur2 years ago
Hi Joshua, I tried building this using a cheap emergency charger for not two but three AA batteries as a base (looks like I have the same brand you use).
With three rechargables it charges my Android phone up to the point that the batteries reach abour 3.7 V, then the red LED (I kept it on) qives a few quick flashes and (although output through USB still measures 5.15 V) charging stops. Do you have any idea what could be going on?
JoshuaZimmerman (author)  Tuur2 years ago
Sorry, I really have no idea.
mde santis13 years ago
iknow not important but i have the same soldering iron
latte873 years ago
I have two questions for you:
1) What does the white "useless" LED on the USB Charging Circuit really do?
2) Is there a easy way to add a LED that will light when the solar panel is charging the batteries?

Thank you, love your educational tutorials :)
JoshuaZimmerman (author)  latte873 years ago
1) LED badly lights things. It's a horrible flashlight.
2) You could always add in an LED in parallel, but you'd be wasting valuable amps. You'd want a switch or something to turn that on and off. A blue LED would be good as it's higher voltage. (Though this is a poor indicator overall.)
hi mm this project works with an ipod touch, because i saw the other day that you have another post but specifically on ipod/iphone.would this one work well? thanks
JoshuaZimmerman (author)  steelierdruido3 years ago
The other post uses a circuit that has an iPhone cable attached. Back when I originally did these the USB circuit wouldn't charge Apple gear, the USB circuits I have now work just fine. I guess it depends on whether or not you want a dedicated iPod cable or a generic USB port.
just a quick question, as you stated above the usb circuits you use now work for Apple products but on your website it still says that the usb circuit wont charge apple gear. Has the website just not been updated or is this still the case?
DoctorDv3 years ago
Hey thanks for the great post! I was wondering if a transistor would be necessay to the completion of this project so you don't overcharge your batteries? Thanks again!
JoshuaZimmerman (author)  DoctorDv3 years ago
Nah, we're doing simple "trickle" charging with NiMh batteries. They'll top off, but not overcharge. Thus why we use NiMh batteries. (Also because they're cheap and easy to get.)
JeenJogi3 years ago
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swimfan24893 years ago
Great instructable! This has inspired me :)

I am looking to build a slightly different version of this instructable, but with supercapacitors instead, to make this "super-green". Do you know if it would be possible to just use supercapacitors to completely replace the batteries? Even if it would only work while in the sun, that would be fine with me... Any help would be great!
If you're worried about how "green" the components are, the NiMH battery is not the #1 candidate for concern: Unlike lead acid and NiCd cells, NiMH cells do not contain toxic heavy metals that need to be kept out of incinerators.

The biggest environmental impact will be the energy used to make the refined silicon for the solar cell, most likely from coal burnt in China. Switching to super caps would not resolve that.
JoshuaZimmerman (author)  swimfan24893 years ago
I don't see why not. You'd have to have solar panels to provide power, but I don't see why not.

The only downside is that super caps cost a lot of money compared to just using some AAs. Plus because of how little power this thing uses a set of AA batteries would last a very very long time.
Will this work for Ipod touch 2nd Generation and ipod touch 4?
if you get the right MintyBoost it may:

Apple has apparently changed and rechanged their load protocal to make it difficult to charge. Adafruit has tried to keep up with it.
JoshuaZimmerman (author)  JoshThebBoss3 years ago
No idea.
What wires am i supposed to solder the USB cirquit ?
There is also the issue that supercaps do not hold as many watt-hours of power as batteries do and they have no internal resistance. So, in addition to putting a 1+ watt dissipation resistor across the caps, a flagrant waste of power, but a necessary element, you would not get nearly as much charge out of them.
OT43 years ago
I have a couple questions an di would love it if the author would please clarify. First i assume that when the phone is not connected to the usb the solar pannels will charge the battery. Second how will i prevent overcharging the batteries. Thanks.
OT4 OT43 years ago
Also, i want to use this on my android and on my ipod. How will i wire this for apple products? Again, i would realy appreciate it if the author would clarify. Thanks
JoshuaZimmerman (author)  OT43 years ago
Actually the newer circuits I use in my kits work for both regular USB items and Apple gear.

You also don't need to worry about overcharging. We're not throwing enough current at the NiMh AA batteries to overcharge them.
MyTopFan3 years ago
Could I use 4 1.2v rechargeables instead of just 2? Or would that be too much for the USB?
If it makes a difference, I'm using the same USB from the same emergency charger as you did.

Thanks in advanced.
JoshuaZimmerman (author)  MyTopFan3 years ago
Most certainly. Just wire them up in 2 sets of 2. In parallel. You'd double the capacity.
Snowbox1173 years ago
Will there be enough power to completely charge a smart phone?
JoshuaZimmerman (author)  Snowbox1173 years ago
Depends on the battery inside of a smart phone. Plus if you're getting sun at the same time.
OT43 years ago
Awesome idea. I will sooo do this. One question though. Shouldnt we use a tip31 transister to make sure the voltage doesnt get too great. Or maby itwas a resistor. Well i mean wichever one will stop the voltage from getting too great.
OT4 OT43 years ago
Also. Does the battery holder have to be especialy for rechargable batteries or just a plain one
Fashiondez3 years ago
Which is more powerful for usb charging: 5V 1A Solar Panel 5W DC Power Supply or a 5.5V 320mA Solar cell?
zkus Fashiondez3 years ago
The wattage is what defines power, and (i believe) how fast it will charge. your dc power supply is 5 watts, while your 5.5v 320 mA solar cell will do about 1.76 watts (which you can find using's_law). So your solar cell will be much less powerful.

I dont know if this curcuit would handle the 5watt DC power source (beyond my EE knowledge)
Fashiondez zkus3 years ago
Also, I was looking around and i was directed to the 5w solar cell i mentioned, and it is directly attached already to a usb port. He says it is good. But the disadvantage in that is, since it bypasses using batteries, it will not save the charge, right...because it is just a solar cell? So that means that the device I am charging has to stay out with my solar cell while it charges, whereas if i have a solar cell running to batteries, I can charge them up and then charge my device inside, right? If you are not sure, that is okay too.
JoshuaZimmerman (author)  Fashiondez3 years ago
Fashiondez zkus3 years ago
Thank you. Appreciate it!
Alexjoy3 years ago
Do you know if excessive heat damages the solar cell? And if so, how hot does it have to get for that to happen?

Also, I know heat will damage the batteries for sure, however, again I'm not sure how hot exactly they can get before it damages them.

My situation is that I live in Phoenix Arizona and I really want to make one of these, however, I don't know how long I will be able to leave the charger in the sun without it getting damaged due to excessive heat. It's really the solar cell that I am concerned about as I am sure I could find a way to keep the batteries fairly cool in the shade while the solar cell is in the sun.

Do you have any suggestions?
JoshuaZimmerman (author)  Alexjoy3 years ago
The solar cells are rather solid bits of technology. Unless you're baking them you shouldn't have an issues.

But yes, the batteries may be a different issue all together. Keeping them cool might not be a bad idea.

Try this out. External solar cell, long wire, jack and plug setup.
gatorgirl163 years ago
Would it be OK to use a wall usb charger to get the circuit? I was able to find the positive and negative points. I connect the battery back and the light turns on but nothing charges. Is it because I left the light on?

Help? :/
twright83 years ago
Can I still play my games on my iPod while it is being charged with the solar USB charger or will my iPod died before it can be charged?

Does it create enough power to do this?

I would like to use the 4v solar panel or do I need a larger panel?
JoshuaZimmerman (author)  twright83 years ago
It'll charge while you're playing, as long as the batteries have juice inside the charger.

The solar cell isn't powerful enough to power an iPod all by itself.

A larger cell, one outputting over 200mA, will probably be enough.
Do you sell a solar cell of that size on your web site?
JoshuaZimmerman (author)  twright83 years ago
I sell several. There is a nice big 5.5V 320mA solar cell which is a beast, and a 6V 240mA solar cell which has a good kick to it. Both work well.

I just posted a new Instructable on how to make a Solar Charger using a big solar cell along with a Jack and Plug setup. Might be up your alley.
coloskibum3 years ago
Actually original poster has a good question. I have a 2w 6v solar panel and bought a handful of bulk .9v-6v to 5v USB circuits like you have. The way you have this wired I'm trying to think through if this will push 8.4 or just 6 v to the usb circuit if I'm in the sun and have fully charged batteries (I'm a noob but go with me here)...I guess I'll just wire the panel and fully charged batteries and see what the good old meter says before I wire it to the USB...
JoshuaZimmerman (author)  coloskibum3 years ago
It depends on how well your circuit handles the extra voltage. The voltage regulating chip on it may be just fine, or it may burn down your house. I'd most certainly do some testing before hooking up any gadgets.

(Though I'm guessing you're going to be ok.)
granolabar3 years ago
How would I wire the diode if I were to solder two 4V panels together in parallel? I'm trying to get a setup with two sets of 2 rechargeable batteries, and two solar panels.
JoshuaZimmerman (author)  granolabar3 years ago
Put the diode between the solar positive input and the battery pack.

Two solar positives together, then the diode off of them.
chreaus3 years ago
hey, i tried to scan through all the other comments on here but i couldnt find anything about efficeincy loss... any idea how to calculate for this build?
hpfev4 years ago
Will it work charging an ipad? Cause i think iphone and ipas have different amp setting for chargin. Or maybe it doesnt matter?
JoshuaZimmerman (author)  hpfev4 years ago
As a general rule I have been saying that this circuit doesn't work with iPod, iPhones, and iPads. I tested the circuit out on my iPhone 4 and it didn't work.

Well I recently tried with a new batch of these circuits and my iPhone 4 charged perfectly. Big surprise to me.

If you're going to be using this with only an iPad or iPhone you might want to use a different circuit. I have one that has a retractable iPhone/ iPod/ iPad cable on it, as opposed to a USB port. Handy.
If you have any left can you let me know, I would like to get my hands on one of those.
do you have any left of the batch that worked with the iphone4? If so, I would like to get a few of those, thanks! just let me know
swimfan24893 years ago
Since your saying keep the input current at about 10% of the rated battery capacity, is that 10% for just one battery? Or is that for the total capacity if batteries are wired up in parallel?

For example, if i wire 2 packs of batteries, each cell with 1.2V and 2000mA together in parallel to make a combined total of 2.4V and 4000mA, should i buy a solar panel with a current output of 200mA or 400mA for best results?


JoshuaZimmerman (author)  swimfan24893 years ago
2 AAs in a holder are in a series and will come out to be 2.4V at 2,000mAh

Parallel = 1.2V at 4,000mah
Series = 2.4 at 2,000mah

10% of total capacity.

I've gone over 10% before, it really depends on your batteries and how trusting you are of them.

So in your case you'd want to use two battery packs, with a total of 4 batteries. Giving you 2.4V at 4,000mAh.

Go with the bigger cell. You'll never ever reach your max power for solar anyways.
I figure i might as well ask too.. I'm going for a bigger setup and want to use a 12v that puts out 100ma to charge 8 AA rechargeables. (that's 9.6V, i haven't bought said batteries yet so I'm not certain what mah i'll have)

will the 12v be sufficient? ... too much? will the 100ma allow me to charge the batteries in a reasonable amount of time given that it's solar trickle charge we're working with?
JoshuaZimmerman (author)  Matieland883 years ago
From what I've read you should always go half again as much voltage as needed.

Meaning a 12V system should have at least 18V of solar panel in it.

So if you're doing 9.6V you should have at least 14-15V of power.
a number of sources have mentioned needing 1.4-1.6V/cell which calculates to 11.2-12.8V for the 8 cells.

It sounds like I can't very well blow anything up with 12v so I'm going to proceed with wiring the mock up and testing on the next sunny day.

also I might add, the panel only puts out 100ma, and that for 2500mah batteries would take forever so i've got two panels. Should suffice. The idea is that i can strap the device atop my backpack while hiking, trickle charging as i do, and then flip open to reveal both panels when the opportunity presents itself.
budabob073 years ago
Don't you mean 2000-3000 mAh of capacity, not 2000-3000 ma of current?
If I wanted to do this but use 1 or 2 of the cheap solar yard lights from Lowes as donor parts, what would I need to modify? Do those have the right diode in them between the solar panel and the battery pack? Or is that irrelevant due to the USB circuit?

The ones I bought for the yard claim to be 4x bright. What would be the proper way to determine if I need 1 or 2 solar cells of these? Just test output of the panel with a voltmeter?
JoshuaZimmerman (author)  MorNiLachnan3 years ago
The only thing you'd be taking out of the garden light would be the solar cell. (You could use the batteries, but they usually are low capacity and not worth their weight.)

You'd still need to get all the other parts. AA holder, 2 AAs, diode, wires, charging circuit.

Plus you should really use a multimeter to figure out what the voltage of your solar cells is. You need a combination that is greater the 3V. The bigger the better.
lespaul553 years ago
I am completely new to this experience of making USB chargers. I have an ipod touch 2nd gen and an iphone 4th gen. I've read online that it takes 5 volts to charge these devices although I'm now reading that this 5 volt charger will not charge newer apple products. Why won't it charge newer apple products and what do I need to change to get it to charge newer apple products?
JoshuaZimmerman (author)  lespaul553 years ago
Newer Apple stuff does charge off 5V, but the gadgets check the data tabs on the USB to see what it's plugged into. Now seeing as no other product on the planet does this nearly every USB charger isn't compatible as the data tabs are not used. (Why would you throw perfectly good power at the data tabs when you'r just charging something up?)

Long story short you just need to find a newer charger that has this problem fixed.
T-Prime3 years ago
Will this diode work for an 80mA panel?
JoshuaZimmerman (author)  T-Prime3 years ago
Sure. I've used higher amp solar cells before.
RelientOwl3 years ago
Amazing Project! Thanks for posting!
Question: Do you know what kind of capacitors are on that circuit...just curious.

-Relient Owl
JoshuaZimmerman (author)  RelientOwl3 years ago
Umm... just a couple of little 10uF (I believe, don't quote me on this one) electro caps. Nothing too fancy.

The caps just help the power flow more smoothly in the circuit. They're not for storing large amounts of power. That is why we have batteries in the circuit. Though some people have instead used some massive capacitors instead. They're nice, but cost an arm and a leg.
What wires am i supposed to solder the USB cirquit ?
pigione3 years ago
Hello Joshua. I have some questions for you.
I don't understand two things:
1) i have a lithium batthery 3.7V 2800mAh with a internal circuit for the protection: can i use it in your circuit? I need an battery charching circuit for it? Can I disassemble something to use?
2) if i put in parallel a simple AA ni-mh battery, the 10% of their maximum limit for charging it from a panel will double it? So i have a solar panel that give me 700mA, so if i put in parallel a 2200mah battery to arrive at 6600mAh, is it sufficient?
Thanks a lot.
JoshuaZimmerman (author)  pigione3 years ago
Either stick with NiMh batteries or your lithium ion battery pack. Don't mix and match batteries.

You would need a small changing circuit to handle your Li-ion pack. You can pick them up most anywhere. For instance I know has some that work well in similar circuits. Otherwise ebay is your friend.

I wouldn't try and take a li-ion charger out of something else. Just buy a small circuit from somewhere. has directions on how to hook up a li-ion pack to a very similar circuit to the one I use in my project. Seriously check out her site.
Thanks a lot Joshua. I've understood. I have found something in

JoshuaZimmerman (author)  pigione3 years ago
No problem. I do what I can. Adafruit is a solid site with really good stuff. I've been known to buy things off there from time to time.
spete6533 years ago
Ok, so I'm trying to figure out what I'm going to need for this. In your opinion, what is going to be better to get, an emergency charger, or a wall charger?

Also, I saw a video on youtube and this guy used 4 AAA's. Which is better, AA's or AAA's?
JoshuaZimmerman (author)  spete6533 years ago
AAs hold a higher capacity, use them.

Wall chargers step down voltage, we need to step it up. This means you need a little emergency USB charger that uses 2 AA batteries. It'll boost the voltage up to the right levels.
Ok, thanks for the reply, I'll be working on it soon. I got my diode and switch yesterday at radio shack and my solar panel is on order!
One more question, as far as the diode goes, I bought a 5.1 volt diode, is that too big? I saw that you said you only want a trickle charge going to the batteries, hence the smaller diode? I'm afraid of over charging, I don't know anything about diodes so before I start, I want to know that the parts I put in are correct.
T-Prime3 years ago
Hi, having some small problems. I purchased and built the MintyBoost Circuit, which works wonderfully. And I purchased a 4V 60mA Solar Cell from you, but my 2000mA rechargeable AA batteries don't seem to be charging very well. Any idea why that could be?
JoshuaZimmerman (author)  T-Prime3 years ago
2000mA divided by 60mA gives you the total hours needed to charge your batteries to 100%.

(Assuming they're completely dead, though you'll always need about 10% more time than needed to charge up NiMh in my experiences.)

You'll also need full sunlight. If it's a bit cloudy then charging will take longer.

If you want fast charging (like very fast) you're going to need a bigger solar cell or several small solar cell. Solar is great, but you have to know it's limitations.
Okay. so to fully charge a pair of AA Batteries, each rated at 2000mA with my 60mA solar cell takes ~33 hrs of direct sunlight (you don't add the Amperage of the batteries do you?). And if I wire in a second cell parrallel to the first I got 120mA for a total of ~17 hrs correct?
JoshuaZimmerman (author)  T-Prime3 years ago
Correct. Or you could also buy a bigger panel and use that instead. You have many options.

Plus your batteries will never be 100% dead (well, usually) so you'll never need to charge them up all the way.
Thanks. I have ordered bigger cells for my next project, but I have the other 60mA on hand.
JoshuaZimmerman (author)  T-Prime3 years ago
You can never have too many solar cells around. They're always handy.

Shoot, I have a few hundred in my basement and I want more...
Mr. walrus3 years ago
so i want to make this but not sure about super capacitors but if i did use one, would this be acceptable?
JoshuaZimmerman (author)  Mr. walrus3 years ago
That should work. Though batteries would be a bit better option. Better capacity for your money.
cherylcaleb3 years ago
Can it work on a DS?
I bet you could,
Tabula Rasa3 years ago
do you know if this would work for my android? it is a Samsung Intercept 3G
JoshuaZimmerman (author)  Tabula Rasa3 years ago
Probably. A lot of people have either bought or made these. They seem to work for the vast majority of things out there. (Minus iPods and iPhone. Well, usually. Most of the circuits I get in these days do in fact charge up iPods and iPhone, but I'm never sure how reliable they are.)
JJman213 years ago
Like other comments, I was wondering if we could get any specs on your "DC to USB converter circuit,"? I have been looking on ebay and have found simple and cheap car chargers as well as wall chargers, but these deal with 12V Dc and ~110/240V AC. These both step to a 5V output, but I know these are not the circuits you are referring to. Could you help us out a bit and maybe give us a link or source to a possible circuit or charger we could pick up without bulk buying from Hong Kong? I think this idea is awesome and I want to build one but this part of the design has me hung up at the moment and would appreciate any input into this. Thanks!
JJman21 JJman213 years ago
I may have found something that will work for under $3. This seems just what I need, let me know what you think:

Just ebay "emergency USB charger" and I believe any of those work that are portable and take two AA batteries.
JoshuaZimmerman (author)  JJman213 years ago
Yup, those can work. Just be careful, I've gotten some bad units from various China eBay supplies before.

I also have the circuits on my website as well if you need them.
kanito1073 years ago
so an AC to USB circuit would not work?
JoshuaZimmerman (author)  kanito1073 years ago
Correct. Would not work. Different type of circuit completely.
achraf523 years ago
Hi, there are pretty much USB chargers for less than $10 and slim and stylish design but works like your device and have circuit protection for who want to use it really .
mlambrose4 years ago
im trying to build this with a 12v dc circuit board i ripped out of a usb car charger.

im assuming that the batteries allow the usb to charge even if there is no sunlight (like the minty boost) and the the solar cell merely charges the batteries it works fine when i hook it up to a 9v (i do no have the solar cells yet) but when i try to use 2 AA batteries it doesnt work.

if you cannot tell i am a complete noob. the only thing that i can thing of (and it may totally be laughable) is that since the 12v dc is higher than the 5v ubs there is some mechanism on the board that lowers the voltage. that or im just a moron and i put the thing together wrong.
The circuit you are attempting to use is different than the one specified here. The circuit in this project steps UP the voltage from two AA's to reach 5 volts for USB. The circuit you are attempting to use is designed to step DOWN the voltage from the 12 volts of a car battery. In order to make this circuit work, you need to use at least a 9v battery. Consequently you will need a lot more solar cell capacity in order to charge this larger battery (i.e. at least 9v worth of solar.)
JoshuaZimmerman (author)  jwhitehouse3 years ago
Super correct. Stepping up with solar is a low easier, and cheaper, than trying to step down.

Smaller cells, less batteries, and less overall weight.
can anyone help?
gwbonline3 years ago
Do you mean the total capacity of all batteries together when you say not to throw more than 10% of their capacity at one time? And when I want to use for example six batteries, do I need a solar panel with more volts and an other charging circuit?
gwbonline3 years ago
You mentioned that I can't use a 12V car charger for this project. On I can buy several usb chargers. But what is the right one? I mean, an usb car charger is dc to usb. Can you point me to the right device?
stubbs3214 years ago
if i am using a 5.5v 100mA 0.55W solar panel what is the best way to make it so it wont output more than 4v

could i use a diode with a large voltage drop?


A diode with a small voltage drop then a resistor?

also the batteries wont stop charging will they? will the batteries become damaged if device is left in the sun for too long?
JoshuaZimmerman (author)  stubbs3214 years ago
You need a panel that is AT LEAST 4V. The 5.5 at 100mA is a great little panel. You should be fine.

Use a 1N914 diode.

No resistor needed.

The batteries will be fine once they top off. You don't need to worry about over charging them.
I have a question in regards to any solar panel with greater than 5 volts. I built the Mintyboost kit from Adafruit and they warn that you should never put any battery larger than 5V in this charger because it could damage the circuit. That said, your solar panel is linked directly to the circuit. Thus, any solar panel greater than 5V will go directly into the circuit and potentially damage it. Does that seem right to you?
JoshuaZimmerman (author)  cmcwilliams3 years ago
That does seems right.

I do say to use one greater than 4V, otherwise you'll not be able to get the batteries charged up.

Now a battery vs a solar cell... The thing with solar cells is that it's rating is the "optimal" rating. Noon on a sunny day. Are you going to be getting that at all times? Probably not.

If you're really really worried you could always put in a a nice SPDT switch. Flip it one way to charge just the batteries, flip it the other was when you want to power the circuit. That would make things very safe and allow you to use any solar cell you'd like. (Just don't overload the battery.)
It's actually not quite right. Adafruit warns that you should not put more than 5v into their circuitry as one of those disclaimers that companies always give you so you can't blame them for freak accidents. I have personally built identical circuitry to Adafruit's version several times using several different boost topologies to experiment (for the record, theirs is not the best possible arrangement) and I found that the one thing in common no matter what chip used was that they all would adjust voltage upward or downward as needed. Granted, adjusting downward from above 5v, the circuitry becomes less efficient, but it still works perfectly safely. I once put 30v into one of these things and all it did was get a little warm (with 500mA load on the output mind you). I would not recommend the switch approach as it would not allow you to use the solar cell while charging a device, the time when you would most wish to use it. Also it would ruin the sleekness and stylishness of the final product.
JoshuaZimmerman (author)  Thermiter3 years ago
Some good info there.

Something to keep in mind is that unless you plug a USB device into the circuit, it doesn't become active. The USB device completes the circuit, which is why the circuit doesn't suck power when charging.

What is happening is that the batteries and solar cell are making a circuit, which is charging up the batteries.

Long story short you shouldn't worry. Just watch your charger and test it out. That and don't put it on top of any piles of oily rags in the middle of a fireworks store. Just in case.
Quite right, long story short you shouldn't worry. There are more complex explanations for what's actually going on here, but for now, I can guarantee that 5.5v will in no way harm the mintyboost circuitry. If it does, PM me and I will personally build you a new one :)
cbgthree3 years ago
How long does it take to fully charge the batteries under optimal conditions? Let's say you have two batteries @ 2400 mAh each, and the 4v/60mA solar cell.
use ohm's law and do a little math :)
Since the batteries will be wired in series, that will double the voltage, but keep the capacity the same @ 2400mAh. So under ideal conditions, 2400mA*h / 60mA = 40 hours to charge both batteries.

Correct me if im wrong?
NeMewSys3 years ago
Dont you need a circuit to manage the batteries charge state? Wont this "directly connect the solar panel to the batteries' ends" harm the batteries? What if they are already charged? I dont know nothing about NiMh.
Im thinking of using a lion polymer btw, not sure yet.
"USB Charging Circuit" is what you need. It's on the list.
Im talking about NiMh batteries, not USB charging ones (that are made of li-ion).
Im asking if we can charge NiMh safely just like that "directly connect the solar panel to the batteries' (NiMh) ends".
NeMewSys3 years ago
Hi, could you show us the schematic of your DC to USB converter?
This one:!prettyPhoto[494]/0/
matria8013 years ago
Very happy that there are more recent comments, can anyone confirm that this'll work with the 4th gen iTouch?
JoshuaZimmerman (author)  matria8013 years ago
It depends on what circuit you're using. Some of the new cheap USB chargers work perfectly fine with iPod Touches and iPhones, others still do not.

Just make sure the circuit you're using is made for use with new Apple products. They have special requirements.
twalsh23 years ago
could u post some examples of "cheap chargers". that would be helpful. thanks
WhiteTech3 years ago
I love this tut!

I just have a few questions
the 1N914 Diode. Ive been to many stores. Every 1N914 is different. What one should I use?

And I see on you're site it doesn't charge New apple devices. Do you think there's a way to make a universal one? IE: not just Apple or just USB
JoshuaZimmerman (author)  WhiteTech3 years ago
1N914 is a type of diode, they should all be the same. I originally got mine from Radio Shack. If you're trying to find a random diode, one with a low voltage drop is best.

Oddly the circuit I've been ordering in now seems to work with newer Apple stuff. Or at least with my iPhone 4. You could always just fine an "Emergency USB Charger" for cheap online and see if it works with your Apple stuff, and then gut it.
Great thanks! We have an actual electronics store for this kind of stuff. I should probably head there next and see what they have

For the Emergency USB Charger, that's a great idea, You get all the components just need to modify it for Solar.
shneddie3 years ago
Hi, thanks for the tutorial, I think I'll be giving this a go. Only one problem, I can't seem to find a DC to USB converter, can you please tell me where I would be able to buy one, or what you get them in (Or is it a trade secret?) ;)

Thanks Edd.
Oh, I forgot to mention, I'm in the UK...
madmanmoe644 years ago
I was planning to replace the 2 AA's with a 3.7v Li-Ion battery (needs to be flat).

I know that you need a complex charging curve to charge Li-Ion batteries but I was going to use a charging IC for that.

Apart from that is there any reason this might not work?

Solar Cells > Charging IC > Li-Ion > USB Converter > Phone (etc.)
Apparently Li-Ion batteries don't like being trickle charged, so are they right out?

Ni-Mh are comparatively expensive and lower in capacity, and thicker :(
JoshuaZimmerman (author)  madmanmoe644 years ago
NiMh are found everywhere and quite cheap. Plus you can find NiMh batteries in various shapes and sizes if you look around.
didooo4 years ago
acampbell54 years ago
Is there a way to use a 12v to USB car charger circuit and adapt it for use in this project?
JoshuaZimmerman (author)  acampbell54 years ago
No. You'd have to use 12V worth of batteries, which would mean you'd have to use 10-12 batteries.

You need a circuit that boosts the voltage, not drop it.
Alright, so what did you get your solar cell from? I'm not following this at all. Haha.
JoshuaZimmerman (author)  Bakenshake094 years ago

You can also take one out of a solar garden light, provided it is at least a 4V cell.

I get mine in bulk from China.
Gotcha. Thanks, man.
Wareagle4 years ago
Hello and thank you for making an excellent instructable. I wanted to clarify a few things before I decided to buy the kit off of your website. You say how you need at least a 4v cell to charge it. But I thought that USB was 5v? Does the cell charge the batteries and the batteries charge the device? And does the 7v 60ma cell charge the batteries faster than the 4.5v 80ma cell? If I needed to, could I replace the rechargeable batteries with normal alkaline batteries to charge my device? Thank you very much :D
JoshuaZimmerman (author)  Wareagle4 years ago
Yes, the solar cells charge the batteries and then the batteries charge the device. Most USB devices need a much higher current (mA) than what solar cells can provide.

The circuit boosts the voltage up to the 5V that USB requires. Which is how we can get away with using two AA batteries.

The speed at which the batteries recharge is controlled by the amperage, or in this case the mA. The higher the mA the faster the battery charges. Now on the flip side you need a certain voltage level, in this case we need at least 3V power to charge the batteries. Now we user a higher rated solar cell because sun is a tricky thing. A 4V cell gets 4V in the best conditions only, usually less. The higher rated your cell is for voltage the less sun it needs to get that minimum level that you need.

Overall the best all around cell is the 4.5V. The reason most people get the 4V is that the 4V fits into an Altoids tin. The other cells do not.

You can replace the batteries at any time. In a pinch you could use alkaline batteries, just don't try and solar charge them. Doing so will cause the alkalines to leak or to explode. In fact if you were to make a habit of that I'd suggest that you put a switch on the inside to cut off the flow of power from the solar cell to the batteries. Just to play it safe.
ericb14 years ago
thanks for this great instructable. While I like using rechargeable AA batteries because they're cheap and plentiful, I was wondering if it's possible to add a charging circuit that has a usb and/or DC charging input, so that I could charge it with a DC wall plug before leaving, then use solar power and the batteries when I have to?

The USB/DC LiPo chargers (like this one: can do that, but I didn't know if there was something else I could incorporate into this to give it that ability? I guess a USB charging circuit that would have USB/DC input on it that works with AA battery chargers.

thanks again!
JoshuaZimmerman (author)  ericb14 years ago
You might as well just get a regular store bought AC to USB plug. You can buy really small ones these days.

No point making what you can buy for next to nothing.
Thanks for the reply, but I meant a dc charger to quick charge the batteries. From household power as opposed to solar only

I was under the impression that the usbport was power-out only and wouldnt change the batteries directly.

Thanks again
JoshuaZimmerman (author)  ericb14 years ago
Yes, the USB is power out.

A customer of mine added a power plug to his so he could plug in a wall adaptor. That was he could charge up from the wall.

Though to be honest a much much easier solution would be to take the AA batteries out, put them in a "smart" wall charger and then put them back in. From what I've seen you can get AA chargers that will charge stuff up in 2-3 hours.
stubbs3214 years ago
hey i am currently in the process of making one of these, will be ok if i use a 5.5V 100mA PV cell to charge 2 AA NiMH 1800mAh.
will the batteries be damaged with a voltage that high?

if i were to use 2 sets of AA in parallel would this dissipate the current across the two sets so i would have 5.5V at 50mA for each set of AA's?
JoshuaZimmerman (author)  stubbs3214 years ago
Your PV cell is ok for what you're doing.

Two sets of AA in parallel would only increase the capacity. So instead of 1 pair at 1800 mah you'd have 2 pairs at 3600 mah.

So think of it as 100 ma over 3600 mah of battery.

I'd personally add the extra batteries. You can never go wrong that way.
blueblobbs4 years ago
where did you get the solar panel?
JoshuaZimmerman (author)  blueblobbs4 years ago
Ebay or try my website
on your website do you have a solar altoids usb charger that can also charge an iphone
JoshuaZimmerman (author)  blueblobbs4 years ago
It seems my most recent batch of USB circuits work with iPhones, which hasn't been the case before. I make no promises though as these are surplus chips that I get from the most sketchy parts of China.
could you try to save one for me i might order one
and how do you sign up for your webstite
Mmm... pie
JoshuaZimmerman (author)  fryingsquirrel4 years ago
Solar pie.
If I'm not mistaken, those cheap solar walkway or landscape lights you can get at walmart or harbor freight tools (around $5 each) have good potential for this project. They each contain a PV cell, 2 AA rechargeable batteries (the smaller ones might have AAAs) and a charging circuit with diode. As an added bonus, you get a photo-sensitive switch and LED plus reflector.
JoshuaZimmerman (author)  fryingsquirrel4 years ago
I found the cheapest in my area was at Menards. They had $0.99 ones. The solar cells were 2.5V and easy to remove. Plus you got a 300 mah AAA battery and dark detecting circuit.

A lot of it depends on how easy they are to remove... I've broken a few solar cells due to them being too tough to get out of the solar light.

Also, you need to be aware of the current on these cells. They may have a high voltage, but probably have a low current. Not a big deal for the lights as they have small batteries, but we want to change up larger capacity batteries. This is why getting a solar cell with a higher current (miliamp) really helps things out.

Thank you for your instructable, but whcih part do I nedd of my ''cheap usb charger from ebay''?

Thank you, pic below ;)
Looks good, you probably don't need to change anything.

Just hook up the batteries, solar cell, and diode.
Probably all of it. I'm not familiar with with the one you've shown, but you can probably just leave it as it is.
devilmaycry4 years ago
can you please show the circuit from underneath please. thanks
Ive browsed this fantastic DIY start to finish and i have a question regarding the DC-USB converter you use in this project.

It appears as though the circuit you used is one from a prior device and not one you mocked up and soldered yourself. I am curious what device you pulled the circuit from as i am interested in making once of these badboys myself. Since im relatively new to DIY electronics i want to follow your walkthrough as thoroughly as possible.

Thanks for your time and contributions to the greater good.
ericb14 years ago
Thanks for posting this! This will be my first attempt at something like this. Was wondering if a 4-AA battery holder can be used instead of a 2? I know it will fit inside an altoids case, or a bigger case if I use something different, but I didn't know if the solar panel would just take too long to charge 4, etc?

JoshuaZimmerman (author)  ericb14 years ago
No, not a 4 holder.

A 4 holder would put the voltage at 6 volts for regular batteries and 4.8 volts for rechargeable batteries. The capacity would stay the same. Plus the 4V panel wouldn't be able to charge 4.8V worth of batteries.

What would be better would be to wire in two sets of 2 AA holders in parallel. Then your capacity would double but the voltage would remain the same. The downside would be that it would take longer to charge up. You could then always ad another solar cell and put the entire thing in a bigger case.
awesome, thanks! For the solar cell, would something like this work?

It says it's 4.5 volts, and it's 2 3/8" square.

Also, how do I wire the 2 AA holders in parallel? Just meaning solder 1 to the other, then the next one to the circuit?

JoshuaZimmerman (author)  ericb14 years ago
Yes, that solar cell is really nice. Though it won't fit into an Altoids tin. You can always strap it on the outside. Also, I sell it for less than half the price on my own website...

What you just described is wiring in a series. To wire it in parallel you would hook both positives from the battery packs to the positive intake of the circuit, and both negatives from the battery packs to the negative of the circuit.
Ok, thanks. Is there a bigger solar panel? I'm less concerned with fitting it in an altoids tin, and I may just put it in a clear pelican box or something similiar.

Like a 4"x4" solar panel?
Engi4 years ago
Is the DC-USB converter entirely necessary? If you gut a female USB cable, you'll get a positive/negative lead along with data+/data- leads. Couldn't you just solder the pos/neg wires to the battery holder?

Also, awesome instructions. I found a great place where you can get 2V solar panels off of garden lights for $1/piece, so I'll definitely be trying a lot more of your creations out.
JoshuaZimmerman (author)  Engi4 years ago
Yes and no.

In this project yes, because we need 5V worth of power to charge up USB devices. The circuit boosts the 2.4Vs from the rechargeable batteries to 5V, as well as regulating the current.

In other projects no. You could always use a whole bunch of batteries to achieve a voltage greater than 5V, and then use a voltage limiter to keep it at 5V. You'd also need a bigger solar cell to charge up the batteries at a higher voltage.

The circuit just makes things a whole lot easier and a whole more compact. You can use a smaller number of batteries and a smaller solar cell to charge them.
Woody714 years ago
As a complete neophyte to solar I was wondering if a set up like this could work with "bigger" solar cells. For example if I added one (or more) 7V 60ma solar cells would the internal components change? Would it require add'l diodes per each solar cell? Thanks!
JoshuaZimmerman (author)  Woody714 years ago
Depends, are you wanting a higher voltage or higher current?

You could hook up several 7V @ 60ma in parallel would increase the speed of charging the batteries. You would need a diode for each solar cell you used (or wire it up to all use the same diode).
Not sure. I'd like to be able to charge a greater number of batteries in a reasonable amount of time and/or (possibly) use it to maintain a charge on my gps/cell while it's in use. BTW, love your 'ibles!
JoshuaZimmerman (author)  Woody714 years ago

Since we're only "trickle" charging the batteries we have to be careful not to overload them. They can only take in, at the most, 10% of their capacity. So if your batteries are rated at 2000 mah you can only throw 200 ma at them. Otherwise they'll die. Thus the problem with such a simple circuit.

If you want to charge up stuff faster you may wish to use a more complicated setup of a lithium ion battery and a lithium ion battery charging circuit. Then you could use a much more powerful solar cell (say one with 500 ma of power coming down) and get a faster charge going on. There are a couple really good instructables out there on how to do that if you're interested.

I like taking the more simple approach because the less complicated it is, the less can go wrong. Especially when you're making things yourself.
LOL! Gotcha and copy all. I think in a past life I was an engineer since I have a propensity to increase project complexity for no other reason than to see if it can be done.

Thanks for the help and keep posting 'ibles...yours are great!
E.Coli4 years ago
I love the simplicity of idea! Is this capable of charging iPhone 4gs too?? I already got 5V solar panel (about 6V 77 ma in the direct sunlight) and a DC to DC usb charger cracked open for this.(but the usb charger says the 'input 12V ~ 24V' would this be the problem? ) all I need now is proper soldering skill and a diode!

Thank you very much for the nice instructable!
JoshuaZimmerman (author)  E.Coli4 years ago
Your DC-DC isn't going to work. You need the output to be 5V, and the input to be low enough for your solar panel or AA batteries.

The other problem is that iPhones (3GS and 4) need a special USB circuit to charge from. Long story short most USB chargers won't work with an iPhone unless they're made for use with them.

In fact my USB chargers won't work with them. My iPhone 4 has been very sad because of it.

Also your solar cell doesn't have enough current to charge up an iPhone. They require at least 500 ma to charger, which is why most chargers use internal batteries. Solar cell charges internal battery, battery power is sent through a booster circuit to charge USB device.

I did, however, find a circuit that works for iPhones and that would work for you.

I'll be putting together a kit for it as well once I get more parts in. Probably in the next week or two. You would need the circuit, rechargeable batteries, and a battery holder. Your solar cell should be just fine.
SeedRally4 years ago
First off, I love all of your solar gadgets! I have two questions 1) if you were to increase the mah, would the recharge time of the batteries or the gadget go down? and 2) when you say that you increase the volts, that just means that you do not need as much light to power up the cells?

If you get higner mAh batteries the batteries will take longer to charge, but they will hold more power. This will not have an effect on the time it takes to charge a gizmo but it will effect how much of the gizmo's battery can be filled by the charger.

Yes, higher voltage cells mean you don't need as much light to charge stuff (I think).
JoshuaZimmerman (author)  spasysheep4 years ago
Correct. The higher voltage cells you use the less sun you need to get your minimum charge.

For example, if you're charging 2 AA batteries you need at least 3V of power to charge them. Well if you're only using a 4V solar cell you need full sunlight to get that 4Vs. However, if you're using a 12V cell you only need 1/4th sunlight to get 4Vs out of it.

Increasing the capacity (mah) of the batteries would give you more charge, but would not increase the recharge rate of your gadget. The recharge rate is determined by the charging circuit as well as the internal battery of your gadget.

If you increase the capacity of your batteries that also means it will take longer to charge those batteries up via solar. So either you'll need more sun or you should get a solar cell with more current (amps, or in small cells miliamp (ma)).
jshuler4 years ago
This is an awesome instructable! I love to find little gadgets and hacks like this that can be made on the cheap. I don't know spit about electronics/circuits, so I went ahead and bought one of your kits.

I tried beforehand to rip apart an AC to USB converter like for a wall charger, but not only did I almost slice open my hand (Safety Third!), but I pulled the darn thing out, and don't know what to make of it or how to split off JUST the USB converter.

Also, I've attached a pic of the converter I cannibalized, if anyone out there in DIY-land can help make sense of it. I'd like to salvage it, if I can.

Keep up the good work! I'll definitely be attempting more of these projects.
JoshuaZimmerman (author)  jshuler4 years ago
Goodness. Thats a lot of stuff. What you have there is a whole lot of AC to DC converter hooked up to a USB port.

You don't want to be messing with that as 95% of what you see is probably useless to this project. Plus if we're making a solar to USB we need a boost circuit, not an AC to DC circuit.

If you can find a busted battery powered cell phone charger you could always steal that circuit (it's a booster) and then wire it up to a USB port. That should work exactly the same as the circuit I'm using. I used to see those emergency cell phone chargers at every convenience store in Japan, but I'm not too sure where you'd find one around here.

Otherwise I have the booster circuit for sale on my website ($9), or you can build your own from ($20).
Yeah, I realized my error in taking the thing apart after the fact. Truth be told, I mostly just wanted to see the guts of the thing. I suppose it's still functional, if I just wrap the thing in electrical tape. Thanks, though.
ThaDoktor634 years ago
Now.. I totally like the instructable and I think it's great, but I have 1 question. I have seen an instructable on this sorta thing but all they did was solder a solar panel/cell to a diode and a female USB port. It works to charge things like new Apple products and stuff. In this Instructable, you use a battery charger also. I can see that it helps to like charge it with solar power or, if you're in a dark room, batteries. But does the solar cell charge the battery charger too? And would the too of them overload my device with power together? Thanks.
If you don't have the batteries then you can only charge the device when in the sunlight. With the batteries the solar panel first charges the batteries and the batteries then charge your device. Therefore it won't overload your device and you can charge the device without sunlight.
JoshuaZimmerman (author)  Squid19304 years ago
Exactly. That is the beauty of using an internal set of batteries. Easier to regulate and to use even when it's not sunny outside.
noah4724 years ago
i am kind of new to solar cells and i was wondering. say i wanted to add six rechargeable batteries at 1.2 volts each i would get 7.2 volts and i connect that to a 5v regulator in it. would i be able to just get a 9v solar cell to charge my batteries. would that work or would i need add something. please help thank you
JoshuaZimmerman (author)  noah4724 years ago
You could, but you would need more than 9Vs to be on the safe side. Plus you'd be losing power along the way with the regulator.

A booster circuit is just a lot more simple and saves a lot of room. Less solar panels needed, less batteries needed, and less solar panels needed.
Talulla4 years ago
I got a very strange look from my husband when I told him I wanted a soldering iron. Tee Hee.
Which brands/web sites do you recommend for chargers?
JoshuaZimmerman (author)  Talulla4 years ago
To be honest I don't really know that many. What I do know is you should find one that has adjustable heat on it. You're looking to spend $20-30 on one. You don't need a super fancy one, just a basic one.

Try amazon.
toughstuff4 years ago
awesome charger! where did take the dc to usb circuit from?
JoshuaZimmerman (author)  toughstuff4 years ago
I bought a bunch of USB chargers online and stole the circuit from them. I tried out several and found a couple I liked. A lot of them are complete crud.
Sweet build! I just have one question, would it be easy to build my own dc to usb converter? It seems like just a few capacitors, an LED, and a female usb port.
JoshuaZimmerman (author)  crf250rider144 years ago
You totally can. sells a kit that you can put together for $20. She also posted an instructable on how to make one. The problem is you really need a circuit board printed off for the project.

In many ways it's just heaps easier to buy something and take it apart.
Oh cool. But could I maybe get a list of parts that are in the circuit board, buy them at radio shack and install them all myself? If you could you can private message me. If you think its possible I would like to do that more then buying them online.
Thanks again.
JoshuaZimmerman (author)  crf250rider144 years ago
It's already an instructable. I've even provided a link for you.!---Small-battery-powered-USB-charger/

It tells you how to make one there. You'll be hard pressed to buy the parts cheaper on their own. Parts are always quite cheaper in bulk.
iPodGuy4 years ago
I love your solar gadgets. Please don't stop making them!
JoshuaZimmerman (author)  iPodGuy4 years ago
Ohhhh don't worry. I plan on making many more, as well as posting them online.

Plus it's summer! Summer should be all about solar.