Step 4: Add the solar cell

There are a couple of different ways to connect the solar cell. The first is by simply shortening the connector leads and plugging the barrel plug into the barrel jack on the charging circuit.

The second method is to replace the connector with another JST connector and plug it into the third connector marked 5v on the charging circuit. I didn't have another JST connector handy so I just soldered a salvaged two pronged connector to the charging circuit where there are two open pins on the 5v line.

Using the second method certainly is a bit cleaner since you don't have the big barrel plug sticking out of the side of the tin.

UPDATE- Since the original charging circuit has been discontinued, the best way to connect the new version Sparkfun LiPo charger is to splice a mini USB cable to the solar cell wires so it can plug directly into the charger. There is a simple guide on how to do this here-

Now attach the solar cell to the top of the Altoids tin using some 2" wide Velcro. I wrapped the battery pack with a layer of clear packing tape to help protect it. Then the battery pack is simple set down on top of the two circuit boards- it's a near perfect fit.

Now set your MightyMintyBoost out in the bright sun and charge it up! You should see a little red LED on the charger board light up. Once it's fully charged connect your iPod/iPhone/USB powered device and enjoy!
dvgs3 years ago
sweet - Thanks for the help!
dvgs3 years ago
would a mini usb that comes on the cell phone chargers work?
Honus (author)  dvgs3 years ago
Yep- that will work fine. I find chargers like that all the time in the trash and save them as they come in handy.
dvgs3 years ago
In the picture your using the old lipoly charger but i have the new one that dosent come with the barral jack and the new lipoly charger looks compleatly different the the old one and i cant figure out how or were i would conecct the solar panal to the lipoly charger. Can you help me figure out were to connect the solar panal on the lipoly charger?

Honus (author)  dvgs3 years ago
Yeah it stinks that they changed it- kind of frustrating, especially when a lot of people liked the old version.

The best way to connect the solar cell would be to connect a mini USB cable to the solar cell and then plug the cable into the board. There is a guide here that shows how to splice a mini USB cable to a solar cell.


aahuja3 years ago
Great guide but im having some trouble is thier a way i could contact you. IM a middle school student doing this as my science project.
Honus (author)  aahuja3 years ago
What do you need help with?
dailj25 years ago
I've been using mine for about a month now, but the red LED is always on when it is in the sun. I thought once the battery was fully charged, the LED would cut off. So I'm assuming my battery has never reached full charge. And I've only used it a few times to charge my iPod. Any ideas?
Due to the design of the sparkfun li-po charger circuit, if there is a load on the SYS output the battery will never fully charge as the output is connected directly to the battery, thus the charger IC will never see the battery fully charged condition due to the load of the boost converter, hence charge LED does not extinguish.

Have you tried just charging the battery using the solar cell and not with the ipod/iphone connected?

I have done a similar application and designed a customised charger/boost circuit using ideas from a microchip application note, when an external supply is available this takes priority and supplies the boost convertor and charges the battery separately.

Honus (author)  dailj25 years ago
Do you have a multimeter to see if the battery is being fully charged?
xbarracuda4 years ago
I've bought a solar charger with a mini USB output. Its output voltage and current is 5.5v and 400-800mA. The problem is that my iPod Touch won't charge. Do you know what may be causing the problem? Maybe not enough current? What could I do to solve the problem?
Thanks in advance!
Great guide!! - if I had seen it before I wouldn't have bought this charger ;)
Honus (author)  xbarracuda4 years ago
There are probably several problems. How are you connecting the charger to the iPod Touch? An iPod Touch doesn't use mini-USB.

The other issue is that iPods and iPhones require some interaction over the USB port data lines so you will probably have to modify the charger to make it work by soldering resistors to the USB data pins.
sjclark244 years ago
hey, mine is charging but the LED is not on. Do you know what the problem may be?
Honus (author)  sjclark244 years ago
It's still showing an output to the LiPo (I'm assuming you're measuring the output using a multimeter while the LiPO is connected) and the LED isn't on? Did the LED ever turn on? If the LED never turns on maybe the LED is toast.
sjclark24 Honus4 years ago
Well I don't really have a multimeter around at the moment but the LED never came on at all when either the battery, mintyboost, or solar panel were plugged in so I'm hoping the LED is just blown.
Honus (author)  sjclark244 years ago
You should definitely check the output of the solar cell in direct sunlight first. Then connect the LiPo and solar cell to the charging circuit and test that. You should get around 4V at the LiPo connector.
cnpsp4 years ago
This's great~!
How about make a 5V input (e.g. PC USB port) for the 3.7v 2000mAh LiPoly battery recharge instead of this small solar cell??
Honus (author)  cnpsp4 years ago
There is a mini USB port on the charging circuit for charging the LiPo battery.
lorddavis65 years ago
is it 100% your idea??
Honus (author)  lorddavis65 years ago
Yep. I knew a few people had talked about it but nobody had actually done anything at the time. There were a few companies that were producing commercially available products at the time that were somewhat similar but not as versatile.
SFquestion5 years ago
Does the battery come fully charged? I used all of the exact same materials, but mine doesn't seem to be working. Anyone have an idea as to why?
Honus (author)  SFquestion5 years ago
I don't think so. Is the battery charging? Is the LED on the charger lit? Can you check it with a voltmeter? I would check the output of the solar cell, then the charger. If that looks OK then check the output of the MIntyBoost circuit.
ricksl5 years ago
 I have a question, what would be the maximum mA input from a wall wart charger, before it damages the circuit, I know that it has voltage control but...
Honus (author)  ricksl5 years ago
It shouldn't really matter- the charger will only draw so much current.
rseni6 years ago
. I'd like to know the total cost of MightyMintyBoost. . What is the avantage of using a LiPo battery in place of Ni-MH? . How would you charge it in absece of electricity and enough sunlight?
Honus (author)  rseni6 years ago
The cost is listed on the FAQ page. LiPo batteries have a higher energy density. I don't understand the third question- you have to have some means of electrical current to charge the battery.
Ryenthelion6 years ago
Hey HONUS, first off I appreciate your effort in creating this project and posting it. Also your generosity in answering questions.
Is there anyway possible you could post or email me instructions on how to hook up the SPARKFUN LiPoly Fast Charger - 5-12V Input ???
I'm going to use the Sparkfun Solar Cell Large ...
as you can probably tell i dont care about fitting it in an altoids tin, haha

Last question is: do you think it would be possible to charge without the battery? As in making it a Solar charger only? as that would also cut the cost down alot.
Honus (author)  Ryenthelion6 years ago
I haven't personally hooked up the fast charger but I did post some suggestions for it in the FAQ section. I haven't tried charging it without the battery but it should work.
cbrodine6 years ago
Do you think the battery charger could safely accept input from a Bicycle Dynamo Hub instead of solar? Something like http://harriscyclery.net/itemdetails.cfm?ID=2974

Check out www.vintagebicyclepress.com Vol 3 Number 4. Has output and efficiency info on dyno hubs at various speeds. Got the article off of Wiki searching dynohub. Interested on how it turns out. I have the SON 28 and have been interested in trying something of this type but have been discouraged from trying after reading the hub can be damaged if it is riden with the light turned on and bulb burned out. Guess the battery charger unit will prevent damage?
Honus (author)  cbrodine6 years ago
It sure can, and being a cyclist myself (former bike designer) I think that's an awesome idea! That hub puts out 3Watts@ 6v, which would give you 500mA current (provided my math is correct.) The charger would limit that to 280mA current but it should work just fine. To use the 500mA maximum you'd need the other Sparkfun 1A charger.
cbrodine Honus6 years ago
I'm kind of assuming the 3W@6V is a nominal value. I'm guessing I don't typically pedal fast enough to produce the maximum current. I think I will start will the smaller board for now. I think I will put the barrel plug on the solar panel. I want to put a barrel plug on the bike dynamo also. Then I can carry the charger in my backpack and hook it up to whatever source I want easily.
Honus (author)  cbrodine6 years ago
You're probably right about the output -it would be interesting to check the output with a multimeter. The barrel plug is definitely the way to go for this application.
wasutton36 years ago
i saw the higher capacity battery. my only concern is if it would fit in that case. i see how he has it lined up and it looks like its resting on the circuit boards. an altoids tin is only .75" deep so that battery would take up the entire thing. unless you managed to stack the circuits in some other way
Honus (author)  wasutton36 years ago
Yep, there's just no way that battery is going to fit in an Altoids tin. The single cell fits in there with a little room to spare, but not much.
wasutton3 Honus6 years ago
true. unless you build a different circuit. the parts are all available to the public. they even have all the schematics online. so really one would just have to make the existing circuitry smaller. EXTRA CREDIT: if you redesign it in a feasable manner to allow the fitting of the charging board, the mintyboost board, and the giant battery in the same altoids tin, ill buy you a pizza
What you can do is reconstruct the bottom to indent just enough to rest the battery and wire the circuits over top of the remaining space. Thus making the bottom weak, unless you add more tin to accommodate. By then the tin adding idea would get messy but its worth a try. And no I don't want the pizza. I donate it to Honus. :)
Honus (author)  wasutton36 years ago
Yep- I've posted about this. I would love to see a mini surface mount board that incorporated both the charger and MintyBoost circuit. Maybe someday I'll take the extra credit since I'm a big fan of good pizza!
borito46 years ago
Is it possible with that Li-charger board to connect 2 LI bats to it so u get 4k mA capacity with or without the solar charger?
I believe Sparkfun has an OTS high capacity LiPo pack, already wired up.