Introduction: Portable 20w Solar Charger

Picture of Portable 20w Solar Charger

I've been charging 18650 rechargeable batteries from a small 12v battery solar charger for a few months now. Not impressed with the charge rate, spending an entire sunny day only to maybe have a single 18650 battery charged. I decided to step it up a notch & bought a 20w 12v solar panel from an ebay auction. Now I had to decide either to mount the panel outside & run wires into the house or to make it portable. I decided on the latter, as 20w is a bit meager for a rooftop installation.

Researching charge controllers one can quickly see the better ones are MPPT & cost around $100 or more. MPPT's are worth the money if you have a roof-load of solar panels. In this case a very basic charge controller is all that is needed. This 10amp unit is as basic as it gets, & for a paltry $10.

After a lot of research on the web I believe I've come up with a decent portable charger for not a lot of cash.


20W poly solar panel auction price $36.00

10A CMP Solar Panel Charge Controller 12V/24V 10.00

4 x 12v SLA batteries aprrox. $25. ea x 4 = 100.00

DC 9-35V to 5V 30W 6A Car Charger 4-USB Port Step-down Power Supply Module 6.00

5 Digit DC 0-4.3000-33.000V Precision Digital Volt meter 8.00

9 Volt 400mAh Ni-MH 6F22 PP3 Rechargeable Battery 8.00

3amp fuse & holder 5.00

wiring 20.00

luggage cart


Total cost $200 more or less.

I used the batteries from a computer power backup (UPS) so the cost is nil. Luggage cart, scrap plywood, etc.

Step 1: Wooden Frame

Picture of Wooden Frame

Two small pieces of 3/8 or 1/2" plywood screwed together with a 2 x 2" for added support. Size is determined by #1: number of batteries to be carried on base #2: spacing of electronics fastened to backboard & #3: the size of the cart. I used a small frame from a luggage carrier I believe. One small bungee cord holds the back panel to the cart. The weight of the batteries also helps to hold it in place.

Step 2: Batteries

Picture of Batteries

I used 4 x B.B. Battery HR9-12 Valve Regulated Lead Acid (vrla) 12 volt 8.0 amp hour batteries which I found in a computer back-up power supply. These I wired with 12AWG in parallel to maintain the 12 volts & increase the number of amp hours to 32 following the design by ch5 (above) with the battery bank wiring going to the charge controller. The roll of 12AWG cost close to $20 at Home Depot so I only purchased one roll of red, hoping to have enough black wire around the house that I could use. I didn't, so I used the red wire putting black heatshrink on the negative wire ends and some strips of black heatshrink every few inches along the length. Placing a stiff board beneath the 4 batteries they could be lifted all together & placed into a shoebox, which holds them together as one neat package. The 2 wires connecting the batteries to the charge controller are left purposely long to allow the lid of the shoebox to close, the lid creating a small work surface to hold items being charged.

It is important when wiring to the charge controller that the batteries are wired first, the solar panel second, the power out last.

Step 3: Wiring 20w Solar Panel

Picture of Wiring 20w Solar Panel

Thanks to khaleel123 & his drawing "solar controller wiring" (above) found on his instructable Solar Panel Setup around $100 - I was able to wire things up

Found a couple lengths of 14AWG red & black wire to run from the solar panel to controller. To determine the length I wanted to keep it as short as I could. In normal operating mode the aluminum frame of the solar panel will hook onto the top of the plywood. This not only angles the solar panel roughly towards the sun but keeps all the electronics beneath it dry, sheltering stuff from the occasional rain ( I hope!). Otherwise the panel only needs to move from one side to the other to allow access to the electronics.

Step 4: Battery Monitoring

Picture of Battery Monitoring

After attaching the pos & neg 14AWG from the battery bank to the charge controller, bringing the controllers leds to life I should add, I felt I needed some way know the state of the batteries. Other than the 3 leds on the face of the charge controller that is. I splurged on a 5 digit voltage meter, roughly 9 bucks. A 9v rechargeable battery is needed to power this little puppy.To fasten this panel to the plywood I used double-sided tape then drilled a hole to each side of it & fed a zip tie through, snugging it up in the rear.

The next step is connecting wires to the power out of the charge controller. Attaching a Barrier Terminal Strip Block with screws to the plywood next to the charge controller. In the positive line going to it I added a 3amp Fuse. This is just a guess as I don't know if 3A is enough so over the next few weeks I'll try to find out the proper value. I think an on/off switch is probably a good idea to include at this juncture also.

Step 5: Using the Harvested Power

Picture of Using the Harvested Power

Attached a 4 usb port device I snagged off ebay to test the system. It's cloudy out today but definitely noticed some charging before the rain forced me to pull things back inside. Success! Took 2 hours to fully charge my 2100mAh Nokia cellphone from 35%.

Placed an order with BangGood for a 12v/ 2 x usb/ voltage meter (shown above) which I think will fit nicely on here. It has a 12v power point which will allow me to plug in a 300w power inverter. Will a 300w inverter work with a 20w solar panel? Suppose I'll find out.

This project is small enough to take camping or out on a picnic. During a power outage it will keep the laptop, cellphones, flashlight batteries charged so it's definitely worth making just for that.

Hope you find this a worthwhile project. If you have any questions or ideas for improvements do pass them along!

Oh Yeah. I've entered into the MAKE ENERGY: A US-Mexico Innovation Challenge. I'd appreciate a vote. The Buttons' at the top of the page on the right, I do believe.

Step 6: Update Aug 2015

Picture of Update Aug 2015

I've made some changes, for the better. I've replaced the 5v usb charge ports with a meter/2x5v usb/12v module. Quite happy with it & I'll explain why. Charging my Nexus5 cellphone or batteries using the 5v usb ports I found would never provide me with more than about 450mA's. Knowing my phone capable of accepting a greater rate I began looking into this.

With the 12v power point I tried different inverters. The 300w, then 90w & finally a 30w which actually works well with this 20w solar panel. I found I can charge the battery of my grass trimmer among other things. I also tried charging my Nexus5 using the mains charge cord but still no improvement in charge speed.

My original batteries conked out & would no longer hold a charge. Luckily a friend donated 3 used but still functional 12v batteries.

Step 7: & Finally

Picture of & Finally

I did some research on the web & found to charge my phone faster I needed a charge cable that can handle more current & a 12v charge plug That can handle it too. On Amazon I found

[Qualcomm Certified] Aukey Quick Charge 2.0 30W 2 Ports USB Car Charger Adapter &

Anker® 5 Premium Micro USB Cable Pack (3X 3ft, 1X 6ft, 1X 1ft) High Speed USB 2.0 A Male to Micro B Sync and Charge Cables

With these cables & car charger adapter I realize charge speeds of 1450mA's! Of course this speed isn't accurately measured as I don't have a way of measuring but I know it's close to accurate as my pnone charges in way less than 1/2 the time. Well worth looking into if anyone wants faster cellphone charge times.

Thanks all that voted for me in the MakeEnergy contest. I won a consulation prize which I truly value!


Equuss25 (author)2016-09-27

Thx, keep those panels shade free and tracking when possible

corbin1950 (author)2016-09-05

project looks good, just one thing always give a difinition for acronyms what is MPPT?

Im afraid there are people out here that havent a clue what that means.

terrible tinkerer (author)2016-05-21

BenjaminS87, Sounds like an interesting project. As you, I don't have a lot of experience in this huge field of electronics. Google is the answer my friend. Wish I could be more help. Hopefully someone smarter than you & I see your post here & can offer you assistance.


BenjaminS87 (author)2016-05-19

Im working on a solar briefcase for my bug out bag, im doing 20watt bp solar panels, was wondering if i will need a different type of charge controller for a array of 18650 batteries instead of SLA? Also curious as to how many batteries i should get, parallel or series, i was an electrician for a year so i have a little experience, but when it comes to DC power and batteries i am clueless

sigmaluis (author)2014-11-18

Very nice! How do you go about increasing the number of solar panels . Should they be wired in parallel or that will create current flow between them due to differences in output ?

Dr.Bill (author)sigmaluis2016-03-01

Works good like that check mine out...It's expandable!

Hi Dr.Bill. So glad I was able to inspire you to make your own & put it to good use. Can't believe you found a similar cart! & for only 5 bucks, that's fantastic. Of course you've found your own way to put it all together to make it work for your own applications. Kudos to you. Thanks for including the photos. Helps to visualize both of your projects, your 80w & your 20w.

I'm not an expert on batteries but I think you'd get more life from dry cell or gel batteries. The car battery is built for high cranking amps to start a car & not for a slow drain. But hey, you use what you have on hand & so long as it's not a danger then why not? Happy Tinkering!


NnamdiE (author)sigmaluis2015-03-22

thats a nice question

LiamOSM (author)sigmaluis2014-11-18

You can wire solar panels in parallel as long as they are a identical. Also, you need to try to make sure they are all receiving the same amount of sun.

sigmaluis (author)LiamOSM2014-11-18

That is the theory but in practice there are no identical solar panels nor will they receive the same amount of solar radiation so , in real life , how can one interface them to account for all that . There must be a way or all those huge arrays will not work.

Damian7 (author)sigmaluis2014-11-22

Those huge solar farms have 'strings of panels' connected to combiner boxes, which send the power each string produces to the inverter. The inverter has software to detect each input. I know what you are saying about each panel not producing the exact same amount of voltage of amperage. Each panel has a tolerance depending on the system and the manufacturer which allows it to work in the system they are connected to.

LiamOSM (author)sigmaluis2014-11-18

You are correct. However, the slight differences in power output can be ignored for small scale projects like this one. No two batteries re identical either, but we put them in parallel. You can ue a diode to isolate multiple panels though.

Hi sigmaluis, The bypass diode might be the solution. Check out the link provided by Daedalus62 below for a more complete answer.

ASCAS made it! (author)2014-11-17

Very inspiring! Here's a slim version that I'm working on :))

Dr.Bill (author)ASCAS2016-03-01

That looks like an inspiration from the Sol-In-One by Lazar Sabre.

Dr.Bill (author)ASCAS2016-03-01

That looks like an inspiration from the Sol-In-One by Lazar Sabre.

beic (author)ASCAS2015-08-20

Nice on the picture, but where is your project link?! ;)

NnamdiE (author)ASCAS2015-03-22

perfectly constructed.

BrownDogGadgets (author)ASCAS2015-03-06

Your slim project is quite nicely done, with some fine workmanship.

ASCAS (author)BrownDogGadgets2015-03-13

Thanks! :)

terrible tinkerer (author)ASCAS2014-11-17

Looking good! How does the arduino fit in?

ASCAS (author)terrible tinkerer2014-11-17

The arduino only acts as a programmer, I made a standalone circuit that only uses an Atmega328 chip, slim enough to fit in the panel's frame :))

Dr.Bill (author)2015-12-06

I made this !

80 Watts

Hey this looks really great Dr Bill. You've brought my project to a whole new level! Hows it working for you?


Dr.Bill made it! (author)terrible tinkerer2016-03-01

The 80 Watt Solar Cart can power a Dialysis Machine all night. It don't do it anymore though, now it powers my Ham Radio Station, LED Lights and a whole string of other things.

You inspired me to build your idea out. There is even a stick to prop up the panel to various angles for the different latitudes. The panel is mounted on an aluminum angle that is tie wrapped to provide the hinge and there is an extra plug behind the panel for expansion with other 20 Watt panels.

The plywood power panel is Pop Riveted to the pipes. You Had One Hell-Of-An Idea! Thank You.

Dr.Bill made it! (author)2016-03-01

You Inspired me.

Dr.Bill (author)Dr.Bill2016-03-01

This is a 20 Watt Portable System that uses a lead acid 'used' car battery. It has in the connector box a switched DC to DC Converter set for 6 Volts. I power an AM/FM radio, LED Lights and a Blood Pressure Monitor. This unit has already been used to jump start a car from the battery direct with jumper cables. The cart was a Salvation Army purchase for $5. It has a 10 Amp SunForce Charge Controller and a switched WattsUp Meter. There is an extra plug under the panel so more 20 Watt panels can be connected to expand the system.

This Is What Winter Boredom Does To Me...I make things.

leseagle (author)2016-01-05

terrible tinkerer - got to my website: to see what I am doing around the world to put to use great ideas in solar and solar thermal to help emerging countries grow bottom up technology reach. From the people to the higher levels as the gap is TOO long to get to the point of countries instituting large systems and the people ever actually able to get to use them based on poverty. Let me know what other ideas you have on the big picture of solar. Thanks for your reply.

leseagle (author)2016-01-04

Your low charging rate has to do with where your panel is located. The panels efficiency is greatly reduced by having even on tree branch or leaf covering the panel in shade. It will completely shut down the panel and therefore give you no energy or very low amounts. Best to get your panel out in the open with now trees. Also, watch the front of the solar panel for any shadows and move it until none are seen. Hope this helps. Also, you are trying to charge small batteries. As the solar panel receives trickles of energy, batteries on the other hand require constant flow of electricity. Therefore, you should not use the small batteries but one more like a sealed Nicad Gel battery with at least 8-10 AHrs. Then by charging the large battery it produces a constant flow of electricity. This is especially important for the new Lithium batteries which require a special charge controller as they need a slow consistent charging, very touchy. So your best course of action is to get yourself a few USB converters from 12V and then you will have an excellent system. How many Watts do you get from your solar cell? Is it 12V? You should bet at least 10-35W to run a good recharging solution.

Hello leseagle, Thanks very much for your input, all relevent points to be sure. I do appreciate your bringing them to light. Especially since my instructables are created on-the-fly so to speak, developing the project & recording to ible similtaniously, sometimes things aren't explained as clearly as I'd intended.


gearup500 (author)2015-12-17

Awesome. I need to find a way to charge my batteries without draining them; I already have a solar panel. Any suggestions to this problem? Thanks, and please, keep em' comin.

Later dude

jbrown146 (author)2015-06-11


spylock (author)2014-12-02

Just my opinion,I would use deep cycle batteries,more even current and long charge life.Also,I would use a battery for each 25 watts of panel.

Errol1951 (author)2014-12-01

If you use a schotty diode the drop is between 0.1 and 0.5 also called solar panel diode

Errol1951 (author)Errol19512014-12-01


GoatgodA (author)2014-11-23

Be careful with that charge controller. That model needs to be connected to the batteries BEFORE connection to the PV panel. I have had these controllers fry from this fault. The earlier, better labeled units have a yellow sticker across the terminal block warning the user to connect the battery first.

Daedalus62 (author)GoatgodA2014-11-26

Thanks for the heads up, GoatgodA... I was just getting around to connect my unit, timming couldn't be better... Appreciated!!

terrible tinkerer (author)2014-11-23

Thank you for pointing that out GoatgodA. I will edit my text to be sure all are aware.

rocketman221 (author)2014-11-16

The inverter will work fine since you have batteries connected as well. Just don't connect it straight to the panels, they can supply over 20V open circuit.

TY rocketman221. I really wasn't sure if the inverter would work. Would you know if 14AWG wire would handle the load of the inverter? I know the fuse needs to be upgraded cause I wired in the inverter - it squealed & the 3amp blew right away!

The wire should be sized to handle the load of your circuit and the fuse to protect the total load of it. There are many website or apps you can download to find out which wire you need as well as fuse. A fuse too big would not protect your devices, battery or you! in case of short in the circuit. This applies for DC circuits and AC circuits.

14 AWG will work, but keep it short (1 or 2 feet) 12 AWG would be better. You will need a 30 or 40 amp fuse to run at full power.

Cool! Very much appreciated.

14 AWG will work, but keep it short (1 or 2 feet) 12 AWG would be better. You will need a 30 or 40 amp fuse to run at full power.

Damian7 (author)2014-11-22

Good work on the instructable. I would like to add some input based on a project I recently did. If there is any errors on my information feel free to reply. Thanks.

There are rules for parallel and series circuits.

For series circuits, Voltage total is the sum of each power supply, so you can connect different panels with different outputs, while in parallel is the same voltage, I will not recommend connecting different panels that have different voltage output. Current(amps) in series circuit is the same, in parallel the current is the sum of each power supply or panel. This applies for the batteries. The higher the voltage the smaller your wire, the smaller the voltage the bigger your wire.

There is a calculation for voltage drop, which takes in consideration the distance of your run( cable/wire), the material of your wire (usually copper), the total load of your circuit( amps). I wired a work shop in my yard using 24v. LED bulbs and to avoid any overheating on the wire I did some research. I may take some time and do an instructable about

najslepsi (author)2014-11-19

Hello, nice instructable, I already made one setup very close to yours (same panel and controller). Just two things to mentoin:

1. The 8A fuse on picture (from battery to charge controller) is VERY needed, and has to be as closest as possible to battery connector. This fuse protects batteries and leads in case of short circuit somewhere between fuse and charge controller.

2. why do you use 9V battery to power panel meter? If it is because it needs 9V, you just could use cheap linear voltage regulator. If it is because it needs separate voltage potencial, throw it away, there are cheap panel meters on ebay which are suitable, and needs 12V which is fine for you

Hi najslepsi,

Appreciate your comments. I've noted your safety concerns & see how a fuse is needed between batteries & charge controller. I have some on order.

I used the led battery monitor with its own power supply only because that's what is shown in the Solar Controller Wiring diagram above. It does seem a waste of power having the 9v powering it, but what do I know?

sb4 (author)2014-11-19

Would you explain more why a 5 amp and 3 amp panel in parallel gives 4 amps? Maybe some equations? It doesn't seem intuitive. Seems like they should add, not average.

sigmaluis (author)2014-11-19

Thanks to all for pouring in all that useful information.

iam_maker_leo (author)2014-11-18


And I learn how to control solar system from your project.

Thank you.

I want to have it.

About This Instructable




Bio: Let's not take life too serious. Enjoy any bright spots that happen to come by.
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