Portable 20w Solar Charger




Introduction: Portable 20w Solar Charger

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

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

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

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

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

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

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

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

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!

MAKE ENERGY: A US-Mexico Innovation Challenge

Fourth Prize in the
MAKE ENERGY: A US-Mexico Innovation Challenge

3 People Made This Project!


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47 Discussions

This is a great instructable! Thank you so much for making this!

Thx, keep those panels shade free and tracking when possible

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.

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.


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

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 ?

8 replies

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!


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.

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.

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.

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.

terrible tinkerer - got to my website: www.GlobalEnergyNow.org 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.

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.

1 reply

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.


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

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.