Introduction: Inexpensive Solar 18650 Battery Charger

Picture of Inexpensive Solar 18650 Battery Charger

Having recently completed my 20w solar charge controller well almost, I still have to finalize the power output. As it stands I'm able to charge such items as battery banks & cellphones via 5v usb. To charge 3.7v 18650 batteries the voltage has to be reduced from 5v. A simple matter with TP4056 lithium battery charge module.

3.7v 18650 rechargeable batteries can be purchased through a variety of distributors or salvaged from discarded laptop batteries. When the battery in a laptop can no longer keep the laptop charged properly, the fault usually lies in only one or two of the group of 18650's found bundled together to supply the needed voltage. Instead of discarding these very useful batteries they can be salvaged & used in e.g. flashlights (either diy or bought off the net), arduino or other electronic projects.

This instructable explains a simple & inexpensive way of solar charging 3.7v 18650 batteries.

Read On.....

Step 1: Parts List

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In the picture above I'veincluded on the right a prior version of this project. In this earlier version I mounted the solar charge module & the battery holder onto a thick piece of plastic. This time we'll omit the plastic piece & glue the solar charge module directly to the back of the battery holder


3.7v 18650 battery holder with 6" leads from ebay roughly 50 cents to a buck - I would pay more for a more "robust" battery holder if I could find one. These are very flimsy but do the job.

TP4056 mini USB Lithium Battery Charging Board 1A 5v again about a dollar, less if you buy more than one

usb to mini or micro usb cable depending on which TP4056 charge board purchased


Hot glue gun to attach TP4056 charge board to back of battery holder & keep wires in place
Soldering iron

A word about buying from the Chinese market vs buying local. Fantastic bargains can be had when purchasing from the Chinese marketplace. How they can deliver to my door for the cost of not much more than the price of the postage in some cases mouth-watering electronic goodies is beyond my comprehension! Being new to electronics I do make many dumb mistakes, converting brand new parts into smoldering piles of useless stench! Point being even those of us on limited incomes can afford a mistake here & there when the parts are cheap to purchase.

The reasons we must buy local are many. Sure when comparing prices local can be a bit pricier. But with that bit of markup come benefits. Better packaging, faster delivery, understandable specs & instructions, better quality along with product guarantees, & what about the jobs of the people involved in manufacture & sales?

I've barely touched on this topic as it's much too large an issue to get into here. Something to keep in mind when buying parts.

Step 2: Solder Then Glue

Picture of Solder Then Glue

There is very minimal soldering in this project. The positive & negative wires from the battery holder need to be soldered to the TP4056 after trimming off a couple inches from the ends of the wires. Once soldered hot glue the TP4056 module to the battery holder. Then add more hot glue to better adhere the module to the battery holder & to keep the wires firmly in place.

Please work safely being mindful of hot surfaces. Especially true for the hot glue as it can look cool to the touch when in fact it can cause a serious burn to one's probing fingertips!

Step 3: Done

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Allow the glue time to harden. Doesn't take long. Attach the mini usb cable & slip in a battery that's in need of charging. While this project is all about solar charging 3.7 volt 18650 li-ion rechargeable batteries, the usb cable can be inserted anywhere 5 volts (& 500mA to 1 amp) are available - be it laptop, pc, power bar, battery bank, etc.

Thanks all for taking the time to read my instructable. Please inform me of any errors should you find any &/or any improvements you come up with. Happy Tinkering!

Step 4: Solar Charging

Picture of Solar Charging

That's it. Since they're cheap to make it wouldn't hurt to make a couple or three.

I've entered my instructable in the MAKE ENERGY: A US-MEXICO INNOVATION CHALLENGE. A vote for my project would really be appreciated! Cast your vote at the top of this page if you please! Thanks!

Step 5: UPDATE:

Couple items

Found same board but with circuit protection on ebay for about 50 cents US apiece but you need to buy 5, I'd say that's a great deal!

If any of you like this project but don't have the time or inclination to put this together I've found on ebay someone has put together a version of this project & are selling it here for under 5bucks US.

Since posting this instructable I've found others also posted li-ion battery chargers using tp4056 here & there on the internet. Proving it's a simple, functional design worth repeating! Truth be told, they were posted before mine! lol


MichelF20 (author)2017-07-29

I made it on my own. But I have discovered some limitations.

I have used a 7V 5W panel.

On bright sunny days that panel delivers 4,8V by 800mA and charges perfectly the cell in a couple of hours. However once the cell is charged, the charger becomes up to 8,5V at the input, which is far over the specs of the charger IC. It than overcharges the cell by up to 4,5V, which is absolutely dangerous!

So please use at least the charger modules with built-in cell protection.

On the other side, on rainy days -and we have much of them here- the panel delivers only 40-50mA by 4,2V which is too less to power up my attached device.

For that reason I don't want to waste voltage and power by adding a voltage converter in front of the cell charger, the 40mA delivered by the cell will be just enough to run the converter! :-(

For the time being the best solution I've found is to load the solar panel with a 12V fan once the cells are charged, that drops the voltage down to 6,5V which is just fine. This happens only on hot sunny days, so the fan is useful anyway.

The Arduino data logger monitors the cell voltage and triggers the fan as soon as that voltage exceeeds 6,5V.

nikian.aghababaie (author)2017-03-12

I'd like to charge 3x 3.7v 9800mAh 18650's in series from a 5w solar panel. Can the TP4056 charge them?


petebarchetta (author)2016-10-14

On your solar panel project how are you dropping from 12-5v?

netbuddy (author)2016-05-30

Your local guy will be buying from the same places as the Chinese seller, only his buying power is made by buying in bulk or if Chinese, via an old family friend or school friends or wherever he has people he knows in factories that make this stuff.

So if you don't know what you are doing, buy local, get advice and be assured.

If you know what you are doing, know what to buy and can wait up to a month then save yourself a load of $$$'s and buy international.

netbuddy (author)2016-05-30

Your local guy will be buying from the same places as the Chinese seller, only his buying power is made by buying in bulk or if Chinese, via an old family friend or school friends or wherever he has people he knows in factories that make this stuff.

So if you don't know what you are doing, buy local, get advice and be assured.

If you know what you are doing, know what to buy and can wait up to a month then save yourself a load of $$$'s and buy international.

18650 battery (author)2016-03-14

I would love to see the charge curve as I'm worried perhaps the charge current drip is not steady. I have noticed from some power sources and it will mess up the cell over time.

Thanks for your interest 18650. Looking back at my instructable I see I haven't said much about the tp4506. Online I found at the Candlepower forums a member has created a number of graphs where you can hopefully find the charge curve.


Dr.Bill (author)2016-03-01

If you buy an AH-55 DC to DC Converter on Amazon it will charge a Li-ion battery as big as yours @ 300 mA for hours and hours. I put the AH-55 into the wood box in the left of the cart. There are several of them that I use to charge all my Li-ion batteries. Never had a problem with it and they don't get hot like in commercial chargers. Works on NiCad's too and the 12 volt battery drill motor as well

u971 made it! (author)2016-01-30

Made x2 Had them about half a year now still charging and powering arduino's.

jimthree (author)u9712016-02-10

Hi u971! Yours looks like a great little setup. that looks like quite a small panel, what are it's specs? Does the charging circuit have any problems with the low current that the solar cell provides? Have you kept it charging for any length of time, i.e. trickle charging?

u971 (author)jimthree2016-02-10

The Solar panels specifics below same i am using with the battery's,as for leaving them alone to charge yeah many times,being dumb chargers though have to check the battery voltage with a multimeter to see if they have charged.

BrandMiniisw ,ModelSW-008

MaterialPolysilicon + PET

Max Current160 mA


SpecificationSolar powered, high transmittance, matte PET.

Other FeaturesFor users DIY power supply to electronic products. Use high transmittance matte PET lamination workmanship, light gathering power 15% better than normal solar panel, improve solar power's conversion rate.

Dimensions: 3.35 in x 3.15 in x 0.12 in (8.5 cm x 8.0 cm x 0.3 cm)

Weight: 0.99 oz (28 g)

jimthree (author)u9712016-02-10

Thanks for the Info! so you use them to charge batteries and then take the charged batteries and use them somewhere else? I was thinking about this setup as a way of keeping an 18650 charged while connected in circuit in a project.

u971 made it! (author)jimthree2016-02-10

I use them with various arduino's for experiments some pics below batterys powering a arduino nano,as for keeping them hooked up to the solar power supply would be fine for data logging motion detectors so on but only temporary,would need a battery protector circuit along with the charger or would flatten and kill the battery,used them to power an old dynamo radio too.

u971 (author)2016-01-28

Thanks for the inspiration made 2 for charging battery to power an arduino.

terrible tinkerer (author)u9712016-01-29

Hi u971, Glad to inspire, 2 eh? Great stuff


Errol1951 (author)2015-08-10


I have been doing some research into these batteries and it is interesting how many fakes there are as you can only get about 2600 mHr's the rest are fakes you have to weigh them to find out if they are real their weight should be over 40 grams if not I'm sorry you might have a fake or you can use a watt master to measure exactly how much charge you have put in to it. Have a look around and see if you can find a reputable supplier and look on the internet to see. I have started to build some bigger units with radio and the ability to charge phones and a light as well

jmorsebrown (author)2015-03-16

Hi. Thanks for this. What's the spec for the solar panel that I'd need for this project?

Hi jmorsebrown, your welcome & thanks for your interest.

This project includes a female usb port and thus requires 5v input. I'm not an expert but in order to maintain 5 volt input it would be prudent to use a solar panel specifically rated for 5v with a usb connector attached or a panel rated higher & you attach a step-down buck converter with usb connector as in my earlier project here

Thanks - that's helpful. I've bought the bits and am using it to light my garden workshop. Thanks for the instructions!

petebarchetta (author)2014-12-28

Hello, I'm loving the build, I have one question, can the circuit be enlarged to allow multicell Li-ion packs? Ie 6pack (3sets of 2 parallel) giving a massive cell

This is a very minimal circuit.You would need a different module/circuit to accomplish what you're after, beyond the scope of this ible. Sorry

Errol1951 (author)2014-12-01

there is a new circuit board similar to yours but has output terminals as well and you could hook it up to what ever you want saving taking the battery in and out its called Nice 5V Micro USB 1A Lithium Battery Charging Board Charger Module+Protection

Hi Errol1951, Thanks for your input. Where can I find a Nice 5V Micro USB 1A Lithium Battery Charging Board Charger Module+Protection? I'd like to check one out.

It's on ebay I recently bought 2 I'm doing the same as you $1.74 ea

That's great. I'm glad you've found my instructable of use. The sun hasn't been out much the last few days but I'm still managing to get my batteries charged.

About This Instructable




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