Picture of Solar Battery Charger For Your Cordless Power Tools

Solar power is a great way to get electricity out to a remote project site. One simple way to do this is to use a solar panel to charge the batteries of your cordless power tools. In this project, I am going to show you several ways that you can do that.

Safety Note: Any time that you use a DIY battery charger instead of a commercial charger, you are accepting a certain amount of risk. So always use caution. Don't over charge the battery and don't try to charge it faster than the manufacturer recommends. There are many different kinds of batteries and they all need to be treated differently. These instructions are designed for batteries that are made of Nickle-Cadmium cells. I make no guarantee that these instructions will be appropriate for other battery types such as NiMH or lithium batteries.

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Step 1: Watch the Video

Here is video walk through of the project.

Great idea.

parth_bhat7 months ago
why we cannot use some other batteries? except NiCd? I want to use it for lead acid batteries also will it harm the batteries?
DIY Hacks and How Tos (author)  parth_bhat7 months ago
Different batteries need to be charged to different voltages and at different rates. I designed this charger for use with NiCd batteries. So for safety, I am saying that it should be used with NiCd batteries. The charger would probably be fine to use with other types of batteries. I am just being extra cautious. Proceed at your own risk.
ok thanks
tutdude988 months ago
Ive put led instead of relay and i set to reset at 10v and cutoff at 12.6v but it reset at 9.3v and it doesnt cutoff
anybody know why?
DIY Hacks and How Tos (author)  tutdude988 months ago
Sorry, I can't really see any of the parts from that picture

its same as on schematics but when it tried to put 5v (instead of 7805) on my adjustabe psu i got reset at 11v and again no cutoff

DIY Hacks and How Tos (author)  tutdude988 months ago

Sorry, I am stumped. Try checking all the connections and component values. Good luck

parth_bhat8 months ago

thanks a lot for ur replies i'll work on it.

warpspeed8 months ago

Wrong video was displayed, the video being shown is for a water to wine trick. Please fix.

DIY Hacks and How Tos (author)  warpspeed8 months ago
Sorry. It should be fix. Thanks for letting me know.

Its a miracle though!

parth_bhat8 months ago


can you please please help me to find out my resistors value?

i have a black and decker cordless drill machine whose battery voltage is 14.4v and when fully charged 15.5v and its adapter's voltage is 17v @ 200mA

i am going to use this project for automatic charging. instead of solar pannel ill be using the original dc charger.

Please can you help me to find the voltage divider's resistor's value?


parth temkar

use 1k ohm's

DIY Hacks and How Tos (author)  parth_bhat8 months ago
If yo are using the original charger, you shouldn't need a charge controller. But if you want one just use the formulas at the bottom of step 7.

"The 33 kohm resistor can be replaced using the formula R = (3 x Vcutoff) - 10 (in kohm's). The 68 kohm resistor can be replaced using the formula R = (6 x Vreset) - 10 (in kohms)"

Doesn't Ohm's law for direct current fit here ?


U = R * I; R = U / I; R = 17V / 0.2 A = 85 Ω.

Otherwise you might have to manually measure it step by step.

carlos66ba8 months ago
Clever non orthodox use for the 555 circuit. Clever.
deba1688 months ago

Can I use a MOSFET instead of relay??

DIY Hacks and How Tos (author)  deba1688 months ago
As long as it is rated for a high enough current it should be fine. I just used a relay because it will work for almost any application.
brmarcum8 months ago
I was just looking for a solar charger solution. This is perfect, thank you.

This is awesome, I just got a cordless drill, I'll have to try this!