DIY : 100w Led Flashlight




About: My name is Alen and i study electronic engineering. I love to make anything that needs electricity, hack and mod things as well building anything AWESOME...

You ve probably seen something like this.

I needed something that is bright, can be used on bicycle and also you can carry when you go exploring.

I made simmilar thing to DIY Perks portable sun but instead of using big CPU heatsink i used smaller one and whole body of flashlight to cool down LED.

Flashlight can work almost 1 hour on full brightness but i added potentiometer so i can dimm it and use it alot longer.

Battery that i used is 4S2P from old laptop batteries

Step 1: Building

I used 8 18650 batteries, 100W LED and 150W boost converter.

For monitoring batteries i got cheap Li-ion buzzer alarm that shows me voltage of all 4 batteries.

Fan is running on 6-7v and instead of step down converter i used resistor.

I installed small thumbwheel potentiometer from old headphones to control the light intensity.

I almost never use flashlight on full brightness becouse its really bright.
LED lenses could be added but since i use this in close enviroment i didnt put one.

Its really nice to carry this in forest becouse you can see everything in front of yourself.

Switch is on the handle so i can turn it on and off really easy.

Step 2: Battery

You can find cheap laptop batteries online or you can buy 18650s.

Good 18650 has about 2Ah capacity but they cost about 5€ per battery.

If you buy lot of laptop batteries you can get 2€ per battery and maybe even less.

When i tested batteries i used resistor across 18650 and i measured time.

First i soldered them together but later i got 8 holders and use that instead.

To charge them i made 4 cell balance charger from 4 usb charger and 4 TP4056 usb lithium charging boards.

Each battery charges with 0,5A of current so it takes about 4-5h to fully charge it.

Flashlight can be powered from any source from 10v to 30v that can deliver 100w.

I just need to unscrew 2 terminals that are going from battery to booster and connect any other source



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10 Discussions


2 years ago

Thanks for sharing... very good


2 years ago

Iinteresting build. The heat needs to be exhausted from the enclosure else it will cause early failure of the LED and Li-Ions. Also, soldering those non-tabbed 18650 will permanently decrease their service life. In the future use cells with welded tabs. Otherwise a good first try.

4 replies

Reply 2 years ago

Heatsink with led doesnt get hotter than 60c with led on full power (which is good since i dont use it on full power)
Same thing with li ions, i am only drawing 1,5C from them at full power


Reply 2 years ago

60C is still quite hot and 1.5C from those 18650 is too high a current draw. Be very careful with thermal runaway with Li-Ion chemistry. Too many people learned the hard way about that.


Reply 2 years ago

They are rated at 8A max discharge (thats 4C) and 4A continous (at least something like that)
But i dont use flashlight for long periods on full power (i barely used it at 100w)


2 years ago

Great instructable!