A Very Powerful 20W LED COB Flashlight

I built a flashlight using garbage parts and only paid for 2 parts (the LED itself and the buck boost converter). I needed a flashlight for when i need more light so I assembled this monstrosity.

DANGER: THIS PROJECT HAS LITHIUM ION CELLS THEY MAY SEEM HARMLESS BUT ARE DEADLY DANGEROUS DUE TO THE RISK OF FIRE PLEASE FOLLOW INSTRUCTIONS CAREFULLY BUT I AM NOT LIABLE FOR ANY DAMAGE YOU CAUSE TO YOU; YOUR HOME; YOUR FAMILY AND WHOEVER ELSE MIGHT BE INVOLVED!!

This project requires a few supplies that you can outsource from some trash.

1. The LED Itself; it doesn't matter the specifications all too much except for the current and voltage the specs of mine are: 30V-33V, 2000lm-2200lm, 6000k-6500k, 700mA.
2. A buck boost converter on the basis of the XL6009E1 the specifications of which are;

Input voltage: 3.8V ~ 32V;

Output voltage: 5V ~ 37V;

Maximum output current: 3A;

Conversion rate: <94%;

Potentiometer for setting the output voltage;

Board size: 43mm x 21mm x 14mm;

1. A switch of any type that you would like
2. A BMS board that supports the battery type so for example 4S BMS for 4 18650's in series; I used LG INR18650 cells because I like their specifications; salvaged cells from laptop batteries could work but BEWARE they will have less capacity = less runtime
3. The battery pack can be any of your choice but the minimum is 4S and the maximum should be maybe 6S but I think that 6S is overkill since its a 20W LED with a input voltage of 33V and it would mean junking the boost converter and just adding a constant current limiter for whatever mA is your LED.
4. A NO (Normally Open) Bimetal thermal switch with whatever temperature rating you want
5. A few heatsinks
6. Hotglue

First off; to do this you need to have decided what kind of battery pack you want and the cells you will use. Always test the cells before putting them together because one could be defective or have less capacity thus lowering the runtime of your flashlight! As I said I used the LG INR18650 cells that I got for free from a friends old scooter. The batteries are perfect for this but they are a year or so old so they might not be perfect.

Wire up your cells in a 4S or 6S or whatever configuration you see fit and remember not to short the batteries!

Add the BMS (you can google how to do this because going in depth into this is just useless)

Above I have added the scheme, It's quite easy to connect everything, I used wires from a old furnace to get high amperage cables because regular ones wont cut it in my opinion. It's very poorly drawn but you get the idea.

Well it's not as impressive as you might think. The efficiency of the boost converter is 90% in total but what about the battery life? Well:

Power Required by LED:

1. Power = Voltage × Current
2. = 36V × 0.4A = 14.4W (maximum LED power).

Power Drawn from Battery Pack:

1. Accounting for efficiency:
2. Power from battery = LED power ÷ Efficiency
3. = 14.4W ÷ 0.9 ≈ 16W.

Current Draw from Battery Pack:

1. Current = Power ÷ Voltage (14.8V max):
2. Current = 16W ÷ 14.8V ≈ 1.08A.

Battery Life:

1. Battery life = Capacity ÷ Current Draw
2. = 2.9 Ah ÷ 1.08A ≈ 2.69 hours.

So you will get around 2 hours and 30 something minutes of use before it inevitably needs to charge but this assumes its running at 90% efficiency and at 36V and 400mA.

To conclude this project i hope you guys enjoyed it or found it useful, please send any criticism you might have to my design in the comments or like it if you want!