Direct drive and matching MCPCB / emitters to 18650 batteries


Newly Enlightened
Aug 15, 2016

Reference would be QTC lights and in particular. Scenario is when the QTC fails or is removed causing the light to be in direct drive.

Have an option to install different 16mm MCPCB's (SST-20 in this case).

Have a wide availability of single 18650 cells with different capacities, maximum output (10A-30A), protected or unprotected.

How would one determine the relationship of MCPCB's/emitters to battery options? Safety, durability, optimization, efficiency?

For any given combination of MCPCB/emitter to battery, would like to determine:
1. Safety levels
2. Maximum output in Lumens
3. Runtimes
4. Maximum required Amperage from a battery

Thank you in advance!


Flashlight Enthusiast
Apr 24, 2021
If QTC fails then you'll be in 100% full-send.
Look at the data sheets of various LEDs and you'll get a good idea of everything you need to know.

The question is what pushes and what pulls power? Voltage is pushed to the LED, which in your case will be 3.7v, and the LED pulls current from the battery. Enough current and the LED phosphorous burns and the color becomes blue.

If the pull of the LED is more than the battery can handle then the battery heats up and eventually becomes unstable. Some will paint the picture like we're playing with explosives. Luckily I haven't caused an explosion yet.