Please help me determine vF for XM-L2

I agree that it looks different. It still looks linear above one amp though.

@FlashPilot: While I can understand that you want low Vf to get better regulation, I wold certainly be interested in sorting them for light output. That's a whole other story than Vf.

A variable that might maybe possibly not affect the readings is a poor substitute for just eliminating the variable altogether.

Interest for one variable does not exclude interest for another variable.

Both Vf and efficacy are important parameters.

Ok. I'm interested in your positions. Please show me where I went wrong.

Did I read that correctly? I didnt realize that I could test the voltage of each individual emitter while it is operating within a series string. :bigsmile: Could I complete the light and test the emitters that way? If any emitters tests with an unusually high voltage, I could just swap it out.

Nomenclature recap:
2 separate driver circuits will power 40 emitters. Each driver will supply 20 emitters wired 4S5P.

Could I complete the wiring for the light, tune both drivers for the same amount of amps (they have turn pot adjust) and test each emitter? I could put a fan on the sink and wait till the temperatures stabilize before testing.

Make simple current source with two 7135,use one li-ion battery to power it,and measure Vf of each led after for example 5sec,and that's it.

Measuring Vf in series-paralel string isn't good idea,since each series string could draw different amount of current.

I think we assume that all the emitters will probably be within a close tolerance of each other, so we’re just verifying that none of them have an unusually high vF at max current (3.4A). If I turn on all the emitters to max current (3.4A) and I test the voltage of each emitter in each serial string of 4, and any of those test much higher than the other 3 in the same string, wouldn’t that be enough to identify a culprit for replacement? Im more concerned with vF at max than below it.

Im still trying to locate a bench power supply to test these.

@Bucket - thanks for your graphs and suggestions. I have a 24 cell parallel 18650 pack and could use it to power a 3.04 qlite… which Im starting to think about doing.

@sixty545 - at this stage of the game, vF is probably going to be more important than lumen efficiency. If I come up with more than 40 emitters with decent vF, I might go back through and test which ones produce the highest lux… its certainly a good idea.

I’d like to recommend this, but i don’t know how good quality it is or how it works

Thanks, but the problems with the ones Ive seen reviewed so far arent all that encouraging. They fluctuate and dont deliver repeatable performance. Maybe good enough as an LED driver but not good enough for test conditions. Also, that one is from bangstupid… home of the grossly incompetent sales staff. lol

While talking to the driver engineer, he suggested a 5 volt 4 amp power brick to drive a 3A 7135 based driver. There are several on ebay from US based suppliers. At least I have a spare 20 lb heat sink to use for the tests.

thanks for the heads up, i’ve been wanting to know if that one is worth it or not, and i’m not a fan of that store either, but i have heard of worse elsewhere and have bought from them twice (not the best of transactions of course)
i would also like a 5 volt 4 amp power brick but have never seen one (that i can remember) and i don’t like fleabay


no shipping to canada, but i will keep an eye open, maybe someone around here sells one of those