Hi guys, I have a de-domed Cree XG-G2 S2 mated to a 4.2A Qlite. However it only draws 3.2A and the tailcap. I not sure if I understand how QLITEs work. Does that mean that on the MAX setting the light is out of regulation right off the right. If so, does that mean I should remove 3 or 4 7135 chips?
BTW, I have ruled out any problems with the chips being stacked. I have test this LED with many different drivers and that’s all it seems capable of with a single high drain 18650. Also, my DMM is reading accurately and has short 12ga leads.
My first thought would be a weak/old cell…
Possibly an emitter with a high internal resistance/high Vf or other current limitations within the light? It sounds like your emitter is running at a Direct-Drive level; if the emitter is only capable of 3.2A at direct drive, then any 7135 capacity above this point is superfluous. Do you have a spare XM-L/L2 emitter to validate the 4.2A max of your driver?
Lately I’ve hooked up triples directly to a cell with a DMM to measure amps, just to see the max current I can ever expect when turning the FET pin on my drivers full on. You might want to do the same. If it pulls the same 3.2A you will know that stacked chips for 4.2A is pointless with this LED.
I probably wouldn’t do this with a single Nichia LED, but now days high VF seems to be a limiting factor with many Cree LEDs. Disclaimer: I wouldn’t really know from any personal experience, it’s just an assumption based on stuff I’ve read and I could be completely wrong.
Check the Vf by measuring voltage directly at the LED when powered on. I’d have to read around here a bit to find out what constitutes a high Vf though.
Hi keltex78, I have tested using new 30Qs. I have also tested the driver with a XP-L and it pulls 4.2 amps. I also tried reflowing the LED to a different Noctigon.
Thanks Mike C, that’s a great idea; I’ll tried measuring right off the battery. However I’m not so concerned about output in this case. I understand that the extra 3 or 4 chips are not doing anything, but what I would really like to know is if it is bad to leave the driver this way. Is it negativing affecting anything or should I remove some chips?
Yeah, that’s a good question and I’m not qualified to answer. I could guess that you can keep the chips, but that would only be a guess. Hopefully someone with more knowledge will step in, I wouldn’t mind knowing myself.
If I understand the situation correctly, the driver can supply 4.2A but not to a particular led. That does sound like a Vf issue with that particular led. It might be resolved by doing spring bypasses to eliminate parasitic resistance but a lower Vf led is a better notion IMHO. What the extra 7135’s will do is increase the output of all of the modes over the same driver with fewer chips and lowers the efficiency overall since every mode is a pwm’d percentage of max and LEDs all run more efficiently at any lower current. Each added chip also has it’s own power requirements as well. It’s pretty nifty how they can adjust internal resistance to maintain a constant current but it’s not free. I would suggest you not use that particular led in a parallel led set up unless you use similarly high Vf LEDs to go with it or it will just be dimmer than the others.
Thanks Rufusbduck, that makes a lot of sense. In that case I’ll definitely stop being lazy and remove those extra chips. I always welcome lower low modes.
No problem. The moonlight special and FET +1 drivers were both created to give a consistent very low moon mode by pwming just a single 7135 and using the rest or an FET for the higher modes.