I have recently changed out a couple of XM-L2s The first being a Maxtoch Mission—I had braided the tail spring and had gotten it to a stable 3.75 amps. I decided I would install a new XM-L2 U3 2A same type copper board—now with a VTC5 lucky if it reaches 2.75amps
I have noticed this on a couple of other occasions with a T6 1D dedome on a Qlite driver went from 5.12amps to 4.6amps and recently with a fet driver I was getting a ridiculous 7.2amps with a U2 1A and after installing a T6 4C it’s only pulling 5.4 but this is closer to the new normal I’ve been getting with fet drivers
I’m wondering if this is what’s going on with the X6 in the group buy
If I put this thread in the wrong place I didn’t know where else to put it
You can check to see how high the Vf of the emitter is while the light is on. Just set your DMM to DC Voltage and place one probe on each of the two electrical contact pads on the copper base.
You may also want to inspect the base of the emitter to see if it looks like it was properly reflowed to the copper base.
Higher Vf corresponds to lower current if power out is held constant. On linear drivers the higher Vf is closer to the high point of cell voltage so with a DD driver you get less top end current and with regulated 7135 drivers less time in regulation.
Yes, it seems like the vF on some of the newer emitters (not just the U3s, but I've seen it with newer batches of T6s also) is higher than it used to be. At first a bunch of us thought that it was the reflow process that had changed, but then several of us reflowed our own using bare emitters and the results were identical, so I'm pretty sure something has changed with the LEDs themselves. The higher bins do make up for the lower amps somewhat and are more efficient, but those of us who like to hotrod would always like to be able to pull more amps!
Richard - what's the deal with the U3's though? Same issue of higher Vf or something with the batch of U3's? Haven't seen anything posted on your site or IOS making any note of it. I recall you posted you talked to Hank about it all, but what's the current state of this issue?
Same issue of higher vF. Like I said, initially I thought it was the reflow, but DBCStm, myself, and several others have reflowed bare U3s and the results have been the same as those received already reflowed. I also don't think it is just the U3s, as some of the newer LEDs from other bins are the same way. I have been talking with several other members who told me that LEDs purchased from other sources (not me or IOS) have also not been able to pull as many amps as the older LEDs. My guess is that there was a process change somewhere along the line, but it is just a guess.
Is anyone else apart from me and one other member here using the latest XML-2 U2 and U3 leds having a hard time getting these to run over 5 amps before they die? Around 5.5 amps seemed to be the magic mark. It may be our setups and with the help of others got to the last of my abilities in testing without finding an answer.
I think I have posted this elsewhere but cant find it. The measurements were taken at the led for both current and voltage. Keep in mind that my DMM are not calibrated. Power was supplied by a bench power supply.
XML-2 U2 XML-2 U3
Volts Amps Volts
3.11 1 3.1
3.4 2 3.38
3.64 3 3.69
3.86 4 3.87
4.11 5 4.08
Taking into account tolerances these are pretty much identical for both leds. It was suggested to me that the way that I was driving the leds that perhaps I had an issue with voltage ripple killing the leds.
I'm not trying to derail the thread but maybe there is a change in these leds apart from the higher voltage requirements that others may have picked up on as well?
Die over 5A? or 5.5A? So do you mean it kills the LED at 5.5A? Are the fine wires melting? Dunno - most of my stock is older. Only have a couple U3's and the ones I've built up in a light are not being pushed (under 4.5A).
All testing was carried out with heavy wiring to try and eliminate losses. The leds are dying around the 5.5 amp mark. The driver in question about the voltage ripple is a taskled and my power supply was also suggested as being suspect. Hooked directly to the led regulating either the voltage or current from the power supply made no difference to the outcome. I hate to think how many good leds have died in testing and in my lights trying to get above 5 amps. In my C83 l went through a heap of leds until I found three to reliably run at 6 amps each. In the XMTG light I settled on 5 amps per led after lots of testing.
On the top end it’s hard to say the amount of light output—If you were to have a medium at 5.4 amps and a high at 6.5 amps not sure if there would be much difference
What I have noticed is I buy drivers pre programmed (I’m older and can’t see s….t) the lower modes are always lower than programmed to be—with the patience of RMM I have drivers more to my satisfaction—this is more of an issue to me—lets face it who uses their lights wide open for any period of time
Some of them seem like they are coming pretty close to that. DBCStm has measured some lights with a U3 at around 5A that are doing about what the old ones did at around 6A. Dale, care to chime in? I know that the M6s I build with the U3s all measured 400-500 lumens higher on average than the U2s did. I have built 100+ of these and measured dozens, so I know the usual range, and the average U3 was as good as the best U2s I've ever measured. This surprised me a bit, but I can't argue with those numbers. In some lights, however, the lumens have gone down a little bit but the efficiency has still improved.
Hmm, needs to be someone with access to cells of all types, hosts with DD drivers, well acquainted with high current testing, and the means and time to do so. It would also help if they were handy with a camera. Hmm…
