I had took the r150 resistor off and i lost it, but i found two r130 resistors and and soldered both on and now getting 3 amps on 1s and 2.53 amps on 2s. I had a dedomed xm-l2 that i put on.
To help you better understand what happened, think of shorting the sense resistor as putting the driver into DD. Because that’s what happened. Never short sense resistors.
EDIT: Based on your initial results and your modded results, your driver is (and was) operating just fine on 2s. Working on 1s is a pretty tricky situation for a buck driver like this, your driver was (and is) clearly failing to do that 100% properly. The QX9920 is uncommon in it’s ability to work on 1s - most buck controllers just can’t do it. It sounds like you got some bad luck with your driver (assuming your cells are fine). Normally I might suspect that the LED might have an unusually high Vf, but you’ve already had to replace the LED and are still seeing the same problem. I don’t know exactly where the issue might be, but checking the driver for any components that do not look exactly like Tom E’s pics would be a start.
With them shorted it wasnt DD with 1s. Maybe with 2s. With it shorted it was only 2.63 amps on 1s. That was with the other led though.
I guess im happy with the 3 amps on 1s and 2.53 on 2s, it is 1.53 on 3s. I am not happy with the dedomed led, even though the kcd is alot higher, the beam is to narrow for me, so i will get a new led soon or maybe a mt-g2.
How does the mt-g2 compare to the xm-l2 in this light Tom?
DD in the sense that it applies the full battery voltage to the LED. There may have been some pulses of off mixed in there, but I think it’s very fair to say that the LED saw long pulses of the battery voltage. There’s also the inductor providing a little resistance. The controller will attempt to get it’s sense voltage to go up and be unable to since you shorted the resistor which generates the sense voltage. It’s not actually the same thing as a DD driver, but it is a direct connection between the LED and the battery [via the inductor]. TLDR: don’t do it.
Well the MT-G2 turns the beam into more like a good 3 LED light, but the tint and general profile of the beam, to me, is the classic MT-G2 everyone raves about - nice tint, nice single emitter pattern, etc. I measured throw at 43.5 kcd in my 2,329 OTF lumens, 4.6A setup. I would think is the ballpark for being in a thrower host, but could be better because I know the lumens is low and the reflector is rattling - not tweaked to fit well and focused.
FWIW aw73 you may run into the same problems w/ an MT-G2 on 2s that you ran into with an XM-L2 on 1s. You might not too, I sure don’t know. Sounds like you’ve got enough extensions to deal with that anyway.
Ok thanks Tom!
I updated the OP at the top. Trying to help people find things - dunno if it helps much. This thread has gone all over the place, not such a bad thing though... 
I will probably run it on 2s mostly.
I need to get off my butt and do some things outside, its so beautiful down south today. Mid 70s for the high temp today instead of 90s just a few days ago. Great day to be fishing!
I’m thinking about the Y3 and do the MTG2 swap.
Can anyone confirm if the noctigon is a direct fit, or requires a slight raise to press against the reflector?
Thanks
Post #425 here: https://budgetlightforum.com/t/-/27963 has details. Yes, you need to do something - shim the MCPCB or you can follow what aoeu did - see this thread's OP - Post #145 description.
How did it handle the heat as at 4.6 amps it should start getting hot quickly?
Yes it did heat up quick with the MT-G2, not sure how it did over several minutes. I don't have it configured like that anymore - it's back to a XM-L2 U2 1A on a 26mm MaxToch. I fixed the switch problem - the driver fits a little loose so the driver mounted switch can get out of position a little, or pushed back with use. So I jammed in some copper braid on the edge of the driver, opposite side of the switch and seems to be working 100% again. The R100 mod is holding up well. Here's my results:
Single KK4000 cell, 3.30A tail, lumens: 1,112 @start, 1,081 @30 secs, throw: 79 kcd measured at 5m
Two KP 26650's, 2.70A tail, lumens: 1,380 @start, 1,343 @30 secs, throw: 100 kcd measured at 5m
Note: all my lumens and kcd measurements are my own taken on a older LX1330B meter - kcd taken indoors and lumens in a PVC constructed lightbox, accuracy can be freely debated
You weren't happy with the MTG or just experimenting?
Can't recall (I'm bad), think the MT-G2 died? There were so many things goin on here with the R100 resistor - if it works single cell, etc., so decided to go to a MaxToch 26 with XM-L2 in that unit. That MT-G2 LED I've had a long time, and it's been re-flowed a couple of times - just not sure if it was ok. I think the MT-G2 was shorting on the reflector, so not sure if it's fried. Didn't know I should have used kapton tape or something - didn't know what was commonly done to mount these... I pulled it off the Noctigon - but again, totally forgot what the problem was. Think I was gonna xfer it to a MaxToch MCPCB... But I did just get in a new bare MT-G2 from KD ($14.50), so will probably use this with a custom zener mod driver - probably a BLF17DD, and mod another Y3.
I upgraded mine for MT-G2 (6V). I drilled the reflector hole a bit larger as well as the original white plastic spacer that was over the led. I used the white piece as an insulator wit MT-G2. It works well, I did not try to optimize spaser any further because during tighening it seems to get pretty good already.
I replaced the original sense resistors with 3 x R100 in parallel (ie. about 33mOhms). It measures about 3.6-3.8A at the tail with two 26650 cells. I’ve not used it for long periods, but for occational use it is one heck of a light now. The beam is somewhat large but it brightens up quite a long large area now. It does get warm in use, I’m not sure if it would take constant full power in summer temperatures.
(I modded another with noctilux XML2 and 2.45A current at tailcap with two cells which should equal about 4-5A at led.)
@boffid: Am I reading correctly that you pulled both the R150 and R180 and replaced them with three R100’s? Was that for both lights? Any chance you measured current at the LED? I thought some of the other guys were seeing currents similar to your MT-G2 light with the R150 + R180 + 2x R100’s. I’ve got one modded with one R100 added that’s pulling roughly the same current as your XM-L2 (mine has a dedomed XM-L2).
So… are the currents going up with lower total resistance or with more? As I’ve said before, my understanding of modding existing drivers is pretty limited.
Original resistors removed and replaced with 3x0.1R resistors in parallel for my MT-G2 3.6-3.8A drawing mod.
Originals kept (0R150 and 0R180) and R150 or R180 added in parallel for my XM-L2 mod drawing 2.45A or so.
(Both with two cells)
Unmodded version drew about 2,4A with one cell and less with two cells.
Sorry, no measurement on the led but assuming a reasonable efficiency one can do rough estimates. Both are bright enough for my use.
Less sense resistance gives higher output current. I’ve got to write a sticky on this I guess.
In most cases, including this one, the math is very straightforward. First you must calculate the total resistance: use a parallel resistor calculator and remember that the ‘R’ is a decimal point, so R100 is 0.1 Ohms. Second you must plug the total resistance into the appropriate formula - for this QX9920 based driver it’s [ Iout = 0.25 / Rsense ] where Iout is current to the LED and Rsense is the total resistance of the sense resistor bank. And then you’re done: that’s the target current, figured out in 2 steps!
Remember that we are setting the target current. For XM-L2 (& similar voltage) especially affects single-cell applications with this driver since it will have a lower maximum current in single-cell applications when compared to a DD driver. So for currents above 3-4A I’d guess you’ll only see the target current on 2s or more. This same logic applies to MT-G2 on 2s instead of 1s: it will be limited to lower than DD performance on 2s.