I need a new driver for a XHP70 build, Should i stick with the stacked chip Qlite or get this one:
Product Code: FET17-SS http://www.mtnelectronics.com/index.php?route=product/product&path=67&product_id=227
I use the 2 purple 10a 18350s with the xhp70
Should i get the no 6v LVP zener or the other option?
I like FET drivers, as long as you are OK with a constantly declining output and using your modes to extend runtime. It’s the way I usually go if I’m going to be stacking for more than 4 chips to a Q.lite to get the current I’m looking for.
Run time? 
Using 2 18350’s running a XHP70? This is just a WOW light right, I say Go for it! I’m running 2 Efest red 18500’s with a XHP70 FETDD zener mod no lvp (it’s a 6v thing) guppydrv. rev 1 and pulling 9.98 amps, run time never came into the equation… FUN yes!! Longevity - NO! :_(
Damn 9.9A? isnt that Past the amp rating of the XHP70?
This is the reading at the tail cap. I really don’t think that’s whats at the emitter at all. It’s in a Surefire M3 Combat Light with a zero rez switch, It’s been running well, and it smokes my other M3 961 weapon light with a MT-G2 on 2 25R’s running just over 10 amps at the cap, same set-up and driver. I have a EESEX6 and a Supfire F13 running the FETDD guppydrv, with a dedomed XPG-2 single 25R, single Purple Efest 26650 reading 6.2amps, so why aren’t they toast? I don’t hold too much to tail cap readings unless I poof an emitter? And it has happened more than i would like but that’s part of the game. I check my lights with a Fluke and Klein clamp on meter’s and they repeat the same numbers?
So you would say XHP-70 draws more than 4.8A (which is the max. current according to the datasheet) at the FET, so does it mean we need at least 6V 10A LED driver for this led to illuminate at maximum level?
personally I would not draw more than 7A
heat gets much more while the output gain is low
7135 driver wont work because voltage is too high
No problems at all with 6V LEDs and 7135s. Many have done it for a long time, and so have I. I have MT-G2s and XHP-70s running on 7135 drivers, works fine.
12 volt LEDs like XHP-35 HI are another issue though, I’ve tested with 7135s and they don’t mix well.
Using the FET DD drivers you first have to determine how much current the led can tolerate best case scenario and for that I look it up in Djozz’ tests he’s done a great job of crash resting an incredible variety of emitters. Having the led mounted on a direct thermal path (DTP) copper star is critical for any use approaching or exceeding max current specs. The use of DTP mcpcb’s allows us to do this because of their exceptional ability to wick heat away from the emitter. After looking up that info I decide where along the current/voltage/output curve I want my light to play. Matching your cell voltage to the voltage readings to the right will tell you what kind of current you can expect to deal with and a ballpark for output. 7135’s allow for quantum increases in current (in 350 mA or 380mA amounts) and FET DD drivers deliver whatever current can be pushed by the cells for a given led Vf.