So I tore apart my TK-35 and replaced the cold white XM-L with a 3C XM-L2. I believe I read some general comment at some point regarding sense resistor modding of the tk35 driver but there was no specific info. So my query to the hive is three fold. Has anyone messed with the sense resistors of a tk35 and what was the result? Following up, I would like to know where in the below photographs the sense resistors are located. Thirdly, in the absence of specific information, do any of the sense resistor gurus here have some idea what a safeish place to start would be in terms of resistor stacking? All I know is that it's advertized as constant current, 4 mode, and runs off two 18650s in series. Fenix brags 900 lumens with XM-L2 so I figure emitter current must be near 3 amps. Driver pics below.
Did you ever get around to Spec’ing those sense resistors, kyfishguy? Looks like its been some time. Did you ever measure the current at the led?
I’m going to tear down my light and see what can be done as well, I’d like to drive the XM-L2 a bit harder, as it can easily handle it. When I get a chance, if you don’t have the info I’ll add it.
I never did get around to stacking any resistors. If I'm reading the code right (R100?) it looks like the resistors are around 0.1 Ohm. I'm not sure where to start with that low of a value. I'll look at my resistor bin to see what I have and maybe give it a try as I'm between mods. Best of luck and please do let us know what you come up with.
Testing of emitter current turns out to be simpler than in many lights as all the circuitry in in the bottom half of the light. No messing with emitter wires! The stock light gives 2.85 amps to an XM-L2. I dug around in my resistor bin and found a single R100 which when stacked on one of the sense resistors would lower total resistance from 0.05 ohms to 0.033 ohms (assuming all three are in parallel). After stacking the resistor the driver put out 3.78 amps! Looking at the crash test graphs by Djozz and applying some math to the Fenix claim of 900 lumens I figure the increase in amperage amounts to a boost of around 250 lumens OTF.
This is a very easy mod that requires only a small phillips screwdriver, one R100 resistor, and some basic soldering technique to get an extra 25% more light out of your TK35.
I'm far from a sense resistor expert but I believe these resistor banks are electrically in parallel which means you should get the same result regardless of your stacking configuration.
Bravo, Brian. I’m going to respond in kind on my light. Though, I’d also been considering a different emitter. Not sure if the MT-G2 or XHP50/70 would be an option, but Its in my mind. The XHP line is 6/12v, so would have to take some significant changes, likely a different driver. On one hand, may not be the light for it, but I’d like to make an XHP light of sorts at one point.
I’m quite new to the resistor modding, so this helped sort me out, as well. Check my Eagtac breakdown, if interested. I’m working on getting better hi res photos today.
The XM-L TK35 driver won't light up a 6 volt emitter, I've tried it. I have had the urge to mod a TK35 clone with an MT-G2 and a zener modded BLF17DD driver but haven't bought the host yet. Best of luck.
In particular I was looking at one driver that will fit and work with it, can’t recall where, but people are r-moding it on here. I’ll find it, it was out of a flashlight, which they now sell just the driver as well on the side.
Thanks kyfishguy [Brian] for posting your successful mod and your pics of the driver and the sense resistors, very helpful info . I was wondering if you noticed if the led pcb is copper or aluminium.
The LED pcb is copper, rather large (25-30mm?), and is held down with screws/thermal paste, I do not know if it is direct thermal path like a noctigon.
I can’t believe the stock buck driver won’t run a 6v emitter. The clone’s (like the New-117 and others) will run 3 and 6v emitters no problem up to about 5A (an MT at 5A, didn’t do any 3v testing). I’ve done a few of them now, I do a R-mod and then strip the factory MCU and add in my own PIC MCU to run “Ultimate Flashlight Code” which is perfect for that switch/button setup.
