I have an Ultrafire 7XT6 from DX and whilst I really like it, particularly the shorter form, it's actually no brighter than my 3 XM-L FandyFire.
Obviously this means the emitters are driven quite gently, so I was wondering if any of you electronics wizards could suggest any simple mods to the driver to increase the maximum output a bit.
I think the section R10 to R13 on the board is a row of 4 resistors, and perhaps I could wire across one or more of them, but my electronics knowledge is very limited, so any help would be appreciated.
I was also wondering if those wires to the switch are limiting the current flow, because they are very thin. Would it be worth replacing them with something slightly more substantial?
The wires to the switch are ok, not much current goes through them.
Before you are advised any further can you post shots of the heat sinking of the LEDs?
I had thought the full current would travel through the switch, so I've already learnt something today thanks! :-)
The led board seems to be screwed to a fairly substantial aluminium plate, about 2-3mm thick.
Drawing inference from your post I left the light on high for over 10 minutes, and the head and body became pleasantly warm, and the light level remained constant.
See that row of R130’s, that is a resistor bridge [R10 thru R13], that limits the total current that can flow to the emitter, by either stacking another R130 on top of them (you would need to keep the resistors balanced) you can more or less effectively double current output to the emitters, or you could simply bridge them which will then allow full current to flow from the MOSFET.
The big chip in the middle is a MOSFET, it is controlled like an solid state light switch by the small 6 pin IC
Either Jumper the resistors or I believe you can move the black wire from the pad on the right where it is currently to the L pad which bypasses the resistor bridge entirely, choice is yours
Definitely looks like a pretty beefy heatsink you got there…might want to check to make sure there is a squirt of heatsink compound between them to help thermal flow
1. Why would you need to keep the resistors balanced? OK, so the current heat distribution would be uneven, but it really isn't a big deal here. (please correct me if I'm wrong)
2. If you move the black wire to the L pad it would just bypass the MOSFET, making the light direct drive, unable to turn off.
In parallel the current flows evenly thru the resistor, if you unbalance the lower resistance path the current increases, if too much current flows thru one path it can overheat and burn out the component…a piece of wire jumpered across in lieu of a resistor might be able to handle the current.
2. It is possible it might make it always on…, but in order for it to be always on the bat+ and ground must be connected physically by the trace on the board, the MOSFET should be between the paths electronically Moving the wire will make it always on, don’t move the wire
Best bet would be remove R10-R13, take a chunk of wire, lay across pads, bridge the gap…expect max current flow and max heat output though…your pleasantly warm Ultrafire 7XT6 might now be quite hot if left running that way for long (but that is what modes are for)
or get some R065 resistors and replace the R130’s, 1/2ing the resistance, or solder another R130 on top of the current R130 doing the same thing
i can’t tell, but does that heat sink screw into the head? Those 4 resistors lead me to believe that it does not. Explaining the need to limit the current to the LEDs
oh no no no…didn’t take it as a challenge or anything
Always best to have more than one set of eyes on something…and I would rather admit I was wrong (which I am ALOT!) than give someone incorrect information and they damage their light or create a hazardous situation
I will have a further exploration into the construction of the torch to check the heat sinking before I do anything, but wiring across the resisitors sounds like a fairly easy way to get a major improvement in output.
Can I assume that the two modes (high and low) will remain, but just high will be effected?
I would rarely use the high setting for more than a few minutes, so an increase in heat would not likely be a problem, but it would be good to still have a low light mode too.
No, all modes will be affected, since lower modes come from just running the output at less than 100% duty cycle. The low mode, at probably 15%, will be full current 15% of the time, and 0% 85% of the time.
Many many many drivers use different value resistors in parallel for sense resistors, often the lower value one will be larger to hande the higher current it will see, but it usually doesn't matter. Like, a 0805 R500 and a 1206 R130. In most cases that doesn't matter though. Also, on this driver, those are simple limiting resistors, not sense resistors, since this driver doesn't do any current sensing/regulating. Just add a jumper across from one side to the other, wherever it's convenient.
So if I understand correctly, I will still have a low mode but it will increase proportionally by the same amount as the full power mode.
Can I leave the resistors in place and simply wire across over them? If I can (or even if I have to remove them), would wiring over one resistor give full power, or would the increase be divided between them; ie a 25% increase for each resistor bridged?
If so, then perhaps I could bridge one at a time until the right balance was achieved...(wishful thinking?)
I have just soldered a wire across one of the resistors (R10), but it appears to have made no change.
I switched the light on and there was no discernable difference at all.
Maybe the fet is limiting the output with pwm on high. You never know what a guy does with the pwm pin from the mcu far as code goes. I wish we could decompile back to source and see what’s going on there.
Could bridge the fet and see if it increases. I’m just saying that’s what I would do. These guys are way smarter than me though. I’m just thinking out loud
It looks like the PWM coming out of that modes chip has to go through Resistors R15 and R5. R15 look like it might be labeled 102 (not clear on my screen). 102 would be 1000 ohms, right? I imagine lowering the resistance will increase the voltage to the FET's Gate and may increase how much current it allows to pass.
Let one of these more knowledgeable chaps verify that before trying it out.
If the PWM really goes to 100% then changing the resistor in between won't change anything, since the resistor will only slow the current down while it is actually flowing (gate charging and discharging). When PWM is at 100% (no PWM), the resistor shouldn't change the voltage the gate sees. That said, we don't know what the MCU is actually doing.
ledtorchforum: You said that there was no discernible difference, but that doesn't mean that there wasn't a chance, even possibly a rather large one, without an external measuring device. I have built a lot of lights, and I would have a hard time telling you if a light was 2500 or 3000 lumens unless I saw them side by side. I could maybe do it, but the difference my "human light meter" sees is not that significant, especially when the light is used up close.
I say stuff that's wrong all the time. Please don't take what I said as a personal challenge. 
I’m just thinking out loud