Go and goggle “yn-20-5” here. I did a “breakdown” of that and the –3 version.
That row of resistors are all parallelled together to act as a ballast resistor.
The 9435 is a 30V FET, which is switched on/off for PWMing the LED.
That little 3-pin doodad is the µC itself! The cap next to it (brown rectangular thingy next to it) holds up its power long enough to sense mode-changes.
So yeah, you can parallel some more resistors across them, or just short them for direct-drive (for the 5-10sec the poor LED would last, haha). Just need to short one of them, and the bulk of the current will go through that bridge.
…or just connect the LED+ lead to one of the solder pads below the bank of resistors. Yes, that does (also) make it direct drive. As Lightbringer says, the LED may not last long, especially if you have multiple cells in parallel pushing power through that FET.
Edit: Then again, if you happen to have a Luminus SBT-70, or other such high-current ~3V emitter lying around, you could put it in there.
Thanks for all the input guys! I’ll snap a pic later if I’m able to get one to come out well so that it’s useful, but the gap between the led plate and the driver shelf is minimal. I’m measuring between 2mm and 3mm with a handheld tape measure, but its probably closer to 2mm.
I’m probably going to try the suggested mods above and hope it creates direct drive that won’t blow up right away but if it does, then the 46mm SRK 7135 based driver from mountain will probably wind up in this light.
The good thing is since the led plate is so large ~50mm diameter, I can order one of the large 30+mm MCPCB’s from mountain, put an xp-l hi on it, and really drive it hard if I can figure out a way to bolster the thermal path from the plate to the light itself. Pics to come, thanks again.
Ok here are some pics of the head of the light. If nothing else, maybe this thread will give some info for future mods or decisions on which light to buy. It's a shame that its relatively difficult to mod this light for series cells. I know its been done, but its waaaaaay above my skill level, so I'll stick with an xp-l hi and enjoy the longer run time of 4 parallel cells.
Also, I suck with computers in general. I added captions to each of the photos for a little explanation, not that its really necessary, in the "image description" portion of the add image box, and none of them are showing up in my post. Any ideas why? or is that normal?
Is adding resistance to the bank the same as doubling the resistors, like someone suggested earlier? How is this different from removing a resistor and shorting it by connecting the two points with solder or a small bit of wire? Thanks for educating a noob
Thanks so much for the education!
If I have some resistors that are similar in shape to those on the board but don’t have the same value (I might harvest some from a broken macbook magsafe charger), would they work? Do the resistors added in parallel over the top have to be the same value, or can they be different values? Starting with your calculations above, is there a way for me to calculate/estimate the increase in current? Does V=IR work for estimating the current in this way? Many thanks
On that same note, I do have a small pile of 5 or so drivers that I’ve somehow partially rendered inoperable while trying to mod some lights. Mostly Njang/qlite 7135 based drivers but also a buck driver or two. Would harvesting the fet from any of these and adding it to or replacing it in one of the labeled “9435” spots on the board provide and theoretical benefit?
I’d be very careful, and if anything, do this in steps vs going whole-hog and frying the LED.
Those are “2R2” resistors in the pic? So divided by 8, that’s 2.2Ω / 8 = 0.275Ω.
That’s just a ballast resistor, and how much current goes through the LED depends on the cell voltage and Vf of the LED.
I’d maybe try parallelling a 1Ω resistor (“1R0”) at a time, and measuring the current with a fresh cell each time (when current would be maximum).
And even that’s pushing it, because that resistor would be hogging a proportional amount of current (ie, more than twice what any of the other 2.2Ω resistors do).
Safer would be just stacking more 2R2s one or a few at a time.
Yeah, frying it would be a “learning experience”, but…
They use 8 to divide the current and heat among them. One stacked pair will pass more current than any one of the others so more heat will be produced by that pair in that spot. Each additional stacked pair will further reduce resistance. Resistors have power ratings which if exceeded will cause them to burn out. Generally we can get away with upping the current with “resistor mods” but at some point something gives. Heat has the added consequence of reducing power ratings so the harder you push things the more likely they are to fail at an accelerated rate. If you’re like some of us you will keep adding resistors until you find you added one to many. while others with a more restrained disposition will try only a few. Not being an electronic engineer and having only the rudiments and experience to cling to I’m guessing that this particular board will fall short of any hot toe expectations so personally I’d just go ahead and order an SRK driver(in fact that’s what I did for my SRK and as soon as I can crack it open it will get the treatment. For a single led fed by 4 cells I’d still recommend the 7135 version(available in kit form only right now) to control current through the led to match whatever heat sinking improvements you manage. If you can’t build it yourself either wait for Rich to list more or ask for aid in getting one built.
While hardly ideal (resistance of metal goes up with temperature, whereas carbon more or less stays the same), standard 30ga wire-wrap wire has a resistance of 0.339Ω/1m ( AWG American Wire Gauge Diameter and Resistance ).
If you want to try a 0.1Ω resistance, that’d be (0.10Ω/Xm) = (0.339Ω/1m), X = 0.295m or roughly 1ft.
So coil 1’ of wire-wrap wire into a loop (inductance shouldn’t be an issue) and that’s your cheapie resistor that can handle some decent amperage.
The lower the resistance, the less wire needed. The more resistance, the more wire needed.
Oh, and I’d use that instead of the parallelled resistors, not parallelled with them.
Although this driver is intended for multiple LED in an SRK, what do you guess would happen if used for a single emitter? would 2300mah multiply by three and give something like 6.5-7Ah? or would it just not work at all with a single emitter?
It’s been a while. I know I replaced the factory emitter PCB with a Maxtoch copper DTP board from Mountain and replaced the LB emitter with a good XM-L2. IIRC, I just moved the LED+ wire to one of the pads behind the bank of resistors. Due to the design of the light, I never checked the tailcap current to see what it pulls, but I’ve never had any issues with overheating or burning out.
The earlier Ultrafire 1226 lights had a good multiple-7135 based driver. I wish those were available separately so I could replace the driver in mine…
Great question and now that I think about it, doubtful. Cheap though, so I might try it and then use it for something else if it doesn’t work out. Any speculation on what the current would be with a single emitter? Still just 2300mah or would it go up since the driver is intended for 3 XMLs? It says the input is 3.7-4.2, but we know fastech’s descriptions aren’t always correct, but based on that voltage it would have to be putting out the current for XML’s in parallel?
I doubt it will fit in the small space though :( so maybe I'll try it in another soup-can style light if I can figure out how to get a better thermal path to the LED with that high current
Thanks! yeah they look identical to me. Did the output seem to go up to somewhere near a direct drive level when you bypassed those resistors by moving the +led lead? Or just up a little bit? Any chance you got a current reading while you were modding it? A couple more questions: I see mentioned in that thread that the 9435 is a mosfet. Im googling what that is right now, because I know nothing, but would adding additional 9435’s in those empty spaces have any positive effect? Any speculation on why there are spots for 4 of them? Also, I hate lights that have strobe that isn’t hidden, but I know that’s just what you get with most budget lights. That single yellowish-tan thing looks like a capacitor, is that likely to yield the same results of removing next mode memory with the graphite pencil trick? https://budgetlightforum.com/t/-/26205
This has helped a ton, thanks for everybody's input
but if it does, then the 46mm SRK 7135 based driver from mountain will probably wind up in this light.
