If it was in series or replacing the sense resistors I would agree but since it’s in parallel and the original sense resistors are still in place then the ‘amps’ are still flowing through the original sense resistors.
No! If you reduced the current sense resistance by half with the pot, half the current would be going through the pot.
Also, the power rating of the pot only tells half the story. There is a maximum (often unspecified) current that they can handle due to the wiper contact.
Actually, yes you’re right. For this application (9 amps) the variable pot wouldn’t handle the power.
AFAIK the sense resistors usually see between 30-90 mV. So 0.09 x 9 is 810mW… and even with half the current as you said, that’s still 405mW so too much for these 250mW variables.
Mind you it’s been 25 years or so since I studied electronics at college so I have an excuse 
FlashPilot: Is there any chance you can take a voltage reading at the sense resistors ?
It’s 49mm , it must be close to yours the two flashlights must have the same battery body only bigger head (yours)
Thank you for checking. I again overlooked the fact that the DRY is 12.6V, mine is 4.2V.
Thanks for all the great replies. So If I understand correctly, I should:
- Find out if the driver is regulated. -I should run a battery pack through my DMM and measure current. If its regulated, the current should increase as voltage drops. Also, my lux meter readings should remain fairly constant as voltage drops.
- If the driver is regulated, there should be a good chance of finding a few extra amps. If so, I should buy some 10 ohm trim pots, solder one in parallel with one of the existing sense resistors and slowly turn it clockwise, while the cells are hooked up to my DMM and see what increases are realized… to the point I either achieve 9A or melt the pot. Looks like Im going to need several pots for spares.
So assuming the driver is regulated, how do I find the resistance value of the pot before it blows? Maybe solder one leg of the pot to the driver and the other to a wire. Make small adjustments while making contact with the free wire end then disconnect and measure resistance before I go further. Repeat the process before it finally melts, which should give me an idea of how much further I might need to go using resistors. Can I measure resistance while one side of the pot is still soldered?
Having said all that, Id still be stuck with the darn blinky modes and a driver that might fail at some point, so I wonder if it would be easier and more reliable to do as I had mentioned in my original post:
•Im thinking about removing all the components from the stock driver and using it as a contact plate. Then attaching 1 × 3.04A 7135 driver per emitter/pair of emitters. Would this be a good one? Im considering the 3rd Star option : Low (5) – Medium (30) – High (100%). Can I ground the memory on the drivers to prevent synchronization problems between the drivers? (so it would always come on in low first and have no memory). That, or is there a way to sync the drivers modes and maintain memory without having to go to a master/slave configuration.
Thanks again for all the help. Maybe this flashlight will turn out to be a descent user after all.
Yes
Yes but you can buy some resistors too for permanent modding
You can desolder the controller from two nanjg and connect the remaining controller with the two extra boards…so you have what you want. There are threads about this here, I haven’t done this successfully by myself but I know a lot of people use it.
Standard trimpots may not last long enough for you to determine anything. A trim pot is rated at its power (usually 0.25W) when set to 1/2 or more of its resistance. When a 10 Ohm pot is set to something like 0.2 Ohm, only a very small portion of the wire/carbon inside is being used. That fraction of the pot will not dissipate the heat and will likely burn. I would suggest axial 1/4 resistors or the snazzy SMD resistors now available at Fasttech (already ordered one of each value).
You can buy single mode NANJG boards (No MCU) that are ready to be ganged together as well. I think you can probably control up to 32 7135 chips with the one output of the MCU (about 6mA Vcc current needed).
Anyone controlled that many with one I/O before?
Werner - Thanks bro. I found a great post by Old-Lumens that explains the parallel set-up in great detail.
relic38 - It sounds like the trim pot will probably light up like a cheap chinese bulb filament before it breaks and sets the plastic housing on fire. Thanks for the warning. I think Id like to try the axial 1/4 resistors you mentioned. Can you please post a link… so I dont buy the wrong ones.
Also, looking around for NANJG boards without the MCU’s didnt turn up any results. If you dont mind, can you post a link for these as well? Yeah, I feel helpless…
Im now considering 4 x NANJk boards total for around 12A. Sure, the light wont have the mass or surface area to properly cool it in high mode, but then there is always medium mode. Hill, you might be into something there. Have you made any progress?
Thanks again for all the help!
Here are the metal film axial ones, comes as a kit.
And, here are the SMD ones, come in strips of 100. It costs more to have a variety, but I find them easier to work with. I suppose not everyone is comfortable with SMD, however.
From the photo, those sense resistors look like at least 1206 sized ones to me… 0805’s will be too small to fit.
Yeah I noticed that. I use both interchangeably; just a little extra solder to ‘drag’ up to the well-centered resistor works for me. If they happen to be larger than 1206, I use a piece of wire-wrapping wire to guide the solder. OK, maybe that’s trick is not for SMD beginners, but it works.
If you have the space, go for the axial resistors. They can be easier to work with when bent to the right shape.
I have these axial set ordered too, very nice 1 W resistors for a cheap price.
Everyone should have them at home.
You’re right! I just ordered a set for my grandmother. 
What a sweet boy…
Thanks Relic. Those are just about the right size to handle without needing tweezers.
I just tested the driver. As voltage drops, so does amperage when powered on. So it sounds like a resistor mod wont work with this driver. Are we all in agreement?
Can someone please answer this? Thanks. 
It depends on the drive, however if it varies the current directly with voltage over the whole range starting from 4.2V, then it’s not in regulation. Any change of sense resistor will not make much difference. That’s strange for a driver built like that. If it’s a buck regulator, then current should have went up when voltage dropped, at least for the higher part of the voltage range.
Thanks relic. It looks like I’ll be converting this to a 7135 based driver.