Good point. I have a bench power supply that I use for this. For some reason I assumed everyone has one. oops
I am wondering about the same things for my j-18. please let us know how this goes for you. and if it is the right driver. thanks I think my j-18 could be brighter , It is only about as bright as my SR King now. I tried three 26650 s but they were a little too long so I’m running it with two 26650s and one 3400, 18650.
Mi Bill, I’m sure somebody more knowledgeable will chime in soon but my understanding is your should ALWAYS run matched cells when having batteries in series. Unmatched could cause really big problems (read explosion).
As for the drop in power, mine was fairly noticeable. I means when I first got the light it was bright, bright enough for it to be unusable in a room. It also had the power to basically completely wash out a single t6 light.
Now, the flashlight is easily overpowered by a single T6 light
The light on the right is a UltraFire KF-T60. This is a heavily used and fairly old T6 light I have. Both lights are on high for the picture. The result is also the same if I run 2 or 3 cells.
yes Jonney_ Boy I think we could benefit from some electronic parts.
I measured a UV S5 (SRK) at 2159-2077 lumens, and a TR-J18 at 3808-3155 lumens (1st reading is at start, 2nd reading is at 30 secs). Definitely noticeable the J18 is brighter.
that is what I read so I sent for one but they seem about the same brightness.
Ouch! Something wrong there, definitely. I'm running TrustFire 5000 26650's, but tried 18650's but only tested the output with 26650's, but it looked about the same.
That is good to know. I may be able to improve the tr-J18. I tried some king kongs but they were a little long. now I’m using 2 trustfire 26650 and one Panasonic 3400 protected 18650.
Interesting combo... I ordered 4 of the TF 26650's from FastTech when I ordered the J18 from them. Did you try the 2 26650's by themsevles? Wouldn't recommend you run them at any length of time (melts springs), but just to see how they work.
yes I also ordered TF 26650’s from fast tech, I ran the J-18 with two of them and it was dimer with just two. let me know if 3 of the TF 26650’s fit. I also wound some solder braid around the tail spring.
3 26650's definitely fit - I'm using the light that way. I got some wall beam shots - need to post them FF STL-V2 vs. SRK vs. TR-J18.
Slight update,
Parts are ordered and on it’s way. I ended up picking up the KD modified driver along with a bunch of AA/AAA springs. We will see how it goes in a couple of weeks time when I try and swap this driver in.
One question I do have tho is, is there a “need” to attach the driver to the flashlight?
What I mean is, when I took the original driver out to look at it, it was just sitting in the flashlight, held down by a spring (which is in turn held down by a retaining ring).
Looking at the guide for the driver upgrade on the smaller Tr-J12, I see that they where destroying the original driver to get it out, followed by soldering the new one into place… Do I need to do the same on the Tr-J18 or does the new driver just ’drop in”?
This is a pic of my J18 driver: https://budgetlightforum.com/t/-/10808#comment-289413
Can't recall exactly, but didn't have to do anything nasty to get it out or get it back in. Think I describe later in that thread how to remove it.
To install the new driver, you will need to de-solder the + and - LED wires, then solder them to the new driver at the places indicated for the + and -.
I ordered the I-O driver, looks the same, specs are the same, little cheaper, great support from Hank at I-O, rated for 3 batts, includes thermal pad.
Thanks Tom,
Yes I can get to the driver the same as in your pic, unscrew the battery tube, take out the retaining plate and the driver just “falls” out… I guess there is no need to solder in the new driver (onto the head) as shown in the thread where they modified the J12’s… yay 
Now, my next noob question. What is the thermal pad for? From what I see the driver just “sits” in the flashlight. There is not any “flat surfaces” for you to “glue down” the driver.
Actually I emailed Hank about the thermal pad - it goes in between the 2 boards. Haven't gotten the driver yet and haven't worked with a double board driver before, so not sure exactly how to fit it until I get it and see. I know the 2nd board just dangling by itself hanging by wires is probably not good - you want a path for the heat to go along, escape to. I think guys have been potting the driver in these cases, not sure (potting is taking thermal grease or epoxy and smothering the driver, and maybe filling the inside of the pill).
Got the I-O driver, installed it, wow! just wow! 3 simple modes, easy to install, fits perfect, sandwhiched in the thermal pads it came with between the 2 boards, cutting into pieces to fit. Measurements of the J18:
Before with 3 TF 26650 5000 batteries, as is, not fully charged but in the 4.05v range:
tailcap reading: 3.8A down to 3.1A, fluctuates, usually dropping steady
lumens: 3330 @start, 2940 @30 secs, throw: 34 kcd
After with same batteries as is, not charged in between:
tailcap reading: 5.78A
lumens: 4930 @start, 4726 @30 secs, throw: 48 kcd
Waiting on the TF batteries to charge, takes long on an i4, but should get 5000 lumens.
Wow!
I see one of these drivers in the fit-40s in the near future, thanks for the update tom. Any ideas on a more heavy duty tail switch or are we crossing that bridge when we come to it?
I'm taking my caliper home with me to measure the driver for my UniqueFire S7; if it's the same size, I'll be checking the possibility of completing either the resistor mod or hitting up I-O for the high-power driver. I'm just not as satisfied with my S7 since I have my King clone which is not quite as bright, but too close for the difference between a 3-LED and 7-LED light.
Anyone with experience with the resistor mod; what wattage resistor should be used? and what's a good source for a single low-resistance resistor of the appropriate sort?
Dunno what to do about the switch - where do you find better ones? Only thing I've seen is where O-L makes them out of copper - no idea how he does it, amazin stuff though. There is a lot of power going through it. The best I see is the conventional type rated for 2.5A, 240v. Can't recall now what's in the J18, though I had it apart a couple of times - it was flaky when I first got the light, did something to fix it, maybe just tightened it up, re-assembled.
That’s my problem, the only high current switch I’m aware of is that mega bucks mosfet jobbie, not seeing that myself. I suppose the other answer is braid the spring and buy in a rook of switches, just swap em when they burn out. 