TR-J18 upgrade options?


I currently have a Tr-J18 that I think has a blown driver. Like a few other people I’ve been reading on here, the light has suddenly lost most of it’s power. I have tried by-passing the tail-cap and there is no difference. New batteries do not seem to help.

So, this leaves me with 2 options.

1) Contact the seller and ask to have the light fixed or replaced (it is only about a month old).

2) Mod it… for a bit more “ooo… wow” factor

Please bear with me though as this would be my first modified flashlight, and first time modifying a flashlight. To be very honest, this light is only really for the “oooo… wow” factor. For daily use I use a few single mode G10’s with 14450’s in them and a couple of smaller single T6 lights.

What I am looking for out of this light.
a) Ability to throw a “lot” of light for short periods of time… say few mins? More Specifically, I want to ensure there is no doubt that when you turn on the flashlight, there is more OTF lumens than a Coast HP21.
b) Ability to turn down the light and light a room, 30-45 mins runtime here would be ok
c) Ability to run on 18650’s. (currently using 3 18650’s. TF flames). I want to try and avoid the initial purchase of 26650 batteries if I can avoid it do to cost.

Looking around, do see a few upgrade paths but am not sure what are the pro’s and cons of each route. Or if one driver is “better built” than the other one

Option One

modify the existing driver. This seems difficult (as I’m not that skilled soldering) and may not even work as I think my existing driver is blown. Furthermore it seems that there are more than one driver shipped with this light.

Option 2
Seems like a good option

Option 3
Also seems like a good option.

So, between the 2 drivers, besides the number of modes it has, are there any real differences that would make one better than the other?

Also, it seems like none of the drivers ships with the battery spring in the middle. Where can you buy this spring (and of the correct size).

When installing the driver, do I just connect the existing wires black to black and red to red…. The driver just sits in the head? (no glue or tape).

Finally, does the tail cap switch need to be upgraded to handle the increased current? If so, where you would you get the parts for it?

Are there any good walk through’s posted that can how me “how” to upgrade the light? I think I have an idea but a few pictures would make life so much easier.

Thanks in advance for your help, and sorry for the noob questions.

You could try this one from KD. You will need to rewire the LEDs for series instead of parallel.
Here is the same driver with special firmware ; gives three-modes, 100–30–5%.
Good luck with your mod!


Thanks for the suggestion, that driver does look good too :slight_smile: :slight_smile:

Just one question tho, I was under the impression that the J18 ran the led’s in series from the factory. Can anybody confirm… or… is there an easy way to check?

While I can get to the driver, I have yet to figure out how to take the head appart to get to the led’s.

I’m pretty sure it’s parallel. Most of the factory multi-emitter lights like these are parallel. If you can get the reflector off, it should be easy to do with some basic soldering skills and good wire (recommend silicone wire, 22 AWG, no smaller than 24 AWG).

We be talkin’ bout the LEDs :wink:

Which are also in series.

OK, sry, I must be mixed up with another light then. Maybe the J12? Anyway, if they are already series, then the KD drivers are the best bet.

wow, thanks… yes the second “reprogrammed” KD driver looks good. Modes are perfect. One questions is that will this driver work with 3 cells? I reason I was looking at the IO driver was that it states it will operate on both two and three cells.

I’m currently using 18650 TF flames and I am not sure if they have enough “guts” to fully drive the light with only 2 cells. Furthermore, I’m worried the increased amperage from running 2 cells on a modded light will just smoke the parts inside (tail cap switch + springs, etc).

Yes, that driver will work with three cells. If you plan to run 2 cells, you will need to get better cells, possibly unprotected cells or 26650’s. The KD drivers could pull up to 5-6A from the batteries. The switch can be a problem at those high currents. I’d recommend 3 cell operation, monitor the cells, and even though it’s a thermally protected driver you should limit the run time on high.

A final note on the LED configuration (series vs. parallel). I looked around, and there definitaly isn’t a consensus on how the J18 LEDs are wired. The best way to know is to check it yourself. If your flashlight still lights up at all, put a volt-meter across the LED wires coming from the driver; if you measure 2.5-3.5V it’s parallel, 17-20V and it’s series.
Better to be safe than blow up another driver.

Yes the light still works, it is just very dim. I tried by-passing the tail-cap and there is no difference.

In this case, how would you go about measuring the volts to the led’s? The wires/contacts are in the head and if I pull the driver out to gain access to the wires I can’t turn on the light (battery tube is disconnected). Sorry if this sounds like a really dumb question.


I’m not 100% but the reflector is screwed in from the back, pop the driver, if there is a screw in there, its probably holding the reflector down. If not, unscrew the bezel on the front, remove the lense, the reflector should just come out then and you can see the led stars.

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.