Question about TR-J20 modding

You would have more than an awkward tri-beam. You would have three sets of four beams. The XHP-70 looks like it’s a single emitter but because it’s actually 4 XM-L2’s jammed together they are still separated by enough space that under an aspheric they will come out as four beams that never do intersect. So even if you could get the three emitters to intersect perfectly you would still have four beams. I imagine they would get pretty close eventually IF you could somehow manage to line them all up perfectly but it still wouldn’t be the most throw from the light because the XM-L2 is not the best throwing emitter under even the best conditions. I have built one multi-aspheric light and that was with 4xXP-G2’s, which throw further than XM-L2’s and it was still a waste of time because the lenses needed to be relatively small. Theoretically if you wanted to turn this light into an aspheric thrower your best bet would be to use a single de-domed XP-G2 S4, right smack in the middle and one huge aspheric lens. When you are going for max throw it’s the same with reflectors or lenses, the bigger the better and multiple small ones don’t cut it.

I’m not saying it would be a complete waste of time, it would make for a neat light but it would be an unbelievable amount of work creating the housings to get those three beams focuses and it would still not get you the most throw or a very nice looking beam.

On the batteries frying the emitters. If you put Two batteries and wire them to Two emitters in Series you are fine. Wire them to Two emitters parallel and it will fry both of them. I suspect that if you were to somehow manage to wire 12emitters all parallel to two batteries it might not fry them if you got the wires exactly perfect so that none of them got any more power than the others. This could create enough battery sag to save the emitters, but I wouldn’t count on being able to get the wires perfect and once one emitter fried the next would go and the next and the next.

And yes when you take a tail-cap reading you are only reading the draw from that end. A more accurate way is to read the current at each emitter. I am no expert on this part at all. Although I have built hundreds of lights I haven’t taken a current reading in years and I don’t think I ever did one correctly anyway. I know roughly what you get from each configuration and try not to post too much on exact amp draws or even exact lumens or KCD. I’ll do so in a general way but I stay away from making too specific of a claim. I give ballpark figures and that’s about it. People have been trying for years to come up with a perfect measurement system for these things and I leave that to others.

Yes, using the driver as a contact board means running wires from your old board to your new one and then on to the emitters. After you take all the stuff off the old board you use your DMM to isolate a positive and negative and solder the wires there.

I’m not even close to an electronics expert, others here are way past me on that part. However, even though I’m no expert on the electronics part, I’ve become fairly expert on the actually building of lights and even building and modding drivers. I guess what I’m saying is that you don’t need to know every detail of how the electronics works to build a great light. For some people here the electronics is the most fun, for others it’s the software design. For me it’s just the actual construction of the lights and seeing the final product.

Modding the existing driver is great way to start and good luck.

Oh yeah, that’d be painfully strange( strangely i’d had such a dream once about this), but i’d really been planning on a dual aspheric, a pre-collimator positioned just far enough to get all the light onto the main lens, which will be a 100mm FT lens, which is focused to infinity. That’d make it 3 circular beams. Unless i get the new XHP70.2’s?

I would go down the XPG way, but what i understand is that it’d be not particularly bright and have a very tiny spot, and at the distance it will throw to, one would need visual aids to see where it hits. My rationale behond XHP70’s (and the dual aspheric hence) is partly due to their massive output, so even though due to their large area they wouldn’t ever throw as far as an XPG, they’d still go quite a distance and light up a broad area, but could illuminate a varied area size by adjusting the main lens. If this idea i have in mind can achieve the sort of results i’m anticipating that’d be awesome.

Knowing how aluminum is a poorer conductor of heat but better at dissipating heat than copper, would it be necessary to maintain a minimal distance between the sinkpads, if i stick with XHP70’s? And are the Arctic Alumina grease and paste the best to secure the sinkpads to the heatsink shelf?

So it is because of the voltage drop across each LED in series as opposed to the full voltage from the batteries across each LED in parallel that makes the difference, is that correct?

By getting the wires perfect, do you mean using the correct gage and length?

Lastly, how do i use the DMM to isolate a positive and negative? Aren’t the + and -ve poles on the drivers marked already?

I’m not so sure i’d want to go as far as being an electronics expert myself, but i’d be more than content to reach your level of expertise. Inspired!

Always use the thinnest possible layer of thermal paste/grease, even the very best is not great at conducting heat. What it’s best at doing is removing air pockets. Those tiny air pockets are insulators and the point of putting down paste/grease is to get rid of that air. People debate endlessly on what is “best”, but arctic silver is very good. There are products that are “better” but it’s debatable if it’s worth spending any extra money on getting the very best. I use Wakefield Deltabond 153 but it’s $40 and probably not any significant amount better than Arctic silver. More important is making sure you use a very thin layer and that you have mated the two surfaces in a way that doesn’t allow any large gaps at all. If the area you are mounting the emitter to is rough it’s important to sand it down as smooth as possible. I use various grades of sandpaper until it’s basically polished. You want as much metal to metal contact as possible between the bottom of the sinkpad/noctigon and the heatsink. If both were absolutely perfect you wouldn’t need thermal paste at all, you could hold them in place with screws.

When you put the emitters in series it takes twice the current to get the same amount of amps to two emitters. When you put the emitters parallel you get roughly the same amps to the emitter no matter how many emitters you wire that way. I say roughly because it’s a bigger drain on the battery if you have a bunch of them wired in parallel, but usually not enough to consider wiring them safely hoping on thermal sag to save them. How should I put this? Hmm. OK, Wiring them in parallel is the same as if you were to run a separate set of wires to each emitter, think of it that way, because it’s essentially the same thing. It would take a lot of emitters wired that way to drop the amps quick enough to save them from burning out. It’s not really worth trying to do it and trust me, I’ve tried it and lost emitters a bunch of times. I’ve also tried running thinner wires hoping the loss of current to the resistance from the small wires would stop them from frying. All I did with that one was to cook my wires. So it’s best just to remember that each emitter can handle a full load from one battery. In the case of XHP’s and MT-G2’s it’s TWO batteries though, because they are 6 volt emitters. It’s just with XPG’s XML’s and XPL’s that it’s a one to one ratio. It’s convenient that it works out this way though. It makes it much easier to figure out the correct way to wire them.

It makes it more difficult when it comes to wiring XHP’s with a FET driver though. For instance your light won’t work right in the 3xbattery mode using XHP’s and a DD FET. Three batteries run into a single XHP or a group of XHP’s parallel is too much and will kill them. So if you do go with XHP’s you have to hope that modding that driver will actually work with XHP’s and I wouldn’t count on it. The difference is that the XHP’s are 6volts and I don’t know how that driver will react. From my experience using a wide range of stock drivers to attempt to build 3xMT-G2 lights I wouldn’t hold out much hope. I think ComfyChair might be the only guy I know who managed to get a Stock driver to work for any length of time with 3xMT-G2 (also a 6volt emitter). I tried at least a dozen different drivers and they all died after a short while. It wasn’t until we started building these FET DD drivers that people started having any real luck building triples with these 6volt emitters. I know a bunch of guys who tried it who failed.

I built a Triple XHP70 diving light the other night and used the FET driver but that was because the diving light uses 2x26650 and I could run all three emitters parallel. If it was a three battery light it would not have worked and I don’t know of any stock driver that will reliably drive 3xXHP70 although there must be because they sell a few triple XHP70 lights. I haven’t had a chance to tear one apart yet and see what they did. For all I know they might just be using a FET driver too.

Thanks!

So thinnest possible layer of Arctic Alumina, and both surfaces must be smooth as possible. Got it! I guess the J20’s shouldn’t be needing any sanding down then?

So basically i’d be better off just doing a resistor mod if sticking with the stock driver, and if i want to do any 6V or 12V emitters i’d be better off using another driver, is that what you’re saying?

In the J20, since it by default uses 3 batteries in series, unless i were using single 12V LEDs, 2 6V or 4 3V emitters in each parallel string, it wouldn’t work, correct?

Yep that pretty much sums it up.

Thanks! By the way, would you happen to know anything about this driver on eBay? I’m not sure if direct links are allowed so i’m just pasting the full listing title.

“0-10+ Amp capable LED Flashlight driver board 17mm, Cree XHP70, XHP50, XML2, XPL”

The size of the driver doesn’t usually have anything to do with how much power it can handle does it?

You can post direct links here no problem. Affiliate links where you make money from sales are different but I’m not even sure where that stands now. Even those were fine for the longest time and I they were debating changing the rules but I don’t know if they ever did.

And that is the driver that I was talking about. That’s one of the ones that I build and it was developed and tested by the guys right here on this forum. I call it the BLF FET driver because it really is a BLF driver. It’s the result of a ton of work by the modding crew here. Richard at mountain electronics sells them but Ventures of Blood who is selling the one on e-bay is also a great guy and a member in long standing here as well. In fact I think he’s been around here longer than Richard (BLF name RMM). That driver will easily handle the current you need and then some. It will give you the most power possible to each emitter without breaking a sweat.

That’s amazing, how does one get started on building a driver?

That’s good to know. Are there any disadvantages to a driver with more modes? I’m thinking of choosing one with memory, 5 modes (Moonlight to Turbo). As to the other options i see on the mtn website, i’m completely overwhelmed! No idea what to choose.

If i haven’t got it misunderstood, this driver can work with up to 3 batteries. So it can work with all 3,6 and 12V LEDs i assume?

By the way, how does a contact board + repalcement driver setup look like? Would you mind posting a picture of such a setup, because i can’t imagine what one looks like, or how i can fit that into the J20 at the moment? Thanks.

I simply stripped the existing driver and piggybacked in an FET with Zener mod, put 4 of the 9V variant MT-G2 on individual 20mm Noctigons then a Ledil reflector in it’s holder on top of each of those. I’m getting right at 15,000 lumens on 3 of the big Trustfire 32650’s.

To handle the heat, I put a 1/4” thick aluminum spacer on the emitter shelf and made a massive head filling heat sink to spread the heat more efficiently to the finned area.

Original switch is handling it fine.

So yeah, 3S cells to 4P 9V MT-G2 emitters. Definitely not a throwy light, but a very nice tint and just a huge amount of output.

Edit: With the cells rested and not fully charged I’m seeing 20.85A on the 3S cells at the tail end.

Five modes is nice. No particular advantage to any of them, really just personal preference. I like to keep them simple and don’t really go for all the hidden mode stuff, but lots of people seem to like that too.

These FET drivers will work with pretty much any amount of batteries and any emitters so long as you match the correct current to the right emitters.

I don’t have any pics but it’s fairly simple. The existing driver just ends up with two wires hanging from it with the new driver hanging just below it. You can “pot” the new driver. Which just means you encase it in something like a thermal epoxy and stick it to the old driver. This helps to keep the new driver running cooler. But you don’t have to do that part really.

Nice!





The finned head section is hollow, a retaining ring holds the driver in from inside the head instead of below… there are 4 screws originally through the emitter shelf into the reflector, so I machined the inside heat sink to have a hole to fit around the holes and allow passage of the wires through to the emitters, the base doesn’t screw all the way into the head by about a 1/4” so the heat sink sits on top of the base such that when the parts are screwed back together the heat sink is pressed up against the bottom of the emitter shelf. I flared the hole in the sink out as it drops down to the driver so it clears everything easily and directs heat outward.

The first picture shows the additional 1/4” thick aluminum plate under the emitters. I used a sheet of copper to join all the positives on the mcpcbs with an 18ga lead soldered into the sheet. 18ga leads leapfrog around the perimeter to join all the negatives.

The light is rather large, so this heat sink is bigger than the pictures make it appear.

Now that’s a work of art, wow!!

That sounds insanely awesome! Must look one hell of a lightsaber haha. Just one thing though, is it then impossible to do 6V XHP’s with the piggybacked driver in the J20? If so, is that because it is direct drive without a voltage step up/down function? Sorry if this is a stupid question by the way.

Would copper do just as fine? I mean it does conduct heat much quicker, although it also dissipates much slower than aluminum, from what i’ve read. If i were to run the light at turbo for a few minutes would the material make a difference?

Damn, that makes me want to learn something about CNC machining! The things i’d do with it… maybe go overkill and do a 10” LED spotlight! But i guess by then there wouldn’t be much sense having the relatively minute XHP35HI, but rather an HID setup…

…. you know if you hadn’t told me that i’d have done it the exact opposite way!

Is there a good thermal epoxy at a reasonable price? I reckon i’ll need that if i’m going to go all out on this. And the fact that i haven’t got any CNC lathes to mill some custom heatsinks or whatnot

You can see the white epoxy potting my little 17mm FET driver to the big contact board, on the left in the second and third pictures. I figured with this big heavy light it’s inevitable that it falls or gets dropped so I potted it for durability.

Since I am using 3 cells I wanted to match the emitter voltage. Pushing the 9V MT-G2 pretty hard it has about a 11.3V forward voltage so it takes the 3 cell configuration nicely. I’m doing the same in a BTU Shocker as well, with 3 of the same emitter and using 18650’s in the beefed up carrier.

You could run 4 6V emitters, 2S2P and they should do fine. There’s all sorts of ways to configure a light this size of course. Richard replaced the XM-L’s with XHP-50’s and I made him an extension tube for a 4th cell along with the big heat sink. He got 39,000 lumens and it would run with the sink to kill cells. Initially, without the sink, it was too hot in about 30 seconds. So yeah, there’s all sorts of things you can do with this huge beefy light.