Testing a Cree XHP50.2 J4 3A led

I am actually surprised that the current is that low with the 30Q, although be careful your springs don’t melt. I find that long 24AWG wires are a better option for the resistance and then small 26awg bypasses on the springs.

Cool beans Jozz! Ordered some 50.2 J4-1A’s to compare against a Convoy L2 with a old XHP50 J4 1A that’s shaved and pulling 8.57 amps. at turn on. I plan on putting it in my spare L2 and add resistance to around the same current maybe? I can’t believe what I just said! :person_facepalming: Can only measure throw, but at least it will be apples to apples, and see what it looks like out of a smooth reflector! :+1:

[following on from this post]

I was thinking about having the bolt head hold the LED MCPCB down against the shelf, and the nut hold the FET MCPCB up against the other side of the shelf. The hole in the shelf wouldn’t need to be threaded, so the shelf wouldn’t need to be thick enough for that.

Admittedly, there are other issues, as you say: at least one extra wire taking up even more space in the driver cavity, for example, and there’s a risk that the bolt head would experience clearance issues with the reflector.

Just chucking ideas around, basically :slight_smile:

It is a reasonable idea for a purpose built light that would work, the only issue I see is universal retrofit abilities.

You could actually make something like that with an oshpark printed pcb fairly easy. While not ideal it should be good enough to vastly improve the heat dissipation so it can handle almost any single LED on the market right now. Particularly if you stay away from the 50% range where heat dissipation is highest.

My thinking with a MCPCB mounted FET is that it should fit almost any light fairly easily with just 1 extra wire needed. It might have to use a lfpak33 fet but that should be ok. You could use parallel FET’s but that would get more complex.

Wouldn’t it be less than ideal putting both high heat sources, led and fet, in the same location? Wouldn’t be better to keep the fet in the driver cavity and add a small smd heatsink potted to the fet and the closest body contact point?

As to my earlier question regarding buck driver voltage, I suppose the only way to safely test would be while watching a scope and thermal image simultaneously


Edit: or the “squeeze it in your fingers til it burns” approach might work. This is how I did some testing on the t25c driver. Actually, I might just put that driver back on the bench for a voltage out test. . :smiley:

I like that OshPark PCB idea :beer:

I see what you’re getting at with the universal retrofit now, though, especially if you were switching to different FET package sizes to make it / them fit. Once you had a supplier for the new LED+FET MCPCBs, you could buy them to use in any size-compatible light, and no worries about space in the driver cavity either.

Having both heat sources in the same place while not ideal is not going to make much if any difference compared to mounting the FET to the bottom side of the shelf. The heat still has to travel through the shelf in order to make it to the body either way. The mcpcb is FAR better at dissipating heat though so it should be able to easily handle the heat from the FET and keep it from overheating.

Now you can have a custom aluminum pcb made for the fet separately but it would add a fair amount of cost.

This option is far from ideal anyways and the best idea is to put the effort into a good buck driver. Also moving to 21700 cells would be a very wise idea as it would give more room for a larger driver.

The opamp driver is simply an easy way to drive high currents if you can heat sink it well enough.

Yes, that is the idea. I always try to aim for the most universal solution to a problem so that the work can be used over a wide array of situations. Never been a fan of 1 off custom solutions unless there are simply no other options.

djozz I don't understand what you mean by lower Vf is more efficient. Is this a general property of LEDs? Yes for the same current it's using less power (and in some ways maybe it's better to plot power instead of current), but without understanding output and binning is there something else to this? For two LEDs with different Vf hooked up to the same battery and same linear current regulator, the one with the lower Vf will use less power at the LED but it just means more heat will dump into the driver instead. Of course that's not the LED's fault.

I meant exactly what you say, if a led compared to another led has the same output at the same current but with lower Vf, it consumes less power and so is more efficient.
And as you say, it is not the led’s fault but in a typical flashlight situation with lineair driver, that advantage is completely gone because you just burn up that voltage gain. But in a boost or buck driver you do see something back of the higher efficiency.

Last night I apparently was bragging too much about the expected throw of my direct drive XHP50.2 thrower. I just measured it at a modest 70kcd. So not the 200 I was expecting, the big hotspot looked a lot brighter than it actually was.

But perhaps that was to expected, with the die size and dome this is not a thrower led.

If a HI version would come out however, that has about 1.8 times the throw, in the BLF thrower with 12cm reflector the led would do 900kcd at 3500 lumen. So we will have to extend that thread for as long as possible :wink:

Posted the mod in the what did you mod today thread:

Direct drive on 2 freshly charged litokalla 26650s = 14.5/15a of juice showing on my clamp meter. Suprised it didnt pop it. Host got very hot but no immediate problems

If the host got “very hot” that probably means the LED got to 100 or 150C


Aww Man!

You can do that with MCE’s too! :wink:

It’s not a desired effect. Blew it with two 14250 cells :laughing: . Bad reflow.

I’m going to keep running it at max power see how it goes i didnt even put a driver in and all springs are bypassed 22 gauge wire so no resistance

Reflow very important to have an excellent thermal path. Also soldered the sinkpad the brass pill (i have a copper pill too but the xhp70.2 is going on there when i can get one!)

Just because it has a good thermal path doesn’t mean it has good cooling.
Also, unless you use a superconductor there is going to be resistance.

I’ve got 3 of the 5000K 50.2’s in my latest scratch build, pulling 21.12A from a pair of Sony VTC6’s for 11,696 lumens. The cells were at rest at 4.13V at the time of the test. The KaiDomain triple reflector makes for a decent hot spot, just a hint of a dark spot but I probably don’t have em perfectly located height wise. I’m using 20Ga Teflon wires, cut out the area’s around the side of the reflector where the pads are for clearance, have filed down centering rings.

They rock, for sure!