Testing a Cree XHP50.2 J4 3A led

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!

You have taken my post to literally by no resistance i meant there is no FET/springs to reduce the current thus its a low resistance as it possibly could be.

You could use 8 gauge wire like I do, that has less resistance than 22 :wink:

It also means that with a regulated driver(either boost, buck, or linear) the more efficient lower Vf led will stay in regulation longer and half a volt means something there.

Another great test thread Djozz!

Boost or buck? yes and and no. Without enough voltage difference between source and load you just shouldn't be using a buck. With too much, you shouldn't be using linear. Once you get to where a buck (or boost) works well, further marginal differences in voltage won't matter, and it becomes a big advantage of a buck. In the transition though I'd turn this around as a disadvantage. Lower Vf led's are bad because they require a buck, and because without one the setup on the whole becomes more and more inefficient.

If you sliced the dome off your xhp70 you would also get a little less lumen’s, but more throw.

Then I wonder if the new xhp50.2 is an upgrade or pretty much the same?

One advantage the xhp50.2 may have over a sliced dome xhp70 is less of a donut hole. Then again, I think the K60 has an OP reflector so it’s not likely to ever get a donut hole. On a SMO like my L6, the xhp50.2 may have a slight advantage.

Do you guys know off hand if a sliced dome xhp70 has a smaller or larger hot spot compared to a dome-on xhp50?