Testing a Cree XHP50.2 J4 3A led

I’m going for practical. Even in small lights 3000 lumens could be possible and still have some run time before the batteries drain or the host melts. 6.3 volts 3.9 amps 24.57 watts, not to shabby.

Very nice test, I was thinking it should be around 5k lumens, although I was hoping for a bit more.

The real issue with this LED is actually using it in a flashlight. I can’t think of any driver options that would work with it right now. It would need a buck driver for sure an FET driver could try to push a buttload of power though it. It is possible that PWM it from a 2S setup would be ok like in the xhp35 but it is not ideal.

With these new low Vf LED’s on the market a good high current buck driver is becoming a must.

Excellent, thanks for testing and sharing :+1:
I have a couple of these in the mail.

FX-30 ?

If you want it in an L6 (which I am considering) then yes but outside the L6 or S70 there are not exactly a lot of host options for drivers of that size.

Nice review djozz

So no more dark + in the center. I wonder if this out throw XHP70 in convoy L6 in smooth reflector.

Can u test it out if it’s no trouble :slight_smile:

I have no L6, I do have a Thorfire S50 doing nothing, I could have a go at that one, but the reflector is OP.

Yeah, it’s a biggun…
Off topic, but can the FX30 handle 3S batt. config?

Yes, it should vastly out throw the XHP70. I have an old XHP50 in a much smaller ~60mm reflector and it has a much tighter hotspot then my L6 but it has a cross in the beam, even with a shaved dome so it doesn’t get used much.

Great test again, djozz!

The best improvement is the much better beam, I think. steel also posted some beamshots here: The new LED XHP50.2

I hope I can make some with a deep smooth 52mm reflector and a Ledil Crystal optic next week.

What about using a current limited driver like the LD3 set up for 2S with a max amps of 6 or 7?

Simple enough to use an FET Zener modified and use something less than a top cell so that 10.5A isn’t surpassed. Should be pretty easy with the GA and MJ1 and such out there. Or the 20700B.

Dale, perhaps you know this: what I have with the few zener modified FET drivers that I made (diode replaced with 220 Ohm, Zener parallel to D1) is that the low voltage cut-off is too high (at 3.6V or so, edit: I mean double that of course). I know that it has to do with the voltage divider resistors that are wrong for the altered circuitry, but do you have a suggestion for other values that should at least be closer to the correct voltage cut-off?

The LD3 would melt if you tried to use it with this low Vf LED. It will need a buck driver.

With the Vf that low I am betting that you would have to drop down to laptop cells to keep the current low enough and most of those are only rated for ~5A at most so you would be asking them for twice what they can handle.

I have run into this issue with various low Vf LED’s. You simply can’t get the current low enough even with super thin wires, low drain cells ect with an FET driver without either melting the wires, over driving the LED or pulling more then the cells are rated for.

The only practical option I can think of going forward for FET drivers are custom MCPCB’s with pads for some SMD resistors. The star will heat sink the resistors to deal with the heat and they will reduce the power.

The downside is they are very inefficient and will make the light even hotter.

Or another rather interesting option would be to have a pad for an FET on the mcpcb for heat sinking and then use an opamp LD3 style driver to control it. By having it on the MCPCB the heat sinking should be good enough to allow it to handle it.

Still lots of extra heat and inefficient but at least it is variable and as such the efficiency will improve as the voltage drops.

With LiFePo cells you may be back in business with FET drivers. They provide a load of current but the capacity is way below li-ion.

This is an option, although what sizes are they available in and what prices?

https://www.fasttech.com/search?lifepo4%20battery

This one should do an adequate job :innocent: :
https://www.fasttech.com/products/0/10007811/1683800-a123-anr26650m1a-3-2v-2300mah-rechargeable-lifepo

Thanks for the test. The lack of donut hole could make this a game changer, but the low Vf is an issue.

From HKJ’s data, the A123 maintains right about 3.25V at 5A, which is right around the XHP50.2 forward voltage (6.5V). With circuit resistance factored in the resulting current will be a bit less than 5A. A good solution for some applications, and since the discharge curve for these cells is nearly flat, it will be nearly constant current through the discharge. Probably not bright enough for some, though.

A possibility I just thought of is using one LiFePo cell in series with one standard Li ion 18650 (close to capacity matched). My estimate is that this would result in 8-10A.