Testing a Cree XHP50.2 J4 3A led

Djozz, how do you think the lower voltage of the xhp50.2 would do with a boost driver?

I might pair it up with Kaidomains H1-A 3 amp boost driver.

I think it will be a pretty good match, I have one on order for that reason, and khas akready did a mod with that combination (in an EE X7). The lineair drivers that burn up overvoltage are getting pretty inefficient with these new leds, a boost or buck driver may just be the better choice nowadays.

There is a very simple fix to the battery life, simply reinstall a sense resistor to limit current. The XHP50.2 has such a low Vf I would not be surprised if you are running 12A+.

If you install a sense resistor to limit power to around 6-7A the batteries will last about the same or possibly longer then the xhp70. Although most likely with a bit less lumens naturally.

I want to swap to an XHP50.2 or 70.2 in my L6 and swap back to the stock driver with the sense setup to limit it to 7-8A.

A better choice would probably be for Cree to not use this new lower voltage. :slight_smile:

I can see people hoarding the older designs already. Lol

Thanks TA. I’m charging my batteries back up right now to test the amperage.

I don’t have enough resistors to put it back to stock, but I should be getting in an order of 20 each R082, R100 and R120. Once they arrive I’ll be back in business. :slight_smile:

Heres a question for you.
If my FX-30 driver had the stock resistors (two R082’s) would the 50.2 draw more amperage that the xhp70?

I’m curious how the lower emitter voltage effects the drivers output.

The lower voltage is actually a massive improvement in everything not flashlight related and the only reason it is not a positive thing for flashlights at this point is that we don’t have drivers designed to take advantage of the low voltage.

We need some current controlled drivers, buck being the best but also impractical solution.

I have a few ideas floating around for drivers that would take advantage of the lower Vf and once we have drivers that can control the current then these will be the better option for sure.

That way you will actually be able to regulate the output instead of the output flat out dropping with the voltage.

In your case by putting the sense resistor back you will get a regulated current output instead of an unregulated voltage output. Thus the light will remain at a steady brightness until it falls out of regulation and net you better real world lighting.

With the XHP70 the Vf was so high that you had to pick between max brightness and regulation, with the XHP50.2 you get both.

In theory the sense resistor is only effected by current, so the stock 2x 0.082ohm should give about 5A regardless of the LED used. Although depending on exactly how the circuit is setup that can vary a little.

Also remember that the FX30 is a buck driver, so the tailcap current draw will vary depending on the input voltage while the output will remain more or less the same. Better batteries will actually cause a lower amp draw at full charge.

Thanks for explaining things.

It seems these new lower voltage emitters, including the 70.2 which should be out soon, are not the easy upgrade many were hoping for.

It depends on the light you will be upgrading. Most lights that came with an XHP already installed will be a simple drop in swap to the newer LED as they already use a buck driver.

With the stock L6 driver it would have easily worked as a direct drop in, the only reason you are seeing worse battery life is because you modified the driver to remove the current regulation.

In fact at the stock output level of the driver the xhp50 should be more efficient and give you longer battery life (with less lumens naturally) due to it being a more efficient LED.

The xhp70.2 will give you better battery life for sure with the buck driver at the same current as the lower Vf means it will be pulling less total watts. It will also remain in regulation longer and should give you a bump in output as well along with hopefully eliminating the donut.

All the guys running FET/DD drivers will be sad. I, myself, just ordered a Texas Avenger driver. :person_facepalming: Oh well, I’ll just stick with the regular xhp70 for now.

What are all the hot-rodders gonna do when these new emitters make FET drivers a bad choice? Will they just avoid the new emitters or find new drivers that can push them, but not too far?

Simply use a cell that can’t supply beyond the 10A or so.

I don’t have a problem hooking them up, my triple 50.2 “only” pulls a little over 20A.

The thing is, at 10 to 12A on the 50.2 you’re beyond the max output level and just burning amps for heat. The XHP-70 can still make output levels at the same 12A so it’s got the advantage. The MT-G2 can do 16A, but peaks around 7-9A. I’ve had em doing some 4300 lumens at 16A. And the XHP-70 makes around 7200 lumens at 12A. The 50.2 can’t compete. And the new phosphor aka XP-G3 gives an odd tint to the beam so it actually has losses in comparison to other emitter choices.

Now that there is a reason, there will be new drivers made to take advantage of the lower Vf, just a matter of time.

The easiest fix right now is to simply turn the max PWM down on the TA driver to get the current you want, it will still drop off as the battery drains but at least you will limit current to what you want.

I do this with 219C’s or small lights that I want to limit the heat in. I simply set the max PWM to keep total power where I want.

A firmware upgrade could allow for very crude “regulation” using this setup. While not perfect, it is better then we once assumed. In my testing you only loose about 10% efficiency @ 50% duty PWM. This is a worthwhile tradeoff for the low cost and compactness of a PWM driver over a buck driver.

Although I do have slightly better improvements in mind PWM regulation is the way of the future for cheap and compact drivers. For lights that can use larger drivers buck drivers will become much more popular.

If you PWM a XHP50.2 at 12A, you still get the inefficiency that the die has at 12A, just not the heat sag. The output drop at high currents is not solely caused by heat. Do you know what the individual contributions of those two effects are?

I agree with Dale’s post above. I think these low-Vf emitters can be used advantageously in multi-emitter lights (triples and quads). Direct drive with a single emitter (XPL2 or XHP50.2) usually results in a lot more current but not a huge output increase because the output curve tends to level out at high current. But in a triple or quad the low Vf allows to drive each emitter more optimally. For example a triple XPL with a single cell might draw 12A, or 4A per emitter, but a triple XPL2 might draw 5-6A per emitter which is near the optimal current before the output curve levels off too much.

Of course these low-Vf emitters also tend to not have as good throw, but that’s another story.

I don’t have a function generator to test this as completely as I would like but in my testing I have consistently seen results in the same ballpark as the XHP35 PWM I posted.

In that test it lost about 11% efficiency @ 50% duty tapering to 0% loss at 100% duty. In other tests I have seen similar numbers.

Thus as the battery voltage drops the efficiency loss will taper down to 0%. So it could actually be brightest on a slightly drained cell.

That loss ~11% is really not so bad. However, the loss should depend on the peak pulsed current, so it could be higher with these low-Vf emitters.

Yeah, it does depend on the pulsed current although the xhp35 is a pretty good comparison from my un-publised testing.

I have tested a few other low Vf emitters and they had very similar numbers, some slightly better like the XP-L2 I played with and some slightly worse (like the 144A I played with).

At 50% duty it appears to range between 10-15% loss. Which like you say, is really not that bad, the higher the duty the lower the loss. Using thin wires and low drain batteries improves the numbers as well. As the battery voltage drops the efficiency loss drops to 0 as well.

The lower ranges can be taken care of with current regulation in most cases without much trouble.

PWM is not ideal but it is cheap, effective, simple and compact. It does have some advantages as well such as little to no tint shift in different modes, seemingly better tint / CRI in my experience ect.

Future drivers will most likely use a combo of constant current and PWM if I had to guess.

What would a change to a 50.2 from a 50 in a standard light like EA81 do? If anything.

One of my build plans was to take a single 26650 light (ultrafire F13) and run a pair of 26350 batteries from Banggood along with a direct drive 22mm driver from Mountain Electronics then put in the xhp50.2 that I tried out in my Convoy L6.

Now I know that will pull way too many amps. I can’t switch to amp limited batteries as they don’t exist. I don’t know of any non direct drive drivers that will work. Do you guys know of any?

I guess I’m gonna have to shelve the 50.2 and buy a new xhp70 to run in it. Does that sound right?

One thing to keep in mind with the 26350 cells is they can’t handle much more than 7A. See discharge curves at the bottom of the banggood listing. Banggood says they are out of stock, by the way.

These 26350 cells with an XHP50 V1 resulted in about 7A on a full charge. Using an emitter with a lower Vf would, in my opinion, probably be asking a bit too much of these cells.