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.
Oh HELL no! Don’t mix LiPo and Liion! I sure ain’t gonna do it, y’all are free, of course, to take your own chances!
Jos, I use values in my firmware of 245 and 228 with a 22K resistor paired with the 4.7K normally used. YMMV
So those are the common values, and you adjusted the firmware, that is fair enough. For me changing firmware is out of the question within the foreseeable future, so I hoped to solve this by adjusting the resistor values to match the existing (105C) firmware. But have no clue in which direction to start, I need an educated guess.
I have seen people use a 36k for a 3s setup and 48k for 4s IIRC. Although they still needed fine tuning in the firmware IIRC. Still it shows you need to increase R1.
This test was done on the J4 looking pretty spectacular. Cree list a K4 that does 350 more lumen at 3 amps than the J4. So 5000 lumens is very doable, just not as pretty as this J4 A3 5000K LED. Now just sit back and wait for the Cree XHP70.2 cause the Heart of Texas is going to have scorch marks all over the place.
Thanks TA, exactly the ballpark information that I wished for. I will try swapping R1 for 33K and see what happens. 
You would need a fixed voltage drop of 3.0 Volts over the 220 Ohm resistor, so that when the Voltage goes down to 6 Volts the driver will get 3.0 Volts and low voltage warning will happen.
So i think you can replace the 220 Ohm resistor with a 3.0 Volts zener (in ‘anti-series’) and forget about the parallel zener (from the zener mod).
But, that means the MCU gets maximum 5.3 Volts minus the 0.6 Vf of the protection diode = 4.7 Volts maximum.
I don’t know how much Voltage the MCU can take though, and i haven’t tried this idea either…
When I tried using the zener without the resistor the zener fried in a matter of seconds.
Yes, but that’s when you use the zener in prallel, and that’s to be expected.
What i’m proposing is putting a 3.0 Volts zener in series (but the ‘wrong way around’) in stead of the 220 Ohm resistor so you use its reverse voltage drop.
It will then just eat 3.0 Volts of 6.0 to 8.4 Volts, so that when battery drops below 6 Volts, the MCU will think it’s 3.0 Volts and starts blinking in low mode.
[edit] i suppose “reverse Vf” is called Vr
Yeah, and you still need a 10Uf on C1. The Zener likes having it’s own 10Uf for stability, but the designed C1 I always populate too.
I’ve used a 39K at R1 but got away from it by changing the firmware.
This is getting a bit off topic i guess…
But my idea is to avoid SMD soldering as much as possible, so i’m thinking about using a fixed 3 volts voltage drop in stead of a 220 Ohm resistor and the parallel Zener.
You can obtain 3 Volts drop with 5x Si diode in series, but that’s a but bulky…
So i though about using a 3.0 Volts Zener in series, that is, if they even exist… :person_facepalming:
…more on topic, i superimposed Djozz’s XHP50.2 test graph on Djozz’s XHP70 test graph:
.
The XHP50.2 is plotted in green.
More on the XPH70 test: Cree XHP70 up to 4022 Lumens and XHP50 up to 2546 lumens - Multi-die leds. - #576 by djozz
Nice work Jerommel.
Basically what I figured, the xhp50.2 should give the xhp70 a run for it’s money without a donut hole. Not a bad LED option for sure if we can find some drivers capable of driving it properly.
I think I will buy one to try in my L6 which is bumped to 7.4A. And I have a SMO reflector for it.
I have a couple stock SD75’s with OP and SMO reflectors, FETDD drivers, LD2-3 at 12 amps that I would like to try this in, but is 5000k the highest tint/kelvin/temp out? If possible a link to it would be greatly appreciated.
Alternatively, could there be a special FET MCPCB that would mount to the driver side of the LED shelf? Starting from the front of the light, there’d be a sandwich like this:
LED
LED MCPCB
LED Shelf / Pill
FET MCPCB
FET
Airspace
Driver
with a couple of small bolts keeping the FET MCPCB in place, and suitable amounts of thermal compound.
This assumes enough space in the driver cavity, of course, but it might help to avoid space problems on the LED side, given that reflectors / optics tend to sit quite close to the surface of the LED MCPCB, and the LED itself sits so inconveniently in the middle
It also allows the use of any stock LED MCPCB and keeps the FET gate wire wholly inside the driver cavity, if that makes a difference.
Anybody already tested these drivers?
5A is not too bad, imho.
Jerommel has given the graph an incorrect fuzzy title (although he did refer to the origin of the graph where the correct information can be found). The title says that the the XHP70 test was ‘in less than ideal circumstances’ while in fact in the graph two XHP70 tests are to be seen, of which the purple one is wrong and must be ignored (the led was reflowed on a bad performing makeshift board), the red graph is correct, on a quality copper DTP board, under as perfect circumstances as I can create them.
I always make a point of giving my graphs headers that describe the contents as complete as possible so that they can be copy-pasted without loosing their context, but Jerommel (unintendedly), by writing a new header, has removed that context here.