Powering an XHP50

sween1911

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Okay gang, working on solutions for my homebrew M3 head with an XHP50. Had some success sticking one in a Night Ops Gladius, so I tried putting one in front of a Dr Jones H17Fx. It no worky, so I learned that my simplistic approach was incorrect in that voltage only mattered for incans and current was all that mattered to LED's, the "6V" designation for the XHP50 still mattered for this application. I stuck an XM-L2 in front of it and it works fine, but I still want to get an XHP50 running.

(I know there are high powered 3V led's out there, I'd like to try an SST40, and I would like to eventually get the light bored for 18mm cells. I just love the beam and the output of the XHP50 and want to see it running in this light. Also like the idea that in a pinch, I'd be able to run primaries so I like flexible solutions that allow higher voltage.)

So I have a few drivers on the way to experiment with and going to try them out with some 6V XHP50's. Want to level set myself so I'll be able to get things working. I know I still have some things to learn so feel free to school me if I'm misinformed. My main question is I learned I need at least 6V to run the XHP50, but how much more is too much if you still keep the current down?

1) 17mm simple 2.7 to 14v buck driver that outputs 2A, I should be able to put two li-ions (17500) in series and run the XHP50 safely, right? Even though the 2 li-ions are 7.4 to 8.4 off the charger and exceed 6V. Despite short runtime, what would happen with 2 or 3 primary batteries?

2) 17mm FET driver with Zener mod, no LVP. Since the description is "​This means that the input voltage must be closely matched to the output" it specifically references running a 6V LED with 2 li-ions, so I should be okay right? Again, how much more voltage is too much? What about 2 or 3 primary batts?

Thanks in advance!
 

id30209

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Happy new year Joe!![emoji1690][emoji1635]

1.) 3 primaries under 2A load will have 7,4V. That's why everybody use 2 liions instead of 3 expensive primaries. Your first option 2.5V-14V driver can take 3 liion setup in that case safely.
Running 17500 under 2A it would be very dangerous for the cells cause it's their , almost, maximum. I would suggest Enercig 16500 800mah 15A. Less capacity but worry free operation.
(Strongly suggest boring...#Nitroz)

2.) vestureofblood has in his store great driver for 10ish bucks, FET. Since XHP50 is 6V then only 2 liions you can use safely in this configuration. And since it's FET then amps will go high, as much as the emitter will take and if i'm not mistaken XHP will run up to 5A (or more) so 17500 is a NO GO! Again, 16500 (poor capacity). So think again about boring and running IMR18500 1100mah 15A or simple high capacity Panasonic 18500 2000mah 5A cells.
UPDATE: running primaries in this configuration with FET is not an option. They can take max 2.5A and FET will destroy them
Link to the VOB driver here

I hope this helps a bit.
BTW, where did you get that D36 reflector? How does it fit into the Z46?

Cheers
 
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sween1911

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So three primaries would theoretically work. Thanks! By the way, my 17500's are AW 1100mah.

The D36 reflector I have is an orange-peel finish borrowed from a Nailbender module from Customlites. I asked Nailbender where he got the reflectors as they thread right onto the standard P60 bases and the supplier doesn't carry them anymore. However I think I found the exact part on the 'bay in smooth finish. I'll PM you the item. I have a couple on order to see if they fit and function.

Fitting the LED module in the Z46 bezel is an art. You really have to play around with it. In the stock incan M3, the shock foam sits in front of the reflector sandwiched between that and a black plastic ring. I keep the shock foam, but drop the unit in on top of that, then the black plastic ring, rubber o-ring, lens, thin plastic ring, and then screw down the bezel ring on top of that. I should take pictures of the various ways I configured it (maybe I'll stick those in my build thread). One of the challenges is if you play with the position of the reflector relative to the lens by moving the foam, you change the height of the battery stack and have to use a longer spacer. I have an M3 bezel tool from RPM and that makes it a lot easier to reassemble after trying different configurations.
 
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sween1911

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Okay, I realized that the XHP50 is still pretty bangin' on 1A. Sourcing the 1A driver instead. Going to see how that works.
 
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DIWdiver

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Assuming you are talking about 3v lithium primaries, the buck regulator will work, not just theoretically. The whole point of a buck driver is to drop the input voltage to the necessary output voltage. In the process of doing this, it has some interesting (and very beneficial) characteristics.

LED drivers are typically current regulators (other types of buck regulators exist too). So the driver actually attempts to keep a fixed current in the load, in this case 2A. It will allow the output voltage to vary over a wide range to accomplish this. Stick an XHP50 on it, and the output voltage will be around 6V. Stick an XML on it and the output voltage would be more like 3.3V. In either case there would be a constant 2A in the LED. As the LEDs warm up and the Vf drops, the driver output voltage will compensate to keep the 2A flowing.

Another nifty thing about buck drivers is that the input current is usually less than the output current. This is because (in the ideal case) the buck driver consumes no power, thus the output power is equal to the input power. Since 6V, 2A output is 12W, the input power should also be 12W. At 9V in, this would draw 1.33A. Or if you used 4 primaries for 12V, you would have only 1A input.

Real drivers aren't 100% efficient, and some power is consumed by the driver. This means that the input power (and thus the input current) will be somewhat higher than calculations would predict. Depending on the driver and the circumstances, this can be anywhere from 1% to 20%, or even more. For most cases, 10% is a reasonable estimate.

The drawback of the buck driver is that the output can never be quite as high a voltage as the input. There will always be some minimum drop. It can be as little as 10s of millivolts, but for flashlight drivers it's more common to see values of 0.5 to 1.5V, or even higher. This is often called a 'dropout' voltage, 'overhead' voltage, or something referring to the minimum difference between input and output voltages.

So what happens when you drive a 6V LED with a driver with 1V dropout, and 2 LiIon cells? Straight off charge you should have 8.2-8.4V input, 6V output, no issues. Halfway discharged (3.7V per cell) you have 7.4V input, still no issues. Approaching end of discharge you may have only 3V per cell, or 6V input. Now you can only get 5V output. Likely the LEDs will still be working, but will be drawing very little current, and will be very dim. You'd get a long 'tail' as the output slowly dims. Eventually either a protection circuit will shut it down, or the LEDs will dim below a useful output.

If the dropout voltage were lower, you'd get full power deeper into discharge, and a shorter tail.

This would change dramatically if you used 3 cells. Even deeply discharged, you'd still get 2.5V per cell, and be able to have full output power. At some point a protection circuit should kick in and the light would suddenly go from full power to completely dead. Similar behavior would be expected with 2+ cells and a 3 or 3.3V LED or 4+ cells and a 12V LED.
 

sween1911

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Experiencing something strange, hopefully someone can shed light on it. I got it wired up with the 2A buck driver and 3 primaries. It appears no brighter than the 1A until I double tap it a few times and it suddenly gets way brighter. Is that a battery current thing or a physical connection thing? I also tried it with two new Keeppower 17500's from Illumination Supply. Marked 1200mah. If I just hold the model in the light and wiggle it around I can get it to jump to the higher setting.

Update: If I crank the tailcap down and press the module onto the light, it goes on high. If I hold the module in and cycle the tailcap, it's lower output. And the module and the reflector heat up. A LOT. Really fast. I suspect I'm at an edge condition with the amount of current I can pack into the light body and how much this thing wants to suck up.
 
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