Thanks Ervin.
I have zero background in the physics of electricity, but I think I can make heads and tails out of your charts. I’m going to sit down with my multi-meter and calculator today and play with some of these calculations. I think the exercise will help me get a better grip on things.
Yes - if 2 cells in series and bucking down to 1 LED, if tailcap is 3A, each cell is pushing 3A with total output of the cells ~8V, 24 watts of power, ~6A to the single LED.
2 4000 26650 in series will have 4000 mAh for providing 8V. When bucked down to ~4v though for one LED, effectively they have 8000 mAh -- hope I'm explaining this right, maybe RMM can confirm. Certaining in practice, you should get about twice the runtime from 2 cells in series driving a LED vs. 1 cell driving a LED, assuming at the same amps to the LED.
I’ve been playing around with Ervin’s charts (just doing math calculations with a C8) but I don’t know how to check resistance. I calculated the resistance using my known factors, but don’t know how to confirm the results. I bridged the battery and tube with my ohm meter, but get no reading.
Checking for small levels of resistance with a multimeter can be tricky. Maybe it's because I only have cheap DMMs but it has always been hard for me to get consistent results. Another easy way is to measure the voltage drop across a conductor. If you're reading 4.0v at one end under a 3 amp load, then 3.9v at the other end, you can calculate the resistance from that drop.
I got the light today, and it has XM-L, not XM-L2. I didn’t really expect it to have XM-L2, so I’m not heartbroken. Probably XM-L U2. Never trust DX.
The light says Kinfire on the side, but the box has a picture of the same light that says COURUI.
:/
Bad DX! Never trust DX. I would try to get a partial refund.
Mine came with XM-L emitters too. I expected that since the aliexpress seller did not mention XM-L2s. I had a little hope mine were XM-L2s though. Not a big deal. I got lots of spare XM-L2s from other lights.
At least mine is OEM. Which I like. :)
I really like the size of the light. :) Its pictured in OP here beside TK61 and BTU shocker.
Ha ha. I knew it would be XML. I had some DX points, so I paid maybe $2 less than yours. I’ll contact DX anyway, and see if I can score some free points or something. Love the light though. I can’t decide whether to eat the expense of swapping XM-L2, or reflowing the XMLs on Noctigons.
I’ve got too many mods on the go, it’ll have to wait.
I used a 2$ coupon code when I bought mine. :p :D
Maybe ill get it done next month. No time to start on it now. Cant do that much either. I have some parts incoming from various places. Still not decided exactly on what do do with it in terms of switch type.
Tried with these yet? https://www.akkuteile.de/keeppower-imr26650-4200mah-50a-3-7v-li-ion-akku/a-12036/
Keepower doesn’t make cells so better to find out what’s under the wrapper.
With a direct drive driver you DO NOT multiply anything by the number of cells. Amps in is amps out. It is 13 amps, and 13 amps is 13 amps, there's no way for that kind of circuit to end up with anything being at 39A.
3 cells, yes. And 3 sets of LEDs. Each series string of LEDs has its own cell. The tail current is divided by the number of LEDs (or in this case, the number of series strings in parallel). That's 4.3A per string of 3 LEDs.
CONVERT TO WATTS on a setup like this if you want to see what's really going on! To get a true number you need to know both the input (tailcap) amps and the input voltage. Using a Vin figure of 4.2v per cell will throw things off, as they aren't going to be anywhere near 4.2v while delivering 13A. Make a guess of 3.8v per cell under load, that's 11.4v input, and 13A input. 11.4 x 13 = 148.2 watts.
Now if you're just using that '39A' number as a way to put the output in terms of a single LED powered by a single cell, or LEDs in parallel with cells in parallel, yes, this 148W setup would be the equivalent of 4.3A per LED, with 9 LEDs in parallel, and an input voltage of ~4.2v = 39A, but that's a clumsy way to do it. Convert to watts instead. It is an actual number and not something that involves guessing.
Have you been away Comfy? I was hoping you’d pop by when I started this thread. I was surprised when you didn’t show up and rap my fingers with a ruler.
Okay. Each string is seeing 4.3A, so is each emitter in the series string seeing 4.3A, or is each emitter only seeing 1.4A?
I know Im wearing your patience thin, but it takes time for things to soak into my brain. I guess I should start learning about watts. I’m lost when people start talking watts in terms of flashlight output.
In series, they all see the same amperage.
Converting to watts is useful because the wiring configuration doesn't matter. Watts is watts is watts. Three LEDs in series, fed 3 amps at 9 volts, is 27 watts. Three LEDs in parallel, fed 9 amps at 3 volts, is 27 watts. Isn't that easier? :)
Well…yeah., but now I have to learn new math.
Amps times volts equals watts. Watts divided by amps equals volts. Watts divided by volts equals amps.
So if I take a tail reading and see 5A and 11V I’ve got 55 watts?
Yessir. It's useful because it's not dependent on the circuit layout to be a useful comparison to some other completely different circuit. You can convert backwards from the watt number if you'd like, as in your light is the same light output as if you had 9 LEDs in parallel running at 39A total/4.3A per LED @ 3.8-4.2v input (but no part of your light is actually doing 39 amps anywhere). The math works the same either way. A given power level (watts) gives the same light output, no matter how that power level is achieved.
3v or 6V emitter doesn’t matter?
Well, the numbers you multiply to get the watts matters. I mean, you can't use 3v in your math if your LED or input voltage isn't 3v.
Your series strings of 3 LEDs each are, as it appears to the driver, a single LED with a forward voltage of around 11.1 volts. 4.3 amps per string, at 11.1 volts, is 48 watts per string, times 3 strings in parallel, for a total of 143-144 watts (this is the theoretical output power from the driver; the difference between the input watts and output watts is the driver efficiency). Doesn't matter how you break it down or how many steps you use to get there, watts is watts.