Am I getting this right? (driver/LED config...)

LED Flashlights – General Info
1

I’m wanting to try another build and have had a couple of ideas, but not sure if my assumptions are correct.

I’ve been experimenting with direct driving Nichia219’s from an ICR li-ion (4.2) and while they get hot, they seem to be quite bright and better performing than my Trusfire Z8 swap.

So taking this idea, could I run multiple Nichia’s off of 2x l-ion (8.4v)?

Like this:

Next up is what if I wanted to run a driver with them?

Q1 - I see some drivers are listed as being able to run multiple LED’s in series. Can any driver do this? Or is it likely to cause problems/over heat?

The drivers I had in mind where the LD29 from IOS:
http://intl-outdoor.com/ld29-28a-12-cell-circuit-board-p-416.html

Or this one which is similar/same: http://www.lck-led.com/19mm-3000ma-driver-modes-p-501.html?cPath=37_135

would these be suitable to run 2 LED’s or do I need to look for a driver specifically to do so?

Anyhow, this is what I’d thought of:

Have I got the right idea? Would running the LEDs in series drop the amp rate in half per LED?

Thanks.

2

No - in series, the 3A has to go thru both LEDs, so each would see 3A. Calculate the power (wattage) and it'll make sense, as LEDs in series require a higher voltage.

Second diagram, use just one driver, with two series strings in parallel. That would give you 1.5A to each LED. (LEDs in parallel split the amperage, in series doesn't)

3

Thanks.

So did I get the direct drive one correct? In that running the LEDs in series would reduce voltage per led, so each led (2 of them) would be like running off a single li-ion?

For the one with the driver you mean I should look at something like this:

And that would reduce the amps to each led?

Would this be ok on any driver, or are ones specced for multi emitters doing something different?

4

Yep, first DD diagram is correct. And the new one with the single driver is as well.

As for which drivers can do what, it... depends. If it's a buck driver, it doesn't care how many LEDs are connected, as long as the input voltage is higher than the total Vf (with some voltage headroom to allow proper regulation). When the cells are dead flat, their voltage should still be above the total Vf, that way you get constant light output through the entire run time - squeeze that headroom down too tight and at some point in the discharge cycle it will drop out of regulation, and from that point on light output will fall as the input voltage falls. I think the generally accepted minimum is 1.2-1.5v higher input voltage than the total Vf.

Then there are boost drivers (if you ran all 4 LEDs in series), but usually those are much lower output than buck drivers. The boost circuitry eats lots of power, if there's any possible way to do it, raise the input voltage (if you need to) and use a buck driver instead.

Now, don't ask me what the total Vf is, with 2 series/2 parallel LEDs. I know LEDs in series you just plain add the Vf for each one. LEDs in parallel, I don't know. I could guess, but... I'm sure one of the actual smart people here can answer that one. (I only do a half-assed imitation of a smart person) :p