Mixed Voltage Emitter Setup: Is this Feasable?

This is a hypothetical setup I've been thinking about.

3 x Li-Ion in series.

3 x parallel leads from driver. Two sets of leads running 2 x XML in series, and the third set running 1 x MTG.

Is this doable? I realize mixing emitter types can cause fluctuations in voltage, but if everything is mounted on Noctigons, are there really any serious worries.

I figured the 6V MTG would balance out the 2 x 3V XMLs.

This setup won't go out of my head, so I need someone smarter than me to tell me if I should stop thinking too much.

3 cells in series + FET driver with Zener + emitters wired 3s2p XM-L works...

So yeah, you should be able to just replace two of the XM-Ls with an MT-G2. I don't see why it should not work.

Edit:

But what you show above are only two emitters in series, not three. Input voltage will be too high.

You could wire the emitters that way if you had two cells in series. Not three.

Thanks RaceR86

All I need now is a five emitter reflector that has a center hole big enough for an MTG. Good luck. :bigsmile:

Why / how does 3 cells work?

I’m still not really sure how the voltage gets divvied up with the MTG in the works. Is there enough to go around?

I suspect that this is a very bad idea. Whatever has the lower vF (pairs of XMLs in series or a single MT-G2) will get amps dumped on it.

It’s a matter of how much amps. The XMLs will be on copper, and I like to drive them hard. As long as they’re not getting 7A + each.

Cereal_killer makes a good point as well. What makes you think that this will work at all without *poof*? 3s is too high a voltage for 2 XM-L2 in series AFAIK. It seems to me that it is also too high a voltage for a single MT-G2, but I don't know that. Do you or does anyone else already have a similar setup working with 2x XM-L2, 4x XM-L2, or 1x / 2x MT-G2?

as current rises, forward voltage does too, so the circuit has to balance out somewhere right?

now whether the leds go poof before that happens…

I assume you meant 2 cells in series? 3 cells will kill them all unless you have a buck circuit in there somewhere.

I was thinking maybe it wasn’t a mistake, 4x XM-L2’s and an MT-G2 is gonna put a LOT of strain on a single string of batteries, without low modes I can see the voltage sag being high enough, even at start up, to keep the emitters safe.

Still tho it seems awful risky, that’s almost $40 worth of emitters your gambling with, to rich for my blood just to see it it’d work.

Edited my previous post. Not sure what I was thinking.

That’s what I was wondering about. I still haven’t got my teeth around what exactly is going on when you take a number of cells in series wired to parallel and then to series. So two cells would be doable with this setup?
What if I used this setup with 3*XML in series x2 and 1 X MTG. I guess most of the strain would then be on the MTG? I’m assuming it’s the DD on high that is the great decider of what’s going to blow.

I don’t really have a light for this XML/MTG mix. The idea has been in my mind for a while and this is the first time I’ve put it out there to find out if it’s possible. I don’t think it’s been done yet. Maybe it’s not possible, but it would make a really cool light.

I would highly recommend against putting a MT-G2 and a XM-L2 in a series string, going with 3 cells and strings of 3s XM-L’s would be fine, but you shouldn’t mix different voltage components in a series string even if the total voltage adds up correct.

I’d say your best bet is 2s, maybe 2 or 3p cells and 2s2p XM-L’s with another parallel string with a single MT-G2, that’s doable, mixing a MT and XP is really asking for it IMO.

I never planned to mix MTG with XML in the same string, I knew that would be bad. So basically, the number of XML in a series string has to equal the number of cells?
Does that apply to the MTG on a parallel string?
If I had three cells in series wth three strings, two of which are 3 x XML and one which is 1 x MTG, would the MTG be running at dangerous level, or would that setup be acceptable. (basically like the OP diagram, but with an extra XML added to the two strings)

That would fry the MT-G2 pronto; it would still be seeing the full voltage from three cells.

If your trying to use more than 2 cells your next option would be 4s cells. From three cells you can’t run a single MT cause its to high and you can’t run 2s MT’s cause it’s not enough.

With 4s cells (16.8v) you could run parallel strings of 4s XM’s and 2s MT’s. But really your best bet is the original diagram minus one cell.

Couple of things going on here:
Ouchyfoot - assuming that you can get the cells to keep sagging the more current you draw is bad. (Frankly this is one of the reasons I wish DD drivers didn’t exist, I think they serve to confuse people with limited knowledge of electronics.) Voltage sag beyond what HKJ shows in his discharge graphs is bad - hard on the cells. HKJ is already pushing many cells beyond reasonable limits (and he says so). What’s more relevant here is that there is a limit to battery sag. They will only sag so far and they will only sag so quickly. This is where you get poofing happening.

Now, I disagree with Cereal_killer about mixing Vf in series. That’s actually one of the major benefits of series setups - you don’t get current imbalances from mixing emitters. All emitters run in series will necessarily see the same current! If that current is too high then you still have problems, but it will be the same current. Hint: with a real driver that has any kind of regulation guessing about this is not required.

If you wire strings of two XM-L2's parallel to a MT-G2, according to my (undoubtedly not perfect) voltage measurements I did on one XM-L2 and one MT-G2 :

-at 3A through the MT-G2 the voltage is 6.4V, the XM-L2 string at 3.2V/led will receive 2A.

-at 3A through the XM-L2's the voltage over the string is 6.8V, the MT-G2 will receive 5A

So it is not really a nice balance, but the led-wiring should work if the driver can deliver the provided voltage and current.

In my OL-fromscratch build from last year I wired a XR-E, a MT-G2 and a XM-L in series (direct drive on a 9V block battery :Bigsmile: ) , again not a nicely balanced light output between the three, but it does work without a problem.

This is getting interesting, and I am understanding the pitfalls. My reasoning for starting this thread is because I’ve never heard or seen any discussions involving a multi emitter XML light that incorporates an MTG. I would have thought someone would have posted some kind of results by now, even if it were a failure.
Is there any kind of buck driver setup that is realistic.
At least when Scaru was around, he would have risked life and limb to just to see what would happen .

Like I said, with a regulated driver of any kind you just run them in series. Done deal - no problem. A buck driver is regulated, so you simply put the LEDs in series and go for it. Make sure you have a higher battery voltage than the combined forward voltage of all emitters at the desired drive current.

For example, a 3A buck driver running 2x XM-L2 and 1x MT-G2 in series would be driving 3.4 + 3.4 + 6.6 = 13.4v or so at that current (according to djozz’s crash tests). So feed that buck driver with 4-5 Li-Ion.

I still don’t really see why you’d want to do this. If I wanted to have a light with both XM-L2 and MT-G2 emitters I would certainly think I’d want to be able to control them separately.