3xP7 in series buck/boost driver?

Is there such a thing? I'd like to be able to supply one of several battery combos to a KT4 with 3xP7's wired in series and still have high output. Battery combos would be any of following:

-3 x CR123 Primaries
-4 x CR123 Primaries
-2 x 17500 Li-Ion's
-2 x 17670 Li-Ion's
-2 x 18650 Emoli's

Is this wishful thinking or a reality? Is one under development now?

Ask Der Wichtel about his driver. It might be able to do what you are looking for.

brighterisbetter said:

Is there such a thing? I'd like to be able to supply one of several battery combos to a KT4 with 3xP7's wired in series and still have high output. Battery combos would be any of following:

-3 x CR123 Primaries
-4 x CR123 Primaries
-2 x 17500 Li-Ion's
-2 x 17670 Li-Ion's
-2 x 18650 Emoli's

Is this wishful thinking or a reality? Is one under development now?

Click to expand...

Not from a regulator point of view, I think the only battery combo that could supply enough power for 3xP7's is 2x18650 Emoli's. That's if they were IMR's and not their ICR cousins. Actually the Molicel ICR-18650J is rated for 5.0 amps @ 45°C, so that's just enough. The IMR-18650E has a max discharge rate of 20 amps, much better.

But the KT4 was meant for use on an M3 body, so 2x18650's wouldn't fit. What kind of body were you thinking of using? I've never actually seen a KT4, only pictures. Are you thinking of removing the reflector and using something like 3x27mm plastic reflectors?

Sounds like an interesting mod.

I basically want to put this head setup on either an M3 or M4 body, and be able to switch between the two for form-factor preferences. That is the requirement for so many cell combos listed. Obviously, the P7's would need to be underdriven to work on 2 cells instead of three, but I'm ok with that as I prefer the slim body over the M6. Wouldn't a buck/boost driver have a 'voltage-detect' feature or something like that which would consequently adjust Vf to the LED's based on cells being used? And yes, the Emoli's I have are the IMR flavor, non button top. And I'd obviously be boring the M4 body to accomodate the 18650's, rather than getting one of Leef's 2x18650 C-M from Lighthound, as the anodization wouldn't match exactly.

brighterisbetter said:

I basically want to put this head setup on either an M3 or M4 body, and be able to switch between the two for form-factor preferences. That is the requirement for so many cell combos listed. Obviously, the P7's would need to be underdriven to work on 2 cells instead of three, but I'm ok with that as I prefer the slim body over the M6. Wouldn't a buck/boost driver have a 'voltage-detect' feature or something like that which would consequently adjust Vf to the LED's based on cells being used? And yes, the Emoli's I have are the IMR flavor, non button top.

Click to expand...

Ok the M4 makes sense. It also comes with the big head without buying a separate KT4. Sorry I'm not a Surefire guy so I don't know. If 4x123A's are the same length as 2x18650's, is the M4 battery tube wide enough to hold 18650's? I know some Surefire tubes are that wide. Maybe Size15's or one of the other Surefire experts could help you with that. Or do you already own an M4 to know for sure? I like the idea of the direct drive M6 setup in your link. That looks cool. But it's a little too fat, yes?

I'm not sure I understand what you mean by the, 'voltage-detect' question. A regulator would automatically draw whatever power it needs to provide a given level of output. Whether it's constant current or just an ordinary voltage regulator. So it would provide the same level of output if you had either 3 or 4 batteries. It wouldn't make a difference. But if you mean is there a regulator smart enough to know a CR123A can't provide 5 amps but an Emoli IMR-18650 can, I never heard of one like that. When a regulator wants more power than the source can provide, it drops out of regulation and goes into what's called "direct drive".

Der Wichtel's regulator is a buck voltage regulator. So you need to start out with more voltage than the 3xP7's require, to buck down. That leaves the only workable battery configuration you listed as 4x123A's. The voltage drop on primaries would probably be too much. Four of AW's 16340's would likely work. Part of the problem is there really aren't many constant current regulators that supply the kind of power the P7 needs. Are you sure an M6 is too fat?

Good luck and keep us posted...

While I do own an M3, I have yet to acquire an M4 so can't attest to that tube accomodating 18mm cells, but I have no problem paying for someone to bore it. Perhaps you're right, the M6 isn't that wide I suppose, I just sold mine on MarketPlace about a week ago cause I didn't like the feel in my hand. And I agree with you on the 4x123 battery config....it's not safe to push the cells beyond 2C. So maybe that's a moot point that I'm going for, I just hate to have to go with a monster as long as Leef's 3x18650 tube. I'd feel like a baton twirler in a parade with that thing . One thing I've been considering is going with something like the x1628 head on a bored M4 body running 2xIMR18650's if it would be safe. Here's more info on that one. I've read that heat is a major issue with 3xP7's, so maybe something like I just linked to is more suited to my tastes. Thanks for the input thus far.

Yeah I think heat is going to be a problem in any 3xP7 setup. 30 watts is a lot of heat. If you had something like a D2Dim in it, you could run it at low power continuously, but still have full blast for once in a while use. The D2Dim isn't really a regulator as such. But it might work nice with a 3x17670-M6 direct drive setup. I'm not sure if the D2Dim's requirement of having power all the time would pose a wiring problem since the M6's switch is in the tail. Even if there was room in the tail cap, you can't draw power through the LED's when they're not actually in use. There would have to be wires running down the body and that could be problematic.

Here is a link of a beautiful mod by cmacclel on a Mag. Ok it's not a Surefire, but as far as a direct drive D2Dim with 3xP7's and 3 Li-Ion's, it's very similar to what we're talking about.