I recently picked up one of the 5C Defiant flashlights from Home Depot. And I’ve been thinking about possibly upgrading the emitter to an MT-G2. But I’m wondering if the voltage will be sufficient. Nominally, 5xNiMH will produce 6V. During much of the discharge cycle, voltage will actually be above this. And a 3A draw is actually fairly low for a true NiMH C cell. So voltage sag will be minimal. But the Vf on the MT-G2 IS 5.7V (at 1100ma). So 5xNiMH could potentially be cutting things close. Has anyone tried running an MT-G2 from 5xNiMH? Does it work fairly well direct driven? Or is there a driver that might be able to boost the voltage just a hair that might make the setup work a little better?
I measured 5.83VF at 1100mA and 5.7V at 700mA.
Just think about that the NiMHs will have around 1.38V and up when they are charged.
Based on this graph I would say they keep a similar discharge curve as the AA Eneloops
Direct drive off two 18650s works fine, voltage sag & Vf limit it to around 5-5.5A. Smaller cells (16340-18350) have more sag and so current settles in around 3-3.5A. Those are initial numbers with freshly charged cells, of course it drops steadily as cell voltage falls.
5xNiMh you won't be able to fully drain the cells (unless you have a buck-boost driver that can switch over when needed), voltage will hit 6v with each cell only drained to 1.2v (and that's the voltage under load, open circuit they'll bounce back a bit, maybe 1.28v?) Current thru the LED at only 6v will be very low, less than 1 amp.
At 6V thought the LED the current will be around 1600mA, I already posted over 1100mA at 5.83V
Cree’s specs are 1100ma at 5.7V. But I guess that’s probably more of an average figure. Anyway, it looks like maybe a 6D Mag might be a better way to go than the 5C Defiant. Unless, of course, an appropriate driver exists. But I’m not counting on that.
What about this: http://intl-outdoor.com/boostbuck-318v-triple-xml-circuit-board-p-542.html
I have a few NiMh lights, but I haven't done the mad scientist experiments with them like I have LiIons so I don't know them as well. What's your operating voltage range with 5xNiMh - 5-7V? That driver might work down to 5v but can't say for sure, but I do know it doesn't work as advertised from a single LiIon cell at 4.2v. 5v might be different but you would have to test it to see how it behaves. At 7v it should be fine and running in buck mode. That transition to boost at lower voltage is the part that's the unknown.
Are you committed to using Cs you already have? If not, think you could squeeze in 6x sub-Cs? Total length is a little longer than 5x Cs but within the range you can usually tweak things (tailcap mods, different springs, moving driver forward a bit, etc.) to compensate for.
Well, I would rather not go with sub-C’s. First of all, C’s are what I have. I would have to buy sub-C’s. And secondly, capacity will inevitably be lower with sub-C’s (which are generally little better than AA’s as far as capacity). Too bad the tubes on the 3C Defiants don’t have the same diameter threads on both sides. Otherwise, I would just screw two together to make a 6C light.
My estimate (loosely based on everything I have read and measured on the MT-G2 and the behaviour of NiMh batteries) with direct drive from 5 NiMh C-cells in series is that at first there will be a short period of high current (4+ or even 5+Amps?), and after that during most of the draining of the batteries the current will slowly go from 3A to 1.5A. After that the current will quite fast drop to 1A and less with the led fading out slowly.
The driver Comfy recommended in Post #6 is what I used in a ZY-T08 running in 2S mode. I think it might work on 5C NiMH, but just a guess. It does not work well on a single Li-Ion (always thinks low batt). Might be worth a try, and would allow for almost any fuel you want to put in there, even 2x18650 or 5C Alkalines.
It might work since Nimh’s can flow so much current. Give it a shot. If it did doesn’t work that great you can put the emitter in a different light or go 18650’s or sub C’s.
I have been thinking the same thing. Both relic and I did a build using a Ultrafire clone of the Trustfire X8, a DRY DD driver, and two very good max charged 18650s, even to 4.35 volts. The two good cells with good heat sinking and copper braided tail spring can draw 4.5 amps at 8.4 to higher volts, for a short bit. Does drop back fast, but runs decent at about 2000 lumens after peaking even higher. Nice build and only about 45 bucks.
To the point:
I bought a 5 cell Defiant, and been talking to relic about what to do with it on a MT-G2 build. Could mod a cell adapter to run 2, 18650s, damn, the tube is so close to accepting 2, 26650s, almost worth boring, not really. but 5 NiMH should work. First could try the OEM driver, then the $5, DRY. People have been Bad Mouthing the new 5 cell HD, but I was’nt that turned-off. Does have a plastic reflector, and a plastic lens, but takes a Standard C8 lens (41.5mm) and probably could use a C8 Al reflector (haven’t tried it). The star is 20mm, and I do believe the oem emitter is a XML U3, definitely a little blue. The pill is big and long, and the circuit board is 22mm, just right for the DRY driver. So the X8 build is cheaper, but the HD 5 cell should work. Have to order a Noctigon MT. Was telling relic, the MT-G2 kind of spoils a person, another BLFer has driven one (well heat sinked) at vf 7.0, and clear to 7 amps, wow, pushing over 3000 lumens, whoa!.
Wow, 7A is a lot! I have to try that when I mod the UF T90 with a copper star. J)
My MTG2 TR-1200 is running an actual 9A at the emitter... it either doesn't like that much current or it has other issues though, tint is a lot cooler but not visibly brighter than the one in the S1100 at only 3.3A. The LED didn't turn blue or start smoking or slide off the star, so they are tough S.O.B.s for sure.
This looks somewhat promising. My only concern is that stupid low voltage protection. I get that it’s needed for Li-Ion. But since this light would be running 5xNiMH (which is not quite 2xLi-Ion), I’m not sure if there would be problems with it cutting in when the batteries still have lots left.
Might be a few days before I can get to it, but I can check that setup for you if it'd help. I have one of those drivers here and a bunch of D-cell NiMh I can rig together with magnets and do a quick & dirty bench test.
That would be GREAT if you could test it out. I also found out another thing with this 5C Defiant. I can actually screw TWO battery tubes together on it. So I coukd theoretically get probably 9-10 cells in there if I want (or fewer if I use spacers). Of course, I would rather just go with five if I can get away with it.