Use of Nimh batteries ok in incand. flashlights?

I was wondering if using Nimh batteries would be ok in relatively low drain incand flashlights such as Minimags and such is ok. I suppose you just have to be careful not to drain them too much. I think the rule is 1.0V if I'm not mistaken. Would the Nimh batteries provide a flatter output than normal alkalines in this type of usage? It seems that Nimh batteries cut out at about 1.0V, while alkalines stop pumping juice at a lower voltage. Would this be better for the bulb life as well. I would think that starting with a lower voltage to begin with and running at a flatter voltage level would be better for the bulb. Is this correct?

Actually, NiMH is routinely used in many of the "hotwire" incandescent lights drawing several amps from the cells for extended periods.

Has anyone tried running an incan bulb on 8AA or 12AA NIMH's? If so what kind of bulb?

Chuck Witherspoon said:

Has anyone tried running an incan bulb on 8AA or 12AA NIMH's? If so what kind of bulb?

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The standard six cell mag bulb works on 8AAs.

Joel

I'm not sure why, but some manufactures recommend against using rechargeables, I think it has to do with the different resistances of the batteries.

It wouldn't really bother me though, burning out an easily replaced cheap bulb early.

The problem is though, taking a 2AA Minimag for example.. the NIMH batteries can toss around more current (amps) more easily than an Alkaline in general, but they don't have as much voltage to start out with, so the output will never be as high to start with in an unregulated lower current draw light like that.

So I guess my question is. Would the incand bulb benfit from having less voltage initially and more consistent voltage overall from the flatter running Nimh batteries? Would the Nimh batteries actually have a flatter output in incand. or would it be similar to alkalines in these lower drain incand flashlights? Simply put, I'm trying to figure out if it would be worse or better on the light by using Nimhs.

My wife's favorite light is her pink Minimag, which she uses a lot and I would like to use Nimh batteries so that we aren't constantly buying new AA bateries. I also use my Minimag quite frequently. I'm thinking that Nimhs would actually be better for the bulbs because they don't overdrive the bulbs initially like alkalines do. I've measured some AA alkalines at as high as 1.6-1.7 volts while my Nimhs usually get to about 1.4 and quickly stabilize at about 1.2v. Two AA batteries running at about 1.2v ea I think would be better for a bulb designed to run at about 2.3-2.4v rather than batteries that start out at 1.6v+ and then fade down to about .7v throughout their life. What say you?

I've seen many conflicting comments about bulb life. Some people say that Minimags use bulbs quickly because the majority of the run time is at sagging voltage levels, while others say that underdriving the bulb will actually increase the bulb life. I've also seen some manufacturers recommend not using rechargables and I'm trying to understand why. I personally think the bulb would actually benefit from not having the initial overdrive from alkalines and the more stabile current of Nimhs. I

lhivernant said:

The standard six cell mag bulb works on 8AAs.

Joel

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Yes, except that the average bulb life is only 35 minutes. You'll get a really nice, pure white light though (when at night. The color temperature is still relatively yellow during daylight).

The bulb is rated for 7.2V, my 8 AA is around 10.90V, 11.5V when hot.

Right now I'm trying a Pelican 3804 (alkaline BigD) bulb to see how long it'll last. It does seem brighter than a Mag krypton 6D bulb.

strat1080 said:

So I guess my question is. Would the incand bulb benfit from having less voltage initially and more consistent voltage overall from the flatter running Nimh batteries? Would the Nimh batteries actually have a flatter output in incand. or would it be similar to alkalines in these lower drain incand flashlights? Simply put, I'm trying to figure out if it would be worse or better on the light by using Nimhs.

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The ni-mh would provide a much flatter discharge curve. They do lack the initial punch that alkalines give in the first couple minutes, but over the life of the charge, they'll give off a lot more light (area under curve) than alkalines.

Ni-mh would give a flatter discharge even under a stock minimag's current. About the onlything where an alkaline would beat a nimh is a clock I believe all alkaline rated capacities are @ 0.025amp (completely useless).

Don't think bulb life is really affected by much. If you look at the bulb ratings, they're actually right in-line with the equivelent ni-mh voltages (i.e. 2 cell 2.5V, 3 cell 3.7V, 4 cell 4.8V, 5 cell 6.0V, and 6 cell 7.2V). Either way it's not really a concern. But when you're overdriving the bulbs (see my post above) it's totally different.

Two AA batteries running at about 1.2v ea I think would be better for a bulb designed to run at about 2.3-2.4v rather than batteries that start out at 1.6v+ and then fade down to about .7v throughout their life. What say you?

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To be honest, I don't think they'll be much different. I can't recall the relationship between voltage and bulb life (search for the formulas), but IIRC it's exponential.

Study a running voltage plot, you'll probably find that for the most part, an alkaline spends more time under 1.25V (nimh running voltage under a low drain bulb) than above it. If the relationship does remain exponential, then I'm sure it'll average out to be about the same. To find the exact difference, you'll have to get the plots, the formulas, and do a little curve area estimation or integration.

But like I said before, any difference is probably negligible provided you're not overdriving the bulb with the nimh.

I've also seen some manufacturers recommend not using rechargables and I'm trying to understand why. I personally think the bulb would actually benefit from not having the initial overdrive from alkalines and the more stabile current of Nimhs.

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The only reason I can think of is that the manufactures (especially a mass market flashlight company like Mag) wants you to see the initial brightness on a fresh pack of alkalines and go "whoa!".

Underdriving a bulb will ALWAYS give you more lift. This is why DRL high beams driven at 6.0V (depends on the car, my Nissan used 6V) takes a lifetime to burnout even though most high beams are only rated for 200 - 300 hours at the full 14.4V.

The ni-mh would provide a much flatter discharge curve. They do lack the initial punch that alkalines give in the first couple minutes, but over the life of the charge, they'll give off a lot more light (area under curve) than alkalines.

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This has been my experience so far. I've been using Ni-MH batteries in my MM for 3 weeks and have gone through about 2 charges. It seemed that with alkalines it was fairly bright for maybe 30min. and just got dimmer and dimmer from that point. With the Ni-MHs its not as bright initially but about as bright as the alkalines were after maybe 15-20 min of runtime. From there the Nimhs keep the light fairly bright for several hours. I think the light is more useful with the Ni-MH and much cheaper to run. I would have to say we that we use our MMs the most just because we aren't afraid to either damage or lose them. For serious tasks I like to use better lighting products. I think that the Ni-MH make a Minimag a more useful light, with a more regulated output.

I put a couple NiMh in a MM for about 10 seconds. It does produce light, but it's pretty yellow from such low voltage. About like alkalines after a few minutes like others have said. If she's OK with the output, run with it. I'm sure the output will be more consistent for her. Just recharge often to avoid ruined cells. I'm spoiled from carrying a regulated LED light. Hope I never have to go back.