FM 6AA>2D approx runtime w/eneloops and Mag* 5 cell lamp?

[willrx]

If anyone has a link with this info, please send me there. I'm wanting to know the approx runtime of an FM 6AA>2D carrier w/eneloops and a 5 cell Magstar lamp. About an hour? How is this calculated? Maybe that's what I should be asking. Thanks.

 

[Valolammas]

You can calculate an approximate runtime by dividing the mAh capacity of your cells by the current that the bulb draws. So if the Eneloops are about 2000 mAh (that's 2 Ah) and the bulb draws about and Amp, you'll get about two hours.

I remember reading somewhere that the Maglite bulbs draw something between 0.8 to 0.9 Amps, but now I can't seem find that thread. I could be wrong, but I think that sounds reasonable. Since you'll be slightly overdriving the 5 cell bulb by using 6 cells, it will draw about 10% more than normally, so it will work out to an Amp or so, maybe a bit less.

 

[willrx]

Great, thank you! I will keep that info handy. One question though, each battery is 2000mAh, what effect does multiple cells do to the equation?

 

[Valolammas]

Multiple cells add up the voltage, if you put them in series, but the capacity remains the same. So in series they will be six times 1.2V per cell = 7.2 Volts and the same 2000 mAh capacity.

If you were to wire them in parallel, the amp draw would be divided between the cells thus effectively multiplying the capacity, but then you'd have less voltage available.

 

[willrx]

Thank you again, now I understand. Really appreciate your help.

 

[Valolammas]

Turns out my memory was a bit off. I did find some threads where people had measured the current draws of Maglite bulbs, and apparently they are more like 0.7 to 0.8 amps.

E.g.
http://candlepowerforums.com/vb/showthread.php?t=131710
(This one measured 0.9 amps, but it's overdriven with 3xCR123s.)

http://candlepowerforums.com/vb/showthread.php?t=117655
(This one says they are made by Carley, and according to them, krypton bulbs draw 0.7 Amps and xenon bulbs 0.77 Amps.)

I had a third link where someone measured 0.75 Amps, but I lost it and I'm too lazy to try to find it again.

I also measured my own, but I only got 0.66 Amps for a 5 cell krypton bulb being driven by 6 NiMH AAs. But then my home-made 6AA-to-2D adapter may not be exactly resistance-optimized. I did, however, get 0.90 Amps for a 6V/5W bi-pin bulb, which is about what it should draw.

So, in conclusion, the Mag bulbs probably draw less than an Amp, so you may get a little over two hours of runtime if you run your cells flat.