Using a RC battery pack to power a flashlight?

I was thinking about buying a couple of these 5000mAh 11.1V battery cells to use to power my SST-50 flashlight when Im on search and rescue, using a cord from the cell stored in my vest to the flashlight. However it can't take more than 8.4V so I was wondering how I would go about limiting the voltage and current so that I dont fry the flashlight? I suppose I would have to add a driver somewhere that can handle the incoming voltage and current from the battery? The flashlight in question is http://www.dealextreme.com/details.dx/sku.36352

The description reads "Digitally regulated current 1800mA" however knowing UltraFire, its most likely direct driven, which means I'll want to add a driver to it anyway.. I also bought a 502D with the 2x18650 tube which I suspect will fit the C8.. The plan is to mod the 1x18650 tube with a cord to use with external pack, and use the 2x18650 tube with batteries.

Could someone please recommend a good quality driver for the SST-50, preferably one that can handle at least 12V input, and even better if it has a trimpot to adjust output current.. Max 3 modes and no strobe or SOS crap please..

Thanks,
Fredrik

You have couple choices,

Easiest: Talk to your RC guy and see if he can make you a large MAH 8.4V pack.

kinda easy: look for a regulation circuit you can mount to the pack, since size wont matter you have many more choices.

Hard: fit all that in a flashlight housing like you are planning.

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Circuit wise, if you stick with flashlight drivers you will have a hard time finding a 12v capable driver that is more than one mode. (they seem to use AMC chips which limit you to 6v)

I was actually thinking about making my own packs using AW 18650 2900mAh batteries, I guess if I build it with 2x 18650s in series, and 3 of those in parallell, I will get a pack with 8.4V and 8700mAh. The idea is to use thick acrylic and drill out holes for the batteries to make a hard shock-proof battery cell.

I plan to buy http://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=7523 to use as charger anyway as most chargers I have found seem to be very unreliable(especially ones from dx). And those balance chargers get very good reviews, can charge up to 6 cells with high amps with balancing and they are cheaper than the Pila IBC charger.

Regards,
Fredrik

That light has to have a driver in order to run from 3.3 to 8.4 and regulate the power so the led doesn't fry direct drive an sst-50 at 8.4 volts and you're asking to just blow up either the led or your batteries. I think for search and rescue you don't want to get soft lithium-ion batteries. One good hit and they can swell up and vent. I suggest simply getting a 7.2 volt nimh rc car battery since it'll work with the built in driver and is plenty tough in case it gets knocked around. It'll have the proper voltage to run the light and is much easier to charge and take care of. They're easily available with capacities in excess of 5000 mah. Keep in mind the 8.4 is the peak li-ion's reach. If you get a 8.4v nimh fresh off the charger they can easily be 9.6 volts so a 7.2 v pack fresh off the charger happens to peak at 8.4 volts. So a six cell nimh pack would be perfect for this flashlight. It'll be rugged, reliable, safe and easy to charge, no balancing required.

Another direction is to use actual lipo hobby packs. The cylidrical AW cells already have an exterior, and repacking all these cylinders into a hard acrylic polygon case isn't the most efficient use of materials or space. It's also expensive. You could buy some 2s lipo soft packs -or- lipo packs in hard cases. Less wasted space, built in connectors. hobbyking has many competetive lipo pack options. The high C discharge rates are fantastic...hardly any voltage sag on high drain: the decreasing voltage is almost representative of the actual declining state of charge.

re: charger - I have the accucel-6, works precisely for each task I've given it so far.