Join Date: Jul 2007
Location: CA, USA
Bikes: Surly CrossCheck, Xootr Swift
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6V or 12V MR11?
This is a question for the halogen afficionados out there. I have a Turbocat Trailguide helmet light (4.8V 15W MR11) that I would like to modify to take a Li-Ion battery. Motivation here is to reduce the weight and bulk of the battery which I carry in my pocket. Currently, it uses a 5 cell 4000mAh NiMH battery at 12 oz.
In changing the battery, I also have the opportunity to go to the more readily available 6V or 12V MR11 bulbs (over-volted of course), of which I plan to use the 20W variety. Checking out batteryspace.com, I see a 7.2V 4000mAh li-ion for $27 weighing in at 7 oz. In comparison, a 14.8V 2000mAh li-ion (equivalent capacity) costs $30, weighs 6.9 oz. The 14.8V charger is also slighter more expensive, but cost differences will not be a deciding factor here obviously.
So, what are the pros and cons of 6V versus 12V systems? I have a few items to get the list started.
1) Higher voltage means lower current at the same power draw (power = current x voltage), so less resistive losses through wiring. If memories of freshman physics serve, this is true...however Turbocat uses 18 gauge wiring, which is pretty darn thick so losses would probably be minimal. Still, +1 for 12V.
2) More cells, more chances for failure? Smaller fire if the battery explodes? Kinda reaching here, but...+1 for 6V.
Ok that's all I have...need more inputs please!
Edit: BTW, I'll have a Turbocat TG NiMH battery pack + charger for sale soon (asking $50, normally $120). PM me if interested
Last edited by Sir Bikesalot; 10-29-07 at 04:16 PM.