vroom9 said:
At a first level analysis that is 100% true. However, looking a little deeper it's not quite true. In general you will find that 12 volt halogen bulbs are a little more efficient than a six volt bulb. Usually the 12 volt bulbs are about 5% to 10% more efficient at turning electricity into light than a 6 volt bulb. Using your typical G4 based bulb rated at 2000 hours a 20 watt 6 volt makes 300 lumens while a 12 volt makes 350.
And..
If you compare a 12watt light system in both 6 and 12V versions, the 6V system will be drawing 2 amps and the 12V system will be drawing 1 amp. Desolder is correct in that both systems are using the same power, but you tend to experience other inefficiencies at the higher current levels of the 6V systems.
The wiring, connectors, and switches tend to have fairly similar resistance values in both systems. Therefore you lose more power in those components at the higher current of the 6V system due to resistive loses. Yes, they can use thicker wire in a 6V systems, but the wire size is also limited by flexibility issues so there doesn't tend to be that much difference in practice.
Batteries also are less efficient at higher discharge currents relative to capacity. That wouldn't make any difference if the 6V system used 8 amp-hour batteries and the 12V system used 4 amp-hour batteries, but again as a practical matter, it doesn't usually work out that way. There just isn't that much selection in battery capacity in the cost effective sizes.
So converting the system to 12V will tend to give a marginal boost in runtime assuming you stay with a similar wattage bulb. But, as a practical matter, you will likely end up with a bigger battery pack. If you go with NiMh batteries, by far the best cell is the 4/3A that come in 3800-4500mah range. You also want to stick with a high quality cell like Panasonic or Sanyo. Cheap no-name nimh cells are really bad compared to the name brand. I use to build all my packs with Sanyo cells from batterystation.com. So with nimh you would likely end up with either a 5-cell 6V 4500mah pack or an 11-cell 13.2V 4500mah pack. 11 cell because all 12V MR11 bulb can be run at 13.2V with long life and much more light.
There are also huge differences in the quality of MR11 halogen bulbs. The bulbs used by companies like Niterider and Jet are many times better than cheap no-name bulbs. I've never found a source for these high quality bulbs other than buying the replacements from Niterider or Jet.
If you're coming from a Nicad system you'll probably have to buy a new charger if you go with anything besides another 6V Nicad pack. Once you add up the costs of a battery pack, a charger, possibly a new bulb if you go 12V, I really have to go with what others have said, It would probably be better to put money into a modern LED based light. The only somewhat cost effective way to keep the existing system going would be to buy 5 Sanyo nicad 5000mah D-cells with solder tabs from batterystation and rebuild the existing pack.
