Originally Posted by DannoXYZ
If you're driving a 12v halogen at 11.1v, you'll be losing A LOT of light, much more than -9%, probably closer to -15%. Better to run another cell to get 14.8v and use an efficient, nearly-lossless regulator to keep it around 13v.
I got 13.2v so that I can overdrive the halogen light by about 10% and get 20% more light out of it.
Thanks for the feedback and link, guys. I hadn't yet thought the effect of dropping the voltage by 9% all the way through. Looks like that will drop the effective wattage by 15%, and light output by 30%. Yikes. Makes sense of course -- if overvolting bumps up the efficiency (basically twice as fast as it increases the wattage), undervolting would cause the reverse to happen.
Bumping all the way up to 14.8v Li-ion (with a PWM regulator) would work for the halogen, but I'm also going to be running Xenon strobes and a Luxeon III LED (in an MR16 package, rated for nominal 12V) with this system too .. those can't run off a PWM regulator, and hooking them up directly to the higher voltage would likely blow those out pretty fast ... so I'd either need 2 regulators or live with the inefficiency of the conventional regulator. In any effect, this ends up adding more complexity to the system than I'd like without much benefit.
So now I'm thinking it will be better just to stick with a 12V or 13.2V NiMH system, despite marginally more weight than a Li-based system and the fact that I'll have to put the battery in a water bottle myself. Will the Night-Sun/Lightman 12V strobe run OK off a 13.2V system, or does it really need to be hooked up to a (nominal) 12V source?