How long would micropuck and NiMh D-cells run 1w?

[pedalinbob]

how long would two hi capacity 9000mah nimh d-cells and 2 micropucks run two 1w luxeons?

i know someone creating a bike light in this configuration, and he wanted to know runtimes.

i cannot seem to remember how to calculate approximate runtime!

edited to add: what would be the best configuration for driving two 1w luxeons with the absolute longest runtimes, while keeping the weight reasonable? he wants to use nimh bats.
i thought 2 d nimh w/micropucks would be best.
but maybe a downboy/other driver would be better? he wants 30+ hrs runtime--not an easy request.

all opinions greatly appreciated!

Bob

 

[paulr]

Re: How long would micropuck and NiMh D-cells run

Yes, a downboy should be more efficient than a boost converter. But look, assuming 100% efficiency (unattainable), two 9000 mah cells at 1.25 volts is 22.5 watt-hours, so at 2 watts that would be 11.25 hours. For 30 hours of runtime you need either more batteries or less power to the leds.

Why does your friend care about 30 hours of runtime for a bike light? Rather than going after such extreme runtime, maybe he should just look for ways to make recharging more convenient.

 

[pedalinbob]

Re: How long would micropuck and NiMh D-cells run

i know, paulr...i was wondering what was up with the 30 hr requirement.

he stated he wants to only have to charge once per week, and i suppose he calculates his ridetime at 30hrs/week.

it does make things more difficult...

myself, i will be building a similar system, with a quick release so i can use ultralight nimh aa or heavier but much longer running nimh d cells.

i also can use nimh or alkies with the micropucks.

peo[ple think im nuts, but i had no problem mountainbiking an unknown trail at night HOLDING a sl4aa led. for my needs, 2 well driven luxeons should be great.

thanks for the help!

Bob

 

[paulr]

Re: How long would micropuck and NiMh D-cells run

If he's bringing the bike inside when not riding, he may as well charge the light. Or if he's leaving it outside in a place where he has to worry about getting parts stolen, he better bring the light inside, so he may as well charge it.

If he's leaving the bike outside in the daytime in a place where he doesn't have to worry about getting parts stolen, or if he's riding it in the daytime, he can put some solar cells on the bike to keep the light charged.