Author Topic: Basic Electronics question, Bike Light Power (Read 2408 times)

thegallery · « **on:** September 19, 2005, 17:14 »

Not sure where to put this....

If I have a 10AH 12V (10 Amp Hour 12 Volt) battery, and I'm running a 50Watt Lamp, how do I work out my approximate run time?

For those who are interested, the battery is NiMH, and the bulb is a 50W Halogen MR16. I had a smaller homemade light last year for MTB, but this year I want more

I know Watts = Volts x Amps, but I forget what to do with the equation? (it's Monday, and that stuff was 20+ years ago)

sam · « **Reply #1 on:** September 19, 2005, 22:53 »

by definition power = watts per unit time.

so P = delta_E / delta_t

and P = IV

you have I - the current and V - the voltage. You can now determine the power and thus you can determine the time it should last. Obviously this is an overestimate and doesn't account for many things.

If you need more try: http://scienceworld.wolfram.com/physics/Power.html

thegallery · « **Reply #2 on:** September 19, 2005, 23:14 »

Thanks Sam,

I guess it's simpler than I thought: 12Volts x 10Amp Hours= 120 Watt Hours. So a 100 watt bulb would burn for 1.2 hours, or a 50w bulb for 2.4 hours, of course, subject to temperature, resistance, etc. So I reckon the system will safely give me at least 2 hours for the 50Watt bulb.

sam · « **Reply #3 on:** September 19, 2005, 23:40 »

should do, though you can probably find more efficient bulbs and will lower the wastage of energy. I'd suggest having a look at maplin (if your in the uk that is!).

I'm not an electronics person (I'm a theoretical astrophysicist) and I'm affraid I had to think about that a bit longer than I should have, just dont tell the undergrads that I will be teaching this year! LOL

thegallery · « **Reply #4 on:** September 20, 2005, 03:42 »

We got Radio Shack, but no Maplin...

Yeah, the best systems use HID arc light lamps (most require a ballast), and Lithium Ion batteries. They are going here for over $500! This is for MTB riding at night in the woods.

I can't figure out a DIY HID system, so this will work for me for now (if I can keep the lamp from melting the encasement!) My total cost for the system will be about $100, and give me as much light and time as these HID systems, but at the expense of more weight.

http://www.performancebike.com/shop/profile.cfm?SKU=19467

sam · « **Reply #5 on:** September 20, 2005, 19:19 »

cool...if it does what you need then no need to spend any more really!