Battery puts out 3.0 watts and 3.5 volts, how many batteries...?

Question

I have an electric motor that uses a 30 amp draw to operate. I have a battery that puts out 3.0 watts and 3.5 volts. How many batteries do I need to operate this motor for a 6 hour period?

Answer 1

Batteries are rated for their energy content in Amp-hours @ the rated terminal voltage.

You don't state the energy content, only the power output (which may be an instantaneous rating). But assuming you did the math (Amp-hours times volts, to get Watts) and your 3.0 watt is really a Watt-hour rating, then each battery is good for 0.85 AmpHours. The math is simple:
30 Amps * 6 hours / 0.85 AmpHours = 212 batteries

However, you should probably increase that by at least 20% because batteries don't just hold a steady voltage over time while being discharged -- the voltage drops. If you want to maintain 3.6 volts for a full 6 hours, you need more batteries -- at least 250 batteries.

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Answer 2

You are missing too many parameters. Is the motor AC or DC. If AC forget it. Batteries won't help.

If it is DC forget it. You are talking a lot of money. A 30 motor is probably running 220VAC anyway, but if not, be real, buddy... Use a generator, instead. With all the money you will have to spend on batteries you can buy a nice one and a bunch of gas to boot!

What have you got against the power company, anyway?

Answer 3

Voltage divided into wattage gives you the amps. Point 86 amps per battery. You would need 349 batteries. But you only need one good heavy duty car battery. They are rated in amp hour draw. point 86 times 349 = 30.014. .