# Motor voltage vs amps vs watts

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drlizardo
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Motor voltage vs amps vs watts

Cant figure this out,

without getting into motor efficiency, load, torque. (Simply) I know if you lower a motor's voltage with no load the rpm's go down as well as the amps drawn but what about the watts.

36v motor draws 16.6a and 600w

Lower the voltage to

24v motor draws 11a but converting to watts 24 x 11 = 264 but wattage should be around 400w.

I can't find any conversion equations for this situation.

thanks,

Dr. L.

dogman
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Re: Motor voltage vs amps vs watts

Not sure if I understand what you are asking exactly. The 24v motor would not be pulling as much amps at no load as it would loaded, like at the max amps of a 20 amp controller. So when you climb a hill with it, you would have 400 watts, if not more.

My WE motor, rated at 600 watts, likey does just about that, on flat ground at 3/4 throttle. The way I ride, its bound to be closer to 900 watts most of the time.

36 volt sla schwinn beach cruiser
36 volt lifepo4 mongoose mtb
24 volt sla + nicad EV Global

jdh2550_1
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Re: Motor voltage vs amps vs watts

Right, I'm confused too.

Are you saying that the two scenarios are for the same torque demands?

Discounting efficiency then if 36V and 16.6 amps is required for your load situation then 24V should require 24.9 amps.

So, either your load is different or you have a really, really, humongously large change in efficiency.

John H. Founder of Current Motor Company - opinions on this site belong to me; not to my employer
Remember: " 'lectric for local. diesel for distance" - JTH, Amp Bros || "No Gas.

reikiman
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Re: Motor voltage vs amps vs watts

W = V x A

deronmoped
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Re: Motor voltage vs amps vs watts

"(Simply) I know if you lower a motor's voltage with no load the rpm's go down as well as the amps drawn but what about the watts."

Why would you want to know what the "no load" ratings are?

As far as a constant load goes, lower the voltage the amps go up. That's why you will find things run at a higher voltage, less amps needed, and that means use can use smaller wire, switches...

Watts (746 watts=1Hp) is work, how much work do you want that motor to do? This little calculator will give you a idea of how many watts you will need to go so fast. I would work backwards from there. Take the watts you need to go so fast and come up with the combination you need. watts= volts X amps. The motor throws a wrench into it, as you need to know what the motor amp draw is at certain loads and voltages.

The only way I could figure the combination for my bike was to try different voltages, 24, 36 and 48. Doing this gave me certain speeds at those voltages for my motor and total weight of the bike and me.

Hope this helps, Deron.

http://www.kreuzotter.de/english/espeed.htm

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