# Voltage versus torque

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jaustinmd
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Voltage versus torque

Need some basic informaton ... I have a 24v gearmotor that runs perfectly fine on 24 volts or 12 volts. Of course, at 12 volts, the motor speed is reduced. Two very basic questons have come to mind:

1) Is motor speed directly proportional to voltage - i.e., does the motor run half as fast at 12 volts versus 24?

2) Does reducing the voltage and speed reduce the torque, or does it remain relatively constant? I have always heard that "electric motors develop 100% of their torque instantly" ... it would seem that would have to be definitely independent of speed!

Regards,

John

antiscab
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Re: Voltage versus torque

Torque is proportional to motor side current:

Torque = motorside current * constant

Voltage = motorside current * resistance + rpm * constant (if the motor has a powered field, then the "constant" is variable with field current)

if operating with a controller, torque-speed relationship is the same (for the purposes of this discussion), its just the speed values halve if you halve the voltage.

Matt

Daily Ride:
2007 Vectrix, modified with 42 x Thundersky 60Ah in July 2010. Done 194'000km

reikiman
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Re: Voltage versus torque

Build Your Own Electric Vehicle has a lot of detailed information and formulas about this. The book is meant for building electric cars, and would be useful if you want deep understanding.

caspar21
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Re: Voltage versus torque

simpler way to put it..
voltage - hp
amps - torque

magicsmoke
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Re: Voltage versus torque

simpler way to put it..
voltage - hp
amps - torque

nearly!

voltage - rpm
amps - torque
hp - (rpm X torque) / K ... constant depending on torque and rpm units

Rob

james joule
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Re: Voltage versus torque

Hi, could you explain the K constant a little more please, cheers james

antiscab
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Re: Voltage versus torque

in metric, the equation is:

Power (w) = torque (Nm) * rpm /(120 * Pi)

in imperial (IIRC):

power (hp) = torque (Ft-lb) * rpm / 6350

im less sure on the imperial one, since i never use it, and the defintion for Hp is different depending on context.

Matt

Daily Ride:
2007 Vectrix, modified with 42 x Thundersky 60Ah in July 2010. Done 194'000km

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