Electric Motors and Horsepower

by Zach

I understand that electric motors can run a car with much less HP than a gasoline engine...why is it that an electric motor needs less horsepower?
Is it because they provide max horsepower at all rpm?

Hi, Zach!
Short answer? Torque. That, and driveline efficiency.
Check out this T-zero edging past this 500 hp. Dodge Viper using about half the horsepower. The Viper will catch up, given enough time, but a well-engineered electric car with a series wound DC motor is very quick off the line. All the motor's torque is available from a standstill; it's simply a characteristic of these motors.
You could see in the video that the driver of the T-zero had his hands full trying to keep the motor from outrunning the car; )
With an electric car's motor, the question of power is less "how many horsepower can the motor deliver", and more "how many amps can I draw from the batteries at once".
And that depends on other components besides the motor.


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Load demands the torque
by: Dan Bentler

The average American car is overpowered because we like those zippy starts and we just gotta have the passing capability. This mean extra or reserve HP.
American engines are vastly overrated as far as HP goes. Divide the factory rated HP by two and you get what the engine will really put out.

The average car about 3000 lb will need 20 to 30 HP to make it roll. That will go up to about 60 or wherever max RPM on motor is. Then you have to add on more HP to overcome wind resistance and even more if you are climbing hills.

If you design for 60 mph and for a 20% grade you should have a fairly good performing vehicle.

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