Gene asked in Science & MathematicsEngineering · 2 months ago

1hp requires how many amps?

Update:

1hp at 120 volts requires how many amps

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• ?
Lv 7
2 months ago

"1hp requires how many amps?"

A lot of good answers here already.  But just remember one thing.  HP is an output power rating.  So the measure of 1HP is 746 watts.  But note that it will take more than 746 watts of power input in order to get 1HP output because of inefficiencies and power factor.  After this you can use Watts Law & Ohms Law to work your way to a solution on how many amps will be drawn at full load.

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• Anonymous
2 months ago

At what voltage?

Update:

The scientific formula is 746 watts per horsepower.

746 ÷ 120 = 6.2 amps

Add some more current for electrical and mechanical and magnetic inefficiency.

Also, the starting current of a typical single phase induction motor of that size is 2 to 3 times the running current.

So make sure you use a 20 amp switch and a 20 amp branch circuit.

I would use no more than a ¾ horsepower motor on a standard 120 volt, 15 amp branch circuit; especially for an air compressor.

• ?
Lv 4
2 months ago

Depends on the specs for the electric motor.  A 115 volt, 60 Hz, 1 Phase electric motor needs 13.0 amps doing 1,075 rpms for 1hp.

• ?
Lv 5
2 months ago

That depends on the winding! A 6-volt motor would require more amps to run it than a 12-volt motor and a 120 volt motor would require less still a 240 volt motor still less

• 2 months ago

120 volts * 6.22 amps = 746 watts = 1 hp

... assuming that the voltage and amps are in phase, which is rarely the case for a motor.

• 2 months ago

depends on the voltage. and number of phases and efficiency.

1 HP = 746 watts

BUT, the 1 HP is output power, not input, you have to factor in engine efficiency.  Say 80%, then input power is:

1 HP = 933 watts input power

at 120 volts, that is 7.8 amps

at 240 volts, that is 3.9 amps