single phase motor -- current 1

[rwelk]

If I have a 120V - single phase motor, is current simply equal to power/voltage?

 

[aolalde]

I= (HP*746)/(V*PF*EFF)

HP= motor power output ( in the shaft)
V = Voltage
PF = Power Factor (per unit)
EFF = Motor Efficiency

 

[eemotor]

Not exactly, you still have to take the power factor into consideration. The actual formula for current in a 1 phase motor is: I = WATTS / (V x PF)

 

[rwelk]

what is the power factor? Can I determine that, or is that a characteristic of the motor? If i can't determine it, can I estimate reasonably?

This motor is ''small'', 0.5hp, 1725rpm, 120V/1ph/60hz used to run a small fan. Unfortunately, those are the only specs I have on the motor.

cheers

 

[rwelk]

one more thing, I don't know if it ac or dc, should that matter? The specs i have are from the company I bought the fan from, and not the motor, and that is partly why I have such limited information.

 

[aolalde]

This is an AC motor as the frequency 60 HZ is in the nameplate data. The formula is for AC moors.

The Power Factor and Efficiency are defined by the motor construction. If you do not have information from the manufacturer you must assume them.For this small motor the product EFF*PF could be around 0.64, then the spected full load (0.5 HP) current is:

Ifl = 0.5HP*746/(120*.64) = 4.85 Amperes.

 

[peebee]

Check NEC Table 430.148.