Amps for 3/4 hp pump?

[Uncle Puck]

Trying to supply architect/engineer with specific power requirements of equipment we have yet to purchase. Can anyone help with Amps for a Top Line 3/4 hp C100MD pump on cart? 115v.

Many thanks!

[rdcpro]

Trying to supply architect/engineer with specific power requirements of equipment we have yet to purchase. Can anyone help with Amps for a Top Line 3/4 hp C100MD pump on cart? 115v.

Many thanks!

I believe FLA at 115v should be 9.2A, and locked rotor amps should be 66A.

Source (page 25): https://cdn.automationdirect.com/sta.../MT-Motors.pdf

I'm sure CPE Systems could answer this if you called them.

Regards,
Mike Sharp

[RipRap]

.75 hp=560 watts

560watts/115v=4.9A

At least that's my understanding of it.

[rdcpro]

.75 hp=560 watts

560watts/115v=4.9A

At least that's my understanding of it.

The tl;dr explanation:

You're forgetting two things, efficiency and power factor.


The much longer explanation:

If you're basing this off the conversion, 1hp ~= 746 Watts, that's a direct conversion of output power, not input. Converting .75hp to 560 watts and taking that as the input power assumes a 100% efficiency.

Also, the power we're talking about is actually "real power" but if you multiply Volts and Amps, you are talking about "apparent power". This is due to the inductive nature of a motor. The ratio of real power to apparent power is called the power factor (pf). You'll sometimes see power factor referred to as cos Φ.

The equation you should use to get the current in this case (assuming 100% efficiency) is (for single phase loads only):

power factor = Real Power / Apparent Power

power factor = Real Power / Volt * Amps

Solving for Real Power:
Real Power = Volts * Amps * power factor

Or solving for Amps:
Real Power / (Volts * power factor) = Amps


According to that PDF, the power factor of this motor is 0.78, lagging, I believe. So in this case, the equation is:

559 Watts / ( 115 Volts * 0.78) ~= 6.2 Amps

For a three phase load, the equation is similar, but with a factor for the phase relationship, which is the square root of 3. Hard to type out here, but:

Real Power = Sqrt(3) * Volts * Amps * power factor

Now you need to figure out how efficient the motor is, and calculate the actual current needed. But it's much easier to look it up in the specifications.


Regards,
Mike Sharp

[Uncle Puck]

Thanks all!


Patrick S. McGinnity
Whiskey Point Brewing Company
Beaver Island, MI

[RipRap]

Very interesting. Learn something new every day!