Pump motor horsepower?

[aylad]

Just curious--my new pump motor is a single-speed, switchless 1 HP motor from A.O. Smith. The sticker on the side with all the technical info states it as 1 HP. However, there's a large sticker stuck on the top of the motor that says, "Total horsepower=1.4".

What does that mean? Is it actually 1.4, or 1 HP?

[mas985]

That is probably the difference between the label HP and the total HP. Total HP = Label HP * SF, so the service factor might be 1.4. As long as the total HP is greater than or equal to the total HP of your old motor, it should be ok.

[aylad]

Yes, you're right (as usual!), the service factor is 1.4. The motor is an exact replacement of my old one, and is working like a charm--I guess I just need a tutorial to explain what the terms mean.....so does that mean it is actually producing 1 HP, or 1.4? I have a 300# sand filter with approx. 26K gallon pool, so I know it's all sized right, I'm just curious?

Janet

[mas985]

Manufactures will size a pump motor based upon the maximum load that an impeller imparts onto the motor over the entire head curve. So if the maximum load of the impeller is 1.4 BHP (braking HP), the motor needs to be at least 1.4 THP (total HP including service factor).

Label HP is somewhat meaningless without the service factor which causes much confusion when talking about up rated vs full rated pumps. Two pumps that have exactly the same head curve and performance may have different label HP because one is up rated and the other is full rated.


Here is a list of common pump and motor definitions:

Pump and Motor Definitions

Nameplate HP (NPHP) - This is the HP rating on the motor nameplate but is pretty much meaningless without the service factor.

Full Rated HP (FRHP) - Similar to nameplate HP and sometimes used when the pump is full rated.

Up Rated HP (URHP) - Similar to nameplate HP and sometimes used when the pump is max rated or up rated.

Nameplate KW = NPHP * 0.7457 - This is the KW rating and is similar to the nameplate HP and is generally used outside the US. Note that this is not the input power to the motor only the rating for the output power of the motor.

Service Factor - This is an overload rating for motors which states that the motor can be safely operated over the NPHP by the service factor for short periods of time. However, for pumps, this overload rating is typically used as the maximum load that a motor would need to deliver to the wet end. Because the load on a pump does not rapidly change over time, the service factor load is often used as the maximum design point for the pump.

Total HP (THP) or Service Factor HP (SFHP) = NPHP * Service Factor – This is the maximum load that can be safely driven by the motor and must always be greater than the maximum load from the impeller. A motor can be driven above the THP but will likely fail in a short period of time.

Electrical Horsepower (EHP) = watts / 745.7 = Volts * Amps * Power Factor / 745.7 - Electrical power input delivered to the motor

Brake Horsepower (BHP) = EHP * Motor Efficiency - Power delivered by the motor shaft to the impeller. This is not the same as THP or SFHP. BHP is a function of the load on the motor shaft and will change with Head, GPM and RPM.

Hydraulic HP (HHP) = BHP * Pumping Efficiency = Head (ft) * GPM / 3960 - Power delivered to the water. Sometimes called water HP (WHP) or pumping HP (PHP).

Motor Power Efficiency = BHP / EHP - I2R, magnetic and mechanical losses in the motor only.

Pumping Power Efficiency = HHP / BHP - Recirculation and internal friction losses in the wet end only.

Total Pump Power Efficiency = Motor Efficiency * Pumping Efficiency = HHP / EHP (note this is why total pump efficiency approaches 50%).

Energy Factor - Gallons/watt-hr = GPM * 60 / Watt-hr; A CEC definition used to measure a pump's true pumping efficiency.

Service Factor Amps - The amp draw when the motor is loaded to the service factor. Also, multipling the SF amps by voltage should also give a good estimate as to the upper limit for power draw. However, sometimes the motor is over dimensioned for the pump so it will not always be an accurate measure of input power.

Full Load Amps - This can mean several things depending on the motor manufacture. It is either the amps at the NPHP or it can be the amps at the THP. I have seen it both ways so unfortunately, there is not a good standard for this one.

[aylad]

Thanks Mark, that's what I was looking for!

Janet