Power factor/efficiency measurement of motor 1

[mjpetrag]

I have a Goulds 1x2-10 1800 rpm 3 hp motor with a 9" impeller putting out 1200 GPH. It keeps tripping the overloads. The motor wasn't sized for curve runout, but still it pulls around 3.6 amps and overloads are 3.74. A small increase in flow trips it out.

So to live with it temporarily, I changed to a 7.75" impeller and it draws now about 2.5 amps. With the 9" impeller, the hydraulic hp is 2.1 at 1200 GPH. With the 7.75" impeller, the hydraulic hp is 1.5 hp.

So I tried to match this up with the motor hp.

W = v*i*1.73*pf*eff

With the 9" it becomes W=470*3.6*1.73*.95*.88=2450 W = 3.3 hp. I estimated pf and eff. But as you can see the power is much higher than the hydraulic hp.
Same issue with the 7.75" impeller
W=470*2.5*1.73*.95*.88=1700W = 2.28 hp, much higher than the 1.5 hp calculated

The fluid has a cp of 10 and a SG of .97

So either my pf and/or efficiency are wrong. I know they are fairly dependent on load, but how do you figure this out? Is 50% load on the motor the hydraulic hp divided by full load of motor ?

-Mike

 

[LittleInch]

Well the curves are quoting about 1.5 kW for your duty = 2hp, so more or less the same power output as your motor.

what is the issue?

you really should be using a different pump where you have better efficiency and hence able to actually pump more.

Is there anything more to say?

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[bimr]

You posted that the pump efficiency is about 24.5% efficiency. From the attached pump curve, you are correct.

Since you are operating the pump outside of the manufacturer's recommended operating envelope, one would expect that the pump will have poor efficiency and a limited service life.

Maximum efficiency is usually near 75% of rated load. Select a pump that will operate near this point if you want efficiency.

Why bother evaluating pump efficiency with such a small pump that is operating outside of the recommendations.