Pump numbers Electrical Draw. Does this make sense?

[bobodaclown]

Hello all.
I hope Mas will chime in, but all comments welcome.

I picked up one of those clip on amp meters today and I check my pump amp draw. It showed 3.0 amps.
I think that number is too low.
Volts = 120V
Amps=3.0
Filter Gauge PSI = 5 PSI
Flow Rate = 50
Pump is Sta-Rite 1/2 or 3/4 uprated (see signature) 180L

Motor is a AO Smith B2852.

Could it really only be 3 amps. I was expecting at least 10 or so amps.

 

[JohnT]

The plate on your motor should show maximum current. 3A at 120V is about 360W, which is around 1/2HP not counting inefficiencies.

 

[JasonLion]

The power factor won't be exactly 1, so the actual electrical usage will be slightly higher, though probably not by too much.

 

[mas985]

That pump should draw around 900 watts so something isn't right about the measurement. The motor is wired for 115v and not 230v correct?

Also, VA will always be higher than true power draw. Power factor reduces the actual (real) power draw not increases it.

 

[darbyj62]

When you use a clamp on amp meter it can only be around the hot lead wire not both of the wires at the same time. You usually have to make a small length of wire that separates the wires in order to only clamp around the single wire. If you connect the meter around the complete cable you get amp draw from both the hot and neutral wires which can throw off the draw amounts.
The nomenclature plate is a more exact draw result.

 

[bobodaclown]

OK. I measured wrong the first time. I thought the wire was to go in the ring, but in the picture they said in the clamp. Wasn't clear, I remeasured with the wire in the ring of the meter. My numbers make more sense now.
Motor plate states 10.8 amps, measured 10.7 amps.

With the SWCG on it jumps up to 13.2 amps or a load of 2.5 amps, 300 Watts at 80%.



using the formula V*I=Watts
The pump uses 1284 Watts and the SWCG (80%) uses 300 Watts. Total of 1584 watts.
1.584 Whr * $0.15 = $0.24 a hour. run time is approx 7 hours or $1.68 a day.

3000 GPH/1284 Watt Hour =2.34 Gallon per watt

 

[JasonLion]

The 3000 GPH figure is unlikely to be accurate, especially if you got that from the pump rating. Real world numbers are almost always lower.

Also, the units on your final number are GPH/watt. The 1284 is watts, not watt hours, so the hours do not cancel out and remain in the final result.

You can get more precise watt numbers from your household electric meter, you have to measure watts hours over a fixed time period with and without the pump on, subtract, and then convert back to watts.

 

[mas985]

That seems a bit on the high side. CEC measurement data for Curve-A: 48 GPM @ 916 watts = 3.14 gallons/watt-hr