Quote:
Originally posted by Alchemy
Okay, dragging out the last bits of my ECE know-how, this is because pumps have electric motors, which are inherently inductive, and measuring Vrms and Irms would yield volt-amps, which be slightly more than the watts.
Is that anywhere close?
Alchemy
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Yes.
Here's some stuff I posted in a thread a while back:
"I measured simultaneously:
The voltage applied to the pump.
The current through the pump.
And the power consumed by the pump.
I had previously measured the winding resistance of the pump at 14.1 Ohms.
I got the following results.
In the unrestricted case with 123 Volts connected to the pump:
The current was 0.801 Amps.
The power consumption was 35.3 Watts.
In the restricted case with 123 Volts connected to the pump:
The current was 0.757 Amps.
The power consumption was 24.6 Watts."
This was with a Danner Mag5. (Spec'd at 45 Watts.)
As you can see, in the AC case, Volts X Amps doesn't necessarily equal Watts.
And yes, it's because the motor windings are inductive.
BTW, the larger Iwaki's (MD-20 and up) seem to have a power factor correction capacitor to reduce the difference between VA and Watts.