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Joined: Jun 2007
Posts: 20
A
Member
I have A customer Who has asked if I could calculate the cost per month fo her 1/2 H/P
Single phase well pump motor.This pump is currently running on a 240v 20Amp circuit.The pumpruns on average 3hrs per day.

Joined: Apr 2002
Posts: 7,279
Likes: 3
Member
Angel:
Pure theory math is...
746 watts per HP
746 x 1/2 = 373
373 x 3 hrs = 1119 kw = 1.2 KWHr

Now, reality check....
either clamp the feed, or use the nameplate amperage and plug those numbers in....
xx amps times 240 volts = actual wattage, times the 3 hours

Multiply the results by the KWHr fees charged by the local POCO.

John

PS: You could check into the Technical Forums here for any additional formulas you may need. Or, post away!
Welcome to ECN

Last edited by HotLine1; 06/04/07 08:09 AM. Reason: Added a "PS"

John
Joined: Dec 2004
Posts: 329
I
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If you are just estimating I would use a little more than 746w/hp. Remember you have to take into acount things like slip and motor efficiency. I have, from my experience, found that most motors are typically closer to a KW per HP.
Still, an amp clamp or some other direct measure of actual current draw is the only way you have to be close to accurate.

Last edited by IanR; 06/04/07 10:36 AM.
Joined: Aug 2002
Posts: 402
J
Member
Originally Posted by IanR
If you are just estimating I would use a little more than 746w/hp. Remember you have to take into acount things like slip and motor efficiency. I have, from my experience, found that most motors are typically closer to a KW per HP.
Still, an amp clamp or some other direct measure of actual current draw is the only way you have to be close to accurate.

Yes but the pump will not be using the full 1/2 hp while running. The actual rate will vary as the pressure rises in the tank. Clamp on measure of the average current from low pressure to high pressure will give the best results.

Joined: Apr 2002
Posts: 7,279
Likes: 3
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OK, 1 KW per HP; .5KW per 1/2 HP x 3 hrs = 1.5 KWHr.
Based on the resi rates here (NJ) .135 KWHr, we are talking a whopping amount of .20/day; $1.40 week; 6.02month$ 72.24/yr.

Clamp & average, or clamp with a 'min-max Fluke', or if it's really important....I have a clamp on KWHr recorder.

Angel....feel free to use my projected numbers, but...check your utility KWHr rates.

John


John

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