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#1
02-01-2011, 11:07 PM
 don cole Junior Member Join Date: Feb 2011 Posts: 1 Rep Power: 0
Re: Convert volts/amps into kilowatt hours

I have well pump 9 amps 230 volts 3 phase 3 HP

How many kw would it use per hour
#2
02-02-2011, 04:14 AM
 JohnS Moderator Join Date: Dec 2007 Location: SE Michigan, USA Posts: 9,443 Rep Power: 19
Re: Convert volts/amps into kilowatt hours

Quote:
 Originally Posted by don cole I have well pump 9 amps 230 volts 3 phase 3 HP How many kw would it use per hour
In three phase power, you need to know whether the voltage is specified line-to-line or line-to neutral, and whether the three phase currents are equal. Assuming line to line voltage and equal phase currents,

line to neutral is 230/sqrt(3) V
Power is 3*9 A * 230/sqrt(3) V = 3585 W or about 3.6 kW

For each hour of operation, it will draw 3.6 kWh.

The 9 A may represent starting current and not be a continuous draw. The results above imply fairly low efficiency. 3 HP is 2238 W mechanical power at the shaft, and 2238 W/3585 W is 62.4% efficiency, fairly poor for a 3 phase motor. You may wish to measure line current and see if efficiency is this poor or the 9 A occurs only at starting. At 80% efficiency (pure guess, but reasonable) in continuous operation, the motor should only draw about 2800 W, or barely over 7A running current
#3
04-27-2013, 09:48 AM
 Uc44richmondnregistered Guest Posts: n/a
Re: Convert volts/amps into kilowatt hours

[QUOTE=don cole;76070]I have well pump 9 amps 230 volts 3 phase 3 HP

How many kw would it use per hour @3hp 20watts

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