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Anonymous Poster	capacitor selection 11/02/2007 3:12 PM
	how can i select capacitor for 5HP single phase motor? Is there any formula to select capacitor for single phase motor ?
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Bill Guru Join Date: Dec 2005 Location: Clemson, South Carolina Posts: 1722 Good Answers: 18	#1 Re: capacitor selection 11/02/2007 3:41 PM
	The capacitor shifts the phase current in the start winding, and the size depends on the winding impedance. Suggest you either contact the manufacturer or find a similar motor and look at its capacitor. The phase shift is calculated by the vector sum of capacitive and inductive impedances. See Phasor and Phase Shift __________________ We have met the enemy and he is us . . . Walt Kelly
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garth Guru Join Date: Sep 2006 Location: NSW Australia Posts: 1101 Good Answers: 23	#2 Re: capacitor selection 11/03/2007 8:17 AM
	Here are some sizes for motors up to 1Hp. If you are using a higher voltage the capacity required will be smaller, perhaps you can extrapolate from these, these are for starting not run types 200/250 V a.c. supply voltage 275 V max capacitor voltage Motor size Typical capacitor value kW μ F 0,093 20/30 0,124 30/40 0,185 40/70 0,249 60/80 0,373 80/110 0,560 108/140 0,746 138/182 __________________ Dont get on to the roundabout if you dont know how to get off
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lordravindran Associate Join Date: Oct 2007 Posts: 43	#3 Re: capacitor selection 11/03/2007 10:09 AM
	Efficiency, frequency,power factor without capacitor, desired power factor after compensation and the voltage should be known to decide the value of the capacitor to be used. Below is an example:Power of the motor = 5x736W=P1 . Power absorbed by the motor= P= P1/n where n = efficiency (n is less than 1). Let CosA and CosB be the power factors before and after the installation of the capacitor. Power and the efficiency of the motor does not change with installation of the capacitor. Reactive power provided by the source before the installation of the capacitor =Q1 = P tanA. Reactive power provided by the source after the installation of the capacitor = Q2 = P tanB. Thus the reactive power to be provided by the capacitor = Q1-Q2 Reactive power of a capacitor is 2 x 3.14x f x C x V^2 where f = frquency of the source, C is the capacitance in farad and V is the rms voltage of the source. This gives C = (Q1-Q2)/(2x 3.14 x f x v^2) farads
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lordravindran Associate Join Date: Oct 2007 Posts: 43	#4 Re: capacitor selection 11/03/2007 10:16 AM
	I just posted my suggestion on the capacitor selection. I was under the impression that the capacitor is for power factor correction. Excuse me if the question is related to starting/running/starting-running the motor.
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Users who posted comments:

Bill (1); garth (1); lordravindran (2)

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