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From: John Popelish
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X-Mailer: Mozilla 4.7 [en] (Win98; U)
Subject: Re: How do I choose MOTOR RUN capacitor?
Date: Wed, 15 Jan 2003 03:01:08 GMT
NNTP-Posting-Date: Tue, 14 Jan 2003 22:01:08 EST
John Ely wrote:
> What procedure should I use to determine the
> best capacitace to use in a single phase AC
> motor that drives a hydraulic pump?
> What should I consider? Will this affect the
> starting torque? Can this capacitor be too
The best value of capacitance depends on the motor load. The name
plate value is right for a fully loaded motor. Less loading works
more efficiently with a lower value of capacitance. If you want ot
get it perfect (and the load is always the same) you hook a watt meter
up to the line, and try different values and pick the one with the
lowers total power consumption (most efficient operation), assuming it
gives you satisfactory starting. Remember that the motor is operating
into an effective mechanical overload till it reaches full speed.
Using a cap bigger than name plate rating increases the starting
torque, but makes the motor run hotter.
Sometimes a current sensing relay is hooked in series with the motor
line, and switches a second capacitor (with low value series resistor
to prevent shorting one capacitor onto another) in parallel with the
run cap, to boost the torque till starting current falls to normal
current. This is permanent split capacitor operation.
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