On Wed, 25 Jul 2018 13:07:31 -0700 (PDT), wrote:

So, if you parallel a mess
of capacitors to make a run capacitor with the correct value for PF=1,
then the capacitors will dissipate zero power.


not true.

I agree. I screwed up and forgot about ESR.

if there is current flowing through the cap, ESR of the cap will dissipate power.
The purpose of a motor cap is not to correct the PF.

There is no such thing as a single phase motor.
Small motors have shaded poles or other tricks to create a phase shift.
Medium size motors motors use a cap.
Large motors are typically fed with 3 phase.

Also true. However, the original problem is with a 3HP motor, with no
run capacitor. I guess for high torque starting, such as with an air
compressor, this would be an exception.

I think the optimum cap value, is where the current through the aux
winding is 90 deg out of phase with the main winding.

Agreed. This explains it better than I could:
https://www.quora.com/What-is-a-capacitor-start-capacitor-run-in-a-motor




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Jeff Liebermann
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