Run capacitors

Thread Starter


Joined May 30, 2020
Does a run capacitor with a higher mfd lower the strain/boost power on a motor?

Working on old equipment that called for 45mfd, I was sold a 50mfd but when I replaced it I found it was equipped with a 40mfd. The start up doesn't hum like it used to or I'm imagining things.
Just a novice.


Joined Jan 8, 2017
The purpose of the capacitor is to produce phase shift to one winding so there is a rotating magnetic field. If the motor has a centrifugal switch then the capacitor will only be used to start the motor. Once it is up to speed the winding fed via the capacitor is switched out.



Joined Jul 18, 2013
The original sizing is in order for the phase shift to be as close as 90° as possible.
There is some lee-way, especially if it is the starting variety.
As long as it gets up to speed at the normal rate, it should be OK.