and here's the gentleman's reply...........

Ken,

Baldor's experience is that is some applications, frequent starting, long coast down, etc, the start capacitor will discharge as the motor passes from the run winding to the start winding (approx. 1400 RPM on an 1800 RPM motor) creating a shuddering effect as the motor tries to "restart". The addition of a bleed resistor mounted on the start capacitor can mitigate this in varying degrees depending on the application. We recommend a 10k ohm 5 watt resistor mounted between the terminals of the start capacitor. We also recommend a three-pole contactor that is wired so the start winding is completely out of the circuit when power is removed. This allows for a coast down with no regeneration through the start circuit regardless of the charge remaining on the start capacitor.

Baldor has always advised that the starting frequency (number of starts per
hour) of a single phase motor is dependent on the starting capacitor being energized for a maximum of 60 seconds per hour. This is sometimes hard to quantify, fans and pumps do not require high starting torque so the motor comes up to speed quickly with the start capacitor in the circuit for a very short time. Harder to start loads would require the capacitor to be in the circuit for a longer period of time. You are also correct in your comment that frequent starting increases temperature rise within the motor and can also be detrimental to a long service life but the capacitor is really the limiting factor on starts per hour.

It seems reasonable to believe that eliminating the effects of the capacitor discharging during coast down would be better for the motor than to experience the effects of regeneration. We do not have any data that estimates the increase in capacitor, switch or motor longevity.

I hope I have answered your questions. If you have further questions please let me know and I will try to answer them.

This is a copy and paste from the guys email.

So based on what he says...The resistor paralleled to the capacitor may reduce shudder when start capacitor is placed back in the circuit by the centrifugal switch BUT....a 3 pole contactor that immediately removed the start winding when power was removed would eliminate the problem entirely.

It's complex........


and.... Arguing with an engineer is like mud wresting with a pig....ya' get muddy and then you realize the pig's enjoying it......