I am making a 3 phase rotary converter I do not need ant advise on motor run capacitors I understand balancing the third leg. What I do need is advice on start capacitor sizing equation. I understand that I need voltage rating of 1 1/2 times of the potential voltage of the circuit or slightly higher. Now for the mf or uf rating There seem's to be a lot of vague and conflicting information out on the interweb. Two common formula's I have found are 50 uf per horsepower and 100 uf per horsepower? How important is it to choose a rating within 10% of actual requirements for the starting capacitor? Shouldn't the equation include the starting current as well as voltage? Or should the emphasis be directed more toward phase timing as in +120 degree's (+=10%) of the AC cycle waveform? In this case the application is starting a 3 phase 15 horsepower idler motor on single phase power.
Ps. I have seen Rotary converters start up slowly tanking as much as 5 seconds to come up to speed. Also have seen the come to speed instantly hitting the max rpm so hard that they jar the building. Is this hard start detrimental to the components of the motor? Does this mean that the capacitance has hit the 120 degree point of the wave cycle exactly or does it mean that there is too much capacitance starting the motor with too much current?
Thank you my name is Marvin from East Tennessee
Ps. I have seen Rotary converters start up slowly tanking as much as 5 seconds to come up to speed. Also have seen the come to speed instantly hitting the max rpm so hard that they jar the building. Is this hard start detrimental to the components of the motor? Does this mean that the capacitance has hit the 120 degree point of the wave cycle exactly or does it mean that there is too much capacitance starting the motor with too much current?
Thank you my name is Marvin from East Tennessee