Forums » Electrical Engineering

Motor starter capacitor

    • 2 posts
    August 16, 2019 1:49 AM PDT

    I have 1 hp single phase motor but the motor starter  capacitor is burning. I am thinking why the overload relay is not tripping before this capacitor. I need to replace every week. I checked motor there is nothing wrong with it except burning capacitor. No idea why this happens, any idea why this capacitor burns?

    • 160 posts
    August 16, 2019 2:43 AM PDT

    There are 2 basic failure modes for capacitors.  One is voltage spikes higher than the capacitor is capable of handling and the other is excessive heat.  Sometimes just buying a better brand capacitor may do the trick but I question whether the motor is being used as it was intended.  Making the motor work too hard may have an effect on the capacitor but that should trip the overloads.

    Are the overloads sized correctly?  Other than this I don't know what to offer ther than you are using the wrong sized capacitor

    • 33 posts
    August 16, 2019 3:39 AM PDT

    I had a customer with same problem after overviewing found out that he was connecting polarized capacitor in a wrong way instead of unpolarized capacitor. Try with unpolarized capacitor to see it works

    • 156 posts
    August 16, 2019 4:40 AM PDT

    If the capacitor burns quickly, it means there is something wrong in circuit. Voltage rating can also be one issue. 

    This post was edited by Zone4 Engineer at August 16, 2019 5:02 AM PDT
    • 29 posts
    August 16, 2019 9:24 AM PDT

    A couple of things come to mind.  Is this motor starting several times per hour?  A high number of starts in a short amount of time can burn out capacitors.

    Is this a capacitor start or capacitor run motor?  If a capacitor start motor, there may be a problem with the centrifugal switch that takes out the starting capacitor.

    Or you could have bought a bunch of capacitors that had a "production issue" (i.e. a bad batch).