run and start capacitor

Discussion in 'General Electronics Chat' started by Shakespeare Landicho, Mar 6, 2006.

  1. Shakespeare Landicho

    Thread Starter New Member

    Mar 6, 2006
    can someone explain me how a run and start capacitor work?
  2. aac

    Active Member

    Jun 13, 2005
    You need at least two phases to get an induction motor started. Once it is started it can run on a single phase.

    An induction machine starts by having a rotating magnetic field which induces current in the rotor. The current in the rotor iproduces a magnetic field which will chase the rotating field. In a single phase machine the field doesn't rotate but just switches back and forth. In a three phase machine, start ( and running) is acomplished by placing 3 sets of coils 120 ˚ apart and running them from a three phase voltage source. In a single phase machine you don't have the second voltage phase. By using a start capacitor and start winding, you can get some phase shift to get your motor started. Ususally there is a centrifical switch that opens the connection to the capacitor once the motor is spinning fast enough to keep going on its own. The start winding would overheat otherwise. Having a run capacitor also provides phase shift and will help get a little more power out .