Function of Motor Start Capacitor
Function of Motor Start Capacitor
(OP)
I have a small 240VAC motor which I believe has a faulty start cap. When the motor is first started it runs fine, but when it it stopped via a separate control limit switch and the contactor drops out, if the limit switch is closed again the contactor will re-energise but the motor will not start again in that direction. It can however be switched in the reverse direction. This occurs no matter which direction is engaged initially, once the limit switch has stopped the motor, it will not re-start in the same direction. The installing electrician has wired the motor with no protective earth, is it possible that this has in some way affected the operation of the capacitor or is that unrelated (just dangerous!!!!)
thanks
thanks





RE: Function of Motor Start Capacitor
That said you have in order of likeliness:
1) A bad centrifugal switch.
2) Screwed up wiring.
3) A failed starting cap.
4) Open(failed) start winding.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Function of Motor Start Capacitor
RE: Function of Motor Start Capacitor
Keith Cress
kcress - http://www.flaminsystems.com
RE: Function of Motor Start Capacitor
My bet is the mechanism of the reversing relay/switch is sticky. Somehow, making it change directions is making it fully close the start winding into the circuit or allowing another relay that's being held open to drop out before restarting in the other direction.
You might try completely cutting power to the controls and motor after it stops on the limit and then see if the motor will start again in the same direction when power is restored. This would indicate to me that there is a relay held open by the control logic that's disconnecting the start winding until the motor is reversed. If it makes no difference to cut the power, then look for a sticky/binding reversing relay.
RE: Function of Motor Start Capacitor
RE: Function of Motor Start Capacitor
The capacitor is not a problem. Both windings are identical. By connecting power to the common terminal and one end of the capacitor, a phase shift is created between the windings. This creates a rotating magnetic field which develops the torque to start and run the motor. When the power is applied to the common terminal and the other end of the capacitor, the rotating magnetic field will rotate in the opposite direction and the motor will run in reverse.
If you care to share with us what type of machine this is we may be able to provide more help.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Function of Motor Start Capacitor
RE: Function of Motor Start Capacitor
Maybe it's a load problem, meaning it has something to do with a brake or other characteristic of the winch or whatever moves the shade cloth. Any chance of running the system with no load? What about winding the mechanism by hand to feel if there is a point were the shade cloth stops each time that has damage which causes the mechanism to bind there.
RE: Function of Motor Start Capacitor
Keith Cress
kcress - http://www.flaminsystems.com
RE: Function of Motor Start Capacitor
RE: Function of Motor Start Capacitor
RE: Function of Motor Start Capacitor
Whatever direction the motor happens to be travelling in, when the control system tells it to stop by de-energising the contactor,the motor will not start again in that same direction when the control system asks it to. The contactor does come in again, and power is applied to the motor terminals but it will not move. If we force the system to send a signal for the motor to operate in the other direction then it will start. But again when that direction is stopped for whatever reason it will not start again in that same direction. It has to be moved in the opposite direction first.