capacitor start motor

[speedtronic]

For a single phase capacitor start motor, what will happen if we use a capacitor whose rating (capacitance uF) is lower or higher than the actual rating mentioned for that particular circuit?

 

[kung]

Hi Speedtronic
Dont use a lower uF rating if you use a higher rating it wont make any differance if anything it will be better but best to get the stated uF on that circuit.
Regards
Kung.

 

[Guest123]

Hi.

A rating below the required capacitance and the motor will not run up to the desired speed before the capacitor is de-enrgised so therefore will not reach full speed and the centrifugal switch may not operate meaning that the start capacitor will not de-energise so will stay in circuit and break.

A rating above and you risk too much input charge from the capacitor which may then damage the motor itself by causing it to run too quickly before the capacitor drops out.

The centrifugal switch may protect from overspeed but I would not install a capacitor that wasn't fit for purpose. Use the correct one.

 

[Andy Smith]

Hi.

A rating below the required capacitance and the motor will not run up to the desired speed before the capacitor is de-enrgised so therefore will not reach full speed and the centrifugal switch may not operate meaning that the start capacitor will not de-energise so will stay in circuit and break.

A rating above and you risk too much input charge from the capacitor which may then damage the motor itself by causing it to run too quickly before the capacitor drops out.

The centrifugal switch may protect from overspeed but I would not install a capacitor that wasn't fit for purpose. Use the correct one.

Correct little note added.


1. Capacitor Start
This configuration comprises two windings W1 and W2, a centrifugal switch SW1 and a capacitor.
The two windings are wound with a geometric offset, effectively making a second set of poles phase shifted within the stator. The capacitor provides a phase shift to the current flowing in W1 and we therefore have a "two phase" motor while the switch is closed. When the motor is almost up to speed, the switch opens disconnecting W1 and the capacitor. The motor can be reversed by reversing the connections of either W1 or W2 (but not both!) The start winding (W1) and the start capacitor provide for a rotating magnetic field in one direction enabling the motor to start.

 

[Guest123]

Nice little link Andy.

I've always thought of it as being the same kind of principal as a star-delta on a 3P motor i.e starting on one and swapping to the other when up to speed. Not exactly the same thing I know but in theory similar.

 

[Andy Smith]

Nice little link Andy.

I've always thought of it as being the same kind of principal as a star-delta on a 3P motor i.e starting on one and swapping to the other when up to speed. Not exactly the same thing I know but in theory similar.

Ya understand where your coming from not excatly the same but !

Used to have quite a few capacitor start motor in the first comany i worked for on heaters but dont see to many of them now. surriseing how many eople could not work out what was hapening or how they worked.