What Is a Capacitor

What is a capacitor?

A capacitor is an electrical or electronic device that can store energy, and act in part like a switch. As the capacitor stores more & more energy, it will make the passage of this energy progressively harder.

What is its function in an electric motor?

The capacitor or condenser as it is sometimes called, in an electric motor provides a time delay on the power arriving at the start windings of the motor to make the motor start. The start or auxiliary windings are inserted in the motor at an angle to the run or main winding. This creates a starting torque - basically something to make the rotor want to rotate.

Will a larger micro farad (uF) capacitor provide more starting torque?

Yes it can, but usually at a cost. The most common cost is raised temperatures inside the motor, resulting in shorter motor life and increased running costs. Motor manufacturers generally take great care in correctly sizing the capacitors to balance the various important factors associated with motor usage. So if you ever need to replace the capacitor, always make sure you replace it with the same micro farad (uF) rating. Our range of the common size capacitors for pool pumps are available via our website - search for Capacitors.

If the supply voltage is only 240V, why is the capacitor rated at 400V or even 450V?

Induced voltages from the motor windings result in voltage across the capacitor that is higher than the supply voltage. The actual value depends upon the supply voltage, the motor windings & the load. Motors driving pumps at full load would typically see capacitor voltages between 320 & 440 volts.