Pump Capacitors

A common reason for pumps not starting is failure of the start capacitor. There can be two types of capacitors in a pump - a start capacitor and/or a run capacitor.

The A.O. Smith CENTURY POOL & SPA MOTOR MANUAL can help you install, maintain and troubleshoot Century pool and spa motors. It contains details about the motor capacitors, how to test them, and other motor repairs.

Start capacitors have a range between 108 to 300 mfd or uf.

Run capacitors have a range from 15 to 50 mfd or uf. If your replace a run capacitor replace it with the same value mfd as the orginal was. Under no circumstances should a larger mfd run capacitor be substituted in a motor. It can lead to motor overheating or destruction.

All in ground single speed pumps use a capacitor whether they are 120 or 240. Not all motors have run capacitors. The newer VS pumps do not have a start capacitor either.

Some motors are resistive start and the phase shift in the starter winding is provided by the resistance in the winding.

The start capacitor is often under the small bump at the top of the motor. Or it can be inside the motor.

Capacitor with Bleed Resistor

Some capacitors have a bleed resistor connecting the two prongs. If your capacitor has a bleed resistor it should be moved to the new capacitor.

Be careful when handling a capacitor. It can hold a voltage charge for a long time and you can be shocked by it. To drain all the power out of a capacitor you can touch both prongs together with the shaft of an insulated screwdriver. You may get a spark or pop from the current outflow.

The voltage rating should be at least √2 x the intended voltage. Assuming a maximum voltage of 250 volts, the capacitor minimum rating should be 354 volts. So, 370 volts should be fine. 440V is a better quality capacitor and will last longer, especially under high temperature conditions, but the 370 volt should be fine.

It has been reported that many Ace Hardware Stores carry start capacitors if you need something right now.

How To Select the Right Capacitor For Your Pool Pump Motor

How To Replace a Pool Pump Capacitor

A good thread on a successful pump capacitor replacement is at Pentair Whisperflo Suddenly Quit Working - Capacitor

Tips

• Get the model number from the capacitor and Google for a replacement or go to a local electric motor repair shop.
• If it's not the capacitor, it can be a bad centrifugal switch. See Pump Centrifugal Switch
• The Pump Centrifugal Switch is supposed to take the capacitor and start winding out of the circuit as soon as the motor rpm gets close to full speed. This should happen in about 2 to 3 seconds. If the capacitor fails after around 3 seconds indicates that it is still in the circuit when it should not be. A start capacitor cannot take continuous voltage for more than a few seconds. The continuous voltage will cause the capacitor to fail.

How to Test a Capacitor

Many multimeters can confirm the actual micro-fards of a capacitor. Such as the DM300 Pocket Sized Digital Multimeter.

When checking the capacitor you need to kill all power to the heat pump/pool equipment by turning off all of the pool equipment circuit breakers. The capacitance setting on the multimeter will look like this.... -l(- .

A capacitor is good if it is within +/- 10% of its labeled rating. A 7.5 mf capacitor should read between 6.75 and 8.25 mf to be considered good although most do not read very much higher than labeled.

Pump Blowing Capacitor Checklist

• Is it a start capacitor or a run capacitor?
• If it’s a run capacitor, you can use a 440 volt rated capacitor instead of a 370 volt rated capacitor and that will help.
• Make sure that a run capacitor says “10000 AFC Protected”.
• If it’s a start capacitor, it might be staying in the circuit too long.
• Check the voltage, current and power factor on the pump during operation.
• Is the pump getting excessively hot?
• What is the motor shell temperature?

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