Pump Capacitors

Pump Capacitors

Understanding Pool Pump Motor Types from intheswim and How To Identify Pool Motor Types from Inyo Pools are good references to determine the type of motor you have and what you should be looking for.

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

Century Motor Parts Cross Reference can identify the capacitor, bearings, and other parts to repair a Century or A.O. Smith motor.

A common reason pumps do not start is the failure of the start capacitor. A pump can have two types of capacitors: a start capacitor and/or a run capacitor.

Start capacitors range between 108 and 300 MFD or uF. 115 volts is typical for a start capacitor. Capacitors are rated for the maximum voltage that they can handle safely. For a 120/240 volt pump wired for 120 volts, you have two windings in series so that each winding only gets 120 volts, and the start capacitor is in parallel with one set of the windings so it only gets 120 volts.

Run capacitors have a range from 15 to 50 MFD or uF. If you replace a run capacitor, replace it with the same MFD value as the original. 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 resistance in the winding provides the phase shift in the starter winding.

The start capacitor is often under the small bump at the top of the motor or inside the motor.

You may also find a dual capacitor in a 2-speed motor. A dual capacitor would have a rating of 30 + 10uf. You need a dual capacitor if your current capacitor uses three terminal blocks. One is for high speed, and one is for low speed.

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.

If the windings are good, a capacitor should discharge through them, so there should almost never be a charge. However, the safety warning is still valid because there can be times when a capacitor can store a dangerous charge.

If a capacitor is charged, the windings are probably bad.

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

Why Do Capacitors Fail is a video explaining why motor capacitor quality is not the same as years ago.

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.
• One spec to not overlook is the capacitor diameter. Many capacitors are 1 3/4 in, and that will fit into the capacitor cover on a Pentair Centurion pump motor. Many of them come in a 50 mm diameter, about 2 inches, which will not fit many motors.
• it can be a bad centrifugal switch if it's not the capacitor. See Pump Centrifugal Switch
• The Pump Centrifugal Switch is supposed to take the capacitor and start winding out of the circuit when 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, 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 and 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 stay in the circuit for too long.
• Check the pump's voltage, current, and power factor during operation.
• Is the pump getting excessively hot?
• What is the motor shell temperature?

Pump Capacitor Specifications

• You can take a higher voltage, but not a lower one.
• Tolerance should be the same or lower.
• Critical measures are: capacitance (30uF), frequency (50/60Hz), working voltage (370VAC).
• For example a capacitor can be 370VAC, with a max voltage of 450VAC. That means it's rated for a range of voltages.
• With 240VAC, they specify a capacitor that can operate up to 150% of that to accommodate line surges and the like.
• A capacitor rated at a maximum of 450VAC will be more tolerant (less "explody") with higher line surges.
• One spec to not overlook is the capacitor diameter. Many capacitors are 1 3/4 in, which will fit into the capacitor cover on a Pentair Centurion pump motor. Many come in a 50 mm diameter, about 2 inches, and will not fit many motors.
• These days, large electrolytics have a mechanical design that will allow them to swell, then pop an overpressure feature in the case rather than explode (still can explode, just less likely).

Century Motor Date of Manufacture

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