How To Select the Right Capacitor For Your Pool Pump Motor

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This guide discusses the two kinds of capacitors that could be used on pool pump motors: start capacitors and run capacitors. It also addresses how to know a capacitor is failing and how to replace it.

Things You'll Need

Step by Step

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Step 1

CAPACITOR TYPES -  A pool pump can have two types of capacitors: a Start capacitor and A Run Capacitor. The Start capacitor is switched into the the motor's winding circuits on start up to help the motor turn over and come up to speed. When the motor is close to running speed, the Start capaciotor is switched out of the winding circuits. The Run capacitor is incorporated in the motor circuit to help increase running efficiency. It remains in the circuit as long as the pump motor is running. The start capacitor will generatlly be rated at 50-400 MFD and 125 or 250 VAC. The run capacitor will generally be rated at 15-50 MFD and 370 VAC. The capacitor in the picture is a Start Capacitor rated at 124-149 MFD 125 VAC.

Step 2

MOTORS WITH CAPACITORS - Not all pool pump motors use capacitors.  There are four common types of residential pool pump motors: Split Phase, Capacitor Start, Permanent Split Capacitor and Capacitor Start/ Capacitor Run.
The Split Phase motor is used extensively in spa and jetted tubs, and above ground pools. This design has a start winding and a start switch, but no capacitors.

The Capacitor Start motor is used commonly is in ground pool pumps.The starting torque is higher (150-175% of full load) and starting current lower than the split phase equivalent. The operation is similar to a split phase in that there is a start switch to take the start winding and capacitor out of the circuit once the motor reaches 2/3 to 3/4 of full speed.

The Permanent Split Capacitor motor does not have a start switch and is often referred to as a “switchless” motor. It does use a Run Capacitor that remains in the circuit at all times. The PSC design has significantly less starting torque than the capacitor start design.
The Capacitor Start/ Capacitor Run motor design is used to increase efficiency in run mode. Both Start and Run Capacitors are used. In run mode, PSC and Cap. Start/Cap. Run motors are the same.

Step 3

START CAPACITOR LOCATION - START capacitors are usually hard or glassy looking plastic enclosed can that are typically, though not always, found under the non-drive end canopy of the motor.

Step 4

RUN CAPACITOR LOCATION - RUN capacitors are usually the METAL (aluminum or steel) enclosed can capacitors that are most of the time, but not always, found under the "hump" on top of the motor - also referred to as the capacitor housing or "doghouse". This picture shows the location of the run capacitor under a doghouse.

Step 5

START CAPACITOR FAILURE - Usually the effect of a failed START capacitor is a "sluggish startup" or "humming with no startup. When a START capacitor is starting to go bad, you might see some leakage of electrolytic oil,  and when it fails the vent opens and expells the electrolytic oils. A failed start capacitor will have a physical hole in the vent after it has failed.

Step 6

RUN CAPACITOR FAILURE - The effect of a failed RUN capacitor is usually "hi amps" and sometimes "humming with no start" and often times motor won't run in the hi amp condition without tripping thermal protector.  When a RUN capacitor is starting or has gone bad, the end of the capacitor that has the terminals and sometimes the opposite end without terminals bows outward. 
The capacitance reading would be significantly lower than rated if its failed.  There isn't a "vent" typically on RUN capacitors -- they expand/bow outward with a fail safe internal structure so that the bowing out of the terminals breaks the contacts internally in the capacitor in a fail safe mode.

Step 7

REPLACING START CAPACITOR - See our guide on "How To Replace a Pool Pump Capacitor". When you replace a capacitor, never put in a lower rated capacitor. If you can't find your size capacitor, it is acceptable to use the one rated one step higher. If you pump motor is continually burning up capacitors, try using the next one up in size. Capacitors are susceptible topower variations or increases. If you can't control your system power, you may need a capacitor with a little higher rating. Use this link to purchase the Start Capacitor you need

Step 8

REPLACING RUN CAPACITOR - To replace a Run Capacitor, remove the Capacitor Cover (bump)  by removing the two screws. Then follow the precautions above to disconnect and replace the capacitor. As stated above, when you replace a capacitor, never put in a lower rated capacitor. If you can't find your size capacitor, it is acceptable to use the one rated one step higher. If you pump motor is continually burning up capacitors, try using the next one up in size. Capacitors are susceptible topower variations or increases. If you can't control your system power, you may need a capacitor with a little higher rating. Use this link to purchase the Run Capacitor you need

Comments

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(1 to 40 of 245)

 Posted: 8/28/2019 

Hi witch capacitor I have to used for a A.O.smith C48K2N143B3 115/230 volts Thanks
 Reply

InyoPools Product Specialist  Posted: 9/4/2019 

The replacement start capacitor for the C48K2N143B3 is part number 5270-14.
 Reply

 Posted: 8/6/2019 

Hello. My pool fountain pump motor has been spray painted over, but I believe I made out the motor model as C48J2PA105C1. What capacitor part number should I consider replacing to address the "humming and no start" condition? Thanks!
 Reply

InyoPools Product Specialist  Posted: 8/7/2019 

The humming is a symptom of a bad capacitor. The C48J2PA105C1 uses a 124-149 MFD (BC-124) - Start Capacitor
 Reply

 Posted: 7/14/2019 

Hey there, I just need some advice on a replacement capacitor for a USN1252 2.5 H.P. S.P. 1.10 P/N=193689 Hayward Northstar. They capacitor currently is a 55uf, but is that because it was replaced once already? Does is Normally take a 50uf? Thx.
 Reply

InyoPools Product Specialist  Posted: 7/22/2019 

The USN1252 uses the RUN CAPACITOR, 35 MFD (RD-35-370) - 628318-309
 Reply

 Posted: 7/3/2019 

SPX1605Z1M is my motor model and I need to replace start up capacitor. Do you know the location and part number please? Tia
 Reply

InyoPools Product Specialist  Posted: 7/16/2019 

The start capacitor is located under the end cap of the motor, where the terminal board is located. The start capacitor for the UST1072 is the 610807-001
 Reply

 Posted: 7/28/2019 

Motor model is C48K2PA105CS Volts 115/230 I just tried a new packard start capacitor PMJ161 and it popped. What is the correct start capacitor I should use? Thanks!
 Reply

InyoPools Product Specialist  Posted: 7/29/2019 

The USQ1102 (C48K2PA105CS) uses the 161-193 MFD (BC-161) start capacitor.
 Reply

 Posted: 6/20/2019 

I have a Spa, I need a run capacitor for a Emerson pump model K55MYKHF-9557, Part number 9352-9304 , can you help find the rating for this part and do you have one in stock Regards Anthony
 Reply

InyoPools Product Specialist  Posted: 6/20/2019 

Can you look on the jacket of the capacitor for its ratings? This is a special motor with not a lot of information.
 Reply

 Posted: 6/19/2019 

I'm looking to replace my "run" type capacitor 370VAC C65R SH P2 50/60hz. This is part of the info. from the capacitor. Do you carry it and how much to replace?
 Reply

InyoPools Product Specialist  Posted: 6/19/2019 

What is the catalog or part number from the motor label?
 Reply

 Posted: 6/18/2019 

How do you replace the capacitor on a Harris 1.5 pump
 Reply

InyoPools Product Specialist  Posted: 6/19/2019 

How To Replace a Pool Pump Capacitor
 Reply

 Posted: 6/17/2019 

Hi I have an older M Centurion for PAC FAB motor. The capacitor is completely rusted and label is not readable. Any idea which capacitor would be compatible. The label reads :Serial number: BS5-295,1 HP, 1.25 SF, Volts 208-230/115, Amps SF 6.0-5.6/11.2, FR; R56Y. Thank you!
 Reply

InyoPools Product Specialist  Posted: 6/19/2019 

What is the catalog or part number from your motor's label?
 Reply

 Posted: 6/8/2019 

I have a marathon electric spa motor need the capasitor model #5kcr39un6190x
 Reply

InyoPools Product Specialist  Posted: 6/19/2019 

Hello, the USQ1202 motor requires two capacitors RUN CAPACITOR, 20 MFD (RD-20-370) and the START CAPACITOR, 36-43 MFD (BC36M-250-S).
 Reply

 Posted: 6/7/2019 

Can you please give me the start and run capacitor part numbers that go with AO Smith/Tristar pool motor part number 7-196336-20.
 Reply

InyoPools Product Specialist  Posted: 6/7/2019 

Can you see the ratings on the capacitor jacket?
 Reply

 Posted: 6/6/2019 

I replaced the start capacitor in my Hayward Century SP3220Z2ME. Pump runs fine in low, however, when I try to start in high it just makes a humming noise. Any advice?
 Reply

InyoPools Product Specialist  Posted: 6/12/2019 

Hello - have you verified the capacitor was installed correctly? We also have this guide with a list of things to check: Pump Runs On Low Speed But Not On High Speed
 Reply

Anonymous  Posted: 6/4/2019 

Im after the run capacitor value for an A.O. Smith motor, model K48A36C47. The original one has had all identificating numbers rubbed off. Thanks
 Reply

InyoPools Product Specialist  Posted: 6/6/2019 

Can you verify the model number K48A36C47? It does not cross-reference to a match.
 Reply

Anonymous  Posted: 6/4/2019 

I’m looking for the capacitor for a K48M2P104 AO smith pump. It was top mounted and I believe it’s the start capacitor. All I get is humming and then trips breaker. Impeller spins freely. The capacitor info is illegible.
 Reply

InyoPools Product Specialist  Posted: 6/6/2019 

The USQ1202 pool pump motor uses the 36-43 MFD (BC36M-250-S) start capacitor.
 Reply

 Posted: 6/3/2019 

I have a jandy pump with a century 2 horsepower pump motor , the capacitor reads 30 uf and 440 vac. its a 230 amp motor. what capacitor should i get?
 Reply

InyoPools Product Specialist  Posted: 6/6/2019 

The replacement capacitor - 30 MFD (5VR0303)
 Reply

Anonymous  Posted: 5/31/2019 

I need a run capacitor for Magnetek Century 2 hp motor. 4 amp, 3450 RPM. The current cap is 2 7/8" long, so based on your chart, it's either a Run 20 or a Run 35. The motor was built in 1999 but no other info shows online. Model 7-186643-01
 Reply

InyoPools Product Specialist  Posted: 5/31/2019 

According to AO Smith-Century run capacitor for the BN61 motor is actually a 2444 - 30 MFD style.
 Reply

 Posted: 5/29/2019 

Trying to replace a Mallory 124-148 MFD start capacitor for pool pump. Hard to find. Is it ok to buy 124-149 MFD? Thx!
 Reply

InyoPools Product Specialist  Posted: 5/30/2019 

Yes, as long as the voltage matches up.
 Reply

 Posted: 5/28/2019 

Hello, Can you please tell me which capacitor is required for the 2-speed Century Lasar (AO Smith) Cat: BN50, Part: 7-177803-02, Type: CSM, FR: U48Y, PH: 1, Hz: 60, RPM: 3450/1725, Volts: 115, Amps: 16.4/4.4? Do you also know if there's a way to find an old O&M Manual for that model? I have tried doing multiple searches but cannot find anything since the model is discontinued. Thank you!
 Reply

InyoPools Product Specialist  Posted: 5/30/2019 

The replacement start capacitor is the 64-77 MFD (BC-64).The BN50 (still available) does not have an owner's manual as such, just a basic troubleshooting guide that comes with all the manufacturer's motors.
 Reply

 Posted: 5/27/2019 

Need start capacitor rating for Jacuzzi Magnetek Centurion SE switchless motor 10-184950-22 (HP 1.5 1.5 SF). Capacitor is so corroded that can’t find any uf or voltage rating on it.
 Reply

InyoPools Product Specialist  Posted: 5/28/2019 

The replacement run capacitor for the B796 is the 628318-313
 Reply

 Posted: 5/27/2019 

Hi after reading your article I believe I should take a shot at replacing my run capacitor on an older Hayward Max-Flo pump. I can't read much of the writing on the pump or capacitor but believe the model # is sp2800-z-1. Any help with which replacement capacitor I should try would be greatly appreciated. Thanks!
 Reply

InyoPools Product Specialist  Posted: 5/30/2019 

Can you read the HP, or Amps on the label? The SP2800Z1 part/model number is not bringing up any results, no matter which format we try it in.
 Reply