How To Select the Right Capacitor For Your Pool Pump Motor

WRITTEN BY:  Inyo Pools

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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


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


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Inyopools  Posted: 06/22/2017 11:10 AM  Latest Inyo Product Specialist

NaP - I would have to see the label on your motor to know which motor was installed in your SP3215X20 Tristar pump. If it was in the USQ class of motors, it would have a start capacitor installed under the back electrical cover.

NaP  Posted: 06/20/2017 14:25 PM  Latest

My Hayward SP3215X20 2.0 HP pump makes a humming noise for a few seconds and then does not start. I am thinking maybe it is a capacitor issue. But when I search for my model I can't find anything about a capacitor for this pump. Maybe it does not have a capacitor? If not, what else could be causing this issue?

Inyopools  Posted: 06/13/2017 14:32 PM  Inyo Product Specialist

Peter37 - Looks like you have a B661 motor with a run capacitor only. Amps are different than your specs, 6.0 vs your 7.5. I don't have a specific capacitor number.

Inyopools  Posted: 06/12/2017 15:15 PM  Inyo Product Specialist

ATX - If you have a Northstar pump with a 1.5 UPRATED HP motor, your replacement run capacitor is 30Mfd, 370V capacitor p# 5270-05. If you have a Northstar pump with a 1.5 FULL RATED HP motor, your replacement run capacitor is 35Mfd, 370V capacitor p# 5270-02.

Peter37  Posted: 06/12/2017 12:06 PM 

Hi there, hope you can help me please. I have a 3/4HP 240vac 7.5amp AOS Centurion motor running a semi-inground pool circulation pump, but the capacitor has failed and no markings are visible on the can housing or the motor name plate. The motor part number is 8-165890-06. Could you please advise if it requires a Start or Run capacitor, or even better, the required capacitor specifications? Thanks in advance, Pete.

ATX  Posted: 06/11/2017 15:32 PM 

I am looking for a capacitor for a Hayward Northstar 1.5 HP single speed pump (circa 2007). All of the identification has worn off the capacitor. The Only thing left is "no PCB's" "P10000 AFC Protected" and 50/60HZ" beyond that nothing left on the label.

Inyopools  Posted: 06/06/2017 16:09 PM  Inyo Product Specialist

Nelson - For your Motor, 1 1/2 Hp Up Rated (usn1152, SPX1610Z1MNS) we show the following Capacitor, Run 370v 30 Mfd (5vr0303)

Nelson  Posted: 06/06/2017 0:59 AM 

I have looked everywhere for a run capacitor for a Hayward SPX1610Z1MNS motor but no manual or parts list online. This is a Hayward Northstar 1.5HP pump. Any suggestions?

Inyopools  Posted: 06/04/2017 19:31 PM  Inyo Product Specialist

TPN386 - Our files show that your pump motor may have a start capacitor. See if there is another capacitor under the motor end cap. If there is, replace that one first. If not replace the capacitor under the bump. If this doesn't fix the problem, I'd have the motor checked out at a pool or motor shop.

TPN386  Posted: 06/02/2017 9:44 AM 

I have a Pb4-60 booster pump from Polaris, checked the spindle and it turns freely, visually checked the run capacitor and it looked fine (not bowed out), could it be something else? Thanks.

Inyopools  Posted: 05/25/2017 23:39 PM  Inyo Product Specialist

James - The Super Pump motors do not have run capacitors - only start capacitors.

James  Posted: 05/24/2017 11:28 AM 

I have a older Haywood super Pump the hayward c48k2n143b3 run capacitor js what i cannot find to replace. I replaced the start capacitor but now im lost i do not see a hump or housing for the run capacitor. The last pool guy saidnit was the run capacitor

Inyopools  Posted: 05/19/2017 15:39 PM  Inyo Product Specialist

Scott - This pump motor does not have a start capacitor. It uses a 25/370 run capacitor. They are starting to go to a 25/440 run capacitor.

Scott  Posted: 05/18/2017 20:54 PM 

I have a Pentair LA01N booster pump that just hums and requires a manual twist to get it running. It runs perfectly once it gets going. Does this pump have a start capacitor?

Inyopools  Posted: 05/15/2017 0:50 AM  Inyo Product Specialist

chris - The ph1150-6 shows up in our system as an Hi-Flo 1.5 Hp Above Ground Pump. With very few exceptions, above ground pump motors do not have a start capacitor.

chris  Posted: 05/12/2017 21:28 PM 

does the pump model ph1150-6 have a start capacitor...

Inyopools  Posted: 05/01/2017 15:52 PM  Inyo Product Specialist

Don - The manufacturer does not recommend trying to bend the arm of a V-switch. See our guide on "How To Replace the Start Switch on an AO Smith Motor". Note, if you have an older motor before Nov 2001, you may have an adjustment screw to change the gap between the contact points.

Don  Posted: 04/29/2017 10:12 AM 

I have a Dynamo 340197 pump that is only a year old. The contact points on the V-Switch are no longer contacting. Is there a good way to bend the top arm so it makes contact again?

Inyopools  Posted: 04/23/2017 12:01 PM  Inyo Product Specialist

Anthony - This sounds like a start capacitor issue. I would replace the capacitor first. That's easy and relatively inexpensive. If replacing the capacitor doesn't work, you may have a short in the windings which generally means a new motor.

Anthony  Posted: 04/23/2017 2:51 AM 

I have a Magnetek 1.5hp motor driving a waterfall Whisperflow pump.
The motor and impeller attached spin freely in both directions. It takes 4 or 5 hits of the power switch to start the motor. It hums for the first 4-5 tries then runs for hours very smoothly. It uses a quad breaker that also runs a spa booster pump with no problem. do I have a bad breaker sending wrong voltage to one of the two circuits or do I have a defective capacitor? Thanks.

Inyopools  Posted: 04/08/2017 13:11 PM  Inyo Product Specialist

Alex - Like you say, this looks like a run capacitor that generally runs at 370V. If I type 24DB450B220NA into the internet, I get back a 45uf
370V capacitor but it isn't clear that the reply is responding to the supplied part number. I would give the manufacturer a call on this one.

Alex  Posted: 04/05/2017 20:52 PM 

I i have bad capacitor from Jacuzzi Tub Pump.
Looks like it's Run Capacitor, but it's rated 45uf with 220VAC.
I can't find any run capacitors with 220vac. All run 370or440
So confusing... Please help me!
Model of my old capacitor is Genteq 24DB450B220NA
Page 17 is exact label from my capacitor.

Inyopools  Posted: 03/31/2017 11:00 AM  Inyo Product Specialist

Nagy - We would not recommend replacing an 110V start capacitor with a 250V start capacitor. See our list of Start Capacitors. Use the 125V options.

Nagy  Posted: 03/28/2017 15:54 PM 

i am changing the capacitor of the pump
?the start capacitor
?but i can't find the identical one in the stors
?i have 110 vac and i found 250 vac
?is this one suitable or not

Inyopools  Posted: 03/23/2017 16:21 PM  Inyo Product Specialist

anonymous (capacitor) - See if you can match the capacitor to the specs printed on the capacitor. See step 1 of this guide. If you can't read that label, get the motor model number off the metal plate on the pump's motor and give us a call at 877-372-6038.

John  Posted: 03/23/2017 11:04 AM 

Will a 110V, 108-130 capacitor start a 220V, 2 PH motor? Should it be a 220V, 108-130MFD capacitor?

Anonymous  Posted: 03/21/2017 15:56 PM 

Hi folks, what model of capacitor do I need for a portapac demand spa pump.

Inyopools  Posted: 03/06/2017 11:19 AM  Inyo Product Specialist

Mike - Is the old motor an 1102 also. If not, the capacitor may not be interchangeable. Check the motor wiring again and make sure the motor is configured for the right supply voltage, 115V or 230V. Then talk to the service reps where you bought the motor. Sometimes, a bad motor is shipped out and should be replaced.

Mike  Posted: 03/03/2017 6:55 AM 

Have a new century 1102 motor, hums when you hook to power, the old motor still runs, so traded capacitor and still does the same. Tryed spinning shaft so as to boost to start but still only hums.Then put capacitor back on old one and it still runs.

Inyopools  Posted: 01/31/2017 23:45 PM  Inyo Product Specialist

Davi444 - It sounds like you may have an electrical short in the motor, but I would try replacing the start capacitor anyway. It's a cheap fix if it solves the problem.

Davi444  Posted: 01/27/2017 19:12 PM 

Hello I have a Pentair pump and we recently had a lot of rain. I went to turn on the pump and it started to run the all of a sudden I heard a pop and it turned off. The breaker popped as well. Everytime I try to start the pump it make the noise and pops the breaker any idea what it could be? I have a Pentair Part # 177451-03 pump. Could this be the capacitor? Thank for any help on this.

Inyopools  Posted: 11/29/2016 11:12 AM  Inyo Product Specialist

Art H - See step 8 of our guide on "How To Replace a Pool Pump Capacitor".

Art H  Posted: 11/27/2016 14:36 PM 

Hi. Good stuff here. I have a Century (17-187853-01) on my Hot Springs Spa. Its been tripping the breaker when hitting the clean and jets buttons. I have removed the pump and am trying to determine if the capacitors are the cause. I have both a run and a start capacitor. The run is a 370V and the start is a 125V. I have a multimeter ( a really cheap one). Is there a check I can do on these to determine if they are working?

Inyopools  Posted: 10/03/2016 12:24 PM  Inyo Product Specialist

SB - This sounds like a capacitor problem. If the capacitor on your single speed motor is the same, try switching the two capacitors to see if that solves the start up problem. If not the same, I'd try a new capacitor. They aren't that expensive.

Inyopools  Posted: 10/03/2016 10:01 AM  Inyo Product Specialist

Dave B - It depends on what pump you have. If you have a VS pump, they all start up in high to prime the pump. If you have a manual high/ low 2-speed, the problem is probably in the switch.

SB  Posted: 10/01/2016 16:25 PM 

I forgot to mention in first message - it has a run capacitor, 30 MFD, 370 VAC

SB  Posted: 10/01/2016 16:24 PM 

I have a 2-speed AO Smith spa pump motor (Century 7-196012-03) which sometimes fails to start. Since it's the circulating pump a start failure causes an overheat condition. The other day when I turned it on it hummed only, but when I rapped it with my knuckles it started running. The shaft seems to turn smoothly by hand, and when running it doesn't sound bad, but a little louder than the single-speed pump (same motor). The run capacitor in both motors look fine. Does this sound like a capacitor problem, motor problem, sticky pump, something else?? Many thanks, SB (And nice site, I appreciate the tech info!)

Dave B.  Posted: 09/29/2016 12:49 PM 

My pump motor would not turn on at all. It would just hum for 10 seconds or so. I replaced the capacitor and now it comes on fine, but only on high. Any thoughts would be sincerely appreciated!

Inyopools  Posted: 09/02/2016 11:21 AM  Inyo Product Specialist

capacitor - Here is the link to a #628318-308 capacitor.

Anonymous  Posted: 08/31/2016 20:19 PM 

need a replacement capacitor for a genteq 27L1358 30uf 370vac 50/60 hz manufacturer # 628318-308. any suggestions on what to buy