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


(1 to 40 of 70)

Peter  Posted: 08/18/2017 5:37 AM  Latest

I have a beachcomb hot tub with a BN 55 2 speed century lasar pool spa motor 1081/1563.
Coluld you help me what kind of run capacitor I would need for this and what MFD it would be to fit the motor?
The one I had broke and I cant make out what type it is.


Inyopools  Posted: 07/31/2017 15:32 PM  Inyo Product Specialist

Hec - We show the replacement run capacitor for your SN1102 motor is the 628318-308 capacitor you identify (alt ID 5270-05). We show that this capacitor is 2" long.

Hec  Posted: 07/30/2017 20:04 PM 

Greetings. I have the Genteq 27L1358 run capacitor on a replaced motor (Century Centurion SN1102) for a Hayward Northstar. Both ends popped out. Can't find it anywhere, including here. Is there a substitute for it? The closest I found is your 5270-08 with MFG code 628318-307. Mine is MFG code 628318-308 and has a 30uf rating versus your 25 uf on the 307. The 5270-05 matches the uf but it's too long. It needs to be 2 7/8 inches in order to fit in the back cover. Please help. Thank you!

Inyopools  Posted: 07/24/2017 13:57 PM  Inyo Product Specialist

Marty - Here is a link to the 25mF/370VAC run capacitor for your B229SE motor.

Marty  Posted: 07/22/2017 19:49 PM 

We have a Century Centurion B229SE Type CX Frame Y56J with a C65R 25mF/370VAC capacitor. The capacitor has 3 wires and is approximately 1 inch diameter by 3 inches long. What capacitor do I need? I've looked it up online and all the capacitors are not matching the specs of this one. Thanks!

Inyopools  Posted: 07/20/2017 10:10 AM  Inyo Product Specialist

DC - I talked to our motor rep and his comment was: "Since this is a 230 volt only motor, it’s not set up to use a capacitor with a lower voltage rating. It will just fail. Best to get the 610807-012." We do not sell that capacitor but I do see it on the internet.

Inyopools  Posted: 07/18/2017 15:53 PM  Inyo Product Specialist

PAUL G - The B128 motor only has a run capacitor, no start capacitor.

DC  Posted: 07/17/2017 14:48 PM 

I have a Haywood 2 speed motor model STS1152R. what would be the correct start capacitor, the one in the motor shows NGM 25-30 MFD 220 vac. I do not see one in your chart that matches this one in 220 only 125volt. Thanks

PAUL G  Posted: 07/16/2017 16:23 PM 

My pump motor is an A.O Smith 1hp something like a B128 from what I can find. I have removed the outer run capacitor. It looks fine-no bulges- but is 10 years old. Before I take the end off, does it have a start capacitor? No sense taking the end off if there is none.

Inyopools  Posted: 07/13/2017 12:18 PM  Inyo Product Specialist

Mike S - If your motor has a governor, sometimes those get stuck open. I don't know what parts your motor has, but here a link showing the parts and functions of an A O Smith motor. There may be a similarity in functions if not parts.

Mike S  Posted: 07/11/2017 21:30 PM 

Hi guys I have an A.O. Smith pn 7-177803-02 pump which I got 2 years ago. last year it got very loud so I researched and was advised to change the fwd bearing which I did which fixed the loud pump. when I reassembled the pump I noticed that the pump was starting to have issues starting up. this year in order for me to start the pump I have to hit the switch and then turn the shaft to jump start it. I changed the capacitor with the same one I removed (BC-108). i'm hoping its not a motor issue but maybe something with the centrifugal switch? mine is different than the V switch. please help

Inyopools  Posted: 07/10/2017 10:34 AM  Inyo Product Specialist

rick - Replacing the start capacitor, if you have one, would be a good place to start. If that isn't the problem, you may have a short in the motor's windings which might mean a new motor.

Inyopools  Posted: 07/09/2017 15:40 PM  Inyo Product Specialist

Poolgirl70 - Does the motor shaft move freely when you turn the shaft from the back end? If not, the shaft seal may be binding. Take the motor out and reinstall the shaft seal. If the shaft spins freely, try replacing the start capacitor. See our guide on "How To Replace a Pool Pump Capacitor".

rick  Posted: 07/08/2017 9:55 AM 

there was no motor engagement when I turned on the pump; after moving the drive, it connected and ran. Today I had to do the same thing...could this be my capacitor?

Inyopools  Posted: 07/07/2017 12:56 PM  Inyo Product Specialist

Mark - Here is a link to your Start Capacitor, MFD 220-250v 36-43 (bc36m-250-s). This motor also has a Run Capacitor, Rd 20-370 (rd-20-370).

Poolgirl70  Posted: 07/06/2017 16:08 PM 

I just replaced the shaft seal in my hayward pump but now when I turn it on I only hear a loud humming noise.
Any ideas?

Mark  Posted: 07/05/2017 3:39 AM 

I have a Anthony Pools 518R with Motor model K48M2PA105 230 volts 2HP.It shows AOSmith on the label.The pump is an Anthony Pool AR207-L. The motor hums for 5 secs then the breaker trips and it won't start. The run capacitor label was clear and I got one the exact same. However, the label on the Start capacitor is very hard to read. It is a Philips branded capacitor. The only portions I can read are: 36-43 MFD, 60hz & 362041x - last number looks like a 1 so possibly 3620411. I want to make sure I get the correct replacement start capacitor. Can you confirm what one I should get? Thanks,Mark

Smmmfarmer  Posted: 06/30/2017 20:24 PM 

I have a goulds hsc20 2 hp pump with an a o smith motor. The model number appears to be 48n2db11a2 or brt44abm. The starting cap on the motor end has a label that is hard to read. Can you tell me what capacitor goes on the end?

Inyopools  Posted: 06/29/2017 11:15 AM  Inyo Product Specialist

Bosse - You can use an alternative capacitor with the same specs. Just check the dimensions to make sure it fits in your motor's space. Here is a link to our 30uF / 370V run capacitor.

Inyopools  Posted: 06/28/2017 11:14 AM  Inyo Product Specialist

guy - Our units are the same. MDF is short for microfarad. And you should not go to a start capacitor with a higher MFD rating. It would affect the performance of the motor and may not be acceptable. See our list of start capacitors.

Bosse  Posted: 06/27/2017 19:56 PM 

Hi !

I'm looking for a Gentec 27L1358 (30uF +6 -6%) 50/60Hz 370VAC capacitor to replace a broken one fro my Hot Tub.

Believe it i used as a run capacitor for my D1 Lotus Bay Hot tub Motor # 1
The Motor is a Balboa Water Group DJ SPA Pump 3.6 HP 2S230V NO CO, with part # DJAYGB-9173D
(Volts: 230V Hertz: 60 Hz Amps : 8.5/3.0 HPR 3.6/.38 Speed: 2)

Cannot find any online, where can I find them or what is an OK alternative
Input appreciated
Thanks In advance
Bo in Mckinney

guy  Posted: 06/26/2017 20:49 PM 

we have a start capacitor - the pump makes a loud (very) humming noise and often wont start.
The capacitor has differetent ratings than on your pics - I guess cos I am in asia! The ratings is in micro-somethings.... says u(micro)F ( -0%+20%) 250 VAC
any ideas?
is it OK to go to a higher uF factor - we can only find one rated to 100uF...?

Inyopools  Posted: 06/26/2017 15:33 PM  Inyo Product Specialist

glenn36 - Unfortunately, we can't identify your run capacitor with the numbers you gave us. Can you give us the motor part # or motor mod? We can sometimes use that.

glenn36  Posted: 06/25/2017 10:04 AM 

I have a run capacitor by CDE with the markings C10755855066, 370 VAC, 50/60Hz, SFS37T35H291B...any idea which replacement is needed?

Inyopools  Posted: 06/22/2017 11:10 AM  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 

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...