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Old 07-02-2009, 12:45 PM   #1
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problems with capacitor motor for pump


I have a 115V 1/2 HP water pump that boosts the water pressure in the house. When I flip the switch, the motor hums and does not spin. there's a tiny jerk when I flip the switch. it gets very hot and the thermal switch is then tripped. I opened the switch panel and inside is an approx. 3 inch long 1 inch diameter capacitor. It smells fried. The pump spins freely by hand so it's not siezed. I'm thinking either the motor is fried or the capacitor is fried. The whole thing is italian and i'm not having much luck locating the original capacitor. it's 250V 40uf capacitor consisting of a sealed plastic case and wire leads. Not sure if it's a start capacitor or a run capacitor. Can someone let me know which type of capacitor it would be and if that could be the problem? Thanks.

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Old 07-02-2009, 01:17 PM   #2
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problems with capacitor motor for pump


take a picture and bring it to a plumbing supply house. If they don't have the specific part, they can at least hopefully tell you the manufacturer or sell you a new pump if needed.

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Old 07-02-2009, 01:21 PM   #3
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problems with capacitor motor for pump


http://wanywz.hisupplier.com/product...55uf-60uf.html Google search 250V 40uf motor capacitor Lots of different ones.Photo would help
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Old 07-02-2009, 01:31 PM   #4
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Here is a picture of the thing. I have found both "start" and "run" capacitors that are 40uf and 250v so I'm not sure which one it is. THe original is a inco sintex 25s, but that does not come up in any google searches. the pump is italian made and over 10 yrs old.
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Old 07-02-2009, 02:49 PM   #5
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Originally Posted by joeypants View Post
I'm not sure which one it is.
Only two wires, doesn't matter. I'd go with any 370 vac rating or above, near 40 uF, bipolar (AC) cap.
250v may be the DC or the AC rating.
For better prices check Digi-key, Mouser, Jameco, Allied Electronics or AllElectronics.

Check the cap, if you want.
Discharge the cap with a 15k, 2w resistor.
Charge to ~9v with a 9v battery.
Discharge through a 1 megohm resistor.
When the voltage reaches 37% of initial value (e.g., 9.6v), the time in seconds to get there is the value in uF.

Or,
hook the cap in series with a 7-1/2w incand. bulb in series with 120v.
Measure the voltage across and the current through the cap.
At 60 Hz, uF = 2652 I/V
E.g., I = 60 mA, V = 4v, C = 40 uF.

Last edited by Yoyizit; 07-02-2009 at 03:02 PM.
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Old 07-02-2009, 03:13 PM   #6
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problems with capacitor motor for pump


I'd get a run capacitor. It's hard to tell from the pic, but it's entirely possible that the motor is a PSC (Permanent Split Capacitor) type. If so, the capacitor is always in the circuit.

A start capacitor can only be energized for a minute or so, then it'll blow up. Most start capacitor specs limit use to 30 seconds on, then a 2 minute rest. A run capacitor is designed to be energized continuously. Hence, it is physically larger, and costs more.

A Grainger #2GU27 will likely work. It's 40uF, 370 volts, and 2" dia, and 3-7/8 long. It's a bit larger that the original, you might have to get creative mounting it.

When replacing capacitors, the uF must be very close, and voltage of the replacement must be the same or higher.

Most start capacitors have a range of ratings, like 43-52uF. Run capacitors have a single rating, like 40uF.

A word of caution, a capacitor can hold a charge for years. 40uF at 250 volts can be lethal. Before you touch the terminals, short it out using a screwdriver. Usually, if it's installed in a motor, it's already discharged through the windings, but every now and then you'll get a nice SNAP across the terminals.

Rob
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Old 07-02-2009, 03:22 PM   #7
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Quote:
Originally Posted by micromind View Post
A run capacitor is designed to be energized continuously. Hence, it is physically larger, and costs more. 1
40uF at 250 volts can be lethal. 2
short it out using a screwdriver. 3
1 I stand corrected.
2 generally you need at least one joule of stored elec. energy to kill healthy adults
3 may shorten the life of the cap

Just my two cents. . .

Last edited by Yoyizit; 07-02-2009 at 03:25 PM.
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Old 07-02-2009, 06:10 PM   #8
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problems with capacitor motor for pump


Are you sure its the capacitor? Those same symptoms will occur if the starting/running centrifugal switch is bad.

Did you take the backside off the motor, and verify that switch is properly positioned?
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Old 07-02-2009, 10:24 PM   #9
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If it's possible to determine whether a start switch exists, we would then know if we need a start or run capacitor. It's also possible that instead of a start switch, there's a potential relay. It's also possible that it's a PSC motor.

If it is capacitor start, then an open start switch will give the same symptoms as a bad start capacitor, as stated above.

I don't know why, but I get the idea it's PSC.

Rob

Last edited by micromind; 07-02-2009 at 10:27 PM.
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Old 07-03-2009, 10:54 AM   #10
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problems with capacitor motor for pump


Quote:
Originally Posted by joeypants View Post
Here is a picture of the thing. I have found both "start" and "run" capacitors that are 40uf and 250v so I'm not sure which one it is. THe original is a inco sintex 25s, but that does not come up in any google searches. the pump is italian made and over 10 yrs old.
If you do not know how to check the caps, just replace both of them. Or have someone who knows how to check them test them out before you replace. Look at the top of the cap. (where the leads attach) There is a small hole. This hole lets the smoke out. You can sometimes determine which one is bad by looking.
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Old 07-03-2009, 09:22 PM   #11
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Yeah, everyone should know that things like motors, capacitors, etc all run on smoke. The electricity is only there to contain the smoke.

Once the smoke gets out, the device is no longer any good.
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Old 07-03-2009, 09:43 PM   #12
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problems with capacitor motor for pump


Quote:
Originally Posted by joeypants View Post
Here is a picture of the thing. I have found both "start" and "run" capacitors that are 40uf and 250v so I'm not sure which one it is. THe original is a inco sintex 25s, but that does not come up in any google searches. the pump is italian made and over 10 yrs old.
I have tried to order caps from GE and been told $20, $30.

I went to the local motor rewind shop and got the identical parts for about $3 each.
Caps are a lot easier (and cheaper) to try replacing than a centrifugal throw-out switch. Personally I'd rather gamble <$6 than a whole new motor.
Plus the fact that my experience (limited though it may be) it's been the cap 90% of the time.
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Old 07-04-2009, 09:34 AM   #13
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I have tried to order caps from GE and been told $20, $30.

I went to the local motor rewind shop and got the identical parts for about $3 each.
Caps are a lot easier (and cheaper) to try replacing than a centrifugal throw-out switch. Personally I'd rather gamble <$6 than a whole new motor.
Plus the fact that my experience (limited though it may be) it's been the cap 90% of the time.
Yes, You can get some good deals at motor shops. I am a bit surprised at the cost though. Seems like someone forgot to mark the caps up. $3.00 would be about what they pay for the most common ones. Good for you.
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Old 10-13-2009, 04:18 PM   #14
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Join the club on blown caps. My Grunfos (Italian) water pump has blown two caps. The first was a 25 uf 250v and replaced with 30 uf 250v. It is a start cap for the pump. Blew that one today. You can tell, they usually leak a hard aluminum type of goo at the opposite end of the terminals. If you need to check it, take off the top of the control panel (four screws), loosen the control board (2 screws), move aside and you can see the cap. Grey, about 1 in D and 3 in long.

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