# capacitors blew up



## green light (Oct 12, 2011)

Im not much of a motor guy and could use some input. A customer called me and said they have a single phase 240v motor at a sewer pump station. The motor is about 4hp. He said that its a new motor and after about two weeks it seems to have blown up the caps. It has a start and a run cap. What are some causes I can look for if I choose to go and trouble shoot this for them.


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## Expediter (Mar 12, 2014)

Incorrectly size caps, water infiltration, lightning are my first thoughts to look for. 

Is it 3 phase 208V or 240v service?

Is something bound up in the impeller.


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## just the cowboy (Sep 4, 2013)

Make sure the caps are not switched ( run in start, start in run)


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## green light (Oct 12, 2011)

Expediter said:


> Incorrectly size caps, water infiltration, lightning are my first thoughts to look for.
> 
> Is it 3 phase 208V or 240v service?
> 
> Is something bound up in the impeller.


Single phase 240v


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## wendon (Sep 27, 2010)

green light said:


> Single phase 240v


Bad motor. Either start switches stuck or something is overloaded. Did it actually blow up both of the caps?


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## JRaef (Mar 23, 2009)

4HP is a big clue here. There is no such thing in NEMA motor sizes, so that means this is an IEC motor. The reason the HP number comes out odd like this is sometimes because on these submersible sewage pumps, the European mfrs only use a 3 phase motor, because they have to be certified as explosion proof and that's really expensive. So they only use the one motor and for single phase applications here in the US, they add a cheap little static phase adder in an external box as part of the control panel. But using the static phase adder cases them to de-rate the pump power rating, so it comes out to an oddball HP number like that. 

The point is, the blown capacitors might be part of that static phase adder system. They are usually really cheap junk.


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## Expediter (Mar 12, 2014)

just the cowboy said:


> Make sure the caps are not switched ( run in start, start in run)


Could you explain this a little please? I am not as up on caps as I might be, and it may help others as well.
I understand switching a cap but.................never mind, I just realized what you were saying. they both would be the wrong size for the application if they were swapped.
:wallbash:
:stupid::lol::lol:


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## green light (Oct 12, 2011)

JRaef said:


> 4HP is a big clue here. There is no such thing in NEMA motor sizes, so that means this is an IEC motor. The reason the HP number comes out odd like this is sometimes because on these submersible sewage pumps, the European mfrs only use a 3 phase motor, because they have to be certified as explosion proof and that's really expensive. So they only use the one motor and for single phase applications here in the US, they add a cheap little static phase adder in an external box as part of the control panel. But using the static phase adder cases them to de-rate the pump power rating, so it comes out to an oddball HP number like that.
> 
> The point is, the blown capacitors might be part of that static phase adder system. They are usually really cheap junk.


Thanks JRaef. Your knowledge is always appreciated. The motor is not actually 4 Hp. Its like 3 3/4 or something. I couldnt remember what he told me on the phone so I just said 4. I think he said 3 3/4. Not sure if this makes a difference or not.


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## wendon (Sep 27, 2010)

JRaef said:


> 4HP is a big clue here. There is no such thing in NEMA motor sizes, so that means this is an IEC motor. The reason the HP number comes out odd like this is sometimes because on these submersible sewage pumps, the European mfrs only use a 3 phase motor, because they have to be certified as explosion proof and that's really expensive. So they only use the one motor and for single phase applications here in the US, they add a cheap little static phase adder in an external box as part of the control panel. But using the static phase adder cases them to de-rate the pump power rating, so it comes out to an oddball HP number like that.
> 
> The point is, the blown capacitors might be part of that static phase adder system. They are usually really cheap junk.


What's the duty cycle etc. of one of those piece of junk static converters? Aren't they limited as to what percentage of the full load current they can handle?


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## erics37 (May 7, 2009)

When I talked to you about this earlier I was sitting there thinking it was a nice, convenient standard single-phase submersible motor with a set of remote capacitors and a potential relay. Of course it's actually something weird :laughing:



JRaef said:


> 4HP is a big clue here. There is no such thing in NEMA motor sizes, so that means this is an IEC motor. The reason the HP number comes out odd like this is sometimes because on these submersible sewage pumps, the European mfrs only use a 3 phase motor, because they have to be certified as explosion proof and that's really expensive. So they only use the one motor and for single phase applications here in the US, they add a cheap little static phase adder in an external box as part of the control panel. But using the static phase adder cases them to de-rate the pump power rating, so it comes out to an oddball HP number like that.
> 
> The point is, the blown capacitors might be part of that static phase adder system. They are usually really cheap junk.


That's all sorts of crazy. Good ol' cheap junk.


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## ibew415 (Mar 23, 2014)

In VFDs the capacitors have a shelf life....you cant just take a drive that has been sitting for 3 years and energize it....you will blow the caps!

Every 6 months to a year you are suppose to energize the drive ( the capacitors) for one hour WITHOUT load, to maintain them.....

HOWEVER, this is not a VFD....but still could be a cause. new motor sitting on the shelf too long.


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## JRaef (Mar 23, 2009)

wendon said:


> What's the duty cycle etc. of one of those piece of junk static converters? Aren't they limited as to what percentage of the full load current they can handle?


Depends on the brand/supplier. ITT/Flygt is a good brand of submersible pump, but it is a 3 phase motor so it needs the phase adder and derating. So their US dealers can buy the package from Flygt and the phase adder is fairly decent, but some dealers prefer to "roll their own" or buy them from other companies, so who knows what you get. Then there are several other suppliers with less of a good reputation to begin with. If you do a search on the term "static phase converter" you will see some write-ups on what they are and how they affect motors. 

In general the duty cycle is supposed to be relatively low, because the motor has to be de-rated by at least 50% from the 3 phase rating and must be low duty cycle too. So if the float switches are set too close and the pump cycles too much, that could be a problem too.


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## micromind (Aug 11, 2007)

While most pumps like this are indeed 3Ø with a static phases converter, if it is a true single phase motor with a start cap, run cap and some sort of relay to disengage the start winding, it may be a bad relay.

If the start cap remains in the circuit for more than 30 seconds or so, it'll blow. They are designed for intermittent duty.


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## Switched (Dec 23, 2012)

Damn....Some of you guys are so smart! I love checking out all the posts around here, so full of great information and insights!:thumbsup:


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## green light (Oct 12, 2011)

micromind said:


> While most pumps like this are indeed 3Ø with a static phases converter, if it is a true single phase motor with a start cap, run cap and some sort of relay to disengage the start winding, it may be a bad relay.
> 
> If the start cap remains in the circuit for more than 30 seconds or so, it'll blow. They are designed for intermittent duty.


Im actually going to look at this job tommorrow morning. It is as you describe. Its a single phase motor with a start and a run capacitor and a relay. I was talking with eric about this on the phone yesterday about this situation, but I still have some questions. What would tell the relay to switch from start to run. Centrifigal switch in the motor? What percentage of full speed would normally initiate the change? Does any one have a link to a wiring diagram for such a set up that shows cap, relay, and motor wiring? Thanks again for all of the uselfull input and suggestions.


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## wendon (Sep 27, 2010)

green light said:


> Im actually going to look at this job tommorrow morning. It is as you describe. Its a single phase motor with a start and a run capacitor and a relay. I was talking with eric about this on the phone yesterday about this situation, but I still have some questions. What would tell the relay to switch from start to run. Centrifigal switch in the motor? What percentage of full speed would normally initiate the change? Does any one have a link to a wiring diagram for such a set up that shows cap, relay, and motor wiring? Thanks again for all of the uselfull input and suggestions.


If it has a relay external from the motor, it's probably a potential relay. Most of the relays I've worked with are:

Terminal #1 Start capacitor
Terminal #2 Start/Run winding
Terminal #5 Line 1
Terminal #4 Dummy terminal to connect Line 2 to Start and Run capacitors. 
Run capacitor should be connected between #4 and #2
Start capacitor should be connected between #4 and #1
Line 1 Motor common (Black)
Line 2 Motor Run winding (Red)

Make sure the connection between Line 1 and Terminal#5 is good. If this connection comes lose the start relay will not operate and the relay contacts will stay closed because the relay is NC. The other thing is to make sure the coil on the relay is okay (Continuity between #5 and #2 with all the wires disconnected.)

Also, make sure there's a bleed resistor installed on the start cap. It'll help prevent the contacts from arcing in the event of a short cycle.


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## micromind (Aug 11, 2007)

The easiest way to test the start relay is to measure current at the start capacitor when the motor is running. Should be zero. If there's current on either side of the start capacitor, the start relay has failed to de-energize and the capacitor will likely blow up in about a minute. 

If it's cap-start cap-run, there will be current on the start winding through the run capacitor all the time. But the start capacitor needs to be out of the circuit in a few seconds or less.


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## erics37 (May 7, 2009)

green light said:


> Im actually going to look at this job tommorrow morning. It is as you describe. Its a single phase motor with a start and a run capacitor and a relay. I was talking with eric about this on the phone yesterday about this situation, but I still have some questions. What would tell the relay to switch from start to run. Centrifigal switch in the motor? What percentage of full speed would normally initiate the change? Does any one have a link to a wiring diagram for such a set up that shows cap, relay, and motor wiring? Thanks again for all of the uselfull input and suggestions.


I've used this diagram before and found it to be accurate for a few small wastewater lift stations I've worked on.


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## L.I.Electrician (Sep 9, 2012)

green light said:


> Thanks JRaef. Your knowledge is always appreciated. The motor is not actually 4 Hp. Its like 3 3/4 or something. I couldnt remember what he told me on the phone so I just said 4. I think he said 3 3/4. Not sure if this makes a difference or not.


The devil is in the details.....


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