# Single Phase Motor



## John Valdes (May 17, 2007)

I have a single phase motor that was wired for 230 volts, but was connected to 120 volts. The motor was running, starting and stopping.
They called me because it was turning the wrong direction.

This is when I noticed the connections were for high voltage, not low.
So I reversed it (but left it connected for high voltage) and watched it operate a couple times. Scratching my head! 
So I check the current. Its fine. 4 amps no load.
I should have listened to that voice in my head.
(_this is not right, trust the drawing, not the farmer, disconnect it and leave)_

I told the guy to wait on operating it until I got the right size wire and switch.
I guess he did not listen as it will not start at all now. I feel responsible.
I hope its the cap or caps.

590-708 MFD
125 VAC

Any suggestions on checking the caps is appreciated. Or any other observations.
It is a simple motor. Here it is on page 9.
http://www.goevans.com/EHB_pgs0803.pdf

ps...........One cap is oozing oil. Thats what it looks like. Oil coming out of the blow hole. The blow hole looks fine. Oil in a paper cap?


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## ampman (Apr 2, 2009)

in before the lock


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## nolabama (Oct 3, 2007)

ampman said:


> in before the lock


That's messed up


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## John (Jan 22, 2007)

Assume that whoever was there before you did it wrong....especially a farmer.
Capacitor is the wrong voltage.


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## hardworkingstiff (Jan 22, 2007)

If it was turning the wrong way, did it ever really work long before you got there? I can understand why you feel you responsible. I am rather confused as to why you would leave it operational (improperly wired) when you needed to install a properly sized switch.


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## hardworkingstiff (Jan 22, 2007)

John said:


> Capacitor is the wrong voltage.


The wiring diagram shows the 2 capacitors wired in series when connected for high voltage, so they should be fine using 2 caps (125V) in series on a 240V supply.


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## micromind (Aug 11, 2007)

A single phase motor connected for high voltage but operated on low voltage will run, but it'll produce about 1/4 of its normal torque. 

The drawing on page 9 shows a motor with two run windings and two start windings. Fairly common with larger HP. 

My bet would be the start capacitors. Especially if one is leaking. Yes, paper caps have oil in them. It's part of the separation of the two rolls of tin in them.

I'd replace both caps, not just one, and see what happens. 

Often if an electrolytic capacitor is used at a low voltage then subjected to a higher voltage, even if it's still within its rating, it'll fail. 

Also, make sure the start windings are both disengaged when up to speed. No current on 5 or 8.


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## hardworkingstiff (Jan 22, 2007)

micromind said:


> A single phase motor connected for high voltage but operated on low voltage will run, but it'll produce about 1/4 of its normal torque.
> 
> The drawing on page 9 shows a motor with two run windings and two start windings. Fairly common with larger HP.
> 
> ...


If the motor is operated at low voltage, doesn't it draw more amperage? What do you think the chances are that the winding's were damaged?


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## wendon (Sep 27, 2010)

hardworkingstiff said:


> If the motor is operated at low voltage, doesn't it draw more amperage? What do you think the chances are that the winding's were damaged?


The motor must not have been loaded very heavy! It won't draw higher amperage if it's wired high voltage. I'd guess the caps were damaged from held in too long until the motor got up to speed.


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## hardworkingstiff (Jan 22, 2007)

wendon said:


> The motor must not have been loaded very heavy! It won't draw higher amperage if it's wired high voltage. I'd guess the caps were damaged from held in too long until the motor got up to speed.


I would have to question whether the motor ever got up to speed.


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## hardworkingstiff (Jan 22, 2007)

wendon said:


> It won't draw higher amperage if it's wired high voltage.


That kind of goes against everything I've ever heard about motor loads. I'm assuming we are both talking about the motor wiring be configured for high voltage and fed with low voltage.


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## micromind (Aug 11, 2007)

It depends on the load. If it was very lightly loaded (can't imagine that on a farm......), it'll draw way less amperage. Kind of like a 3ø motor that's started on wye and run on delta. 

If it never reached full speed, and cycled the start windings, that would blow the start capacitors. 

I didn't think of not reaching full speed until I read your post. Good catch.


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## JRaef (Mar 23, 2009)

In that type of single phase motor, the two caps are for starting and running, that diagram does not show the centrifugal switch in the circuit. The start cap us usually electrolytic, hence the goo, the run cap may be film type, no goo. If you had the run cap swell and pop the "blow hole", it's toast, you must replace it.

Now WHY did the start cap swell? It comes from over heating. If connected at low voltage but wired for high voltage, the starting torque is reduced by the square of the voltage drop, so at 1/2 voltage you had 1/4 of the normal starting torque. If the load was not connected, it may APPEAR to be running, but if not at the necessary speed (because of not enough starting torque) for the centrifugal switch to operate, usually 80-90% speed, then the start winding is never shorted out of the circuit and switched to the run winding and run cap. The start cap is not made to be in the circuit the whole time, it over heats and swells, the pressure cap pops and that's all she wrote.

In an AC motor, running at 1/2 voltage with no load may not necessarily look wrong in terms of current, because an *unloaded* motor only takes 25-35% FLA to keep spinning. So even if you double that because of the low voltage, it still is below FLA. It's only when you put a load on it that the lack of torque causes the slip to increase and make it draw excessive current. If the thermal protectors were properly wired into the circuit, you likely have not damaged the windings by the way.

But this may have now damaged the centrifugal switch too, it may be welded closed. That actually may have happened first, so even if you had connected it right, it was too late. If the centrifugal switch contacts are welded due to high starting current for too long (they are not intended to be in the circuit for long either), then they never open and the start cap overheats.


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## John Valdes (May 17, 2007)

hardworkingstiff said:


> If it was turning the wrong way, did it ever really work long before you got there? I can understand why you feel you responsible. I am rather confused as to why you would leave it operational (improperly wired) when you needed to install a properly sized switch.


I should have pulled the breaker or disconnected it before I left.
This is why I am/feel responsible.



micromind said:


> It depends on the load. If it was very lightly loaded (can't imagine that on a farm......), it'll draw way less amperage. Kind of like a 3ø motor that's started on wye and run on delta.
> If it never reached full speed, and cycled the start windings, that would blow the start capacitors.
> I didn't think of not reaching full speed until I read your post. Good catch.


It was running no load. And I know the current should not have been an indicator of correct connections.
I really cannot believe I would be so stupid!
If I did not know, that would be one thing. But I do know and I still left it.



JRaef said:


> In that type of single phase motor, the two caps are for starting and running, that diagram does not show the centrifugal switch in the circuit. The start cap us usually electrolytic, hence the goo, the run cap may be film type, no goo. If you had the run cap swell and pop the "blow hole", it's toast, you must replace it.
> 
> Now WHY did the start cap swell? It comes from over heating. If connected at low voltage but wired for high voltage, the starting torque is reduced by the square of the voltage drop, so at 1/2 voltage you had 1/4 of the normal starting torque. If the load was not connected, it may APPEAR to be running, but if not at the necessary speed (because of not enough starting torque) for the centrifugal switch to operate, usually 80-90% speed, then the start winding is never shorted out of the circuit and switched to the run winding and run cap. The start cap is not made to be in the circuit the whole time, it over heats and swells, the pressure cap pops and that's all she wrote.
> 
> ...


Thanks Jreaf.
I hear every single word you said. 
I do remember something now that you mention the switch. I did hear this switch operate, but only after stopping.
Switch must have been closed the whole time the motor was running. 
So its the caps and the switch on the list.
I will replace the caps and check the switch.

Thanks everyone for the feedback.
For the record the machine was a drill press.


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## John Valdes (May 17, 2007)

Any info on how to test the caps?


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## hardworkingstiff (Jan 22, 2007)

John Valdes said:


> I should have pulled the breaker or disconnected it before I left.
> This is why I am/feel responsible.
> 
> 
> ...


Please let us know how the cap replacement goes.


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## hardworkingstiff (Jan 22, 2007)

John Valdes said:


> Any info on how to test the caps?


I just test them with the capacitor setting on my multi meter.

I used to use an analog meter and look for deflection then building of resistance.

Something tells me you know this and are looking for something additional.

Edit: If they are leaking oil, I think that's enough for replacement.


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## JRaef (Mar 23, 2009)

hardworkingstiff said:


> ...
> Edit: If they are leaking oil, I think that's enough for replacement.


That was the point I was trying to make too. Even if you get a cap to test correctly with a multimeter, if the goo leaked out, it doesn't matter, it's toast.


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## John Valdes (May 17, 2007)

Thanks. I just checked on the caps and they are $9.00 each. They are 20 miles away. Nearest Grainger I know of. I will check around some more tomorrow.
I can order them anytime. The job is no hurry as it is my neighbor and he got the drill press for free along with this motor.
He took an old OEM motor off it and installed this monster. 3 HP! Got it for free too.


I have tested both caps with my Fluke 77. No capacitance check/selection on that meter. I have to use the ohms setting.

One shows a climbing reading in the meg ohm range. And droping reading when I change the lead polarity. 

The other does nothing in the meg ohm range. The meter stands still in either polarity. This is the one leaking.

Thanks again. All of you.


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## JRaef (Mar 23, 2009)

John Valdes said:


> One shows a climbing reading in the meg ohm range. And droping reading when I change the lead polarity.
> 
> The other does nothing in the meg ohm range. The meter stands still in either polarity. This is the one leaking.
> 
> Thanks again. All of you.


Yep, the one not changing means it's not storing a charge, meaning it's shorted.


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## micromind (Aug 11, 2007)

JRaef said:


> In that type of single phase motor, the two caps are for starting and running, that diagram does not show the centrifugal switch in the circuit. The start cap us usually electrolytic, hence the goo, the run cap may be film type, no goo. If you had the run cap swell and pop the "blow hole", it's toast, you must replace it.


A small technicality that doesn't really matter, but the motor shown in the drawing has two 115 volt run windings and two 115 volt start windings. Both caps are identical, and they're in the circuit during starting only. 

The start switch isn't shown, it would be better if it were. This can be somewhat tricky, because the start switch needs to open both start windings, not just one. 

Most dual-voltage single phase motors have two 115 volt run windings and one 115 volt start winding. When connected for low voltage, all 3 windings are across the incoming lines, and have 115 volts supplied to them. When connected for high voltage, the two run windings are in series, and the start winding is connected in parallel with one of them. The run windings will act as an autotransformer and maintain 115 volts across each one, even though the current in the lone run winding is much higher than the parallel one. 

With the motor in question, there are 4 windings, two start and two run. When connected for high voltage, one start is paralleled with one run, the other start is paralleled with the other run, and both sets are connected in series. The result is balanced current in both run windings. This is why I recommend replacing both caps, the capacitance of each one needs to be fairly close to the other. 

The advantage to 4 windings as opposed to 3 is that 4 windings will produce more starting torque, and the motor can stay in start mode longer.


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## wendon (Sep 27, 2010)

If the start caps are hooked in series and one of them is open, it'll be a no-run situation!


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## micromind (Aug 11, 2007)

wendon said:


> If the start caps are hooked in series and one of them is open, it'll be a no-run situation!


True. Even if one start winding is open and the other one is ok, it still won't start.


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## John Valdes (May 17, 2007)

micromind said:


> A small technicality that doesn't really matter, but the motor shown in the drawing has two 115 volt run windings and two 115 volt start windings. Both caps are identical, and they're in the circuit during starting only.
> 
> The start switch isn't shown, it would be better if it were. This can be somewhat tricky, because the start switch needs to open both start windings, not just one.
> 
> ...


Thanks Micro. You really know your motors.
I never realized how lucky I was to work in a motor shop. I did not work in the shop itself (I was in the office) I had experts at my disposal anytime I needed it.

I will replace both caps and I will take the back off and check the switch.
I will install the correct breaker, wire and stop/start switch.

I appreciate everyone's input. I really do. Hope I can reciprocate.:thumbsup:


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## JRaef (Mar 23, 2009)

micromind said:


> A small technicality that doesn't really matter, but the motor shown in the drawing has two 115 volt run windings and two 115 volt start windings. Both caps are identical, and they're in the circuit during starting only.
> 
> The start switch isn't shown, it would be better if it were. This can be somewhat tricky, because the start switch needs to open both start windings, not just one.
> 
> ...


Maybe you're right, I don't have a lot of experience with every flavor of 1 phase motor for sure. I was using this guide:

His looks like the diagram that is 2nd up from the bottom of page 27, which is saying it's a Cap Start / Cap Run motor. I interpret what you are saying as it being a simpler Cap Start motor, with separate caps for each winding. Even for the dual voltage version on page 26 of this document, they still only only show one capacitor. That's why I assumed it was Cap Start / Cap Run.


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## micromind (Aug 11, 2007)

JRaef said:


> Maybe you're right, I don't have a lot of experience with every flavor of 1 phase motor for sure. I was using this guide:
> 
> His looks like the diagram that is 2nd up from the bottom of page 27, which is saying it's a Cap Start / Cap Run motor. I interpret what you are saying as it being a simpler Cap Start motor, with separate caps for each winding. Even for the dual voltage version on page 26 of this document, they still only only show one capacitor. That's why I assumed it was Cap Start / Cap Run.


It threw me for a loop too, but a while ago I had to connect a 4 winding single phase motor with no diagram. It had 8 leads, a more typical motor has 6 (7 if it has a built-in O/L). And both caps were the same value. 

So I connected 5-6 in parallel with 1-2, and 7-8 with 3-4. Then I connected the two sets in series, figuring that would be the high voltage connection. Then I blasted it with some 120. 

This is safe, because all 115/230 single phase motors have 115 volt windings. The worst that could happen is it would draw a lot of current and not run. 

This one however, started a bit slowly, and ran fine with no load connected to the shaft. Next, I hit it with 240. it started normally, and the current on the run windings seemed normal. 

So I learned that there are more ways to start a single phase motor than I thought.


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