AC electric motor problem

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  #1  
Old 02-16-15, 04:25 PM
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AC electric motor problem

Motor questions
here are the specs:
Rpm: 3450 60 Hz 120 V single phase 12 Amp

Here are the symptoms:
The motor either does not start -- only hums or else starts but does not come up to speed then the breaker on the panel trips.
Here is what I did. I wrapped some cord around the shaft and pulled it to get the motor spinning as I turned it on. It worked. Then I tried it a couple more times and noticed that it did not start but tried to turn the opposite way each time I closed the switch. So I tried wrapping the cord the other way and sure enough it started and ran.
I noticed the capacitor seem hot after the motor ran a couple of minutes. Is a capacitor supposed to get hot? It is not mounted on the motor but in the switch control about a foot or so from the motor.

I read some troubleshooting articles but they did not help much. I need some help in layman's language. What is probably wrong with my motor?
 
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Old 02-16-15, 05:00 PM
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A model # and mfg.of the motor would help,it could be an end switch in the motor or a bad cap.
Geo
 
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Old 02-16-15, 05:04 PM
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If it was trying to start in the wrong direction then the capacitor could be shot. Replace that first. The motor could also have a centrifugal starting switch that is not engaging properly.
 
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Old 02-16-15, 05:58 PM
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This is in a Sears Craftsman table saw
I don't know the maker of the motor but the model number is KS48YZEK-198
It is an obsolete part but the Sears part number is 62505
There is another number on the motor it is the Manufacturer # 12817
Maybe that is the same as a serial number?

If I get a new capacitor is there a right and wrong way to wire it?

Thanks for the help so far.
 
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Old 02-16-15, 06:21 PM
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The capacitor should be two wires and no polarity.
 
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Old 02-17-15, 08:02 AM
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I don't know the maker of the motor but the model number is KS48YZEK-198
It is an obsolete part but the Sears part number is 62505
That would be an Emerson motor, now Nidec.
 
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Old 02-17-15, 02:57 PM
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I installed a new capacitor. It started and ran like a new one for about 45 seconds then the capacitor popped.
When I went to the motor shop to get the capacitor they told me that this is not a motor they can work on. It looks to me like it is so obsolete that I cannot get a new one. I guess it's time to retire the saw.
Too bad.
 
  #8  
Old 02-17-15, 03:10 PM
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Was the new capacitor within 10% of the values of the old capacitor?
they told me that this is not a motor they can work on
Translation: The charge to repair it would be greater than the cost of a new one.

You might open it and check to see the condition of the centrifugal switch.
 
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Old 02-17-15, 03:12 PM
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Have you checked to see if the centrifugal switch under the terminal board may be welded together?
What HP is that motor?post the nameplate info from the motor,it shouldn't be that hard to find a replacement .
Geo
 
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Old 02-17-15, 03:28 PM
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The name plate on the motor is clearly legible.
part No: 62505
MFG Model ks48YZEK-198
V: 120
A: 12.0
RPM: 3450
Hz: 60
Insul class: B
AMB 40 (degrees, the symbol is used)C
PH: 1
MFG No12817
There are two more numbers: E22922 and LR 2459
There is not an HP rating

The saw is a Sears Roebuck Direct drive table saw

Model: 113.298050
Serial or code date: 1336.M0254 The 0 is zero
I suppose this last number could also be 1336.MO254 The O is the vowel.
 
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Old 02-17-15, 03:46 PM
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There is a klixon type starter relay in that motor. Apparently its contacts are welded together. The part is no longer available from Sears but is available in the link below. The part # 3CR-118-193 may be available other places if you use that number to search. carbonbrush klixon3CR.htm


A breakdown of your motor and interior....
MOTOR/CONTROL BOX Diagram & Parts List for Model 113298050 Craftsman Saw- SearsPartsDirect
 
  #12  
Old 02-17-15, 04:53 PM
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That motor appears to have a special mount incorporated on the casing,tough to replace.
Geo
 
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Old 02-17-15, 05:01 PM
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PJ and Geo,
Yes is has a special mount made for the saw. Now I am an amateur at things mechanical. Is the relay you reference the device in the switch box?
You are not showing me the centrifugal switch inside the motor. Is this correct?

What I really don't know how to do is diagnose things with the meter. I wish I did. I know what I do well. Mechanical/electrical is not it.

Thanks for the help and the link.
 
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Old 02-18-15, 05:02 AM
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There does not appear to be a centrifugal switch on that motor only a start in relay as PJ stated,should not be that hard to replace ,and you will probably need a new cap.
Check this link. http://www.sensata.com/download/4cr.pdf
Geo
 
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Old 02-18-15, 11:49 AM
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Geo
I read the article you linked too. I understand about half of it. The power going through the relay opens and closes it as the motor comes up to speed.
I have located the device in the control box and it looks like the picture in the link PJ sent. I will pull it out and look it over to see if the picture looks the same. Now suppose I order one of these. I will want to know when it comes if there is a right and wrong to it. And yes, I will need a new capacitor. When I blew there was a pop and smoke then I disconnected power. When I got the new one I took the old one to the shop and the man there showed me how to tell it was blown. The new one has the same sign as the old one.

Thanks again. This is interesting. I am a little uneasy about diagnosing by replacement. It could start to add up to big money but it hasn't been too bad so far.
 
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Old 02-18-15, 06:53 PM
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If all else fails, call the manufacturer. Emerson Electric Special Products Division manufactured the table saw and Emerson Motors (now Nidec) manufactured the motor.

Company Overview
 
  #17  
Old 03-06-15, 05:01 PM
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AC electric motor problem

Have you took the motor apart and looked in side. My craftsman table saw was brought about 45 years ago belt drive. last year I was going to use it but it would just hum and kick the breaker. The first thing I did was open it up found a mud dabber had built a nest in it cleaned it up put it back together and had no more problems. Almost the same thing happen years ago with the first RV I bought only they built between the fan and shroud.
 
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Old 03-06-15, 05:54 PM
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Real paying work has made me set this aside for a while. The motor ran just fine until the capacitor blew. The sticky relay switch seems to be the most likely problem. I will replace it if or when things slow down again.

Thanks for all the good advice. I will post again when I get it running again.
 
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