Compressor winding question


  #1  
Old 09-21-02, 08:43 AM
M
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Compressor winding question

Could someone give me a hand with the following question posed to me? The following resistance readings on a compressor winding terminals are observed:
A to B 10 ohms B to C 20 ohms C to A 10 ohms
What is the problem with the motor? (The terminals are not identified)It looks to me that A is the common,right?But shouldnt the start have more than the run,and if so,is the start shorted or grounded or something?This is an exercise,not an actual case,but it could be in reality someday.Thanks for any replies.I really appreciate it.
 
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Old 09-21-02, 09:30 AM
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If this is a written question then in the question the power phase should be noted.

A short would read~ A ground could be to another winding or the housing which should give you a zero reading.

If this was a exam question the besy way to answer it would be to copy the question word for word.
 
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Old 09-21-02, 10:21 AM
M
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compressor windings

Power phase wasn't covered.Would a 3 phase compressor or single phase compressor with same conditions have a different problem?Question is word for word.Thanks again.
 
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Old 09-21-02, 10:30 AM
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On a good 3 phase compressor all terminals will read the same.
 
  #5  
Old 09-22-02, 01:04 PM
Jacque Schidt
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And; on a good single phase compressor, start will be different than run, and the two will add up to the S-R reading:
i.e. S-C=25, R-C=50, S-R=75. (or somethign like that, I can never remember if start is higher than run or viceversa.
 
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Old 09-22-02, 01:47 PM
Nominal
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Draw the terminal configuration on a piece of paper. Measure the resistance between each terminal with an ohmmeter. Record the resistance found on the diagram. The least resistance is between the run and common terminals; the medium resistance is between the common and start terminals; the most resistance is between the start and run terminals.
 
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Old 09-22-02, 02:21 PM
M
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The readings have been taken.They just dont add up.Any ideas why?The start and run windings cant have the same resistances can they?Thanks
 
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Old 09-22-02, 02:45 PM
Nominal
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Just want someone to give the answers to you, don't you? lol

Yes Mark, by the information you stated, it appears that one winding has a less than normal resistance. This would indicate, as you stated in your original post, a shorted winding.
 
  #9  
Old 09-22-02, 04:12 PM
bigjohn
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Most likely the answer they're looking for is that it's a single phase compressor motor and the START winding has a turn to turn short reducing it's overall resistance. The start winding would normally have a higher resistance than the run winding. It's also possible that it's a three phase motor and two windings have turn to turn shorts, but I doubt that's the intent of the question. They're probably trying to get you to think about the resistance difference between start and run on a single phase compressor.
 
 

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