Detemining motor coil configuration

[ballpeen]

This may sound a little off the wall but, isn't there a way to determine the coils within a rewound motor by using an ohmmeter? It seemed to me we went over this in one of our classes I took some years back. In other words, you could measure the ohm readings between the motor leads and tell which coil was which. If this is so then how would you tell which end of the coil you were connected to? For instance, determining A from A Prime, B from B Prime, etc.? Does this make any sense to anyone?? Ballpeen.

 

[petronila]

Hello Ballpeen,

A 3 phase winding is a coil collection strategic connected in simetry in order to create a 3 phase magnetic field-

Each phase is conformed of Groups and each group is formed by unitary coils connected between one to others.

So one 36 Slots 4 pole motor with lap winding would have 12 groups of three coils per group, taking this start point the winder man most to built in the winding machine 12 groups of three coils each one this is 12 G x 3 Coils/G = 36 Coils.

Each group is mounted in the stator and when all groups are mounted you will have to distribute 12 groups in 3 phases so each phase will have 4 Groups and the motor need to be connected, and each group end is called start(A ) and finish (A´) normally the starts are the wires located in the external stator periferia and the finish the wires located in the internal diameter, in this order of ideas to finalize the job the winder man needs to know what connection perform. Lets assume the connection is one star/delta , so all 4 group of each phase most be connected in serie, but the connection most be produce the appropiate magnetic poles, so for the 4 pole motor the winder man neeeds to connect the first group finish with second group finish and the second group start with the third group start and the third group finish with the fourth group finish and do the same for the other two phases so the twelve groups are converted in three series finally the six lead are conected to the start and end of each serials and labelled from 1 to 6 to perform externals star or delta connections.

So with the ohmeter you can detrmine nothing to conclude wich is start or finish, this labor only could donne inside of the winding and when the stator is in rewindding jobs.With the ohmeter you can check continuity and take phase resistance readings for small motors.

Note if the connection between groups are wrong the stator will be wrong connected and not develop the correct agnetic field. For check this possible failure some shop use polarity test that consist in to apply low DC Voltage to the motor´s leads in order to produce check the magnetic field prior to varnish stage.

I hope this could help you

Regards

Petronila

 

[petronila]

Also this link could help:

http://www.uiitraining.com/b51a/100/15104ac_motor_rewind_intro1

Regards

Petronila

 

[electricpete]

That link doesn't get me anywhere.

I'd say there is not a lot that is done with an ohmmeter.

Of course, to wind a motor you have to know the layout: From poles and slots we can get coils per group (which is number of slots divided by number of poles divided by 3 for three phase). And you have to know how those groups are connected: single wye, double wye, two series groups of three parallel, etc. Usually all of this is carefully noted before removing the old winding.

You'll notice each coil has two leads that come out in slightly different location, maybe you might call them top and bottom (not to be confused with top and bottom coil in a slot). Keeping track of those top and bottom leads helps a little:

The coils within a pole phase group are connected in series with the same polarity which means the connection from one lead to the next is top to bottom (or bottom to top), not top to top (or bottom to bottom).

The "adjacent" pole phase groups of the same phase are connected in opposite polarity. So that connection will be a top to a top or a bottom to a bottom.

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[electricpete]

"That link doesn't get me anywhere."
To clarify: I mean the link is broken... doesn't work.

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[petronila]

Hello sorry for the link please seee the attachment

Regards

Petronila

 

[electricpete]

petronila - That's a great link. I was able to page thru all 8 pages by hitting the next arrow key at the bottom.

ballpeen - One more thought - Sometimes the surge test can reveal if there is a miswire since it may show up as a difference between phases.






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[ballpeen]

O.K. I thought that link was due to my computer, because it didn't work for me at first either. It is a very informative link though. I guess that does show that it would be quite hard to determine the phases with an ohmmeter. I didn't realize there was that much going on within a wound motor. Really it's all pretty much up to the motor shop. If they don't get it right, the user is screwed.
I know of one motor in particular we got back from this shop and it was drawing nearly the full load amps at an unloaded state. We knew it would never run loaded. We called the shop and they came back and added more windings and it was okay after that. It seems as though they aren't using the manufacturers specs. to do their rewinds and just going by feel. They will do the work a lot cheaper but, we keep having to send motors back to them quite often to get them right.
Thanks you guys for your interest in my troubles. It is appreciated. Ballpeen.

 

[starkopete]

Hi,
This procedure requires a battery and a voltmeter. It is at the bottom of the page at:

http://mywebpages.comcast.net/rsdoran/motor.htm

 

[petronila]

Hi Ballpeen,

I think the better is you talk with the manager`s shop in order to explain this failures and how to improve more quality control to the repairs. Talk him about Easa.

" I know of one motor in particular we got back from this shop and it was drawing nearly the full load amps at an unloaded state" this is very wrong because this shop is not testing the repaired motors or they don`t know what are they doing. I think you will need another shop, more expensive but with all trained and skill people, knowledge and technologie to provide you a reliance service.

Regards

Petronila