# Insulation of Iron core laminates from eachother ?



## janmarsh (Jan 13, 2009)

Another question for you experienced guys.

Prior to adding winding to an iron laminated core I removed from an existing motor, I detect continuity across numerous laminates. All laminates have an insulating film on their faces. The realisation that all laminate edges obviously have a common earth to the motor shell quickly dawned on me.

Am I to understand that heavy eddy current buildup is overcome by laminate faces only having to be insulated from eachother ?

With thanks.


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## major (Apr 4, 2008)

janmarsh said:


> Am I to understand that heavy eddy current buildup is overcome by laminate faces only having to be insulated from eachother ?


Yes.............


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## janmarsh (Jan 13, 2009)

Bingo........... This is what I call service, Thanks again Major.


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## Georgia Tech (Dec 5, 2008)

janmarsh said:


> Another question for you experienced guys.
> 
> Prior to adding winding to an iron laminated core I removed from an existing motor, I detect continuity across numerous laminates. All laminates have an insulating film on their faces. The realisation that all laminate edges obviously have a common earth to the motor shell quickly dawned on me.
> 
> ...


Yes Laminated active componets like the Armature and the Field poles are laminated to keep the eddy currents down. But I do think they have continuity between them selfs. I never have heard of anyone doing serivce to the actual poles for inuslating them from each other..


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## Georgia Tech (Dec 5, 2008)

major said:


> Yes.............


So If I take my field pole out, and put a volt Ohm meter accross it, it will have high resistance accross the pole (long ways that is)??


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## major (Apr 4, 2008)

Georgia Tech said:


> So If I take my field pole out, and put a volt Ohm meter accross it, it will have high resistance accross the pole (long ways that is)??


I don't know what core jan was talking about, but you are obviously speaking of our common DC commutator motors, right? Then the armature is the member seeing full magnetic reversals at electrical frequency. It is where high eddy current losses will occur and needs to be laminated. In small cheap motors, the lamination surface itself provides enough resistance to the adjacent lamination to cut down on eddies. In the large, more expensive motors, the armature laminations are actually insulated on the surfaces. This is sometimes done simply by oxidation. But the high efficiency method is to core plate the steel before it is punched. Core plate is a very, very thin coating which provides a good electrical insulation between laminations once they are stacked. It is not intended to provide any isolation to the windings, or to the machine case or shaft. So an ohmmeter reading from a scrape at one end to the other end of the stack will likely read zero ohms as the path will be thru the shaft.

Now you mention pole piece. Poles do not see the full magnetic reversals. Often, like in cranking motors, the pole is solid. In the larger motors where efficiency and heat is a concern, the poles are laminated. Often, they will use a thicker, even non electrical grade steel. And likely the pole laminations are not insulated. The virtue of the lamination to lamination contact surface provides enough resistance to cut down the losses. These losses in the pole occur on the pole face and are cause by minor loop flux variation as the slots in the armature cut across the pole face during rotation. The frame or yoke is rarely laminated at all because the flux essentially does not vary.

And to answer your question...NO. Likely it will read close to zero. Even if the laminations are insulated, they would be shorted by the rivets holding them together.

There are always exceptions to the rule. And you see DC motors with laminated frames, like those made by Reliance. You do get a little higher efficiency by doing that when the motor is supplied PWM. But the typical forklift type motor isn't going to see the value to cover the added cost. And also, some DC motors are made from AC motor parts or tooling and have laminated frames, like from Baldor.

I thought I was going to get by with a one word answer.

major


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## Georgia Tech (Dec 5, 2008)

major said:


> I don't know what core jan was talking about, but you are obviously speaking of our common DC commutator motors, right? Then the armature is the member seeing full magnetic reversals at electrical frequency. It is where high eddy current losses will occur and needs to be laminated. In small cheap motors, the lamination surface itself provides enough resistance to the adjacent lamination to cut down on eddies. In the large, more expensive motors, the armature laminations are actually insulated on the surfaces. This is sometimes done simply by oxidation. But the high efficiency method is to core plate the steel before it is punched. Core plate is a very, very thin coating which provides a good electrical insulation between laminations once they are stacked. It is not intended to provide any isolation to the windings, or to the machine case or shaft. So an ohmmeter reading from a scrape at one end to the other end of the stack will likely read zero ohms as the path will be thru the shaft.
> 
> Now you mention pole piece. Poles do not see the full magnetic reversals. Often, like in cranking motors, the pole is solid. In the larger motors where efficiency and heat is a concern, the poles are laminated. Often, they will use a thicker, even non electrical grade steel. And likely the pole laminations are not insulated. The virtue of the lamination to lamination contact surface provides enough resistance to cut down the losses. These losses in the pole occur on the pole face and are cause by minor loop flux variation as the slots in the armature cut across the pole face during rotation. The frame or yoke is rarely laminated at all because the flux essentially does not vary.
> 
> ...


Excelent answers!!! I really enjoy your posts!!!
thanks


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## Georgia Tech (Dec 5, 2008)

Major,
if I take photos of the inside (commutator armature ect...) of my PM motor I bought on EBY could you tell me what you think??


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## major (Apr 4, 2008)

Georgia Tech said:


> Major,
> if I take photos of the inside (commutator armature ect...) of my PM motor I bought on EBY could you tell me what you think??


Sure, post them up.


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