squirrel caged rotor

Thread Starter

Rufinus

Joined Apr 29, 2020
87
Hi everyone.

I have got a shaded-pole motor and I have extracted the rotor to check one thing.

I understood that the squirrel caged rotor based its functioning in a alternating magnetic field that induces a current in a conductive bars, wich creates an another magnetic field and start the movement. But I thought that that conductive bars have to be isolated. But not. I have checked them with the DMM and the hole rotor is in short. The shaft, the block, the bars...

So, what´s the point of put conductive bars if the hole rotor is conductive metal? The induced current can travel by the whole piece.

Thank you.

Kind regards
 

crutschow

Joined Mar 14, 2008
27,727
So, what´s the point of put conductive bars if the hole rotor is conductive metal? The induced current can travel by the whole piece.
That's the point.
The current travels through all the bars to generate the magnetic field for the whole rotor.
If the bars were isolated there would be no significant current to generate the field.

A nit, but the normal name for such a motor is squirrel-cage not squirrel-caged.
 

MaxHeadRoom

Joined Jul 18, 2013
23,620
Now the bars and end shorting discs are all aluminum cast into the rotor, at one time, these were copper bars with copper disc end plates soldered to the bars.
If a motor were to over heat due to load etc, the solder could be flung off, turning the motor essentially into a choke, with no motion and virtually no current.
Think of the bars as secondary turns on a transformer, at initial power on, this is what it is, with a shorted turns secondary.
The copper or aluminum possess the most conductivity over a laminated steel.
Max.
 

Thread Starter

Rufinus

Joined Apr 29, 2020
87
Ahh ok ok, I see.

They are all without insulation, but the diferent metals behave diferent with current and magnetism.

Thanks for your answers
 
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