[GreenKeys] Fwd: Re: ASR LMU12 Motor

[Bruce Gentry]

I fear the short damaged bearings in the motor or shafting. The motor 
mount is resiliant rubber, and if the motor frame was not grounded, the 
current may have passed through the bearings. This arcs and etches the 
bearing balls and races. If the motor frame was grounded, did the wire 
touch the motor shaft, fan, or anything metal connected to it?.  Any 
current passing through  any bearings in the machine can do the damage. 
The synchronous motor in a 28 is 3600 RPM, that is the fastest a 
synchronous motor can go on 60 cycles. No sort of short or other damage 
or change can increase the speed beyond that.  If  you were dealing 
with  a goverened motor, that is a totally different matter.

       Bruce Gentry, KA2IVY


On 1/3/21 14:38, Steve Garrison wrote:
>
> OK, folks what can go wrong with a synchronous motor that can make it 
> seem to be turning at a much higher RPM than it should be?
>
> I had a mishap that shorted a wire against the motor that caused a 
> spark, a pop, and the fuse in the LESU blowing.  After removing the 
> short, replacing the fuse, then powering back up, the machine was 
> running but �sounded funny!�  After removing the typing unit and 
> powering backup I still had the
> �funny� sound, just not quite as loud.  Without the typing unit it was 
> just the motor and the reperf churning.  The TD drive shafts had been 
> removed earlier.
>
> My feeling is the �funny� noise is the mechanisms running at a higher 
> RPM than designed.
>
> I still need to repair the shorted wire, but it isn�t part of the 
> motor circuit anyway.
>
> Steve G./N4TTY
>
>
>
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