Re: AC Split phase motor????

["Bert Hickman" <bert.hickman-at-xxxxxxxxxx> (by way of Terry Fritz <twftesla-at-xxxxxxxxxx>)]

Tesla list wrote:
> 
> Original poster: Tesla729-at-cs-dot-com
> 
> In a message dated 11/11/00 8:44:18 AM Pacific Standard Time,
> tesla-at-pupman-dot-com writes:
> 
> << David,
> 
>  Was your's the case where the spark went though the vent hole
>  in the motor and hit the windings?  I know that happened to someone,
>  but I figure that's a rare case.
>   >>
> 
> Hi John,
> 
> No, it did not go thru a vent hole and I, like you, can't really understand
> why it completely died from a  strike to the grounded frame, but it sure
> did. I probably would have had trouble believing it too, if I hadn't
witnessed
> it myself. I didn't try to take it apart to see what was wrong internally, I
> just figured it was messed up.
> 
> Take Care,
> David Rieben

David and Richie,

I lost a vacuum gap motor in a slightly different manner - a streamer
hit to a hanging lamp that was accidently left plugged into the mains.
In this case, the streamer hit the chain and 2-wire lamp cord, travelled
back through the conduit, and arced between the grounded case of the
vacuum motor and one of the field windings. The follow through current
from the 120 V line melted the wire leading to the winding, stopping the
motor in its tracks. Disassembly of the motor showed where this had
occured on a magnet wire lead to one of the stator windings, and repair
was quite simple. I'm actually lucky that the vacuum motor was the
weakest link... :^)

In the case of your motors, I wonder if a sudden power arc hitting the
grounded motor might have been sufficient to generate a short, high
voltage transient on the case of the motor due to the presence of lead
inductance between the motor and true RF ground. If this transient was
sufficient to cause a flashover between the elevated case and a stator
winding, the resulting follow-through current from the LV mains to
ground might blow open up the connection to a winding at the point of
the flashover. Depending upon where the open occurs, the motor might be
easily repairable without rewinding.

-- Bert --
-- 
Bert Hickman
Stoneridge Engineering
Email:    bert.hickman-at-aquila-dot-net
Web Site: http://www.teslamania-dot-com