Re: AC Split phase motor????

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

Tesla list wrote:
> 
> Original poster: Esondrmn-at-aol-dot-com
> 
> In a message dated 11/11/00 8:44:48 AM Pacific Standard Time,
> tesla-at-pupman-dot-com writes:
> 
> <<
>  >  As reason would seem to dictate this, this does not necessarily seem
>  >  to be the case from my personal experience. I did almost exactly the
>  >  same thing that Scot did a few months back with my large "Medusa"
>  >  system, and my motor's case was indeed grounded to the RF ground.
>  >  The motor still went deader than a hammer and I had to replace it.
>  >
>  >  Keeping 'em Sparkin' in Memphis,
>  >  David Rieben
> 
>  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.
> 
>  John Freau
>   >>
> I would like to question the idea of connecting the rotary gap motor housing
> to the main RF ground.  I know that the main RF ground on my 6.0" coil, run
> at about 7kva, is several hundred or thousand volts above ground.  You can
> draw healthy sparks off the ground rods when the coil is running.  I would
> think this would cause a large voltage differential between the 120 volt
> motor windings and the motor case - possibly inviting breakdown under normal
> operation.  I would appreciate other folks comments on this.  I have always
> let the motor case on mine float.  Possibly connecting it to the main 60 hz
> ground (using a separate set of ground rods) would be better?
> 
> Ed Sonderman

Ed,

I fully agree with your assessment - the motor case should not be tied
to the RF ground because of the presence of large RF spikes that appear
on this line during normal Tesla Coil operation. However, I would
suggest that it be tied to the mains ground instead of letting it float.
Furthermore, the addition of a couple of MOV's (or even 360+ VAC PFC
caps) between the motor case and the incoming motor power leads would
also not be a bad idea as Terry has previously suggested. In the event
of a power arc to the motor case, the MOV's (or caps) should prevent any
damaging voltage transients from appearing across the motor windings to
the case, preventing the initial flashover that can lead to motor
destruction. The same is true if any induced RF is making its way into
the motor due to long leadlengths.

-- Bert --