RE: [TCML] Some general design questions

["Lau, Gary" <Gary.Lau@xxxxxx>]

I believe that the HV spikes that need to be clamped on the mains lines are common-mode, relative to mains (3rd wire or green wire) ground.  This means that MOV between the Hot-Neutral wires as you suggest won't do it, though they certainly can't hurt.  Since you don't (and shouldn't) be using the 3rd wire ground at the coil, you may wish to think about locating Hot-Gnd and Neu-Gnd MOV's within the Variac case, which should have it's case tied to mains ground.  My coil's AC wiring schematic is at http://www.laushaus.com/tesla/sync_gap.htm  A couple of high voltage AC line-rated bypass caps across the MOV's will also help cut down on AV coupled into the mains.

I would strongly recommend NOT tying the motor case to RF ground, leaving it floating instead, since no one should ever be touching it (and you may want to remember this if you're mechanically adjusting the motor phase).  The RF ground can have very high voltage transients on it relative to mains hot & neutral (and green-wire ground).  These transients may exceed the motor's windings-to-case insulation.  I once had a lamp dimmer case (used on a static gap blower) tied to RF ground, and the dimmer died a mysterious death.

Regards, Gary Lau
MA, USA



> -----Original Message-----
> From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On
> Behalf Of Andrew Nettles
> Sent: Friday, November 30, 2007 11:01 PM
> To: tesla@xxxxxxxxxx
> Subject: [TCML] Some general design questions
>
>
> Regarding grounding....I'm using 2 wires of an extension cord coming out of the
> variac to a line filter, then to PFC caps, then to the NST.  The variac is mains
> grounded but everything else is RF (earth) grounded.  Everything except the variac
> will be located under the base of the coil.  After much reading this seems to be the
> right way to do it but some pictures of other peoples' coils suggest otherwise.
>
> I have a srsg that needs to spin up in order to sync lock so I'm powering it straight
> from the mains and it also only uses 2 wires.  The motor housing is RF grounded.  I
> plan on powering up the rotary gap and then applying power to the coil with the
> variac as soon as the motor syncs up.
>
> Since I'm using only 2 wires, I only need one "across the line" MOV and a suitable
> fuse for the NST power and for the sync motor power right?  Should I use a slowblo
> fuse on the NST and a fast one for the motor?
>
> I bought MOVs for line-to-ground use but that was before I realized that I'd only be
> using 2 wires and the RF ground.  Doesn't seem like I'll need them.  The purpose of
> these MOVs is just to protect the stuff hooked up to the mains, right?
>
> Any input?  Much Appreciated!
>
> Andrew
> Fort Worth_______________________________________________
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