Re: [TCML] Variac

["Phillip Slawinski" <pslawinski@xxxxxxxxx>]

On Wed, Jun 25, 2008 at 7:55 AM, Lau, Gary <Gary.Lau@xxxxxx> wrote:

> I'm not sure that using a Variac does anything to reduce stress on the cap
> or MMC.  As far as excessive current, a cap doesn't care if it occurs on the
> charging or discharging cycle; an Amp is an Amp and it doesn't matter which
> way it's flowing.  When the cap is charging, the current is limited to 30 mA
> or 60 mA or some similar modest value by NST, and it doesn't matter what you
> do to the primary of the NST.  In contrast, every time the spark gap fires
> and discharges the cap, the peak discharge current can be 100's of Amps.
>  This is where an over current situation could stress the cap, and this is
> unaffected by the use of a Variac.
>
> A better reason to use a Variac might be that if conditions were such that
> racing arcs occur on the secondary, slowly ramping the voltage up with a
> Variac might give one an opportunity to detect that and shut down before the
> damage is permanent.
>
> It may also be prudent to perform rough primary tap tuning at less than
> full power, since if tuning is off, primary energy languishes in the primary
> tank circuit and this is more stressful to the cap.  But truthfully, I'm not
> sure that I did that.
>
> The best (IMO) reason to use a Variac is to take advantage of the
> additional voltage boost that most Variacs provide.  And of course there's
> that sense of power and control that spinning that big honkin' knob gives
> you!


Isn't it a bad idea to ramp up the voltage with an NST?

>
>
> But seriously, I agree that many do not use a Variac at all with no ill
> effects.
>
> Regards, Gary Lau
> MA, USA
>
>
> > -----Original Message-----
> > From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On
> > Behalf Of DC Cox
> > Sent: Tuesday, June 24, 2008 10:49 PM
> > To: Tesla Coil Mailing List
> > Subject: Re: [TCML] Variac
> >
> > The usual connection is 120 vac input on #1 and #4, with output on #1
> > (common) and #3 (the adjustable wiper).  If unsure, Superior has tech
> prints
> > on their website.
> >
> > It's used to slowly bring up the voltage on the nst thus placing less
> stress
> > on the MMC caps if you happen to hit the power switch at the sine wave
> > peak.  Many experimenters do not use them at all and have good results.
> >
> > Dr. Resonance
> >
> >
> >
> >
> > On Tue, Jun 24, 2008 at 5:12 PM, stamsund <stamsund@xxxxxxxxxxxxxx>
> wrote:
> >
> > > I found a variable transformer among my shop goodies.  It's a Superior
> > > Electric Powerstat, Model Q116U, 120 volt primary, 0-140 volts out, 1.3
> KVA,
> > > 9 Amps.  I understand it should be used between AC power and the NST,
> but
> > > I'm not really sure why it's needed and/or recommended and exactly how
> to
> > > connect it.
> > >
> > > Rob Robertsen, KA7YAK
>
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