RE: [TCML] Calibrating a sync spark gap

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

I don't think it's possible, or at least it's not recommended, to set the timing of a SRSG solely on the basis of the AC mains phase.  The right setting will be highly dependant upon capacitor size, NST current, Variac setting, ferroresonances in your NST, and perhaps phase of the moon ;-)  It's typical to set the SRSG phase experimentally, just adjusting for best performance.  It's best to vary the phase in real time while the coil is running, either by mechanically rotating the motor in its cradle, or by using John Freau's phase shifter circuit and just twiddling a Variac knob.  I find that the SRSG phase is an extremely critical setting and I wouldn't dream of locking it to any particular setting.

Regards, Gary Lau
MA, USA

> -----Original Message-----
> From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On
> Behalf Of Karl Thorkildsen
> Sent: Sunday, January 25, 2009 1:38 PM
> To: tesla@xxxxxxxxxx
> Subject: [TCML] Calibrating a sync spark gap
> 
> I'm in the process of building a synchronous spark gap.  I have
> modified a motor and built a rotor from G10.  My electrodes are
> mounted by drilling a hole the long way through a bolt, then drilling
> a hole sideways into the head and tapping for a set screw.  The bolts
> are mounted through the G10 with some washers as cooling fins, and
> titanium rods stuck through held in place with the set screws.  I'll
> upload some pictures later and link to them.
> 
> The problem is how to set the position correctly.  Here's what I did:
> 
> Hook up an NST to the gap and connect one channel of my scope to the
> AC line of the NST (actually going through a variac too).  I took a
> piece of hookup wire, alligator clips on the ends, and wrapped it
> around one of the output wires of the NST, about 5 wraps.  The ends
> of this wire go across the other channel of the scope, signal to
> gnd.  Basically I built a cheap current probe.
> 
> Now firing the thing up, I set the scope to trigger on the current
> probe.  Basically getting a pulse every time the gap lines up.  And
> looked at the position of the AC line voltage relative to the pulse.
> 
> Using this method I got a fairly consistent display on the scope and
> was able to adjust the position by rotating the motor in the mount.
> 
> Question, I think I remember reading that I should sync to about 85%
> of peak.  In other words it should fire a little early, is that right?
> - Karl

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