Re: [TCML] Calibrating a sync spark gap

["David Rieben" <drieben@xxxxxxxxxxx>]

Hi Karl,

I think Gary's comments covered that aspect of setting
up the synch gap thoroughly. One thing that I would
like to add as well is that titanium does not a good
spark gap electrode make, assuming that you were in-
tending to use the titanimu rods as permanent flying
electrodes. Tungsten is the first metal of choice for
this purpose and pure copper would probably be
the second best choice for this purpose. Titanium
does have excellent mechnical properties but not
ideal thermal and electrical characteristics for this
purpose.

David Rieben


----- Original Message ----- 
From: "Karl Thorkildsen" <karl.thorkildsen@xxxxxxxxxxxxx>
To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
Sent: Sunday, January 25, 2009 2:24 PM
Subject: Re: [TCML] Calibrating a sync spark gap


> Here's some pics:
>
> Scope showing the AC line, the trigger point is at the very left edge of 
> the screen.  The upper trace is the current probe but the pulse is too 
> short to see at this timebase.  In the second pic you can kinda see that 
> it's triggering on both peaks.
>
> http://www.thorbass.com/images/Tesla/ssg/ssgScope1.jpg
> http://www.thorbass.com/images/Tesla/ssg/ssgScope2.jpg
>
> This is a shot of the bolt with the titanium rod through it.  You can just 
> make out the set screw on the left side at the bottom of the bolt head.
>
> http://www.thorbass.com/images/Tesla/ssg/ssg3.jpg
>
> Test setup...
> http://www.thorbass.com/images/Tesla/ssg/ssg2.jpg
>
> At 01:38 PM 1/25/2009, you wrote:
> > 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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>
>
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