Re: [TCML] Calibrating a sync spark gap

[futuret@xxxxxxx]

Karl,

The proper phase position will depend on the power transformer being 
used
and the tank capacitor value.  Different transformers and capacitor 
arrangements
will affect the time it takes to reach full charge on the capacitor.  I 
assume
you're set up for 120  bps if you're in the USA.  In any case the proper
phase setting must be done by trial and error at full power.  You can
get an idea of the proper phase position at low powers, but then
the proper position must be verified at full power.  I adjust my
systems to give maximum spark output.  I use an electronic phase
shifter circuit to make it easy to find the best phase position.

   http://futuret.110mb.com

John


-----Original Message-----
From: Karl Thorkildsen <karl.thorkildsen@xxxxxxxxxxxxx>
To: tesla@xxxxxxxxxx
Sent: Sun, 25 Jan 2009 1:38 pm
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: 
=C
2
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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