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RE: [TCML] SISG First Light

The first time I ran a SISG coil I did something similar. My variac started
to whale smoke almost immediately. I think when the voltage is too high, the
SISG board just conducts, and eats as much power as the ballast will let
through. Mine is wired as you have described, with the SISG in parallel with
the power source. All I had to do was drop the voltage and all returned to
proper behavior. No damage was incurred to the SISG boards.

Miles Waldron

-----Original Message-----
From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On Behalf
Of bartb
Sent: Sunday, October 19, 2008 12:26 AM
To: Tesla Coil Mailing List
Subject: [TCML] SISG First Light

Hi All,

Well, I powered up my SISG coil for the first time today. I'm running 5 
boards at the moment. As I cranked up the voltage and then variac 
ballast (keeping my eye on current), all was rather quiet and then ZAP! 
The coil threw out some hot white arcs striking an old primary coil 
about 5 feet away from the top load. After about 5 seconds, all went 
quiet again. The ballast variac was smoking! I shut it down and started 
looking at components (figuring I must have wired something incorrectly, 
rectifier died, or sisg boards took a dump).

I removed the coil and lid off of the coil cabinet and inspected the 
caps, bridge, and sisg. Nothing burned and no smell of anything bad. All 
looks brand new and none of the hv diodes are shorted. I then started 
looking at the control cabinet which houses my PLC, deadman circuit, 
voltage and current ballasts, etc. I measured the inductance of the 
variac ballast and found that the last time I rewired it, I had 
inadvertently changed the rotation direction (0 to 100%). So apparently, 
I started up this SISG with "no ballast for the pig". When I thought I 
was increasing L, I was actually lowering it. Well, I tried the coil 
again after all this and couldn't get anything to breakout. I could here 
the Sidac's firing however. It's almost as if the ballast was damaged 
and stealing power (it was the variac that was smoking originally).

I did get sparks and they looked great for a moment. But looks like I am 
in for another variac autopsy. I may first double check that nothing 
else is a problem by bypassing the variac (for a quick shot).

If there are other thoughts any of you might have about the incident 
here, please speak up. SISG's are new to me, so it's possible I'm 
overlooking something.

BTW, cap and primary are in series. The SISG is parallel to the power 
supply and before the cap and primary (as would be normal for a typical 
spark gap). I decided to change the wiring to this configuration (from 
my previous) after realizing that since I'm floating the primary, I was 
not limited to hookup configurations.

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