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POLE PIG TESTING

 * Original msg to: Esondrmn-at-aol-dot-com

Quoting Ed Sonderman:

 ES> Richard,

 ES> Yes my new variac is a Powerstat Variable Autotransformer.   
 ES> 240v in  0 - 280v out  28A  7.8KVA.

 ES> Well, last night I spent about 5 hours testing with the new  
 ES> pole pig. I have the welder in series with the line side of  
 ES> the variac.  The output of the variac goes directly to the   
 ES> pole pig.  This is a completely different animal. If I did   
 ES> not know better, I would think this is someone elses'        
 ES> project. Everything is different and confusing. If I would   
 ES> have had your home phone number last night I would have
 ES> called you.  I think I have taken about five steps backwards 
 ES> and two forward. 

Yes, well, ummm. Pole pig coils are a bit of a different animal,
but you can be assured that when you finally get the hang of it
that you won't look back. The other thing is is that you don't
have to worry about a kickback hurting the pig.

 ES> Durring all this testing, I am monitoring the primary        
 ES> current into the pole pig and the primary voltage.  I am     
 ES> still running on my only home made rolled capacitor so I     
 ES> want to keep the pole pig input under 150 to 166 volts       
 ES> (should be 9 to 10kv out).  

Reasonable.

 ES> The first big difference that I found is in the spark gaps. 

Yes. That was the first thing I noticed when I made the switch.
If you had been observing closely you would have noticed the arc
color at the gap whiten considerably when the power supply switch
was made. There is a lot more current at the gap. Neons and pole
pigs are different breeds of power supply.

 ES> When I used to use the neon transformers (12kv -at- 120ma  -    
 ES> controlled to 9 to 10kv max)  I used one cylindrical
 ES> spark gap and it would fire at about 5 to 6kv.  Now I slowly 
 ES> increase the variac up to 150 to 160 volts and the spark gap 
 ES> will not fire.  I tried two gaps in parallel and they will   
 ES> just barely fire.  Finally I used one gap electrically       
 ES> folded in half and it will fire at about 130 volts  - should 
 ES> be about 8kv - but when it's running, it sounds like
 ES> it's tearing the hell out of the gaps.  

It probably is tearing these gaps up a bit.

 ES> These gaps are 7   2.0" dia copper pipe sections about 2.5"  
 ES> long and gapped at about .030".  Then I tried both gaps in   
 ES> series each folded in half.  Now it just barely fires at     
 ES> about 10kv.  Then I tried both gaps folded in half and in
 ES> parallel.  This doesn't work very well.  They won't          
 ES> consistently fire together.  It seems to go back and forth,  
 ES> first one then the other will fire.  I finally ended up just 
 ES> running one gap folded in half.

This gap design is good, but it cannot quench this kind of power.

 ES> I suspect I am now getting a lot more current into the       
 ES> primary of the coil now but less voltage. You are correct,   
 ES> this pole pig is very difficult to control.  The variac acts 
 ES> like an on/off switch only.  I can control the voltage up
 ES> until the spark gaps fire then I have no control.  As I ramp 
 ES> up the variac, the voltage on the pole pig primary goes up   
 ES> to about 130 - 140 volts, current is only a few amps at this 
 ES> point, then the spark gap fires, current jumps up to 25 to   
 ES> 30 amps and the primary voltage drops down to 80 to 90       
 ES> volts.  This should be only about 5KV out of the secondary.  
 ES> If I turn the variac up higher, it seems like the current
 ES> goes up a bit but the voltage across the primary actually    
 ES> goes down. What it seems like is I have control of the       
 ES> current but not the voltage.  How do I get the primary       
 ES> voltage up to say 150 while holding the current to 20 to 30  
 ES> amps???  I tried a 2000w resistive load and got weak sparks  
 ES> and only 6 or 7 amps in the primary. I finally switched      
 ES> dischargers - back to my original 14" toroid.  I get a fine  
 ES> fireworks display.  Many violet discharges about three feet
 ES> long.  A good display.  The primary voltage is still only 80 
 ES> or 90 volts. 

Very good description of the problem.

 ES> I think I finally have a setup similar to yours - without    
 ES> the rotary gap. How do you ever get the primary voltage up?  
 ES> Do I need to add resistive loading in parallel with the      
 ES> welder?  You said it is possible to eventually eliminate the 
 ES> welder, which is good, we will need it back at work some     
 ES> day. I think if I had the variac, the pole pig and the
 ES> line hooked up with no load, the current would go through    
 ES> the roof.

The problem here is with your spark gaps. They are not designed
and constructed to handle the high current output of the pole
pig. Once the gap fires, the arc is so thick and hot that the gap
is not able to "quench" it. Without a gap that quenches, the
power from the pole pig shifts from the tank circuit and into a
short circuit across the gap. This explains the growl, high
current draw, and reduction of secondary spark.

The cylinder static is a passively quenching gap. A series of
short gaps, electrodes that act as heatsinks, and mild airflow
in a compact unit works quite well with moderately powered coils
supplied with neon sign transformers. As you are finding out,
this design falls short when you throw externally ballasted
transformers across it.

The first suggestion I would make would be to balce the capacitor
across the HV line, and move the gap in series with the primary
coil. That may help some. 

The next suggestion is to construct an actively quenched gap.
This does not mean you have to go out and build a rotary right
away, but you do need something with a high speed airstream, or
tight magnetic field, in between at least one gap electrode to
actively disrupt the arc. 

Your photos shows a beautifully made safety gap. A single gap
constructed like this, but heavier duty, with a focused air blast
from a vacuum cleaner motor aimed into the center of the gap
would go a long way about now. This is just a suggestion in an
area that certainly is wide open to good ideas. 

Richard Quick
... If all else fails... Throw another megavolt across it!
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