Re: [TCML] Any one using a 7200 V pole pig?

[futuret@xxxxxxx]

 Charlie,

I used to run a 7200 v. pig.  As you said there's a lot of current and low voltage
so the gaps take a beating and may power arc.  I used a rotary which solved
those problems.  It also helps to run the pig through a step up variac so the voltage
is kicked up to 8300 volts are so.  I also like to use an inductive ballast for lower loss.
The resonance points for the system will be determined by the ballast inductance
setting, so you can tune the ballast too for best performance, and yes larger caps
definitely help the performance.  For 7200 volt operation, I used 4 times the capacitance
than I used at 14,000 volts.  For a pig powered system, you probably want better
caps than beer bottles I would think.   

Regards,
John

 


 

 

-----Original Message-----
From: cbroring@xxxxxxx
To: Tesla@xxxxxxxxxx
Sent: Sat, Mar 6, 2010 7:18 pm
Subject: [TCML] Any one using a 7200 V pole pig?


I've been messing with my first Tesla coil for several weeks now.  It has a 3.5" x 20" secondary, two OBITs in parallel for power, a sucker gap, and 13nF beer bottle salt water primary capacitor.  After fiddling with it a lot,  I managed 28 inch strikes between the break out point and a metal tool chest, my official measuring technique. 
 
Today I replaced the OBIT's with an old 7200V pole pig that weighs nearly 100 pounds and has been out of it's oil for years..  I used 4.7 ohms resistive ballast, and ran it off 120V with the low voltage windings paralleled..  I had to reduce the spark gap to about half of what I was using with the OBIT's to get it to fire.  The result was 8 inch streamers and a screech from the spark gap.  I added another 6 nF to the primary capacitor, re-tuned the primary coil, and the streamer length doubled. The spark gap also sounded more normal.  The ballast resistors are rated at 450 watts and didn't get all that hot so I wasn't putting much power through the system. 
 
I think I understand whats going on here.  The OBIT's were running near resonance with the 12 nf capacitor and along with the wide spark gap setting I was seeing much higher voltages across the primary capacitor then I have with the pole pig.  Now I have low voltage and lots of current available now so I need a lot of capacitance and a small primary inductor with high current capacity.  It's also going to be harder to cool the narrow spark gap. 
 
My question is whether a 7200 V pole pig is worth using?  I see that I am going to have some issues to work around using this low voltage.  Also going to have to drink a lot more beer to provide bottles for capacitors.  I'm thinking it may be a better approach to find a higher voltage transformer or even just a few more OBIT's 
 
Any comments or suggestions? 
 
Charlie 
K3YA 
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