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

[DC Cox <resonance@xxxxxxxxxxxx>]

The pole xmfr will work fine, but you do need to provide a few kW of ballast
resistors, or preferably a series inductor to control current.

Forget the beer bottle caps --- they suck up over 20% of your power in
dielectric losses.  Glass is fine for DC work, but with high freq AC you
need MMC style caps or heavy duty pulse capacitors.  Glass is ok for very
low power coils (first project type), but fails at higher powers like 2-5
kVA.

Usually, if power level is above 4-5 kW you need to run a rotary spark gap.
Below that a hyperbaric will work fine.  If you email me off-list I will
email you the plans for it.  Very simple --- uses an old vacuum cleaner
motor and a 2 1/2 plastic PVC "tee" (Hone Depot) with a cover.

Dr. Resonance

On Sat, Mar 6, 2010 at 5:18 PM, <cbroring@xxxxxxx> wrote:

> 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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