Re: Considering Upgrading to Pole Transformer

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Gregory Hunter by way of Terry Fritz <twftesla-at-qwest-dot-net>" <ghunter31014-at-yahoo-dot-com>

Hi Bill,

--- Tesla list <tesla-at-pupman-dot-com> wrote:
> Original poster: "Bill Vanyo by way of Terry Fritz
> <twftesla-at-qwest-dot-net>" <vanyo-at-echoes-dot-net>
> 
> Thinking about eventually getting a pig - probably a
> 5KVA, 120 to
> 14400.  Not soon, but I like to think and plan
> ahead, and of course, get
> lots of advice first.  Main questions - suitable
> tank capacitor, type of
> spark gap, and current limiting:
> 
> What are people using for caps with their pig
> systems?

I'm using 81nF of beer bottles, but this is hardly the
"norm" for the hobby. I did this as a temporary
measure until I could afford a big MMC. However, the
bottles work so well, I've decided to conserve my
hard-to-replace MMC caps for awhile.

> 
> Using the Geek group caps (Cornell-Dubiler
> 942C20P15K, 0.15uF, 2000VDC),
> what would be the dimensions (number of strings and
> string length) for a
> suitable MMC?
> 
> I'm currently building 8 strings of 11 (with a 9th
> spare string) for a
> very LTR cap for use with four 15/60 NST's and a
> sync triggered gap. 
> Would this suffice?  I know LTR is easier on the
> NST's --- is  there any
> need to use an LTR cap with a pole transformer?  And
> I geuss the answer
> to that might depend on what type of spark gap I use
> (synchronous, async
> rotary, or static).

The reso cap, LTR, etc. depend on fixed a fixed value
of current from an NST supply. A variable power pole
pig setup sort of invalidates the calculations, as LTR
at one current becomes reso or smaller-than-reso at
other currents.

> 
> So, which type of spark gap is easiest on the tank
> cap? (and I assume I
> don't have to ask about what's easy on the
> transformer, correct?)

I'm using a big copper pipe "sucker gap" at the
moment. Performs well on my 5KVA/11KV pole pig system.
I've also gotten good results with a 10,000RPM async
rotary.

> 
> Last, current limiting.  I have a variac rated 240
> volts, 50 amps, but
> don't want to modify it in any way - just want it
> for input voltage
> control.  I've heard of people using arc welders for
> inductive ballast -

I'm using a 230 Amp AC "stick" welder in series with
the pig. I paid $25 for it (used, out of the
classifieds). I usually run it with the welding leads
open for about 7-8 Amps. I don't use any series
resistance. Performance on my 6" x 30" coil system is
excellent even at this modest power level (82"
sparks). With the amp control turned down to minimum
and the welding leads shorted together, the 240vac
current draw jumps to 28 Amps. The sparks are thicker,
more intense, and more numerous. They also scare me by
striking everything in the garage (floor, walls,
ceiling, workbench, vehicles, etc.), so I rarely run
at this power level.

> I don't have one.  Can NST's be used?  Could one use
> one or more

I think NSTs are a bit light for this application.
However, I once used two series MOTs with their
secondaries shorted out for about 240vac/20A. It was
cheap, compact, and effective.

> depotted 15/60 NST's, (perhaps with secondaries
> removed?), and add or
> remove the NST's current limiting shunts to adjust
> current?  I think I
> also read that inductive ballast alone doesn't work
> too well, that there
> should be a resistive element also.  Any pointers on
> how this is done,
> or how necessary it is?

My system runs smooth & predictable with no added
resistance. Try it without any first--you can always
add resistance later if you need it.

> 
> Are people using PFC caps with pole transformers?
> 
> For my NST setup, I've been using a 240 volt 30 amp
> house line (electric
> clothes dryer), stepped down to 120 volt with the
> variac, to power the
> NST bank.  Would this be adequate for powering a
> pig?

I suggest 240vac operation.

> 
> 	Thanks,
> 	Bill Vanyo
> 

Regards,

Greg
http://hot-streamer-dot-com/greg 


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