Re: Considering Upgrading to Pole Transformer

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

Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>" <Esondrmn-at-aol-dot-com>

In a message dated 12/15/01 3:54:58 PM Pacific Standard Time, tesla-at-pupman-dot-com
writes: 

 -  snip  - 
>
> 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 don't have one.  Can NST's be used?  Could one use one or more 
> 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? 
>
> 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? 
>
>    Thanks, 
>    Bill Vanyo 
>
>
> Bill

, 


I would suggest running the 15/60 nsts on 240 volts.  This will allow you to
use the full range of the variac and should provide better control.  Connect
two primaries of the nsts in series then connect in parallel with the other two
also connected in series.  A 240 volt 30 amp service should be ok for a 5 kva
transformer, that is what I use.  I have used an arc welder for ballast but now
use a 50 amp variac.  The nst primaries are not designed for 30 amps and I
would not suggest using them.  I have heard of folks using microwave oven
transformers for ballast.  I use a sync rotary gap.  The new sync triggered
static gap might work up to 5 kva with lots of air flow.  I don't know if other
coilers are using this gap at higher power levels or not.  About the capacitor
size - the 5 kva transformer will supply all the current that you need to
charge a large capacitor.  It depends on the resonant frequency of the system
an! d of course the size of the primary.  For pig powered coils, bigger is
better for capacitor values.  I use .05 mfd, others use larger. 

Ed Sonderman 

Ed Sonderman