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Re: Another ballast question

Original poster: "Bert Hickman by way of Terry Fritz <twftesla-at-uswest-dot-net>" <bert.hickman-at-aquila-dot-net>

Weazle and all,

As I recall, this was reported as a problem (perhaps last year?) on a
variac that was used as a ballast inductor. There will always be a degree
of autotransformer action with any tapped or variable choke. Even with a
tapped choke designed to have a 10:1 current range, the effective "step up"
ratio will only be a little over 3:1. 

Because of interaction with the tank cap, under some operating conditions
you may see peak voltages of 1-2 kV developed across the entire ballast,
but this shouldn't be a problem for a well constructed homebrew ballast.
Connecting a resistor across the entire ballast may add some resistive
damping, but it will otherwise have little effect in reducing the magnitude
of the induced voltage. 

-- Bert --
Bert Hickman
Stoneridge Engineering
Email:    bert.hickman-at-aquila-dot-net
Web Site: http://www.teslamania-dot-com

Tesla list wrote:
> Original poster: "J. B. Weazle McCreath by way of Terry Fritz
<twftesla-at-uswest-dot-net>" <weazle-at-hurontel.on.ca>
> Hello Coilers,
> Someone had mentioned the other day about having taps on the ballast
> inductor can cause it to behave a bit like an autotransformer with the
> windings beyond the tap point being subject to possible high voltage.
> What would the effect be of putting say a 50 or 100 ohm, high wattage
> resistor across the entire ballast winding so that when a tap point
> is chosen that leaves "unused" windings, the voltage developed there
> would have somewhere to go?
> Perhaps it would create another problem, while solving the first one,
> but I didn't think it would hurt to ask about it, as possibly it has
> already been tried by someone on the list.