# Re: progress report, and question

```Tesla List skrev:
>
> Original Poster: Bert Hickman <bert.hickman-at-aquila-dot-com>
>
> Tesla List wrote:
> >
> > Original Poster: Finn Hammer <f-hammer-at-post5.tele.dk>
> >
> <SNIP>

> > I wouldn`t attempt to start the coil up, without a variac, so I`l buy a
> > 16 A variac, (any European members got one?) but are there other ways
> > that I should controll this beast. I have read about ballasting, but am
> > not quite clear about, what it means.
> > In the readme file of rotjit, the author mentiones that it is
> > necessacary to use an inductor upstream, and I could wind a choke if
> > needed be, but which walue should it have, then?
> >
> > Cheers, finn
> >
> <SNIP>
>
> Finn,
>
<snip>
> Typically, the leakage inductance of a distribution or potential
> transformer is very low (Less than 1 mH) compared to the inductance of
> your ballast, and can typically be neglected. You can approximate the
> amount of loaded ballasting inductance you'll need:
>
>    Let V = Mains input voltage
>        f = Mains frequency
>        I = Maximum desired Mains Current (RMS)
>        Z = Desired Inductive Reactance
>        L = Required inductance (H)
>
>        Z = V/I = 2*Pi*f*L
>        L = V/(I*2*Pi*f)
>
> For example, for 3 KVA and 240 VAC at 50 Hz, the resulting RMS current
> would be 3000/240 = 12.5A. Solving for the required inductance:
>
>        L = 240/(12.5*2*3.1416*50) = 61 mH
>
> If you do decide to wind your own, make provision to either adust the
> inductance or provide taps off the winding so that you can later select
> other values for greater power control and higher-power operation.
>
> Hope this helps!
>
> -- Bert --

Thank you for an excellent answer.

Of course I`l do whatever I have to do, there might even be space enough
in the core window to build in a movable shunt, like the one used in
welders, and this, I think, would be the most elegant solution.
But the idea of limiting the short circuit current is counter intuitive
to me. I would think that the faster I could charge the cap, the better.
Particularly with future RSG in mind.
The only reason that I can think of is quenching of the gap: If the gap
presents as low an impedance to 50 Hz, as it does to 150KHz, then an
unlimited transformer would feed a lot of energy into the gap, once
fired. It would be nice if the gap effectively open circuited the
transformer, when it fires, but I guess nature isn`t that kind.

Is this it, or is there more/other reasons?

cheers, finn

It`s better to understand, than poke around in the dark.

```