Re: purpose of a variac?

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Barton B. Anderson" <bartb@xxxxxxxxxxxxxxxx>

Hi Q,

An rsg is (normally) adjusted for minimal electrode spacing. It 
"will" fire at reduced voltages. I haven't read the documents your 
referring to, but I can only assume their thinking rsg (if static 
gap, then I would agree). Rsg's will fire at reduced voltages. As the 
voltage is turned up by the variac, the electrodes will arc sooner 
(before alignment).

An rsg is a voltage variable device. A static gap is fixed and can 
never increase it's voltage level unless there is a mechanical 
failure or simply misadjusted (but of course it can certainly 
decrease it's voltage level, i.e., thermal variation).

As far as "absolute voltage peak", consider the current waveform (bps 
dependent). The maximum power point is not at peak voltage. The 
current and voltage crossing can be looked at for various break rates 
(thinking rsg here, btw). It's been a while since I looked at this, 
but if memory serves, 240 bps develops it's maximum power point at 
22.5 degrees after peak. I believe most coilers running rsg's have 
found they need to adjust their firing a little after peak. Where 
it's adjusted for best operation is dependent on the actual 
breakrate, so there is slight variation between coilers.

Take care,
Bart

Tesla list wrote:

> Original poster: "Qndre Qndre" <qndre_encrypt@xxxxxxxxxxx>
>
> Hey coilers,
>
> I've read several documents on the internet which claim that the 
> power throughput of a TC can be adjusted using a variable 
> transformer to power the supply transformer of the coil. I don't see 
> how this could be done under regular circumstances. If the input 
> voltage of the supply transformer is reduced, it's output voltage 
> reduces as well. The voltage across the capacitors can never exceed 
> the supply voltage (unless you use resonant charging which may 
> destroy the secondary winding of your supply transformer). Since the 
> spark gap in the tank circuit is best to be tuned just to fire at 
> the absolute voltage peak for optimized performance it will never 
> fire with reduced input voltage to the primary circuit.
>
> Regards, Q.