# Re: SISG and primary voltage.

```Original poster: "S&JY" <youngsters@xxxxxxxxxxxxxxx>

Aaron,

One important reason for using higher voltages relates to the energy that
gets stored and released in the primary "tank" capacitor (e.g. MMC).  The
energy is 0.5 * C * V * V  (half CV squared).  In other words, the stored
energy goes up as the square of the voltage.  So comparing a 100 volt supply
with a 10,000 volt supply, the "bang" Joules would increase by a factor of
10,000.

Thus, to use lower voltages and maintain the same bang energy, the tank
capacitor size would need to be increased significantly, requiring the
primary inductance (turns) to be decreased substantially to stay in tune
with the secondary.  This usually is not good because higher inductance
primaries are typically more efficient and reduce the stress on the primary
capacitor.  Better is to substantially increase the secondary inductance (to
lower the resonant frequency) to allow more primary turns with a bigger
primary capacitor.

The other thing one can do is increase the break rate which increases the
average energy into the coil, which, up to a point, increases streamer
length.

That being said, some of the DRSSTC coils perform amazingly well using line
voltage multipliers (several hundred volts DC) instead of transformers to
power their coils.

--Steve Y.

----- Original Message -----
From: "Tesla list" <tesla@xxxxxxxxxx>
To: <tesla@xxxxxxxxxx>
Sent: Wednesday, May 24, 2006 10:34 AM
Subject: SISG and primary voltage.

> Original poster: "J. Aaron Holmes" <jaholmes@xxxxxxxxxxxxxxxxxx>
>
> I've been following the SISG threads closely...even
> ordered parts to play with!  But my experience is
> primarily with classical SGTCs, and my grasp of the
> theory largely limited to rules of thumb, so I'm a
> fish mostly-out-of-water with all this solid-state
> stuff! :-((
>
> In particular, it occurs to me that I now no longer
> understand why one would opt for a HV transformer with
> SISGs around.  I've got more ~2kV MOTs than I know
> what to do with, but why even go *that* high?  Why not
> take an OLTC-ish approach and charge the caps straight
> from the rectified mains?  With SGTCs, the importance
> of quenching and the difficulty of quenching at low
> voltages seems to dictate that some amount of HV-ness
> is *required*, not just *good*.  With the quenching
> argument gone, can somebody attempt to explain (for
> the non-EEs among us--me included!) why one might opt
> for a HV SISG coil versus a LV one?  I'm sure there
> *are* reasons for one over the other (i*i*r losses,
> perhaps?), but the factors aren't all obvious to me.
> Some people are all about efficiency, but if similar
> output can be achieved in the SISG coil by losing the
> HV transformer and bearing some IGBT heating instead,
> that would also be "cool" :-)
>
> ---
>
> Thanks, Terry and company, for proving that modern
> technology might actually be able to *simplify* coil
> construction :-))  Always thought it had to be so, but
> I've seen relatively few examples of it until now.
>
> Regards,
> aaron
>
>
>
>
>

```