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Re: efficiency of spark gaps vs tubes
---------- Forwarded message ----------
Date: Mon, 6 Oct 1997 11:18:17 -0500
From: Geoff Schecht <geoffs-at-onr-dot-com>
To: Tesla List <tesla-at-pupman-dot-com>
Subject: Re: efficiency of spark gaps vs tubes
>
> ---------- Forwarded message ----------
> Date: Mon, 6 Oct 1997 10:59:50 +1200
> From: Malcolm Watts <MALCOLM-at-directorate.wnp.ac.nz>
> To: tesla-at-pupman-dot-com
> Subject: Re: efficiency of spark gaps vs tubes
>
> Jim,
> Correct me if I'm wrong, but....
>
> > From: Jim Lux <jimlux-at-earthlink-dot-net>
> > To: Tesla List <tesla-at-pupman-dot-com>
> > Subject: efficiency of spark gaps vs tubes
> >
> > Geoff Schecht made a comment to the effect that tubes were more
efficient
> > than spark gaps. I made the same comment to James Corum and he pointed
out
> > that really wasn't the case. With a Class C tube amplifier, the best
> > practical efficiency is around 65-70%, that is, the switch (i.e. the
tube)
> > is dissipating 30% of the DC input power. In a spark gap, the switch
is of
> > very low resistance, and dissipates very little power, and with a low
duty
> > cycle to boot. For a short gap in air, the voltage drop is going to be
> > around 50 volts, so on a 15 kW coil with the primary at 15 kV, you are
only
> > dissipating, at most, 50 Watts in the gap. This is 99+% efficiency.
>
> I rather think that Igap seems to have disappeared from the equation?
>
> Malcolm
> <huge snip>
>
Right you are Malcolm. I made a previous post agreeing that gaps will
generally have less drop than hard-vacuum tubes. Sustaining voltage not
only is a function of gap length but also is a function of gas mixtures,
pressure, etc. In the Kettering ignition system used in all petrol engines,
the sustaining voltage of the spark plug's gap increases both as a function
of increased cylinder pressure as well as the changing composition of the
gas mixture that occurs during combustion. It's interesting to watch that
happen on a scope, BTW. A further question, then: what of an air SG? Does
the increase of ozone, H2O and NOx gases in the gap during firing radically
alter the voltage profile?
Geoff