Re: coil running of car battery(s)?

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Ed Phillips <evp@xxxxxxxxxxx>

Robert,
If only I have killed many of them, usually from spikes in the gate,
they
are very susceptible to HV..

Although the circuit is similar to the one I used, being 30+ I have
actually
used the good old 2N3055, which is apparently much easier to kill, maybe
its
my experience, but i've only killed a couple in that circuit, and most
of
them are from shorts whilst playing, not "in service". I do have a 4nF
cap
and a reverse diode across then though.

        Cheers
                Derek"

	The shorts are probably due to "second breakdown" in the forward
direction at the peak of the voltage spike.  When the voltage goes above
a critical value the collector starts to draw a lot of current and
enters a negative resistance region where the current "run away" and if
the circuit resistance doesn't limit it the transistors will short.
There are 2N3055H's which have a somewhat higher breakdown I think, but
still a lot less than that of the 600V or 800V that transistors intended
to drive the horizontal deflection circuits of a TV. Lots of different
ones available as well as transistors intended specifically for ignition
coil drivers.

Ed