Coil Quest Over (or just postponed?)

[garfield at pilgrimhouse.com]

On Wed, 03 Jun 1998 08:28:50 -0400, Clare Snyder <snyder at huron.net>
wrote:

>Just had an idea on the Nissan coils - anyone check them for continuity
>at, say, 80 volts? Mabee, just mabee, they have a HV diode stack in
>them?

Clever fellow. Where did you learn that? Heh.

I couldn't drag my HV diode continuity checker in with me (a bunch of 9V
batteries strung in series, with taps so I can increase forward bias by
9V at a time; I figured the parts guy might just be wise enough to think
of that as a potentially destructive testing appratus B), but there's a
Nissan guy on the list who's gonna see if he can't get a decommissioned
one send me for "further study", including disembowelment, if necessary,
to get to the bottom of this behavior.

Gar

P.S. For those who've never worked with HV diodes, what's going on here
is that say for an individual one that's good for a rev. breakdown of
say 10KV, because it's actually made up of scads of individual diode
junctions inside, it takes maybe 8-12V to forward bias such a critter.
Hence, on a normal ohmmeter, even with a "diode" setting, the applied
voltage (God, I HOPE so!) isn't sufficient to forward bias the diode and
make it come to life. Now, typically when these diodes are used to
isolate a portion of the HV circuit, like joining two coils together to
form a redundant pair (which is why in XAviation we know about these
things), several, up to maybe half-dozen are strung in series to provide
the 40-60KV protection that's needed against the IGN spike. Hence, if
you put 6 of em in series, it can take up to 60-80V to forward bias the
stack. That's where Clare (also an XA guy, BTW) is comin from. Heh.