Coils for ION ...use regular coils? Thought #2

[Walter Petermann]

garfield at pilgrimhouse.com wrote:
> 
> On Fri, 29 May 1998 15:47:16 -0500, Walter Petermann
> <corsaro at brokersys.com> wrote:
> 
> >I read on a previous answer that the coil secondary and coil
> >primary have one end connected together to the minus
> >terminal. If this is true,
> >the firing current must also pass through the primary (when
> >the minus terminal is 'let go' to fire). Wouldn't you be
> >able to monitor the current through a resistor connected to
> >the positive terminal? Then just ignore the current reading
> >during dwell.
> >
> >...disregard if I misunderstood the bits of conversation
> 
> Nope, you understood right. It's just that this common point we're
> talking about is tied to either gnd or +BAT already, during the time we
> need to measure the current in the secondary (that's essentially, as you
> observe, what we need to do, since that's the same current as what's
> passing throught the plug and the ionized gases).
> 
> So OK, mental picture time; you have the common point tied to +BAT, and
> the other side of the primary is of course floating (you've OPENED the
> primary to collapse the field and fire the plug). So here we have a
> secondary winding, one end of which is tied to a low impedence source,
> and we need to impress 80-400V on top of that, and measure the current!
> which is on the order of a microamp!! You don't wanna be doing that in a
> low impedance circuit that has to supply 8-10A during the rest of it's
> workday.
> 
> Lemme just appeal to my betters, and say you won't find any of the
> patent authors trying to do THAT! Heh. Instead, for these kinds of
> autotransformer setups, they just isolate the measurement circuit from
> the secondary with HV diodes and cut to the chase.
> 
> Hope this helps explain the vagaries a tad better. Always need to
> consider the scales of things, like the primary current levels compared
> to the ionization current levels. That's why you need SOME form of
> isolation, at least from the primary, and if not, then from BOTH primary
> and secondary circuits. Hence, either an independent secondary, or the
> HV diodes. Those are the ONLY two alternatives I've seen in ALL the
> patents so far, and also the only ones I can see would work, also.
> 
> Gar

Gar,
I dug through an old Haynes manual for a Volvo 240 (76-93).
A picture of the coil shows primary and secondary connected
to the minus terminal. If this is true (I have found
misleading info before in Haynes manuals), then how's this
sound..

Power through heavy duty diode into the positive side of
coil
One meg resistor to 80 volts (did some homework) on negative
side.
When the ignition lets go of the neg side, the current
through the resistor will flow through the secondary
(primary blocked by diode).
A 1uA current will only drop one volt through the resistor.

PS Are the schematics for the electronics available on the
web? The best I could find were block diagrams and papers
from SAE (I could get those from UH library...)

 Walt