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Path: utzoo!watmath!watnot!watvlsi!ksbszabo
From: ksbszabo@watvlsi.UUCP (Kevin Szabo)
Newsgroups: net.auto.tech
Subject: Re: Hillman Huskey Parts (actually about ignition and condensors)
Message-ID: <2828@watvlsi.UUCP>
Date: Mon, 9-Dec-85 23:23:16 EST
Article-I.D.: watvlsi.2828
Posted: Mon Dec  9 23:23:16 1985
Date-Received: Tue, 10-Dec-85 06:16:17 EST
References: <2922@vax4.fluke.UUCP> <474@scgvaxd.UUCP>
Reply-To: ksbszabo@watvlsi.UUCP (Kevin Szabo)
Organization: VLSI Group, U of Waterloo
Lines: 39
Keywords: 1953 Hillman
Summary: 
Summary: Condensors are essential, but their value is not critical

In article <231@unirot.UUCP> grr@unirot.UUCP (George Robbins) writes:
>	The condenser associated with the points in a distributor is not a
>very critical component.  Any part intended for this application that is
>mechanically compatable should work fine.

The value of the cap is usually around .1 mfd; anything
in this order of magnitude should be fine... but ...

>       Also, the *only* way the condenser can keep the engine from
> running is if it is shorted out.  An open condenser will cause
> excessive erosion and metal transfer on the points, but the motor
> should still run.  There is not much middle ground, except a part that
> only shorts out when it gets hot.

I don't agree with this.  An open capacitor results in a
very weak spark; probably insufficiently hot to reliably
ignite the fuel mixture.  An ignition circuit is a basic
R-L-C combination (Resistor, inductor, capacitor) which has
a time constant and damping factor that ensures the stored
energy is dissapated at the plug.  If you reduce the C to
near-zero value the time constant is considerably shortened.
This results in the voltage building too quickly; it easily
sparks across the barely-opened points (resulting in the
excessive point erosion you noted).  In a correctly
functioning system the points are well open by the time
maximum voltage is created; in this case the spark plug is
the easier gap to bridge and the spark occurs there.

This is easily verified by experiment.  The next time you
are tuning up your non-electronic ignition car, try this:
Pull a plug (before touching the ignition) and crank the
ignition. (you might disconnect the other plugs so the
engine doesn't start).  Notice the nice, fat, blue spark.
Disconnect the condensor.  Now crank again and notice the
weak thin spark that is generated.

				Kevin
-- 
Kevin Szabo' watmath!watvlsi!ksbszabo (U of W VLSI Group, Waterloo, Ont, Canada)