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Path: utzoo!watmath!watdaisy!gvcormack
From: gvcormack@watdaisy.UUCP (Gordon V. Cormack)
Newsgroups: net.auto
Subject: Re: eliminating distributors
Message-ID: <6845@watdaisy.UUCP>
Date: Sun, 6-Jan-85 13:23:03 EST
Article-I.D.: watdaisy.6845
Posted: Sun Jan  6 13:23:03 1985
Date-Received: Mon, 7-Jan-85 02:31:52 EST
References: <458@amdcad.UUCP>
Distribution: net
Organization: U of Waterloo, Ontario
Lines: 47

A number of fallacies have been perpetrated in the discussion of
electronic ignition.  I wish to address some of these.

First, an ordinary ignition coil has a step-up ratio of only 80:1,
not 1000:1 as suggested.  In fact, when the breaker points open,
a potential of about 400 volts occurs across them and hence across
the primary circuit of the ignition coil.  Most electronic ignition
systems operate with a nearly identical coil, but apply a 400 volt
power supply directly to the primary of the coil, rather than depending
on the inductance of the broken circuit.

Supplying the 400 volt supply does, of course, require another step
up transformer .  This transformer is (relatively) low-voltage and
low-power (It is of similar complexity to that found in the 6V
battery replacement that drives your Walkman radio).  Furthermore,
this 400 volt supply can be shared among the ignition circuits for
all the cylinders.

It is infeasible to switch the 32kv output from the coil using
semiconductor electronics.  I can buy conventional coils for <$10
each at my local Canadian Tire store, so I don't see how the manufacturing
cost could be much more than a couple of dollars.  For a production
system, the manufacture of four (or six) -plexes of coils would be
of comparable complexity to the manufacture of the distributor.

I would like to defend the conventional distributor a bit.  First,
it is a simple and reliable device.  I have NEVER had to replace
a distributor cap (except one I smashed in an accident), nor have
I had to replace a rotor.  Shorting is caused either by poor sealing
in the original manufacture or by some nerd removing the cap (which
is not necessary with a breakerless ignition).

Second, the distributor provides dynamic timing adjustment as well
as switching the high-voltage ignition pulses.  A centrifugal 
mechanism advances the timing at high engine speed.  A vacuum advance
retards the timing under heavy acceleration or when the engine is
about to stall.  In order to replace these devices, one has add
transducers and a considerable amount of logic to the ignition system.

In conclusion, I think that totally electronic ignition systems will
eventually take over from mechanical.  However, the complexity of the
system is increased, albeit encapsulated in some multi-hundred 
dollar "control module".  That control module will require no 
adjustment during its lifetime.  But when it fails, don't expect
to be able to dry it off with a rag, or to file it down a bit, or
do anything else other than to call a tow truck and wait while your
local garage orders a new one.