CD Ignition

[John Dammeyer]

At 08:46 PM 16/08/1996 +0100, you wrote:
>In message <m0ur9Rl-000VwGC at comm.amtsgi.bc.ca>, John Dammeyer
><johnd at islandnet.com> writes
>>Hi,
>>
>>Has anyone have an article on the theory or even a schematic of a Capacitive
>>Discharge Ignition.  In particular are they just stepping up battery voltage
>>to about 300V and then switching that with a shorter dwell time or is there
>>more to it?
>>
>>
>Basically the spark energy is held in a capacitor and the coil used as a
>transformer,  i.e. as electrostatic  ( whereas a straight coil system
>stores it as magnetic). I am pretty sure they are not that good for
>starting as the spark can be high energy but is always very short
>duration.
>-- 

Oh contrare.  Back when I lived in Edmonton (-40C temps.) I installed a CD
ignition into my Datsun 510.  Car still had to have the block heater plugged
in just to warm up the oil and so the starter could turn the engine over but
in situations where the car was cold the difference after the CD ignition
was nothing hort of miraculous.

It's just this news group is about DIY EFI and that usually also adds
ignition since the parameters are there for it.

So if I know when to fire the plugs I can program the micro to appy current
through the coil for n milliseconds to keep dwell constant and coil heating
down.  So lets say 5ms dwell at 12 volts and a coil resistance of 12 Ohms.
Then we have 1 Amp for 5 ms and when current is broken, fild collapses and
ignition occurs.  At cold temperatures and a battery voltage of 6 volts
during cranking we get only 500ma and much less energy.  So.... do I step up
the voltage to 24 volts with a switching power supply and decrease dwell by
50% and then still trigger the coil with the FET transistor.  

In other words, before uComputers was the CD Ignition with the Capacitor and
the SCR just an elegant solution to the problem?

John.

Pioneers are the ones, face down in the mud,
with arrows in their backs.
Automation Artisans Inc.      Ph. 604-544-4950
6468 Loganberry Place         Fax 604-544-4954
Victoria BC CANADA V8Z 7E6