My sugestion is to start to research about capacitive discharge ignition.

----- Original Message ----- 
From: "Sascha" <sascha@go.ro>
To: "'Microcontroller discussion list - Public.'" <piclist@mit.edu>
Sent: Wednesday, November 03, 2004 4:08 AM
Subject: RE: [EE]:Coil core saturation


> Hi guys,
>
> I am designing a multispark ignition for my car and I encountered a 
> problem.
> I whant to know how much time the ignition coil needs to be driven so it
> stores the maximum magnetic field in it's core. Unfortunately I can not 
> find
> the specs of the induction coil so I can compute it. Is there any way I 
> can
> find this time? The induction coil has a primary winding of about 200 
> turns
> and a secondary winding of 20.000 turns. That's all I could find about it.
> If I keep the driving transistor saturated too much I loose power and if I
> turn it off too soon I will loose energy in the spark. None of this is
> acceptable.
> First I thought of adding a emitter resistor and measure the voltage drop
> across it. But this again means power loss 1.5V across the transistor, 0.5
> across the resistor and if the battery is not very strong when I try to
> start the car it will drop to 9-10V so the remaining voltage across the
> induction coil will be as low as 7V. And this will translate as a weak 
> spark
> right at the moment where I need the strongest.
> I want to drive the coil with a BUT12 transistor which is driven by a PNP 
> or
> a PMOS.
>
> Any suggestions?
>
> TIA,
> Sascha


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