Multi Spark Ignition...

[Darrell Norquay]

Jim:

>   Has anyone here ever played with multi spark ignition? Where instead of firing
> once the plugs fire 5 to 20 times very quickly. I saw one of them a few days ago

Got one in my beater.  Works great.  Easier starting, better idle, very
slight increase in power, but 40%??? No way...

> know that it will burn out the ignition coils I have (junk ford coils)

It won't burn out the coils, the output is current limited...


> for all you people out there that know what you're doing. Is a 6amp @ 100V 
> transistor enough to switch the power conections to an injector and a 
> standard ignition coil?

Injector, maybe, coil no.  You need a high voltage (450V) transistor for
the coil driver, because the coil gives high back-emf when you switch it 
off.  Also, you will need some transient protection diodes and possibly 
a zener or two to protect the transistor.  Ed Lansingers article in 
Circuit Cellar Ink #63 (Oct 95) has a pretty good example of how it should
be done.  The output transistor is an SK10117.  Rating would need to be
at least 15A, 450V.  (for the cheap solution, use the horizontal output
transistor from an old TV)

As far as the injector goes, if it is a low resistance (1-2 ohms), you will
need to current limit the driver.  Resist the urge ;) to just use a resistor 
to limit current, it will dissipate much too much power and drop the voltage
enough so the injector may not open.  Use active current limiting. 
If it is a high resistance (10-15 ohms), just hook one terminal directly to 
the +12 rail, and the other to the transistor.  The transistor will complete 
the circuit to ground.  The injector will have a much lower back_emf than an 
ignition coil, but the transistor voltage rating will still need to be around 
100V, with a current rating at least 50% higher than the injector draws to 
provide a good safety margin.  You will still need some clamping circuitry to 
protect the transistor from transients.
 
regards
dn

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 Darrell A. Norquay              Internet: dn at dlogtech.cuc.ab.ca     
 Datalog Technology Inc.         Voice: (403) 243-2220
 Calgary, Alberta, Canada        Fax:   (403) 243-2872            
 
       "Absolutum Obsoletum" - If it works, it's obsolete    
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