FW: Driving an MSD Ignition Box

[robert dingli]

Hi guys,

All this talk about the MSD multi spark system reminds me about a VERY
interesting paper on the topic,


> > A scope trace diagram (without units) shows the multi-spark output
> > versus the output of a conventional ignition. The MSD box is shown as
> > producing 5 sparks for each one produced by the conventional ignition,
> > at 1,000 RPM. Each of the multiple sparks is shown as having similar
> > voltage and duration to the conventional spark. As RPM increases, the
> > number of sparks decrease. I can't find anything in the literature to
> > confirm this, but I have heard it said that above 3,000 RPM, the MSD
> > boxes are only giving one spark.
> 
> I did some measurements a while back on an MSD 6A.  I looked at the output
> with an oscilloscope while varying the input frequency (RPM) with a
> function generator.  I plotted the number of sparks vs. RPM for a
> 4 cylinder engine.  I'll post the data hopefully tomorrow.  As I recall,
> the number of multiple sparks drops off quite quickly as RPM rises.  And,
> compared to 4 cylinder applications, 8 cylinder applications will drop
> off twice as fast.  The only way I see of improving this is to use two MSDs
> instead of one, with each firing half of the cylinders.
> 

I have an SAE paper here somewhere (details to be posted upon discovery)
by researchers at Toyota and Nippondenso.  It is a combination inductive/CDI
ignition system which has the characteristics of a huge initial spark
voltage (CDI) and long duration (inductive).  One of the side benefits is
that the inductive and CDI sections of the circuit can be charged while
the other is discharging.  With suitable control, this allows a continous
discharge - ie no charge time delay between sparks.  The setup called for 
a separate coil from the main tranformer coil to store the inductive energy,
and of course a capacitor for the CDI energy.  Both sub sections then 
discharged through a single transformer coil.

> I also have a schematic of the MSD 6A, obtained the brute force way
> (reverse engineering).  It is consists completely of discretes, no
> ICs.  I guess I could send someone a copy if they were interested.
> 

I, for one, would be very interested to see how simple the system actually is.
I have the capability to multi spark my current system but will wait until
I ditch the dizzy totally. The small cap (originally designed for points)
tends to crossfire at the slightest provocation.

Robert 'looking for that paper' Dingli

-- 
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             Robert Dingli           r.dingli at ee.mu.oz.au

Power and Control Systems                 Thermodynamics Research Lab
Electrical Engineering                    Mechanical Engineering
   (+613) 344 7966                           (+613) 344 6728
  University of Melbourne, Parkville, 3052, Victoria, AUSTRALIA
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