[Spridgets] DIY MSD

[Dean Hedin]

I finally finished putting one of these together:

http://www.molla.org/DIY-CDI/SC-DIY-CDI-article-hires.pdf


I'm triggering it with a Pertronix.

It did not proceed without issue.  On the first test drive the
box blew about 1 mile from home.  I towbar'd the car home.

What had happened was that I wound the transformer with the primary 
"inside" (first) instead of "outside" (last).  

The primary gets hot when the rpms go up.  So it ended up melting insulation
and shorting out.  I rewound the transformer properly and with larger gauge
wire and all is OK now.

There is a noticeable improvement in ease of starting and idling,
especially after I opened the plug gaps out to .060 inch.

I think this unit is actually better than a commercial MSD6 unit.  
It only goes to 300v on the primary of the ignition coil which is better
in preventing crossfire between the plug wires.  It will also run on a lower
battery voltage than an MSD.

There are easy parts substitutions that can be made for those ambitious 
enough to pursue this project:

Q1,Q2 MTP3055E can be replaced by IRL540
IC1,IC2 IR2155 are now known as IR21531 in the Digikey catalog.
Q6,Q7 IRF822 can be swapped to IRF840

All the parts can be acquired online from Digikey.

As an interesting side note, while I was hooking up the towbar a couple came
over from a house nearby to check out my car.  Turns out the woman had
inherited a Bugeye from her father.  It's been sitting since the 70's
She does not want to part with it, but she doesn't have the money to get it
back on the road at this time.

I told her I would stop by and give her a ride in mine after I got the bugs
worked out..  Maybe a little motivation will help her along.