Electronics

Scullman · Joined: 20 Sep 2006 Posts: 2

I have a project I'm working on and I wonder if there are any experts/semi experts out there that could look at a schematic from the 60's and see if it could be improved or updated. It's a vintage motorcycle CDI circuit.
I am going to be putting a few of them together and am curious to know if there is a better way or just go with the current design.

The schematic is here and the red boxed items are external of the CDI unit.

neon · Joined: 25 Feb 2006 Posts: 570

Thanks for the clear schematic but i am confused why 3 coils ? I guess i don't know this setup. for a car all i used to have a DC 12v converter to 400v DC one cap of 1mfd 450 volts which translate to about 100 mw per plug. so no suggestion because i have no idea of the setup but i would suggest that you either put one capacitor of lesser value or at least add two resistors across the cap to equalize the voltage like 100k if one breaks down the other can survive.

Scullman · Joined: 20 Sep 2006 Posts: 2

Hey Thanks for the reply.....I should have stated it is for a vintage 3 cyl 2 stroke motorcycle.

On the capacitors, different models use a 2.0 mfd 500v in which I was going to incorporate.

Does anyone know if a "Pulse Capacitor" would work well in the place of the two 4.7mfd-450v cap, but in a 2.0mfd 500v rating ???

neon · Joined: 25 Feb 2006 Posts: 570

right now in your setup you do have 4.7mfd in series which translate to 2.35 mfd you never had 4.7mfd that would make the spark hot and destroy the plug itself. In addition without the equalizing resistors as a sugested you finaly have 2.35 mfd at one capacitor rating whatever that is. 2 mfd is what you want possibly a mylar at 2mfd/>450v.And finaly don't forget capacitors can be lousy in tollarences +-10% or more.

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