CDI component diagram, build your own?

[job-grecos]

Anyone happen to have a component diagram for a CDI/Power pack? Or maybe someone has removed the resin from the little blue case to reveal it's secret.

 

[pnwboat]

Re: CDI component diagram, build your own?

I did away with my Prestolite ignition system with the blue CD modules and coils on my 1988 125HP motor. Installed a later model 1996 - 1999 Mercury CDM ignition. It acts like a different motor now. Fires right up on the first try, I can putt around in gear at 500 RPM's smooth as silk pretty much all day, or I can rum at 4500 - 5600 RPM's for hours at a time. Best modification I ever did to the motor. Much easier to trouble-shoot too.

 

[Frank Acampora]

Re: CDI component diagram, build your own?

Can't give you a diagram, and the potting is permanent--you will destroy the CD box trying to remove it.

BUT: I can tell you the basic operation. Each CD box has two separate circuits. Each circuit is a capacitor that is charged by the stator, and a gate transistor that is opened by the trigger to dump the capacitor into the coil. Of course, there are more components inside, but if you do electronics, you should be able to design a serviceable unit. You simply need to know that the stator voltage is about 250 and one capacitor charges negative while the other charges positive. Gate transistor is low voltage from the trigger coil, about 1/2 volt (I think)

Each box also has a short to ground wire (white) which is used to stop spark and stop the engine. Don't know if it shorts the capacitor or the gate transistor, but seems logical to me to short the low voltage transistor so it can't open and fire the capacitor.