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CDI Ignition System

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alexb1406

Member
The ignition CDI boxes (two of them) have both failed on my Moto Guzzi V65. New ones are not available - I can get aftermarket replacements for a price but I think it might be fun to try to build my own.

I'm sure I'll have more questions along the way but my first is this:
On all possible circuits I have found online, the output of the CDI module is wired to the positive side of the coil (see links 1 and 2 below). On all motorbike wiring diagrams I have seen the module output is connected to the negative side of the coil. The wiring diagram for my own bike shows it wired to the negative side of the coil - and it is! (See link 3 below). I don't remember seeing any vehicle - car or bike - that has the coil controlled from the positive side. I want to keep my wiring original as much as possible and don't really want to swap coil polarities, so how do I make these work to control the negative side of the coil?

https://www.homemade-circuits.com/how-to-make-capacitive-discharge/
https://www.homemade-circuits.com/dc-cdi-circuit-for-motorcycles/
http://www.thisoldtractor.com/guzzi007/schematics/1986_V65_Florida.gif
 

crutschow

Well-Known Member
Most Helpful Member
The first circuit won't work unless you have a high (100Vac) voltage tap available from the alternator.

The second circuit should work okay if you connect the cathode of the output diode D7 to +12V instead of ground.
 

alexb1406

Member
It will be a DC system - I haven't yet decided on the final circuit but it will probably be made up from separate sources, i.e. an inverter and the CDI unit.

Re diode D7, is this what you mean?
 

crutschow

Well-Known Member
Most Helpful Member
Re diode D7, is this what you mean?
Yes.
But physically it would probably be more convenient to connect it to the +12V going to the CDI unit.
 
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