CDI ignitions

[MonsterNine]

Just wanted to find out who else has made their own CDI ignitions before or what other have done to build up an ignition from non OE parts. A replacement CDI for my Tohatsu 30 is ~$180. Seemed too much for what it was and I don't like the power pack and coils all in the same unit. Plus I want to be able to hack and mod it. I disassembled the factory CDI to see what they had in there and figured out the circuit and found quite a few other circuits to build a CDI. Built a simple CDI for ~$30 and discharged it through a couple of OMC coils I had and it works great so far. Haven't had the engine under a load yet but the spark is strong and timing is rock solid (so far). I want to try a dual post coil and different size storage capacitors to see what works best. The pic of the factory CDI is without the 4 mfd capacitor and the two coils (discharged parallel).

[Mark75H]

Good job. I always like breadboard projects

[microbream]

motorcycle cdi boxes can be had from $30 up, the only problem is finding out the advance curve spec. However if you have mechanical advance cdi ignition like my suzuki then a cheap DIY option is perfect.

[MonsterNine]

I have looked at some DIY motorcycle CDI ignitions and have found some schematics that people have reverse engineered. Some are very simple with no timing advance and some use two pulsar coil inputs to change the timing, some use a simple RC circuit to advance and/or retard the timing and some are programmable. Most of the cheaper MC ignitions are for single cylinder motors with no advance and trigger on the negative going edge of the stator charge coil which is different than most outboards as far as I know. My 30 is a twin, has no built in advance in the CDI, and uses the wasted spark method to fire the plugs so I think I need a larger storage capacitor than the single cylinder CDIs have. Some of the dual tower coils require only the power of a single cylinder CDI capacitor as each side of the secondary coil goes to a spark plug. I'll have to check into some of the PWC coils. They have a lot of dual tower coils and MSD makes one for them too. I'll have to check with them to see how they are wired.

My grandson has a Honda 50 in the garage that I may have to *barrow* the CDI from and I have an OMC twin power pack that I will have to try to figure out. The charge and pulsar coils are wired differently.

Another breadboard down and 999 to go :)