quesitions about a CDI ignition design

Greetings, I have a few questions. My outboard 1994 Suzuki 2 cycle 9.9hp two cylinder CDI unit is dead. I have looked at the waveforms from the coils under the flywheel, magneto, charging and the two pickup coils all have healthy outputs. Very little input to the coils that drive the spark plugs. I want to build the circuits, IGBT and charging cap, and get the motor running again. My questions are these:

The waveform from the two pickup coils have a leading negative going pulse followed by a positive going pulse. Which edge do I use to fire the IGBT? Also the plate that holds all the coils under the flywheel rotates with throttle movement. This is some sort of mechanically coupled timing advance. Would I need some sort of electronic control of spark timing in addition to the mechanical one?

Thanks in advance.

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Jerry schrieb:

I would assume that the positive waveform is being used for ignition. But that's just a guess...


I once reverse engineered the CDI unit of a small Honda bike. They used a thyristor design that was fired when the input voltage went above some rather large treshold. Due to the faster rising at higher speeds, ignition time advance was achieved without mechanically moving parts. I believe that the ignition coil was simply a part of the generator...

However, if your bike uses mechanical timing advance, it might as well use the zero crossing of the input signal, or a very low treshold.

I think it's best to try to get a similar CDI unit (need not necessarily be from exactly the same bike type!) for some measurements - and for verifying that your unit is dead and your coils are OK...

Good luck,

Dipl.-Ing. Tilmann Reh
http://www.autometer.de - Elektronik nach Maß.
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Tilmann Reh

Firing point is likely the zero crossing *after* the leading negative-going pulse. This would be independent of speed.

...Jim Thompson

|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
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Jim Thompson

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