quesitions about a CDI ignition design

[Jerry]

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.

 

[Tilmann Reh]

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?

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

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?

Maybe...

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,

 

[Jim Thompson]

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


Maybe...

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,

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

...Jim Thompson