How Yamaha CDI WORKS?
(Thanks to Mike and Gottfried who provide a "nacked" CDI)
Description
In the cover of alternator are two
pickup coil exciting by two
magnets fixed to the flywheel.
Each time a magnet pass in front of a sensor, this one provide a pulse.
The tension is proportional to the engine speed
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The first sensor to be excited supplies pulses on the
white/red wire with 36° advance.
A few millisecond later, the second sensor to be excited supplies
pulses on the white/green wire with 12° advance.
This two sensors produce alternatives pulses. (goes from ±2v while
kick-starting to ±10v at low RPM until ±20v at high RPM)
The
green wire is the common point of these two sensors.
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While kickstarting and when pickups are disconnected from the
CDI, the pickup provide ±2volts :
At starting of the engine, the pulses of the 1st
sensor are blocked.
Only the pulses of the 2nd sensors are used to
obtain 12° advance and not risk a kick back.
The pulses of the 2nde sensor load a condensator.
At the end of the load, the pulses of the 1st
sensor will be used.
Between 12° and 36°: the pulses of the 2nd
sensor (in 12°) load a cell (resistor - condensator) to obtain a
Frequency-Voltage conversion.
(More rpm increase, more the tension increase.)
This tension is going to serve for delaying the pulses from the 1st
sensor (in 36°) through a monoflop.
The monoflop is going to activate the thyristor.
At low revs, the pulses of the 1st sensor are so
delayed that they do not start the thyristor.
The more the revs increases, the more the delay decrease and the more
the spark will be will produce early.
By safety or simplicity, pulses from the 2nd sensor (in 12°) activate once again the thyristor.
The tension of 400Volts produced by the alternator loads a condensator through two transistors to supply the power of the CDI.
Schematic.
Draft:
(Thanks to Gottfried for this draft)
Synoptique.
