CDI & Ignition Coil

CDI

A capacitor-discharge ignition (CDI) is built into the ECU.  Most 4-stroke ECUs provide a simple induction-coil ignition.  Although it would have been cheaper to construct an induction ignition, the TR280i definitely has a CDI.

Two-strokes benefit greatly from having a CDI because the rise-time of the spark event is so brief (which helps overcome plug fouling due to the rich and oily mixtures found in 2T engines).

The CDI uses a DC-to-DC converter to boost/invert 12-volt power to about -350 VDC to charge the energy storage capacitor which is internal to the ECU.

The K-Scan diagnostic software allows you to test the ignition, and create sparks at zero engine speed.  I observed the primary of the ignition coil with an oscilloscope and also fired the CDI into both capacitive and resistive loads.  Firing the ignition coil into a spark plug reveals a -225V pulse that lasts about 20 microseconds.  It has a very fast rise time (less than 500 ns).  Open circuit, the CDI capacitor charges to about -350 V.

This voltage is negative with respect to the chassis because the voltage required to eject electrons from the hotter, sharper center electrode is substantially lower (by about 30% according to some sources) than would be needed to eject them from the cooler, duller ground strap.

Ignition Coil

The ignition coil is marked “Japan 1G7107.”  I have measured the following parameters with a laboratory instrument. 

Primary: Inductance of 337 uH @ 1 kHz and a DC resistance of 0.271 ohms. (If you measure the primary resistance with a typical multimeter, it will measure somewhat higher, but should be well under 1 ohm.)

Secondary: Inductance of 5.08 H @ 1 kHz and a DC resistance of 6080 ohms.

Step-up ratio is 1:106.

The spark plug cap is nominally 5000 ohms.

Incidentally, if you replace the spark plug cap, it must have an internal resistor.  NGK part number TB05EMA (NGK 8636) is a suitable replacement.  They are waterproof (intended for use on watercraft), inexpensive, reliable, and readily available.