1988-1995 Mercury Force 5HP Outboards Service Manual, 90-823263 793, Page 121Get this manual
cc SEM IGNITION SYSTEM
SEM ignition is true Capacitive Discharge Ignition with all of the standard components encased inside one moduleInside the module there are fou wire coils of various size and lengthThe module also contains several electronic components, which are used to control the voltage flow and strengthThe SEM flywheel contains magnets placed inside the outer rim As the flywheel rotatesthe magnetic field will cut through the ignition module core This core in turn creates stronger magnetic field inside the ignition module coilsThe first coil contains approximately 2500 turns of fine wire and is the charge coilFlywheel rotation will cause the charge coil to generate negative, positive and then second negative pulseA diode will eliminate the two negative pulses and supply the positive pulse to the capacitor for storageOnce the voltage is stored inside the capacitor, it is necessary to release this voltage through the primary windingsA small trigger coil with approximately 100 turns of wire will generate small voltage to ThyristorTrigger coil voltage is similar in form as the charge coilThe second negative pulse, the one right after the positive charging pulse is used to turn the Thyristor on The Thyristor, in turn releases the stored capacitor voltage to ground through the primary coilThis primary coilmade up of approximately 50 turns of heavy gage wire, is located closest to the core The sudden flow of voltage through the primary coil, induces voltage rise inside the secondary coilThe secondary coil has approximately 5000 turns of very fine wire Secondary voltage can reach approximately 30,000 volts, if needed, before bridging the spark plug gap and returning to ground