Capacitor Discharge Unit Circuit Diagram

A capacitive discharge ignition unit also called the cdi unit is the modern alternative for the age old contact breakers which were quite crude with their functions and reliability.

Capacitor discharge unit circuit diagram. Capacitor discharge ignition cdi or thyristor ignition is a type of automotive electronic ignition system which is widely used in outboard motors motorcycles lawn mowers chainsaws small engines turbine powered aircraft and some cars it was originally developed to overcome the long charging times associated with high inductance coils used in inductive discharge ignition idi systems. See the completed wiring diagram for the connections to the capacitor discharge unit. A capacitor is a device that stores electrical energy in an electric field it is a passive electronic component with two terminals. When a point is operated the led wilt extinguish then come back on as the capacitor charges.

This video shows how to connect a capacitor discharge unit up to a power supply and a set of points using a switch to set the points. This type of ignition builds up a charge quickly. However 12 volts dc provides too little power to move the points reliably. A cdi ignition starts by generating a charge and storing it up before sending it out to the spark plug in order to ignite the engine.

The input to the cdi unit is derived from two sources of the alternator. The modern cdi is an electronic version of the contact breaker which uses sophisticated electronic parts for generating the required arching across the spark plug. The led can be placed on the main control panel of the layout to indicate the condition of the unit. A capacitor discharge ignition works by passing an electrical current over a capacitor.

Referring to the above capacitor discharge ignition circuit diagram we see a simple configuration consisting of a few diodes resistors a scr and a single high voltage capacitor. Should a solenoid be left in circuit by the switch being held for a long period the current flowing through the coil after the initial surge will be less than 0 05a so it will not damage to the coil. Cdi circuit using an scr a few resistors and diodes. Capacitor discharge ignition system working principle a cdi system.

The led will light to indicate when the unit is ready. The effect of a capacitor is known as capacitance while some capacitance exists between any two electrical conductors in proximity in a circuit a capacitor is a component designed to add capacitance to a circuit the capacitor was originally known as a condenser. Too high a voltage can also be a problem as the point motor may move the point over with so much force the point tiebar is shaken to bits.