Working of the coil
By H. Kishie Singh

SOME weeks ago we talked about the battery and how and why it must be kept at full charge i.e.12 volts. This is the minimum that is required for the computer and electronic system of your car to work.

However to fire the spark plugs in the combustion chamber, voltage of up to 25,000 volts or more is required. That’s right — 25,000 volts!

That’s where the coil comes in. There are numerous wires of different sizes and materials. The coil required to generate 25,000 volts may be a kilometre long! Once the high voltage has been generated, special wiring is needed to transmit 25,000 volts to the distributor. If you look under the bonnet of your car, you will see normal-looking wires running from the battery to the coil. These are high tension (HT) wires . They go from the coil to the distributor and from the distributor to each cylinder, where the big bang takes place. The bang ignites the fuel-air mixture with such force that it drives the piston down.

The working of the coil, that is responsible for making the big bang possible, is as follows:

When electricity flows in a coil of wire, a magnetic field is created. The opposite is also true. When the electricity is cut off, the magnetic field generates its own electrical charge in any coil of wire.

Two windings of coil are better than one! So, the core — iron — which acquires magnetic properties has first a primary winding then a secondary winding. These produce a tremendous magnetic field and an electric charge from the low voltage of the battery.

There is a contact breaker point in the distributor (more on this later) and its job is just that — to break contact. This constant on-off system keeps the electromagnetic field working in the coil and induces the coils and magnet to generate the high voltage to the spark plug. From the plug, the current is transferred back to the body of the car and to the battery.

When you located the HT wires under the bonnet, you may have noticed that there is a wire bolted firmly on to the engine or gearbox and is attached to the body.

This completes the journey of the electrical charge back to the battery.

The coil is as important as the distributor in this whole circuit. The distributor is a mechanical link between the battery and the engine, regulating and distributing the electric charge. It receives the high voltage, the contact breaker point breaks the flow, via the rotor, which rotates and the charge is distributed according to the firing order of the engine!

In short, the process is as follows. You turn on the ignition key, and the connection between the battery and the coil is on and 12 volts flow into the coil. From the coil, the HT wire carries the 25,000 plus volts to the distributor, which distributes the electric charge to each individual spark plug. Bang, the engine fires up! That simple!

Happy motoring!