Ballast Resistor

• The ballast resistor is provided in series with the primary winding in a battery ignition system to regulate the primary current. This increases the life of contact breaker points.
• At low speeds the increased resistance decreases the amount of current in the primary circuit of the ignition system and thus avoids overheating of coil.
• At higher engine speeds, contact breaker points are closed for shorter time and so the current in primary circuit is less due to which the resistance of ballast resistor is also less. Therefore the resistor guards against any secondary voltage drop that may occur at higher speeds and be undesirable.

Capacitor

• Electrical energy is stored in a charging capacitor in electronic ignition systems. At ignition time, when the capacitor- primary winding circuit is complete, the capacitor discharges instantaneously causing a sudden current flow which induces a high voltage surge in the secondary winding.
• This causes spark to occur at the spark plug terminals. This voltage has a very fast rise time (3-10 kV/μs) compared with a conventional inductive system.