An ignition circuit consists of two sub-circuits: the primary, which carries low voltage; and the secondary, which carries high voltage. The primary circuit, controlled by the ignition key, releases 12 volts of electricity from the battery or alternator through the coil to a set of breaker points in the lower part of the distributor, or to the relay in electronic ignition applications. When the points or relay are closed, current flows through the chassis back to the battery, completing the circuit. When the points or relay are open, the flow stops, causing a high-voltage surge to pass from the coil through a rotor in the top of the distributor to the spark plugs. Once the car has started, the voltage regulator protects the battery from being overcharged by the alternator. The condenser absorbs part of the low-voltage current when the points are open.