All R22s use a 14 volt, negative earth, direct current (DC) electrical system. The electrical power is supplied by a 60 ampere alternator, mounted to the rear of the engine on the passenger side, belt driven by the engine.

A 12 volt, 25 ampere-hour battery is located either in the nose of the helicopter under the instrument console on standard, HP and Mariner models or just forward and outboard of the engine on the passenger side for Alpha and Beta models.

The alternator is the primary source of power to the electrical system in normal operations, with the engine running, the alternator produces alternating current (AC) which is converted into direct current (DC) by diodes incorporated in the alternator housing which act as rectifiers.

By their design alternators require a small voltage (about 3 volts) to produce the electrical magnetic field required inside the alternator. The significance of this is that if the battery is completely discharged (flat) the alternator will not be able to supply any electrical power to the electrical system even after the engine has been started by some other means (external power).

Output from the alternator is controlled by a voltage regulator, which is mounted on the right side of the firewall forward of the engine. An over voltage relay is also fitted to protect the electrical system from any over voltage conditions or surges, in the event of a high voltage the relay opens and the alternator becomes isolated, and appears to have failed.

The over voltage relay can be reset should this occur by turning off the alternator switch for one second and then turning it back on. Normally the alternator will come back on line and re-supply power to the electrical system.

The primary purpose of the battery is to supply power for engine starting, the initial excitation of the alternator and as a back up in the event of alternator failure.

In normal operations with the engine running, the alternator provides the power to the electrical system and charges the battery. In the event of an alternator failure, the battery is providing all the power to the electrical system.

The ammeter is located on the instrument panel and indicates the current in amperes, too or from the battery. Should the alternator fail, the ammeter will show a discharge, the flow of electricity is from the battery to the electrical system, and the low voltage warning light will illuminate. In this event a landing should be made as soon as possible. This is due to the fact that all electrically driven instruments (eg. Electrically driven artificial horizon) and many crucial aircraft gauges will become unserviceable, but most importantly the aircrafts radio and avionics will fail once battery power is lost.


The MASTER BATTERY switch controls the battery relay which disconnects the battery from the electrical system.

A small power wire bypasses the battery relay to allow the tachometers and the clock to continue to receive battery power with the MASTER BATTERY switch off.

The alternator control unit protects the electrical system from over-voltage conditions. The ammeter indicates current to the battery indicates discharge). If ALT light comes on or ammeter indicates discharge during flight, turn off all nonessential electrical equipment and switch ALT off and back on after one second to reset. If ALT light stays on or ammeter still indicates discharge, terminate flight as soon as practical.


Continued flight with malfunctioning charging system can result in loss of power to electronic tachometers, producing a hazardous flight condition.

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