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## AC Alternators Control Systems 

Modern aircraft that employ AC alternators use several computerized control units, typically located in the aircraft’s equipment bay for the regulation of AC power throughout the aircraft. Figure 9-81  shows a photo of a typical equipment bay and computerized control units. 

Since AC alternators are found on large transport category aircraft designed to carry hundreds of passengers, their control systems always have redundant computers that provide safety in the event of a system failure. Unlike DC systems, AC systems must ensure that the output frequency of the alternator stays within limits. If the frequency of an alternator varies from 400 Hz, or if two or more alternators connected to the same bus are out of phase, damage occurs to the system. All AC alternator control units contain circuitry that regulates both voltage and frequency. These control units also monitor a variety of factors to detect any system 

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