3-4
Electrical Power Supply Malfunctions
10. Malfunctions in the electrical system can usually be detected by monitoring the voltage
and ampere displays and associated alerts and alarms on the EDM-930. Electrical power
supply malfunctions usually fall into two categories: excessive and insufficient rates of charge.
Although a number of factors may cause electrical problems, the main cause of an alternator
failure is most likely a broken drive belt.
11. An excessive rate of charge, indicated by an abnormally high ammeter reading, will
cause the battery to overheat and result in evaporation of the electrolyte, overheating, and fire
hazard. To prevent this, an over-voltage sensor will shut down the alternator when the charging
voltage reaches approximately 30 volts. Note that no specific current flow has been specified
as the threshold for “excessive rate of charge”. However, in general terms, once the battery
charge has been restored after starting, normal current flow would typically be less than 5
amps.
12. If the ammeter indicates a continuous discharge rate in flight, the alternator is not
supplying power to the system and should be shut down since the alternator field circuit could
be placing an additional load on the battery
13. For an Excessive Rate of Charge, proceed as follows:
4. Essential avionics and electrics
Use only those services
essential to the safe completion
of the flight.
Figure 3-3 Excessive Charge Alerts
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