DA 42 AFM Airplane Description
Doc. No. 7.01.05-E Rev. 8 15-Dec-2017 Page 7 - 55
Alternator Control:
Each alternator has an alternator control unit. It measures the alternator output voltage
and controls the current through the alternator field coils via a pulse-width modulated
signal. To keep the output voltage stable in all load and speed situations, the alternator
field signal is modulated accordingly.
The alternator control unit includes a comprehensive set of diagnostic functions that will
warn the operator using a caution message (L/R ALTN FAIL) on the G1000 PFD in case
of over- or undervoltage as well as a couple of other internal warning levels.
Load balancing: The alternator control unit supports load balancing across the two
alternators via the internal alternator temperature. The temperature is measured and the
alternator control unit slightly decreases alternator voltage output at higher internal
alternator temperatures. Thus the load is partly shifted to the alternator with the lower
internal temperature. This system is able to balance the actual load within a few amps
between the two alternators installed.
Storage
Main battery power is stored in a 24 V, 10 Ah lead-acid battery mounted on the right-aft
side of the front baggage compartment. The main battery is connected to the HOT
BATTERY BUS and to the BATTERY BUS via the battery relay which is installed in the
relay junction box on the center-aft side of the front baggage compartment.
The battery relay is controlled with the ELECTRIC MASTER switch which is located on
the left-hand side of the instrument panel.
In addition, a non-rechargeable dry battery is installed as a further source of power for
the attitude gyro (artificial horizon) and the flood light. When the EMERGENCY switch
is set to ON, these two systems are supplied with power for at least 1.5 hours, independent
of all other electrical consumers. During each 100 hour inspection, this battery is checked
for proper functioning. Every 2 years or after use (broken seal on the switch) the battery
package must be replaced.
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