Technical data

13773-001
24-30
Page 330 Nov 2000
The master switch arrangement, located in the pilot's bolster contains battery 1, battery 2, alternator 1,
and alternator 2 control switches. Each switch disconnects the associated device from the correspond-
ing bus. The switches are located in a side-by-side arrangement and are labeled as to their function.
The BAT 2 switch, when closed, connects battery 2 to the essential bus. This switch activates a relay
located next to BAT 2, providing the ability to connect and disconnect battery 2 from the aircraft.
Buses in the MCU are designed to ensure essential flight and avionics systems remain powered dur-
ing a malfunction of any one of the buses. Five bus wires run from the MCU, through the firewall, and
to the circuit breaker panel. Five bus wires in the MCU are overload protected by fuses and circuit
breakers. Five buses are used to power the majority of the aircraft loads. These five buses supply
power to the circuit breaker panel. The second bus is for the landing light. The fifth is the clock bus
which is fused at 5 amperes and is the only bus powered directly from battery 1 and is not controlled by
the master switch arrangement. The clock bus fuse is externally removable for long term storage situ-
ations to prevent battery drain.
Alternator power flows from the alternators into the MCU. Inside the MCU is where the voltage regula-
tor regulates the alternators output. Each voltage regulator provides transient suppression and con-
stant voltage regulation of the unfiltered alternator power. To protect sensitive instruments, the over-
voltage protection system monitors the primary power bus and automatically limits the peak voltage to
approximately 31.75 volts. During sustained over-voltage periods, the over-voltage system provides a
warning to the pilot. Each voltage regulator will cause the corresponding alternator circuit breaker to
open in cases of field output overloads, and overvoltage. In the event an over-voltage condition
occurs, the corresponding voltage regulator automatically removes alternator field current to shut
down the corresponding alternator. Each voltage regulator has been integrated into the MCU case, for
durability and reliability.
D. Low Volts Warning Light
The airplane is equipped with a red LOW VOLTS warning light in the annunciator panel, located on the
left side of the instrument panel. The voltage regulator within the MCU operates the red LOW VOLTS
warning light. If Essential Bus voltage drops to approximately 24.5 volts, the LOW VOLTS warning light
will illuminate red. The LOW VOLTS annunciator will illuminate regardless of how many or what types
of power sources are connected.
Resetting the ALT 1 and ALT 2 switches (from off and back on again) may reset the voltage regulator.
If the warning light does not illuminate again, normal alternator charging has resumed. If the light illu-
minates again, a malfunction has occurred.
Illumination of the LOW VOLTS warning light along with ammeter discharge indications may occur dur-
ing low RPM conditions with an electrical load on the system, such as during a low RPM taxi. Under
these conditions, the light will go out at higher RPM. The battery switches will not need to be recycled
since an over-voltage condition has not occurred to de-activate the alternator system.
E. ALT 1 and ALT 2 Fail Lights
Two amber colored alternator fail lights are located in the annunciator panel. The lights provide warn-
ing of a overloaded or inoperative alternator. In conjunction with the red LOW VOLTS warning light, the
MCU controls the illumination of the appropriate alternator fail light (ALT 1 or ALT 2), notifying the pilot
of the system at fault.
If either alternator generates less than 2 amps (approximately), the corresponding annunciator light
will illuminate steady. If either alternator becomes overloaded, the corresponding annunciator light will
flash approximately 40 times per minute.