Technical data

13773-001
24-30
Page 2 30 Nov 2000
A. Alternator 1
The front alternator (alternator 1) is mounted directly to the front of the engine on the co-pilots’ side.
Alternator 1 is a 60-amp (rated at 58-amps) engine-driven alternator.
Alternator 1 is controlled by the ALT 1 master switch located in the bolster panel. Battery 1 and alterna-
tor 1 are independently controlled and can be alternately connected to main bus 2. Failure or malfunc-
tion of alternator 1 will not impair the capability of the main battery to provide power to main bus 2.
Failure or malfunction of either or both alternators will not impair the capability of either battery to
power the essential load circuits, because each of these power sources feed into the essential bus. If
either alternator is lost, the other alternator and both batteries are still capable of feeding the essential
bus. In addition, each alternator or battery can be manually disconnected by switching the appropriate
master bolster switch located on the pilot's bolster switch panel.
B. Alternator 2
The rear alternator (alternator 2) is mounted directly to the aft engine accessory pad which is located
at the rear of the engine. Alternator 2 supplies electrical power to the essential bus through a 5-amp
circuit breaker located in the circuit breaker panel.
Alternator 2 is controlled by the ALT 2 switch located in the bolster panel. If alternator 2 fails while in
operation, the essential bus will then get electrical power from alternator 1, battery 1, and/or battery 2.
Alternator 2 is a 20-amp engine-driven alternator.
C. Master Control Unit (MCU)
The MCU is an integrated component which ensures proper electrical output over the entire tempera-
ture and RPM range of the alternator system by regulating and distributing alternator output. The MCU
is mounted to the forward side of the firewall, on the pilot’s side. The MCU controls alternator 1, alter-
nator 2, starter, landing light, external power, and the power generation system annunciation. The
MCU provides protection for external power reverse polarity and alternator 1 and alternator 2 overvolt-
age situations. The MCU also provides low voltage annunciation and an overload annunciation for ALT
1 and ALT 2 fail annunciators in the instrument panel.
The bus structure of the MCU and the circuit breaker panel allows all power devices to feed into the
Essential Bus during emergencies. This action is automatic and does not require pilot intervention. The
Main and Essential Busses are separated via diodes which allow the main bus to feed into the Essen-
tial Bus during failures of Alternator 2 or Battery 2. The MCU regulates Alternator 1 to 28 VDC, while
Alternator 2 is regulated to 28.75 VDC which ensures the diode separates the busses during normal
operation.
The MCU used on this airplane contains a landing light relay, battery relay, ground power relay, starter
relay, ammeter transducer, 15-amp landing light circuit breaker, two buses (one essential and one non-
essential), two voltage regulators, three current sensors, and five 25-amp distribution feeder circuit
breakers.
The pilot has access to the alternator circuit breakers, which are located in the circuit breaker panel,
during flight. If the system is generating more than 31.75 ± 0.25 V, the corresponding alternator circuit
breaker will open, preventing further power generation by that alternator.
The MCU contains a current sensor in the battery bus, this current sensor sends a signal to the amme-
ter (battery charge or discharge). The ammeter will only indicate a discharge when the ammeter select
switch is in the BATT position and the electrical draw on the system exceeds the quantity of power
generated by the system. Diodes in the alternators block reverse current making negative current indi-
cation unnecessary. The current value displayed by the ammeter corresponds directly to the quantity
of power generated by the alternator system. When the ammeter select switch is in the ALT 1 or ALT 2
position, the ammeter drives will only allow the ammeter to display a positive current value because of
the diodes within the alternator block.