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737 MAX Flight Crew Operations Manual
Electrical Chapter 6
System Description Section 20
MN-FLT-OH-201 6.20.1
20 System Description System Description File Highlight
Introduction
Dual Battery
Primary electrical power is provided by two engine integrated drive generators
(IDGs) which supply three-phase, 115 volt, 400 cycle alternating current. Each
IDG supplies its own bus system in normal operation and can also supply essential
and non-essential loads of the opposite side bus system when one IDG is
inoperative. Transformer rectifier (TR) units and the main battery/battery charger
supply DC power. The main and auxiliary batteries also provide backup power for
the AC and DC standby system. The APU operates a generator and can supply
power to both AC transfer buses on the ground or in flight.
There are two basic principles of operation for the 737 electrical system:
• There is no paralleling of the AC sources of power.
• The source of power being connected to a transfer bus automatically
disconnects an existing source.
The electrical power system may be categorized into three main divisions: the AC
power system, the DC power system, and the standby power system.
Electrical Power Generation
Engine Generators
Primary power is obtained from two engine IDGs. The IDG maintains a constant
generator speed throughout the normal operating range of the engine. An integral
electro–mechanical disconnect device provides for complete mechanical isolation
of the IDG.
APU Generator
The APU generator can supply power to both AC transfer buses on the ground or
in flight. As the only power source, the APU generator can meet electrical power
requirements for all ground conditions and most flight conditions.
External Ground Power
An external AC power receptacle located near the nose gear wheel well, on the
lower right side of the fuselage, allows the use of an external power source. Status
lights on a panel adjacent to the receptacle permit the ground crew to determine if
external power is being used. When connected, external power can supply power
to both transfer buses.
March 1, 2021