737 MAX Flight Crew Operations Manual
Electrical -
System Description
MN-FLT-OH-201
6.20.7
Electrical Power Controls and Monitoring Schematic
DC Power System
28 volt DC power is supplied by three TR units, which are energized from the AC
transfer buses. The battery provides DC power to loads required to be operative
when no other source is available.
On the ground, an amber ELEC light comes on to indicate that a fault exists in DC
power system or standby power system. The ELEC light is inhibited in flight.
CPS FREQ
DC AMPS
MAINT
ELEC
TR UNIT
APU GEN
GEN2
GEN1
GRD
PWR
INV
TEST
STBY
PWR
BAT
DISCHARGE
AC VOLTS
AUX BAT
TR1
TEST
BAT
BUS
BAT
TR2
STBY
PWR
DISCONNECT
CONDITION: ENGINE DRIVEN GENERATORS ON AC BUSES
IDG2
AIR
FAN
GENERATOR 1
FROM
GEN 2
OFF
ON
TR2
AC TRANSFER BUS 2
AC TRANSFER BUS 1
BUS
GEN OFF
OFF
SOURCE
BUS OFF
TRANSFER
DRIVE
2
BUS TRANSFER
F
O
U
A
F
O
T
DC VOLTS AC AMPS
DC BUS 2
TR3
March 1, 2021
