D.
Do a Test of the APU Static Inverter

 S 864-017
 (1)  
Supply electrical power (Ref 24-22-00/201).

 S 714-013

 (2)  
Do a test of the APU static inverter:

 (a)  
Set the BATTERY switch to ON.

 (b)  
Set the STANDBY POWER switch to BAT.

 (c)  
Get access to the EXISTING FAULTS page for Chapter 24 (if any) on the CMCS (AMM 45-10-00/201).

 (d)  
Make sure the CMCS messages for the APU static inverter do not show.

 (e)  
Set the STANDBY POWER switch to AUTO.

 (3)  
Remove electrical power, if it is not necessary (Ref 24-22-00/201).

 S 864-015
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 24-29-04
 ALL  ú ú 01 Page 403 ú Oct 10/95
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
 1.

2.

3.

A
747-400 MAINTENANCE MANUAL
 DC GENERATION - DESCRIPTION AND OPERATION
_________________________________________
General
_______
 A.  The dc power system is used to generate and distribute 24/28 volts dc to both the essential and non-essential loads throughout the airplane.
 B.  DC power is supplied by two 24 volt 40 ampere-hour batteries, their associated battery chargers, and four 75 amp transformer rectifier units (TRUs).
 C.  Distribution is accomplished by the four dc buses supplied by the TRUs, the main and APU battery buses, and the main and APU hot battery buses (WDM 24-30-00).
 D.  The two 24 volt dc batteries will supply standby dc power for a minimum
 of 30 minutes in the event of total loss of primary power.Batteries (AMM 24-31-00)
_________
 A.  The main hot battery bus is powered by the main battery and the main battery charger.
 B.  The APU hot battery bus is powered by the APU battery and the APU battery charger.
 C.  The main and APU battery buses can be powered from two possible power sources, dc bus 3 or their associated hot battery bus.
 D.  The APU battery bus will also be powered by the main hot battery bus during an APU start on an unpowered airplane. This is done to ensure that the sharp voltage drop on the APU hot battery bus does not affect the APU control circuits on the APU battery bus. These control circuits include the APU DC FUEL PUMP and APU FIRE/BLD DUCT OVHT loops.
 E.  The relays utilized for applying power and operation of the main and APU battery system are the main battery and battery transfer relays, the main and APU battery charger disable relays, and the APU battery bus transfer relay.
Transformer Rectifier Unit (AMM 24-32-00)
__________________________
 A.  There are four main transformer rectifier units (TRUs) each capable of suppling 75 amps to their individual load buses during normal operation. The transformer rectifier units rectify the 115 volt ac 3 phase power from their respective main ac buses to a 27.75 volt dc output.
 B.  The dc current sensors (DCCS) monitor the current flow of the TRUs for processing by the generator control unit (GCU) to determine operation of the TRUs.
 C.  The dc isolation relays (DCIRs) are used to isolate their individual dc bus or to parallel all the buses onto the dc tie bus for normal operation. The GCUs provide manual and automatic control of the DCIRs in conjunction with the BUS TIE switch on the electrical system control module located on the P5 overhead panel.
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 24-30-00
 ALL  ú ú 03 Page 1 ú Jun 18/01
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
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747-400
MAINTENANCE MANUAL

 D.  There is one main deck cargo handling transformer rectifier unit (TRU). The TRU powers associated control centers and relays for loading and unloading the main cargo deck.
 4.  DC Standby Power System (AMM 24-33-00)
______________________________________
 A.  The dc standby power system supplies 24 volts dc to the flight critical loads for 30 minutes minimum, if a complete loss of primary power occurs. This system consists of two 40 ampere-hour nickle-cadmium batteries (main and APU).
　
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