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DC GENERATION SYSTEM-INTRODUCTION

Purpose

The DC generation system makes a nominal 28v dc for airplane systems.

General

The DC generation system has these components:

- Battery

- Battery charger

- Transformer rectifier units (3).

DC GENERATION SYSTEM - GENERAL DESCRIPTION

General Description

The DC generation system supplies a nominal 28v dc to different loads. The power source for the

DC system is usually the AC system. The battery supplies power if the AC system is not available.

Transformer Rectifier Units

To create DC power from the normal AC source, the DC system uses transformer-rectifier units

(TRUs).

The

three

TRUs

take

115v

ac,

decrease

the

voltage

(transforms),

and

rectify

it

to

a

nominal 28v dc.

Battery Chargers

The main battery charger and auxiliary battery charger give a DC voltage output to charge their

respective battery. Each charger operates like a TRU after the battery gets to full charge. The main

battery charger sends a constant DC voltage

to

the battery and the hot and switched hot battery

buses. The auxiliary battery and auxiliary battery charger power DC buses only during non-normal

conditions. See the standby power system section for more information. (AMM PART I 24-34)

Batteries

Each battery is a 48 ampere-hour, nominal 24v dc power source. The main battery supplies power

for APU starting and is a standby power source if all other power supplies do not operate. The

auxiliary battery helps the main battery supply standby power only.

Control and Protection

The standby power control

unit (SPCU), the battery switch, and the standby power switch give

primary control of the DC system.

The battery switch and the standby power switch give manual control of power to some DC buses.

The

SPCU

gives

automatic

control

and

protection

of

DC

buses.

It

uses

inputs

from

the

flight

compartment and system monitoring to control DC power sources and distribution.

Power Distribution

The DC power distribution system is in the power

distribution panels (PDPs) and in the SPCU.

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DC GENERATION SYSTEM - MAIN BATTERY CHARGER

AND AUXILIARY BATTERY CHARGER

Purpose

The main battery charger has these two functions:

- Keeps main battery at maximum charge

- Supplies DC power to the battery buses.

The auxiliary battery charger keeps the auxiliary battery at maximum charge.

General Description

Both battery chargers have the same part number. Each battery charger has these two basic modes

of operation:

- Battery charge mode (constant current)

- Transformer rectifier mode (constant voltage).

Each battery charger supplies constant current, variable voltage power in the battery charge mode.

The

battery

charger

overcharges

the

battery.

The

battery

charger

logic

calculates

the

amount

of

overcharge. The total charge time is less than 75 minutes.

In

the

transformer

rectifier

(TR)

mode,

the

main

battery

charger

supplies

constant

voltage

DC

power to the hot battery bus and the switched hot battery bus.

The

main

battery

also

receives

a

small

trickle

charge

to

help

keep

it

at

maximum

charge.

The

auxiliary

battery

charger

does

not

supply

power

to

the

DC

buses

in

either

mode.

However,

the

auxiliary battery receives a

small trickle charge when the auxiliary battery charger is in the TR

mode.

The

front

face

of

each

battery

charger

has

two

green

status

lights

(LED).

One

light

is

for

the

battery charger and the other is for the battery. These lights are on when the battery and battery

charger are in operation.

Location

The main battery charger is on the E2 rack. The auxiliary battery charger is on the E3 rack.

Functional Description

Each battery charger takes three-phase, 115v ac power and changes it to DC power. Usually, each

battery charger is in the transformer rectifier mode. The battery chargers supply a constant voltage

output in this mode. Each charger can supply up to 65 amps in this mode.

A

battery

charger

goes

to

the

charge

mode

when

its

battery

voltage

is

less

than

23v

dc.

In

this

mode,

the

charger

supplies

constant

current

power.

The

output

voltage

is

variable.

During

the

charge,

the battery

voltage

rises

until

the

voltage

gets

to

the

inflection

point.

The charger

logic

uses the battery temperature at the start of charging to calculate the inflection point. The charger

logic then calculates the length of the overcharge period.

After

the

overcharge

period,

the

charger

goes

into

a

transformer

rectifier

mode

with

a

constant

27.5v dc output. The battery gets a trickle charge in this mode.

The battery charger goes into the charge mode again if any of these occur:

- Battery charger input power is off for more than 1 second.

- Battery voltage is less than 23 volts.

You use the electrical meters, battery, and galley power module to monitor the operation of each

2

battery

charger.

The

main

battery

charger

is

in

the

charge

mode

when

you

see

a

positive

DC

AMPS indication while the DC meter selector in the BA

T position. Use the AUX BAT position to

monitor the auxiliary battery charger.

The main battery charger cannot go into the charge mode during any of these conditions:

- Fueling station door open

- APU start

- Standby power switch (P5-5) in the BAT position

- Standby power switch (P5-5) in the AUTO position, battery switch ON, and DC BUS 1 and AC

TRANSFER BUS1 do not have power

- Main battery overheat.

The auxiliary battery charger cannot go into the charge mode during any of these conditions:

- Standby power switch (P5-5) in the BAT position

- Standby power switch (P5-5) in the AUTO position, battery switch ON and DC BUS 1 and AC

TRANSFER BUS 1 do not have power.

- Auxiliary battery overheat.

Status Lights

Both status lights are usually on when the battery charger has input power. A malfunction with any

of these components makes one or both status lights go off:

- Battery charger

- Battery

- Connection wiring.

Both status lights are off if any of these conditions are true:

- Input power to the battery charger goes away

- Input voltage to the battery charger is less than 94v ac for more than 0.5 seconds.

The battery charger status light is on and the battery status light is off if any of these conditions are

true:

- Battery charger senses a loss of connection to the battery

- Battery overheat

- Battery temperature sensor open or shorted

- Battery not charged in time limits

- Battery voltage less than lower limits.

The battery charger status light is off and the battery status light is on when there is an internal

battery charger failure. The battery charger fail maintenance message also shows on P5-13 BITE.

DC GENERATION SYSTEM-BATTERY CHARGER-FUNCTIONAL

DESCRIPTION

Functional Description

The battery charger takes 3-phase, 115v ac power and changes it to dc power. Usually, the battery

charger is in the transformer rectifier mode. The battery charger supplies a constant voltage output

in this mode. The charger can supply up to 65 amps in this mode.

The battery charger goes to the charge mode when the battery voltage goes below 23v dc. In this

mode,

the

charger

supplies

constant

current

power.

The

output

voltage

is

variable,

the

current

3

output is 50 amps. During the charge, the battery

voltage increases until the voltage gets to the

inflection point. The charger logic uses the battery temperature at the start of charge to calculate

the inflection point. The charger logic then calculates the length of the overcharge period.

After

the

overcharge

period,

the

charger

goes

into

a

transformer

rectifier

mode

with

a

constant

27.5v dc output. The battery gets a trickle charge in this mode.

The battery charger goes into the charge mode again if any of these occur:

- Battery charger input power is off for more than 1 second

- Battery voltage goes below 23 volts.

You

use

the

electrical

meters,

battery

and

galley

power

module

to

monitor

the

operation

of

the

battery charger.

The battery charger is in the charge mode when you see a positive DC AMPS indication when the

DC meter selector in the BAT position.

The battery charger cannot go into the charge mode during any of these conditions:

- Fueling station door open

- APU start

- Standby power switch (P5-5) to the BAT position

- Standby power switch (P5-5) to the AUTO position, battery switch ON, and DC BUS 1 and AC

TRANSFER BUS 1 do not have power

- Battery overheat.

DC GENERATION SYSTEM - MAIN BATTERY AND AUXILIARY BATTERY

Purpose

The main battery has these functions:

-

Supply

power

to

critical

airplane

systems

(AC

and

DC

standby

buses)

if

the

normal

power

sources are not available

- Backup power supply for the AC system control and protection

- Power supply for APU start.

The auxiliary battery helps the main battery supply power to the critical airplane systems (AC and

DC standby buses).

Location

The batteries are in the EE compartment, under the E3 rack. The auxiliary battery is forward of the

main battery. You remove an access panel in the forward cargo compartment to get access to the

batteries. You must remove the main battery before you can remove the auxiliary battery.

General Description

Each battery is a 20 cell nickel-cadmium battery with a 48 amp-hour capacity. With full charge,

the batteries supply a minimum of 60 minutes of standby AC and DC power.

Each

battery

has

an

internal

thermal

sensor.

The

battery's

charger

uses

this

sensor

to

measure

internal

battery

temperature.

See

the

MAIN

BA

TTERY

CHARGER

AND

AUXILIARY

BA

TTERY CHARGER page in this section for more information.

4

Indication

You can see the output of each battery on the electrical meters, battery and galley power module

on the P5 forward overhead panel. You see the voltage and current output of a battery with the DC

meter selector in the BAT position or AUX BAT position. If the battery's charger has power, you

see the output voltage of the battery or its battery charger, whichever is more.

The amber BAT DISCHARGElight comes on when any one of these output conditions are true for

either battery:

- Current draw is more than 5 amps for 95 seconds

- Current draw is more than 15 amps for 25 seconds

- Current draw is more than 100 amps for 1.2 seconds.

Master caution and the ELEC annunciator usually come on with the BA

T DISCHARGE light. The

light goes out when the output current goes below the limit for more than 1 second. Master caution

and the ELEC annunciator do not come on during a DC power APU start.

Training Information Point

You remove a battery from the airplane before you do a battery inspection or servicing.

DC GENERATION SYSTEM - DUAL BATTERY REMOTE

CONTROL CIRCUIT BREAKER

Purpose

The dual battery remote control circuit breaker (RCCB) puts the output of these in parallel:

- Auxiliary battery

- Auxiliary battery charger

- Main battery

- Main battery charger.

Location

The RCCB is inside the J9 junction box. J9 is in the EE compartment, in front of the E2 rack.

General Description

The RCCB is normally open and closes when the SPCU signals it to close. This lets the 28v dc

battery bus bar receive power from the main and auxiliary batteries at the same time.

DC GENERATION SYSTEM - TRANSFORMER RECTIFIER UNIT (TRU)

Purpose

The transformer rectifier units (TRU) change three-phase nominal 115v ac, 400 hz input power

into 28v dc to supply the main DC system loads.

General Description

The DC generation system has three TRUs. Each TRU can supply a continuous output load of 75

amps, with forced air cooling. The TRUs can supply 50 amps, with convection cooling.

There are no external controls to the TRUs. The TRUs are the same part number.

5

Location

The TRUs are in the EE compartment. TRU 1 is on the E2 rack. TRU 2 and TRU 3 are on the E4

rack.

Indication

You may monitor output power for each TRU from the P5-13. You can use the DC meter selector

to select the TRU. TRU output voltage and amperes show in the alphanumeric display.

The amber TR UNIT light comes to show a TRU failure.

The light comes on for any of these conditions:

- Any TRU fails on the ground

- TRU 1 fails in flight

- TRU 2 and TRU 3 fail in flight.

DC GENERATION SYSTEM-BATTERY BUSES- FUNCTIONAL

DESCRIPTION

Hot Battery Bus Power

The hot battery bus receives DC power from the battery through a 28VDC bat bus bar in the J9

battery is a circuit breaker on the SPCU that permits power to the bus.

The 28v dc battery bus bar receives DC power from the main battery or the main battery charger

under normal power conditions. On standby power the 28v dc battery bus bar receives power from

the main battery and the auxiliary battery.

Switched Hot Battery Bus Power

The switched hot battery bus receives DC power from the 28v dc battery bus bar through a circuit

breaker on the SPCU and relay K8 in the SPCU.

To get power to the switched hot battery bus, the battery switch must be ON. When the battery

switch is ON, K8 SW HOT BAT BUS RL

Y closes and gives dc power to the bus.

With the forward airstair option, the K8 relay closes when the airstair handle is put in the standby

position.

The K8 relay gives DC power from the 28v dc battery bus bar to the SPCU power supply.

Battery Bus Power

The battery bus receives power from the 28v dc battery bus bar or TRU 3.

The BA

T BUS NORM RL

Y (K2) is closed and gives DC power

from TRU3 to the battery bus

when all of these conditions are true:

- BATTERY SW ON

- STANDBY POWER SW not in BAT position

- TRU 3 gets more than 18v dc for more than 0.15 seconds.

- When the K2 relay is closed, the BAT BUS ALT RL

Y(K1) must be opened.

The

K1

BAT

BUS

ALT

RL

Y

is

closed

and

gives

power

to

the

BATTERY

BUS

during

these

conditions:

-

Battery

switch

is

ON

and

TRU

3

does

not

have

power

(less

than

18v

dc)

for

more

than

0.1

seconds or

- STANDBY POWER SWITCH is in the BAT position.

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