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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
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737-300/400/500MAINTENANCE MANUAL
(2) The battery overheat relay R325 disconnects battery charger input power when the battery case temperature exceeds 135 deg F.
5. DC System Meters (Fig. 2)
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A. A dc ammeter and voltmeter are on the forward overhead panel P5. The ammeter operates in conjunction with shunts in the output circuits of the three T-R units. The battery ground uses a critical length wire (0.001 ohm resistance nominal) which serves as a shunt for dc ammeter. The ammeter may be used to determine current drain on the battery and to observe the performance of the battery charger.
B. The meters display amps and volts of the standby power, battery bus (volts only), battery, T-R 1, T-R 2, and T-R 3, which is determined by the setting of S956 dc selector switch on panel P5. Setting the switch to TEST connects the voltmeter to the M400 Power System Test Module.
6. DC Annunciator Lights (Fig. 3)
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A. Lights on the Annunciator Lights Module M238 illuminate when power is on 28-volt dc bus 1, 28-volt dc bus 2, 28-volt dc standby bus, and 28-volt dc bat bus; when the external power T-R is energized; and when T-R 3 has output power. The INDICATE/TEST switch S2 on the module must be set to INDICATE for the lights to illuminate.
B. When the INDICATE-TEST switch is set to TEST, all the lights except EXT PWR TR are grounded and connected to the 28-volt dc bat bus. The EXT PWR TR light, which is always connected to 28-volt dc hot bat bus, is grounded. This verifies that all lamps in the M238 module are operable.
7. DC External Power (Fig. 1)
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A. A dc external power receptacle permits connecting 28-volt dc ground supply to the battery circuit. The connection is made by inserting a three-pin plug into a receptacle below the battery on the control shield. A placard with the procedure for connecting or disconnecting a dc external power supply is near the receptacle. The storage battery may remain connected or removed during application of external power. A circuit breaker is in the positive line to the receptacle.
8. Operation (Fig. 4)
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A. T-R 1 provides power to 28-volt dc bus 1 and T-R 2 provides power to 28-volt dc bus 2. T-R 3 provides power to 28-volt dc bat bus through bat bus relay R1 and bat bus relay manual R326; T-R 3 also provides power to 28-volt dc bus 1 through diode M1220 and energized contact of T-R 3 disconnect relay R9; and T-R 3 provides power to 28-volt dc bus 2 through diode M1220.
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A 737-300/400/500MAINTENANCE MANUAL
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A 737-300/400/500MAINTENANCE MANUAL
DC BUS PWR ONGEN 1NO.1 NO.2TR3FFMT
M238 LOCATION
EXT PWRTR STBY BATT HVLV
ERASE AC BUS
OA NO.1 NO.2
INDICATE OC
S2
TEST
INDICATE
TESTNORMAL
S2 INDICATETEST SWITCH FAULT 28V DC WHENDC BUS PWR ONR2 EXTERNAL POWERIS ATTACHED
G7 BUS PROTECTION PANEL (P6) NO.1
NO.2
TR 328V DC
WW W
BUS 1
DC BUS INDICATION
BUS NO. 1
BATT
28V DC
BUS 2
W DC BUS INDICATIONBUS NO. 2
W
W
STBY DC INDTREXT PWR 28V DC
TR 3
DC BUS INDICATION
TR NO. 3
28V DC
BAT BUS
DC BUS INDICATION
BAT
M238 ANNUNCIATOR LIGHTS MODULE (P6)
28V DC
STBY BUS
DC BUS INDICATION
STBY
P6-5 CIRCUIT BREAKER PANEL
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