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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
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MAINTENANCE MANUAL
9. Power Supplies
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A. The circuitry of each power supply consists of a logic light control circuit and a battery charging control circuit. The prime purpose of the logic circuit is to sense power failure and to make the emergency lights come on. The logic circuit also senses pilots' or attendants' switch directions. The battery charging control circuit provides a trickle charge to the batteries as long as power is available and controls battery discharge cut-off to prevent batteries from completely discharging and reversing polarity. The batteries in the power supply provide 6 volts dc of electrical power to the emergency lights connected to it.
10. Operation
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A. Functional Description
(1)
The 28-volt DC-Bus 4 supplies charging power to maintain batteries in the emergency lights power units. The emergency light lamps always receive their power from the emergency power unit batteries as do the emergency lamps in each lighted EXIT sign. Circuit breakers are located on the electrical circuit breaker panel P7.
(2)
Each emergency light power unit contains a double ground seeking logic circuit that activates a relay or a transistor switch to turn the lights on and off. The power for each logic circuit is derived from the power pack and is independent of airplane power.
(3)
The logic driver provides a ground circuit or logic zero to the transistor switch or relay to turn the lights on. Inversely it provides an open circuit or logic one to turn the lights off. The inputs to the logic circuit are initiated by the emergency lights switch settings (pilots' and attendant's switches) and the 28-volt DC-Bus 4 power status.
B. Control
(1) Primary control of the emergency lights is with the pilot's switch.
(a) When the switch is set to the armed position, the power supplies are supplied with electrical power to keep their battteries charged. This 28 volts dc of electrical power comes from Bus 4. The emergency lights come on if there is an electrical power failure of Bus 4 or the attendant's switch is set to on. The armed position of the switch is the usual position during the operation of the airplane.
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MAINTENANCE MANUAL
(b)
When the switch is set to the on position, the emergency lights will come on. The emergency lights operate directly from the batteries. It is not necessary to have the electrical power from Bus 4.
(c)
When the switch is set to the off position and the attendant's switch is set to normal, the emergency lights are off. If the attendant's switch is set to on, then the emergency lights come on. When the pilot's switch is set to the off position and there is electrical power at Bus 4, then the power supplies will continue to charge their batteries. The pilot's switch is usually in the off position when the airplane is parked.
(2) Secondary control of the emergency lights is with the attendant's switch.
(a)
When the switch is in the normal position, it supplies a ground for the pilots' switch. Control of the emergency lights remains with the pilot's switch.
(b)
When the switch is set to the on position, the emergency lights come on. It is not necessary to have the electrical power from Bus 4.
C. Airplane Storage
(1) For periods up to six days of storage, no special procedures are required if emergency light system was completely charged at the beginning of storage period and no operation had occurred during storage.
CAUTION: IF POWER HAS NOT BEEN APPLIED TO INSTALLED EMERGENCY LIGHT
_______ SYSTEM DURING A LAYUP OF SIX DAYS OR MORE, AVOID TURNING ON ANY ASSEMBLY FOR A MINIMUM OF 16 HOURS AFTER APPLICATION OF POWER, AND 20 HOURS OR MORE IS DESIRABLE BEFORE PERFORMING A SYSTEM FUNCTIONAL TEST.
(2) For periods over six days of storage, or if emergency light system was not fully charged at beginning of storage, or the light was operated during storage, charge emergency light system for 16 to 20 hours before operation.
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