Concorde RG Series - Operation

Document No. 5-0324 Rev G
Page 12 of 21
OPERATION
A. Applications: Aircraft batteries are used to start engines and auxiliary power
units (APUs), to provide emergency backup power for essential avionics
equipment and lighting systems, to assure no-break power for navigation units and
fly-by-wire computers, and to provide ground power capability for maintenance and
preflight checkouts. Many of these functions are critical to safe operation of the
aircraft, so the state of health of an aircraft battery is of utmost importance. Aircraft
batteries are certified to have a certain minimum capacity for emergency
operations in the event of an electrical generator system failure. If the battery is
used to satisfy essential or emergency power requirements, its capacity must be
tested periodically to assure airworthiness. See Servicing Section for capacity test
instructions.
B. Battery Charging: The aircraft’s electrical system automatically charges the
battery when the engine(s) are running. Most aircraft allow charging using external
power as well. The battery charging system in most aircraft is of the constant
voltage type. With constant voltage charging, the battery will accept charging
current inversely proportional to its state-of-charge (that is, the lower the state of
charge, the higher the charging current). When the battery reaches full charge, the
charging current tapers off to a very low value (typically 0.5% of the C1 capacity),
and remains at that level to keep the battery on a “float charge”. Therefore, an
ammeter reading of the charging current (if present) is useful in determining the
approximate state of charge of the battery.
C. Temperature Compensation: Battery service life can be prolonged by
compensating the charging voltage based on the battery temperature. For aircraft
that have an adjustable voltage regulator, the following table provides
recommended settings:
Table 1. Recommended Voltage Regulator Settings
Battery Temperature
Voltage Regulator Setting (Volts DC)
12V System
24V System
Below 0°C (32°F)
14.5 – 14.75
29.0 – 29.5
0 to 15°C (32 to 59°F)
14.25 – 14.5
28.5 – 29.0
16 to 30°C (60 to 86°F)
14.0 – 14.25
28.0 – 28.5
31 to 45°C (87 to 113°F)
13.75 – 14.0
27.5 – 28.0
Above 45°C (113°F)
13.5 – 13.75
27.0 – 27.5
D. Ground Power Units: When aircraft are powered by ground power units, be
sure that the DC output voltage is adjusted to the range shown in Table 1.
Through the years there have been many reports of overcharged batteries due to
ground power units being set too high. High charging voltages will shorten the
battery service life and may lead to abnormal venting of gases or electrolyte.