12.5.6.1 Batteries
The main and auxiliary 24-volt NiCad batteries are located in the lower left nose compartment.
The main and auxiliary batteries have a 40-amp-hour capacity. The standard standby 17-amp-
hour battery (optional 40-amp-hour) is located in the tail compartment, when no APU is installed.
With an APU installed, the standby battery is located in the nose compartment. The MAIN and
AUX batteries are used for engine starting if ground power is not available. All 3 batteries supply
backup power to the aeroplane essential services in flight for 45 minutes or more.
The batteries are connected to the left and right essential buses (Figure 12.5-15) by selecting the
BATTERY MASTER switch. Selecting the BATTERY MASTER switch to the ON position closes 3
contactors and connects all three batteries to the essential buses. The connection required for
the control of the above contactors is directly hard wired and is independent of the EPCU opera-
tion. The EPCU itself is energized from the essential buses.
NOTE: Battery power cannot be applied to the secondary buses.
Battery temperatures, as indicated on the ESID Electrical Page, should be equal to or greater
than -20°C prior to dispatch.
NOTE: There is no battery temperature limitation for starting Engines or APU.
With the BATTERY MASTER switch on, the batteries are connected to the essential buses at all
times. In this way powering of flight safety equipment, which is also connected to the essential
buses, is enabled. In case of emergency operation the batteries are the main energy sources for
the aeroplane.
In addition to the BATTERY MASTER switch, each of the batteries has a dedicated switch.
Selecting the MAIN BATT switch to ON, will directly connect the main battery to the right main
bus. Similarly, selecting to ON of the AUX BATT switch will connect the auxiliary battery to the left
main bus.
The connections of the main and auxiliary batteries to the main buses are controlled by the
EPCU logic. Conditions that require battery disconnection from the bus are the following:
• Emergency operation (defined later)
• Bus fault detected
Manually selecting the STBY BATT switch to ON will connect the standby battery to the left main
bus. This connection is achieved electronically by the EPCU if the following conditions are met:
• DC external power (battery charge option) connected
• No emergency operation
• No bus faults detected
MAIN BATTERY, AUX BATTERY and STBY BATTERY caution lights come on whenever the
related battery is not connected to its feeder bus. A battery temperature indicator on the MFD
Electrical page, continuously shows Main, Aux and Stby battery temperatures when selected on
the ESID control panel. High battery temperature will turn on the MAIN BAT HOT, AUX BAT HOT
or STBY BAT HOT warning light, and cause associated temperature value on the MFD to turn
red. The warning light will go out when the temperature drops below the overheat condition.
17 AMP HR Standby Battery-Forward Fuselage
The 17 AMP HR stanby Battery is re
-
located in the forward fuselage adjacent to the two 40 AMP
Dash8 - Q400 - Electrical
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