Alpha Technologies ECM - Manual (Page 17)

17 TM 744-862-C0-003 Rev.C
Engine Control Module (ECM)
1.2.1 Normal Operating Condition
Under normal operating conditions (no alarms) the ECM's Run-Auto-Stop
(RAS) three-position rocker switch will be in the "center" or AUTO
position as shown in figure 1-2. The ECM has complete control over
the APU while in the AUTO mode. Also, each time the RAS switch is
moved from the STOP position, to the center or AUTO position, the
ECM will run the APU for one minute after a short delay. This is an
indicator to the system operator that the ECM is truly in the AUTO
mode and is fully capable of starting and stopping the APU
automatically.
NOTE: The Run/Stop switch on the 5.0kW Generator Control
Board MUST be in the center (ECM) position before the
ECM will automatically control the Auxiliary Power Unit.
(On older versions, the center position may be marked
“AUTO” or left blank.)
The APU can be controlled manually by placing the RAS switch in the
“up” or RUN position and the “down” or STOP position. If a system
controller is attached to the ECM via the RS-485 bus, the APU can be
controlled remotely. Similarly, the APU can be started via the
transponder interface on the ECM.
In the AUTO mode, the ECM continuously monitors the AC line voltage,
and DC bus voltage, enclosure sensors, and the APU status. If a fault
occurs, the ECM will determine whether to start or inhibit the APU
based on the type of failure.
1.2.2. Standby Operating Condition (less than 10 minutes)
If an AC line disturbance or outage is less than 10 minutes, the ECM will
not start the APU unless the battery bus voltage drops below a
programmable threshold (Low DC Bus Level) which defaults to 1.95
Volts per cell or 35.1/46.8/93.6 Volts for 36/48/96 Volt systems
respectively. However, the ECM will notify the system operator of a line
failure via the front panel LED’s (see alarm section). Otherwise, the
ECM will appear to be in a “normal” operating condition.
1.2.3. Standby Operating Condition (more than 10 minutes)
If an AC line disturbance or outage is greater than 10 minutes, the ECM
start delay timer will expire and the ECM will attempt to start the APU.
The ECM will attempt to start the engine 9 times with either a 30
second or a 60 second pause between attempts (See Table 1-1). If
the engine fails to start, the ECM will report an “Engine Over-crank”
alarm. Otherwise, the ECM will start and continue to run the APU until
either a normal shutdown or Major alarm occurs (refer to Alarm section
3.1).
1.2 Theory of Operation