Alpha Technologies APU Control Module (ACM) - Manual (Page 9)

9 018-340-B0-001 Rev. A
1.0 System Overview, continued
1.2 Theory of Operation
1.2.1 Normal Operating Condition
Under normal operating conditions (no alarms) the ACM’s Run-Auto-Stop (RAS)
three position rocker switch will be in one of two positions: “AUTO” or “RUN”. (See
Section 3, Indicators, Controls and Connectors) The ACM has control over the
starting and stopping of the APU while in the AUTO mode. The ACM is monitoring
the utility input, via an AC sense, the DC buss voltage, Ignition battery charger
output, enclosure sensors and the APU status sent from the APU controller. If a fault
occurs, the ACM determines whether or not to start or inhibit the APU based upon
the failure. The ACM can also receive remote start commands via the RS-485 buss
or the analog transponder interface. The ACM can be removed from controlling the
APU by switch the RAS to run or “manual” mode. In this mode, the APU will run until
a fault condition shuts it down.
1.2.2 Standby Operating Condition (Less Than 10 Minutes)
If an AC line disturbance or outage is less than 10 minutes, the ACM will not start
the APU unless the battery buss voltage drops below a programmable threshold
(Low DC Buss 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 ACM will notify the system operator
of a line failure via the front panel LED’s (see alarm section). Otherwise, the ACM 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 ACM start delay
timer will expire and the ACM will attempt to start the APU. The ACM 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 ACM will report an “Engine
Over-crank” alarm. Otherwise, the ACM will start and continue to run the APU until
either a normal shutdown or Major alarm occurs (See section 4.1, Alarms).
Table 1-1, Normal Mode Crank Cycle
Crank Cycle
Crank Attempt 1 2 3 4 5 6 7 8 9
Cranking Engine 15 Sec 15 Sec 15 Sec 15 Sec 15 Sec 15 Sec 15 Sec 15 Sec 15 Sec
Pause (no crank) 30 Sec 30 Sec 60 Sec 30 Sec 30 Sec 60 Sec 30 Sec 30 Sec
Engine
Overcrank
Alarm