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2 Theory of Operation
2.1 Operating States
The FMPS has two operating states, Normal Operation and Battery Backup.
2.1.1 Normal Operation
The FMPS supplies power to the ONT, while being powered by the AC mains outlet. It may also be charging the
batteries or performing a battery test. While in the Normal Operation state, the FMPS operates in one of three
sub-modes and switches between these sub-modes as necessary. The sub-modes are:
22.214.171.124 Battery Standby
The Battery Standby mode is the normal mode of operation. The battery in the UPS is fully
charged and in good condition.
126.96.36.199 Battery Charging
The Battery Charging mode is initiated by a drop in battery voltage, due either to battery self-
discharge or powering the ONT(s) after an AC outage. In either case, the FMPS initiates battery
charging. Temperature compensated charging is used to maintain battery capacity at the
suitable voltage for the temperature range.
188.8.131.52 Battery Self-test
In order to determine when a battery needs replacement, a battery test program is initiated by
the microprocessor. Battery testing occurs only when AC power is present. See Section 6.10 for
a battery test overview.
From the Normal Operation state, the FMPS can switch to the Battery Backup state. This occurs without DC
interruption when AC power fails.
2.1.2 Battery Backup
The FMPS supplies power to the ONT via the backup batteries. The FMPS backup batteries consist of one or two
strings of 7.2 AH batteries. Each battery string consists of four batteries wired in series. See Section Error!
Reference source not found. for projected battery run times. While in the Battery Backup state, there are two
184.108.40.206 Battery Low
The FMPS sends a “Low Battery” alarm to the ONT(s) when either battery string has discharged
to 46.8Vdc. The FMPS also sounds an audible alarm once a Low Battery condition has been
detected (unless the alarm has been disabled).
220.127.116.11 Low Voltage Disconnect
If AC power is not restored after an extended time, and both battery strings have discharged to
42.0Vdc, the FMPS disconnects the batteries to protect them from over-discharge.
If the depleted batteries are removed from the FMPS, and other (charged) batteries are installed
before restoration of AC power, the LVD circuit automatically resets and provides battery
backup power to the ONT(s).
The FMPS switches from the Battery Backup state to the Normal Operation state on resumption of reliable AC
power. The FMPS initiates the Battery Charging sub-mode until battery capacity is fully restored.