Sentry Model HM-535 Power Supply
Installation and Service Manual
430-535 0104 © 2004 Heritage MedCall, Inc.
6
4.0
OPERATION
4.1 OUTPUT
The DC output voltage is factory set at 14 volts. The supply is capable of 12 Amps
maximum. Load regulation will maintain output voltage to within 2% from no load to
full load. Line regulation will maintain output voltage to within 2% at full load from
102V to 125V AC line voltage. The OUTPUT LED lights when the DC output voltage
is On.
4.2
OUTPUT PROTECTION
A current fold-back circuit is used to protect the supply from over current. When the
12 amps is exceeded, the output voltage will automatically decrease in an attempt
to reduce the fault current. The output voltage will recover when the fault is cleared.
The supply is protected from a catastrophic short circuit, but may require the AC and
battery power to be interrupted momentarily to recover from total fold-back.
4.3
BATTERY CHARGER
The charger is a constant voltage type that can supply up to 3 amps for fast
charging. When the battery is fully charged, the current is reduced to a standby
amount and the battery is maintained with a float charge of 13.8 volts.
The battery charger is automatically inhibited if the DC power supply shuts down
and during the battery test.
4.4
BATTERY PROTECTION RELAY
A circuit protects the battery from being drained to level that will cause permanent
damage. When the power supply is in the backup mode, the battery will typically
supply the load for an hour. When the battery drains to 9 volts, a relay will
disconnect it. When the AC power is restored, the battery will reconnect and will be
charged.
4.5
BATTERY TESTER
The power supply's controller will test the battery every 9 hours. During the 5 second
test, the charger is inhibited, and a test load is connected across the battery. If the
battery tests bad, the LOW BATT LED will light and a Battery Trouble message will
be sent to the console.
4.6
DC SHUTDOWN
A control is incorporated to shutdown the DC output voltage via a special signal from
the Master Controller. If host panels cease data communication with the console,
the power supply will be directed to shutdown for 15 seconds. The shutdown and
power on cycle will usually restore data communication. This action is completely
automatic and does not require operator intervention.
