Alpha Technologies VMX Series - Manual (Page 18)

18 017-940-B0-001, Rev. A
2.0 Theory of Operation, continued
2.3 Charger Operation
The VMX Power Supply uses a three-stage, temperature-compensated battery charger.
During AC line operation, the inverter winding on the ferroresonant transformer feeds the
charger circuit which provides BULK, ACCEPT, and FLOAT charge voltages to the batteries.
Charger Modes:
TEST: When the power supply fi rst starts, transfers back to line, or when batteries are fi rst
connected, the power supply will indicate the charger mode is TEST for a period of up to
10 minutes. The charger will operate the same as BULK mode, but with a slightly different
battery detection method. The charger mode will also indicate TEST during self-test.
BULK charge is a “Constant Current” charge. The maximum charger current is 10 Amps.
As the charge is returned to the batteries, their voltage increases to a specifi c threshold
(2.27Vdc per cell). This cycle ends when the charging current into the batteries becomes less
than 0.5A.The charger then switches to ACCEPT mode. The BULK charger mode generally
returns the battery charge state to 80 percent of rated battery capacity.
ACCEPT charge is a “Constant Voltage” charge. This voltage, 2.40Vdc (adjustable) per
cell, is temperature-compensated to ensure longer battery life and proper completion of the
charge cycle. This cycle is complete when the charging current into the batteries becomes
less than 0.5A, or approximately six hours from the time ACCEPT mode was entered. When
the batteries are fully recharged the charger switches to the FLOAT mode of operation.
FLOAT charge is a temperature-compensated “pulsed voltage” charge, averaging about
2.27Vdc (adjustable) per cell. During FLOAT mode, the batteries are fully charged and ready
to provide backup power. The charger provides a small maintenance charge to overcome the
batteries self-discharge characteristics and other minor DC loads within the power supply. As
the battery voltage reaches the “full charge” level the time delay between pulses increases.
The cell voltage is temperature-compensated at -0.005Vdc per cell per degree Celsius
(adjustable) to ensure a safe battery cell voltage and maximize battery life. The temperature
compensation is limited to an absolute battery voltage minimum of 2.20V per cell and a
maximum of 2.50V per cell regardless of the temperature compensation settings.
Fig. 2-1, Charger Modes
1
2
3
4
5
6
7
8
9
10
2.15
2.25
2.05
2.40
0
Volts Per Cell
Charger Current
Bulk Accept Float