Micro
ARE-M Series 24V Chargers, Single Phase
Circuit Description
PM990-1070-24, Issue 12
5-1
5.0 CIRCUIT DESCRIPTION
Figure 5-1 is a functional block diagram of a
Micro
ARE-M series float charger. AC input power is applied
through the input circuit breaker to the power transformer. The circuit breaker provides over-current and fault
protection in case of malfunction or a short circuit in the input side of the equipment.
The power transformer in a
Micro
ARE-M Series power supply is of the ferroresonant type. This class of
transformer has the output coil on the same leg of the core as the resonant winding. This winding, together with
the resonant capacitor, maintains the core at a high level of saturation, resulting in a constant output voltage
against changes in the input voltage. The high reactance of this type of transformer provides protection against
overload and short circuit of the output.
Single-Phase
AC Input
AC
Circuit
Breaker
Power Transformer
Constant Voltage
Ferro Resonant
Electronic
Voltage & Current
Control
High Voltage
Shutdown
Rectifier
Resonant
Capacitor
DC Filter
Resonant
Control
Operator Panel
Alarms
Battery and Load
Form C Relay
Outputs to
Customer Alarm
Annunciators
Control and Display Board and Interface Board
DC Circuit Breaker
FIGURE 5-1 BLOCK DIAGRAM, TYPICAL MICRO ARE-M FLOAT CHARGER
To improve the output voltage regulation against changes in load and input frequency, the chargers employ a
ferroresonant transformer and UNIPOWER controlled-ferro technique, which controls the level of core
saturation.
This is accomplished by shunting the resonant circuit with a triac in series with an inductor. The electronic
voltage/current control senses the start of the resonant capacitor charge cycle. It also senses the output voltage
level, which it compares with a reference voltage. The error signal that results determines the instant the triac
turns on to interrupt the capacitor charge cycle and maintain the core saturation at the desired level.
The output current sensing and current limit operation is located on the Interface and Control/Display boards.
The output current is sensed by measuring the voltage across a resistive shunt. The Interface and
Control/Display boards convert the shunt signal into an output current value. When the output current exceeds
the preset level, the current limit control overrides the voltage control to reduce the output current to the preset
value.
Over-voltage protection is located on the Interface and Control/Display boards. If a fault occurs that result in
the charger output going to an excessively high output voltage, a high voltage shutdown is initiated. The high
voltage shutdown trips the input breaker via the input breaker’s shunt trip coil to turn the unit off. If the
excessive high voltage condition persists, a second protection circuit, independent from the first, operates to trip
the input breaker and to turn the triac on.
