Kussmaul Electronics 091-106-150-12-120 - Manual (Page 2)

INTRODUCTION
SYSTEM DESCRIPTION
The charger contains a power transformer, control circuit assembly, SCR rectifier,
current sensing resistor, and ammeter. The Power transformer lowers the A.C. Input
Line Voltage to the level as required by the particular model. The transformer
secondary is applied to the rectifier assembly in which the A.C. Voltage is rectified
in D.C. Voltage to charge the battery. A block diagram appears in Figure 1.
The rectifier assembly contains 2 diodes and 2 silicon controlled rectifiers. Voltage
control of the rectifier assembly is obtained by varying the trigger angle at which the
SCR's are fired. Delaying the trigger angle decreases the voltage while advancing
it increases the voltage.
The control circuit board contains circuits which detect the charger output voltage,
compare it to a precise reference voltage to generate an error signal. This error
signal is amplified and converted to a variable phase signal to trigger the output
SCR's. Charger output current is detected with a current sense resistor. The current
sense signal is used to over-ride the voltage commands to limit the maximum
charger output to its' rated value. This protects the charger when recharging a
deeply discharged battery or when a load in excess of the charger's current rating
is applied to the battery. The current signal is also utilized in the Auto-Equalize
circuit. When recharging a battery composed of a number of cells in series, it is
important to fully charge each of the cells. This is accomplished by raising the
charger output voltage. Many chargers have a Float/Equalize switch. In the float
position the output voltage is the desired battery float voltage. When the switch is
placed in the equalize position, the output voltage is raised 8 to 10%. After
recharging at the equalize voltage for a period of time an operator must manually
switch back to the float position.
If this is not done and the battery is held at the
equalize level for a period of time, there is danger of water boil-off. Other
chargers contain a timer which permits the operator to select the time period for
which equalize charging will occur.
The Auto-Equalize circuit as incorporated in the Auto Charge's controller solves
the equalize problem. Whenever the charger output is limited by the current limit
circuits, a signal is fed back to increase the voltage setpoint. The charger is then in
the equalize mode. As the battery is charged up to the equalize voltage, the output
current starts to decrease. When this occurs, the voltage set-point is reset to the
float voltage and the battery is maintained at the float level.
The Auto Charge 150 Series of chargers are precise float chargers packaged in a
powder coated steel industrial enclosure which utilizes control concepts and
circuitry proven over many years and tens of thousands of installations in fire trucks,
ambulances, and emergency vehicles. The charger is designed to be connected to
the battery to continuously charge the battery, pick up any electrical loads and by
precise voltage control, assure that the battery is not overcharged.