Exide Technologies Section 93.20 - Manual (Page 20)

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If it is necessary to adjust the LVA threshold in the field, the user must load the battery bank and allow
the battery voltage to drop while decreasing the float voltage adjustment to the desired cut-off potential. The
LVA potentiometer is then adjusted so that the LVA relay is activated into the low voltage alarm condition.
Note that there is a delay time, up to 30 seconds before the relay operates once the threshold voltage is
reached. It will be necessary to raise and lower the battery voltage several times to ascertain that the
potentiometer setting is correct.
Similarly the battery bank will have to be charged at a high equalize rate in order to set the HVA
threshold. At the equalize rate the charger may go into a current limit condition, depending on the state of
charge, and it may be impossible to reach the desired high voltage alarm voltage. If this is the case, it will be
necessary to substitute a resistive load bank with paralleled capacitance in place of the batteries. Adjust the
output voltage of the charger by using the "EQUALIZE" potentiometer (R5) and then set the HVA
potentiometer accordingly.
It will be noticed that there is an operational delay time and a hysteresis zone (dead zone) between the
drop out voltage and the pull-in voltage of the alarm circuits. This is natural and desirable to prevent
chattering of the relays when the threshold voltage is reached.
The factory preset thresholds for alarm conditions are as follows unless otherwise specified:
LVA 2.00 volts/cell for LEAD ACID
1.14 volts/cell for NICKEL CADMIUM
HVA 2.40 volts/cell for LEAD ACID
1.65 volts/cell for NICKEL CADMIUM
5. CHARGER FAILURE ALARM RELAY (EJ0127) - WITH OPTIONAL INDICATOR LIGHT
Purpose: The Charger Failure Alarm provides an alarm indication whenever the charger output current
decreases to below 2% of rated current for more than 30 seconds. Alarm contacts are wired to TB3 terminals
19, 20 & 21 and an optional front-panel indicator (DS7) is available.
Description: Charger output current is sensed by means of an auxiliary winding on the main inductor
(L1). The CFA PC Board assembly (A3) detects the voltage signal from L1. When the voltage signal
indicates that the current has dropped to below 2%, an on-board relay switches to provide the alarm
indication. When the output current is restored to a value above 2%, the alarm will be automatically reset.
6. BATTERY DISCHARGING ALARM RELAY WITH INDICATOR LIGHT (EJ0120)
Purpose: The Battery Discharging Alarm indicates the condition when the battery is no longer receiving
adequate charging current from the charger and has become a source of current for the load. Alarm
indication is provided by a front panel lamp (DS10) and relay contacts. Alarm contacts are wired to TB3
terminals 22, 23 & 24.
Description: This is accomplished by monitoring the direction of current flow in a DC meter shunt
(SH3) connected in the main battery lead. When this current polarity changes from negative to positive the
alarm circuit is activated.
EJ0120 shows the connection diagram of the alarms. An op-amp voltage comparator senses when the
input signal from SH3 changes from negative to positive polarity. The op-amp output goes “high” and
activates the alarm.
The alarm board derives its power from the battery terminals. If necessary, voltage-dropping resistors are
used to properly match the battery voltage.