Ac Voltmeter/Ac Ammeter; High And Low Dc Voltage Alarm Relays - HindlePower SCR series Operating Instructions Manual

Description: The principle of operation utilizes the normally closed contacts of an AC relay. The relay
is powered from the AC line at the primary of the power transformer T1. The relay, when energized, holds
the normally closed contacts open disabling the alarm indication. When the AC line fails or the AC circuit
breaker is opened for any reason, the alarm contacts will close activating the alarm indicator. EJ0085
shows the circuit with the optional panel indicator lamp and external relay connections for remote
indication. The indicator lamp must operate from the battery power since the AC line power is not
available in an alarm state. As a result, the indicator light operating voltage must match the battery DC
voltage or must utilize a series dropping resistor to compensate for the difference in voltage between the
battery and indicator lamp.
3. AC VOLTMETER AND AC AMMETER OPTIONS
Purpose: These options are to permit the user to monitor the input AC line voltage and line current to
the battery charger. This may be done for either single phase or three phase input power.
Description:
a. Single phase AC: EJ0095 and EJ0134 show the connections to the voltmeter and ammeter. The
ammeter is usually connected to the AC line via a current transformer if the line current is over 50
Amperes.
b. Three Phase AC: EJ0121 and EJ0135 show the connections utilizing a single voltmeter and single
ammeter to monitor the three phase-to-phase voltages and the three line currents. This is accomplished by
using a two-pole, three position switch (SW5) to switch the voltmeter from phase-to-phase to check all
three input voltages. The ammeter switch (SW6) is a special switch that shorts all unused current
transformer secondaries, and upon changing switch position shorts the current transformer secondary in
use before transferring the ammeter to a new position. This prevents very high voltage arcs when the
secondary is open circuited. CAUTION: NEVER OPERATE A CURRENT TRANSFORMER
WITHOUT A SECONDARY LOAD OR SHORT CIRCUIT ACROSS THE SECONDARY
TERMINALS.
4. HIGH AND LOW DC VOLTAGE ALARM RELAYS (EJ0083-XX) WITH OPTIONAL LIGHT
Purpose: The HIGH/LOW Voltage Alarm (HLVA) provides alarm indication for the DC system in the
event of a malfunction of the battery charger or extended loss of AC power which causes the battery
voltage to drop to a dangerous level. Alarm indications are provided by relay contacts and optional front
panel lamps.
Description: The HLVA printed circuit board consists of two independent operational amplifier
circuits, one monitoring the battery voltage for a high voltage condition and the other monitoring for a low
voltage condition.
The board obtains its operating voltage (12VDC) from the battery terminals and if required, an
externally mounted dropping resistor (R57).
There are two potentiometers on the HLVA board (A2 PCB Assy.). Viewed from the component side
of the board, the potentiometer near the top-left of the board is the LOW voltage alarm (LVA) threshold
adjustment. The right-hand potentiometer at the top of the board is the HIGH voltage alarm (HVA)
threshold adjustment.
14