Current Sensing Resistor; Dc Voltmeter, M2; Dc Ammeter, M1; Filter Capacitors - HindlePower SCR series Operating Instructions Manual

h. Current Sensing Resistor
1. In light current chargers, the current sensing signal is taken directly across the DC ammeter. In
chargers with 50 Amp or higher output current, the sensing resistor is a meter shunt which also serves as
the shunt for the panel ammeter. Use a portable precision digital voltmeter and measure the voltage drop
across the current sensing resistor. With a rated current output indicated on the panel ammeter, a nominal
voltage drop of approximately 30mV (in proportion to rated current) should be observed. If the voltage
drop is higher or lower than the nominal indication, replace the ammeter or shunt and recheck the voltage
drop.
i. DC Voltmeter, M2
1. The DC voltmeter is of the 2 percent accuracy type. It is connected across the charger output to
the battery and should indicate regardless of whether or not the charger is operating or the DC breaker is
ON. If it does not, use a precision voltmeter of the 1% accuracy type connected across the meter terminals.
An indication on the test meter will show that the panel meter is open. Check the wiring for an open
circuit, or replace meter if circuit wiring is complete.
2. A shorted voltmeter will show no indication. Battery current through a shorted meter will cause
a visible indication such as smoke from burning wire insulation. Disconnect the charger from the battery
and AC source and replace the meter and damaged wiring.
3. If the meter calibration is in doubt, checking against a precision meter will determine if the panel
voltmeter is off calibration more than two percent.
j. DC Ammeter, M1
1. The charger DC ammeter is connected in series between the charger output and battery. If open
it will indicate zero, or if shorted, it will also indicate zero. First be certain the connections are tight. If still
no indication, turn CB1 and CB2 breakers to OFF, disconnect the charger ammeter (and/or shunt) and
substitute a precision ammeter of suitable range. Be certain to make solid connections; clip contacts may
not carry sufficient current, or may make poor contact and cause the reading to be inaccurate.
2. A reverse-scale indication of the meter indicates the charger is inoperative or internally shorted,
and that the battery is discharging through the rectifier, or that the meter leads have been reversed. Turn
CB1 and CB2 to OFF and check wiring and meter connections. Then check meter operation, using a 1 ½-
volt D-cell as the power source. Momentarily touch D-cell terminals (with proper polarity) to meter
terminals and observe meter deflection.
k. Filter Capacitors, C1 & C2 (Filtered Chargers Only)
NOTE: Capacitors C1 and C2 may consist of one or more parallel connected capacitor units as
required by the filtering requirements. C2 normally is used only in chargers with the filtered eliminator
option.
CAUTION: The filter capacitor is on the charger side of the blocking diode, CR2, and is NOT charged
by the battery when CB2 is turned ON. When the charger is turned OFF (CB1 opened) the capacitor will
hold a charge until discharged by bleeder resistor, R1. Capacitors C1 and C2 should always be discharged
before servicing in the event the R1 has opened and no longer serves as a bleeder.
9