INSTALLATION, OPERATING AND TROUBLESHOOTING INSTRUCTIONS FOR MODEL A75D / A75DE –
THREE PHASE
Page 18 of 20
DC Breaker Trips
Possible Cause:
1.
Shorted power SCR. (repair/replace as required).
2.
Shorted battery cells or customer equipment.
3.
Shorted output cables.
4.
Capacitors not pre-charged.
5.
Loose connections on the DC fuse.
Charger operates but output voltage/current is low.
Possible Cause:
1.
Float/Equalize voltage potentiometers not set correctly (see float/equalize adjustment
procedure for proper voltage setting).
2.
Check SCR’s
3.
Control assembly is defective. (Replace as required)
4.
Unit in current limit.
5.
Defective shunt.
Charger operates but output voltage is high.
Possible Cause:
1.
Float/Equalize voltage pots not set correctly (see float/equalize adjustment procedure for
proper voltage setting).
2.
Control assembly is defective. (Replace as required)
Ground and short circuit test.
A simple ohmmeter check can be performed to check the unit for a short to ground,
primary to secondary breakdown, AC-DC short, or DC ground. Before installation of a
new unit, the above checks should be made before installing. If a short of this type is
suspected on a unit in service, check as follows:
1.
Disconnect AC input power to the unit. Disconnect the DC battery and loads from the rectifier.
2.
Set ohmmeter scale on ohms scale RX100.
3.
Measure from one terminal of the input to one terminal of the output. Meter should not
indicate. If the meter reads full scale deflection, this indicates an ac-dc short. During
shipping, an AC wire may rub against the DC lugs, terminals, etc. and cause a short. These
problems may be eliminated by being very careful in inspecting the wiring to make certain the
AC wires are not touching the DC wiring.
4.
Check the input terminals to ground and check the output terminals ground. If the meter
indicates full scale deflection, a wire is touching a metal part of the rectifier. Look for wires
that are near any metal part and inspect for possible breakdown caused by shipping. The
heatsink of the diodes and the control unit are insulated from ground through the mounting
legs.
CHECKING CAPACITORS
When checking capacitors be sure all AC power is turned off and battery is disconnected from unit.
Check capacitors with DC voltmeter to see that DC voltage is at near -0- volts, then short circuit
capacitor. Momentarily short circuit the capacitor leads to assure complete discharge. Connect the
meter test leads to the capacitor leads or terminals and observe indicated resistance.
A good capacitor will indicate an initial low resistance and gradually increase as the capacitor charges.
The final resistance of a good capacitor is usually several hundred thousand ohms approaching a
megohm.
Initial high resistance approaching infinity indicates an open capacitor. Initial and continued low
resistance readings indicate a shorted capacitor.
When ordering replacement parts, drawings, or schematics, always give model number,
serial number and AC input voltage.
