TYPICAL BATTERY CHARGER
TROUBLESHOOTING EXPLANATION

DOES A.C. BREAKER (FUSE) TRIP IMMEDIATELY?

1. Improper A.C. line voltage. This can mean either the wrong A.C. voltage is being applied (check nameplate for proper voltage), or the A.C. voltage supply is not connected to battery charger correctly. Refer to schematic and A.C. input terminal block label.
2. One, or both, SCR’s shorted will cause the A.C. over current device to trip. Disconnect one transformer lead from the SCR anode (Heatsink). The SCR anode appears as the mounting stud of the device and will always be connected to a heatsink. If the breaker does not trip, the problem is in one of the SCR’s. If the breaker still trips, isolate the transformer by disconnecting the lead going to the transformer primary. Otherwise, the fault is with the breaker which is either faulty or underrated. The A.C. breaker should be rated between 140% and 200% of the A.C. current nameplate rating.

IS THE POWER L.E.D. ON? OPTIONAL

1. L.E.D.’s operate on approximately 15 milliamps. A larger current may destroy the L.E.D., or with less than 10 milliamps, the L.E.D. will not light. The L.E.D.’s power source is the 15 VAC secondary taps of the control transformer. A diode (1N4007) rectifies this to 14.3 VDC, while a resistor (1 KOHM, 1/2 Watt) limits current to the safe operating value of 14.3 milliamps. If 15 VAC is measured across the control transformer leads connected to the L.E.D. circuit, and the resistor and diode are known good, the L.E.D. is at fault. If 15 VAC is not measured, investigate for an open lead, as either L.E.D., or control card can operate without it.

IS THERE OUTPUT VOLTAGE?

1. Check the A.C. source and over current protection. If a voltage is read across the D.C. fuse, the fuse is open. Check current limit setting and D.C. fuse rating. D.C. fuse is rated approximately 150% the rated current value.
2. Use an external voltmeter to verify the operation of the voltmeter in unit. If the voltmeter is at fault, check for loose connections.
3. Check for A.C. voltage on transformer secondary, between the shunt and the SCR anode (Heatsink). If a voltage reading slightly higher than the rated output voltage is attained, the transformer, and the unit up to that point is operational.
4. Both SCR’s would need to be open to block the output voltage. One open SCR will block half the voltage resulting in a maximum of half the rated voltage across the D.C. output.
5. Check for D.C. voltage between shunt and the SCR cathode to verify the choke is not open.
Check for loose connections that would block D.C. output voltage.
6. A faulty control card may not “fire” the SCR’s resulting in no output voltage. Check for 15 VAC between pins 1 and 6, or pins 2 and 6. If no voltage or less voltage than 1.5 VAC is indicated, check the control transformer. The control transformer is fed by a 15 VAC tap from the secondary of the power transformer, and provides a 15 VAC center tap which powers the control card. If 15 VAC is measured at Pins 1 and 6 of control card, the card is suspect.
Replace the control card with a known good card and check for proper unit operation.

IS THE OUTPUT VOLTAGE THE CORRECT VOLTAGE?

1. Verify proper float and equalize control settings. Remember the current limit mode overrides control voltage. Check to see if the unit is not in current limit.
2. One SCR open will cause half waving” resulting in a maximum of half the rated voltage across the output. Check the voltage between the shunt and each SCR cathode. A lack of voltage indicates an open SCR. Remove the SCR from the circuit and check it using an ohmmeter as indicated by using the table on troubleshooting diagram.
3. The voltage program resistor provides the signal which allows the control card to sense the output voltage at any instant. Check for a loose connection from the positive (+) output, through the resistor, to Pin 12 of control card. Without this voltage sense lead, the voltage control potentiometer can not control the output voltage, which will swing from 0 volts to rated voltage and back to 0 volts.
4. To check for a faulty control card, refer to Item 6 under Is There Output Voltage?
5. To check the transformer for proper output voltage, measure between the shunt and each SCR anode (Heatsink). A voltage reading slightly higher than rated voltage indicates that the transformer is functioning properly.

IS OUTPUT RIPPLE WITHIN LIMITS?

1. Standard output ripple (A.C. voltage) should not exceed 5% rated output voltage (RMS). Depending on special requirements, the ripple may be some other value.
a. Measure the A.C. ripple voltage across the output voltage, using a digital A.C. voltmeter. If the measured voltage is not the desired ripple voltage, the filter network may be at fault.
b. Check for a shorted choke by measuring the A.C. voltage before and after the choke.
c. If capacitors are used, check to see capacitors are not open or shorted.
The battery must be connected to the D.C. output to achieve the designed ripple voltage.

IS VOLTAGE REGULATION WITHIN LIMITS?

1. Measure D.C. output voltage at no load, and at full load conditions. Determine voltage regulation using this formula:

% REGULATION = (NO LOAD - FULL LOAD) x l00 / FULL LOAD

If regulation is worse than ± 0.5%, the control card is suspect.
Check for 15 VAC between Pins 1 and 6 of control card. If this voltage exists, replace control card with a known good card.

IS OUTPUT CURRENT CORRECT?

1. If unit is in current limit, the current is fixed at the value set by the current limit control.
2. The control card senses the current, at any instant, from the millivolt drop across the shunt.
Check for loose connections from the shunt to the control card.
3. Check for 15 VAC between Pins 1 and 6 of the control card. If this voltage exists, replace the card with a known good card.

DOES UNIT CURRENT LIMIT?

1. Load does not draw enough current to exceed the current limit setting.
2. Refer to Items 2 and 3 under Is Output Current Correct?

SPECIAL NOTES

On units rated over 50 volts D.C., an auxiliary firing circuit is required. It is used to supply a lower phase voltage to the control card, which alleviates stress on the electronic parts caused by higher voltages. The circuit consists of an additional winding on the secondary which supplies 25 volts A.C., through an RC network, to the control card. The RC network consists of a diode, resistor, and capacitor mounted on a solder lug, which in turn is mounted on the back of the control card holder bracket. An A.C. voltage of about 25 volts should be measured between the SCR cathode and Pin 15 and 16 of the control card.
On units with options, refer to operating instructions for a description of the particular option and the schematic in the back of the service manual.
On three phase units, the method of troubleshooting is similar. Refer to the addendum for three phase chargers and the schematic in back of service manual.