Battery charger testing

Every charger being serviced should be given a routine, step-by-step test procedure that will reveal quickly the cause, or causes, of failure.

  • a. First, remove the access panel, or panels, of the charger case, and make a visual inspection of all parts for any obvious defects, such as burned rectifiers, transformers, and resistors.
  • b. With the battery clips insulated from each other and not connected to the battery, plug the AC cord into the input tester shown in Figure 1-1, in the article Test equipment required for battery chargers, and adjust the controls for charging by turning on the timer and line switch. The voltmeter reading on the input tester should be below the line voltage as the rate switch is turned through each step. If the voltmeter reading is zero, there is a short. If the voltmeter reading does not move below the line voltage, there is an open circuit in the primary circuit. If there are no shorts and no opens, then turn the input tester to full line voltage and do step c. If there is a short, first check the rectifiers, or disconnect them. If they are good, proceed to the selector switch, transformer and the like until the shorted part is located. If there is an open circuit, first place a jumper wire across the timer and line switch. If still open, connect a test cord, as shown in Figure 1-1 in the article Test equipment required for battery chargers, to the two line cord connections, to test for an open in the line cord and plug.
  • c. Connect the battery clamps to the battery, observing correct polarity.

If there is a large spark when touching the clamps to the battery, and the rectifier is not shorted, recheck the polarity of the clips. It is not un­common to find that the cable clamps have been reversed by someone.

Check the polarity with a D.C. voltmeter connected to the clamps with the charger on, but not connected to the battery. The meter positive is the battery charger output positive. A small spark may be caused by the current drawn by polarity protector bulbs, or by a very low reverse current through the rectifier. If there is no sparking, plug in the A.C. cord and proceed to test the unit.

  • d. If the charger has a fan motor, it should be running. If it runs quietly at full speed, just clean and oil it. If it does not run, check for a binding shaft, bent blades, or an open circuit in the motor coil. A slow running motor may just need to be cleaned and oiled. If the shaft has excessive side-play, or is noisy, the fan motor should be replaced.
  • e. If the unit does not charge, the rectifier conducts properly and there is a D.C. output voltage across the transformer-rectifier, there is an open circuit between the rectifiers and the batteries. Check the D.C. cables, clamps, solenoid, circuit breakers, ammeter and the like, including all connections. If the charger is equipped with an alternator protector, and the light indicates "reverse polarity", check three things: (1) reversed polarity of the battery clamps; (2) open circuit in the D.C. output circuit, poor clamp contact, open (broken) cable, solenoid contacts burned, ammeter open, circuit breaker open, and the like; (3) burned out base lamp, such as #313,433, or open base resistor.
  • f. On protector-equipped chargers, the solenoid may "click", but it may have burned contacts, that can not close the D.C. circuit. With the charger set up to charge, and turned on, place a heavy jumper wire across the two large terminals of the solenoid while observing the ammeter. If the ammeter pointer moves upward any detectable amount, the solenoid should be replaced or repaired. Solenoids can temporarily make contact in the heavy contacts. They may work perfectly in the shop, but when moved or shipped back to the customer, the large copper washer contact inside the solenoid may rotate to a bad spot, and not work every time for the customer. Therefore, replace or repair the solenoid when nothing else is found defective, but the charger does not charge every time it is turned on.

If the solenoid does not operate, as determined by the familiar "click", there are several other possible causes, such as an open solenoid coil, a shorted diode across the coil which will cause the ballast lamp to burn brighter than normal, a defective transistor, or a burned out collector or ballast lamp (or resistor).

  • g. Feel the A.G cord and plug and the D.G cords and clamps for any warm or hot spots. Hot spots indicate a high resistance area caused by a poor connection or partially broken cable, which should be corrected. On chargers showing signs of long hard use, remove the strain reliefs, move the cords 2 or 3 inches into the charger, and reinstall the strain reliefs. This gives a new flexing point for continued good service, and prevents premature failure.