Engine Running, Lamps On. Under these conditions, the generator should supply the current for the lights, and still send a charging current of 3 to 5 amperes through the battery. This means that the current drawn from the battery when the engine is not running and the lights are all turned on should be at least several amperes less than the charging current which the generator sends into the battery when the engine is running and the lamps are turned off.
Tests to Be Made by the Repairman
The battery repairman can, and always should, make a few simple tests which will tell him whether the various conditions of operation are normal. This should be done as follows:
1. Install the battery carefully (see page 236), and connect the negative battery cable to the negative battery terminal. Now tap the positive battery cable on the positive battery terminal. If a snappy spark is obtained when this is done, some of the switches are open or are defective, the cutout is stuck in the closed position, or there are grounds or short-circuits in the parts which are permanently connected to the battery.
Even though no spark is obtained when you tap the positive battery cable on the positive battery terminal, there may be some trouble which draws enough current from the battery to cause it to run down in a short time. To detect such trouble, connect a voltmeter (which has sufficient range to indicate the battery voltage) between the positive battery cable and the positive battery terminal. (Cable is disconnected from the terminal.) If the voltmeter now gives a reading equal to the voltage of the battery, there is some condition causing a current leakage from the battery, such as a cutout stuck in the closed position, defective switches which do not break the circuits when in the open position, or grounds or short-circuits in the cables and wires connected to the battery.
If the voltmeter pointer does not move from the "0" line on the scale, complete the battery connections by fastening the positive battery cable to the positive battery terminal, and make the test described in Section 2. If the voltmeter pointer moves from the "0" line, and gives a reading equal to the battery voltage, connect the voltmeter permanently between the positive battery cable and the positive battery terminal and make a general inspection of the wiring, looking for cut or torn insulation which allows a wire or cable to come in contact with the frame of the car, or with some other wire or cable, thereby causing a ground or short-circuit. Old, oil-soaked insulation on wires and cables will often cause such trouble. If a general inspection does not reveal the cause of the current leakage, proceed as follows:
Closed Cutout, or Defective Cutout Windings. (a) If the cutout is mounted outside the generator, remove the cover from it and see if the points are stuck together. If they are, separate them and see if the voltmeter pointer returns to the "0" line. If it does, you have found the trouble. The points should be made smooth with 00 sandpaper. See that the moving arm of the cutout moves freely and that the spring which tends to hold the arm in the open position is not weak or broken.
If the voltmeter pointer does not return to the "0" line when the cutout points are separated, or if the points were not found to be stuck together, disconnect from the cutout the wire which goes to the ammeter or battery. If this causes the voltmeter pointer to return to the "0" line, the cutout is defective and a new one should be installed, unless the trouble can be found by inspection and repaired.
If the voltmeter pointer does not return to the "0" line when the battery or ammeter wire is disconnected from the cutout, see paragraph (d)
(b) If the cutout is mounted inside the generator, disconnect from the generator the wire which goes to the ammeter or indicator. If this causes the voltmeter pointer to return to the "0" line, the cutout points are stuck together or the cutout is defective, and the generator should be taken apart for inspection. If this does not cause the voltmeter pointer to return to the "0" line, replace the wire and see paragraph (d).