1986/07/01 Caterpillar

All Truck Engines Equipped With Brushless Alternators

Charging problems can be encountered when installing new or remanufactured brushless alternators. In some cases the alternators may not begin charging and might be considered defective. Brushless alternators are self-excited. This means they begin charging at start up, without the use of an external power source. Self-excited brushless alternators use residual magnetism in the field core material, to generate sufficient current to start the charging process. Charging problems with these alternators usually result when the residual magnetic field in the alternator is reduced below the level needed to "excite" the alternator. The residual magnetism can be reduced by:

... Dropping or rough handling of the alternator.

... Storage temperatures above approximately 38 °C (100°F).

... Extended storage periods of more than three to six months.

... Manufacturing tolerances in the alternator.

... Alternator disassembled for repairs.

Before returning or replacing a brushless alternator (for failing to charge after installation), use an external power source to restore the residual magnetic field. Use a jumper wire to connect the POSITIVE (+) output terminal of the alternator to the "R" (relay) terminal of the alternator (D+ terminal on Bosch ®alternators) for approximately two seconds. This temporary connection should provide sufficient current from the vehicle batteries to restore the residual magnetic field in the alternator.

If the alternator failed to charge from one of the above causes, this procedure should restore residual magnetism so that self-excitation will occur at the next start-up.