30SI Series and 34SI Series Alternator Caterpillar

1. Before you start the machine, connect a voltmeter between the "B+" terminal and the case of the alternator. Turn OFF all electrical loads.

2. Turn the key to the ON position but do not start the engine.

   Expected Result: This voltage should be system voltage.

   Results:

   • YES - The voltage is system voltage. Go to Step 2

   • NO - The voltage is less than system voltage. Verify that the batteries are good and verify that battery connections are good. Go to Troubleshooting, "T4 Alternator Drive System - Check" if the batteries are good.

2. INITIAL CHECK OF ALTERNATOR OPERATION

   1. The voltmeter remains connected in the configuration from Step 1.

   2. Start the machine. Set the throttle to at least 75%. Read the voltage on the voltmeter.

      Expected Result: The voltage is higher than the voltage recorded in the previous Step 1.

      Results:

      • YES - The voltage is higher than the voltage observed in the previous Step 1. The voltage is also lower than the maximum voltage that is listed in the specifications for the alternator. The alternator is partially charging the battery. See the following diagnostic flow chart for reference in continued testing. Proceed to Troubleshooting, "T1 Alternator Output - Test".

      • YES - The voltage is higher than the voltage observed in the previous Step 1. The voltage is also higher than the maximum voltage that is listed in the specifications for the alternator. The alternator is over charging. Proceed to Troubleshooting, "T8 Alternator Overcharging - Test".

      • NO - The voltage is not higher than the voltage observed in Step 1. Proceed to Troubleshooting, "T4 Alternator Drive System - Check".

Note: Severely discharged batteries can cause low system voltage. This can occur even while the engine is running above idle, and the alternator is working properly. Proper low engine idle is also important. The alternator is self-excited. Self-excited alternators must exceed a turn-on speed before the battery will charge. Alternator output can be very low at idle.

Illustration 1	g00508188