ELBOW 7C1421 - Caterpillar

Test Conditions and Connections
Illustration 1 g00869277
Disconnect the battery from the alternator only when the alternator is not rotating. Alternator must not be in operation (rotating) when the regulator is connected and disconnected. Do not recharge the battery during tests. Do not operate the alternator without the battery.Alternator and voltmeter must each be connected in parallel with the battery. Conduct tests when the alternator and regulator are cold 20 °C (68 °F).
Connect the carbon pile in parallel with the battery.
Connect the negative battery cable to the "D-" or "B-" alternator terminal.
Connect one lead of the ammeter to the positive battery cable.
Connect the other lead from the ammeter to the "B+" alternator terminal.
Observe correct polarity when connecting the voltmeter.
Connect the positive voltmeter lead to the "B+" alternator terminal.
Connect the negative voltmeter lead to the "D-" or "B-" alternator terminal.Note: The N3 series alternator must be externally excited, if the alternator has been reassembled with a new rotor. The alternator can be externally excited by a 3 Watt resistor or a 24 V indicator lamp (3 Watt). Thereafter, the alternator is self-excited.Refer to the Service Manual, "Specifications" section of this manual for additional information.Test Procedure
The following table outlines the alternator speed during testing.
Table 1
Alternator    Test Speed    
7N-9720     4000 rpm    
9G-9538     5000 rpm    
100-5046     5000 rpm    
Set the load current to five amperes by adjusting the carbon pile.
Readjust the alternator speed. Refer to 1 for the test speeds.Expected results:In about one minute, the regulated voltage should read 27.9 0.4 V.Results:OK - Disconnect the alternator from test equipment.NOT OK - The regulator is damaged. Replace the regulator.Note: The N3 series alternator must be externally excited, if the alternator has been reassembled with a new rotor. The alternator can be externally excited by a 3 Watt resistor or a 24 V indicator lamp (3 Watt). Thereafter, the alternator is self-excited.