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[pic][pic]PATH: Engine Electrical > Charging System > Alternator > Testing > Field Circuit Resistance Test
Field Circuit Resistance Test
Excessive resistance in the circuit can be detected by this test. Fluctuation of the instrument panel ammeter may be caused by excessive resistance in the regulator wiring circuit. Refer to the field circuit resistance test illustration.
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|Field circuit resistance test |
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1. Disconnect the ignition wire at the coil side of the ballast resistor. Connect the positive lead of the test DC voltmeter to the battery positive post and connect the voltmeter negative lead to the voltage regulator field (FLD) terminal. Be sure that all lights and accessories are turned off.
2. Turn on the ignition switch. Switch the voltmeter to its low-voltage scale (if so equipped). The voltage reading should not exceed 0.55 volt. A reading in excess of 0.55 volt indicates high resistance in the field circuit between the battery and the voltage regulator field terminal.
3. If high resistance is indicated, move the negative voltmeter lead to each connection along the circuit (see illustration) toward the battery. A sudden drop in voltage indicates a loose or corroded connection between that point and the last point tested. To test the terminal for tightness, attempt to move the terminal while observing the voltmeter. Any movement of the meter pointer indicates looseness.
4. Turn off the ignition switch, disconnect the voltmeter, and reconnect the ignition primary wire at the coil side of the ballast resistor.
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[pic][pic]PATH: Engine Electrical > Charging System > Alternator > Testing > Current Output Test
Current Output Test
Internal malfunctions of the alternator will be indicated by this test. After completing the charging circuit resistance test, continue with the procedure below.
1. Start the engine and, immediately after starting, reduce the engine speed to idle.
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|Current output test |
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2. Adjust the rheostat and the engine speed in increments until an engine speed of 1,250 rpm and a voltmeter reading of 15 volts is obtained.
|CAUTION |
|Incremental increases in engine speed should not be large enough to allow voltage to go above 16 volts. |
3. Observe the ammeter reading. The output current should be within the limits listed in the "Alternator and Regulator Specifications" chart. If the output is slightly less (5 to 7 amperes) than specified, it may be an indication of an "open" rectifier or other alternator internal problems. If the output is considerably lower than that specified, it may be an indication of a possible "shorted" rectifier or other internal problems. In either case, it is recommended that the alternator be removed and replaced with a new or reconditioned unit.
4. When this test is completed, adjust the idle speed to specification, turn off the rheostat, and switch off the ignition.
5. Disconnect the battery ground cable.
6. Disconnect and remove the ammeter, voltmeter, tachometer, and rheostat.
7. Remove the jumper from between the alternator FLD terminal and ground. Connect the FLD lead to the alternator FLD terminal.
8. Connect the battery ground cable.
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[pic][pic]PATH: Engine Electrical > Charging System > Alternator > Testing > Charging Circuit Resistance Test
Charging Circuit Resistance Test
This test will indicate excessive resistance in the charging circuit.
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1. Disconnect the battery ground cable.
2. Disconnect the BAT lead at the alternator output terminal.
3. Connect a 0–75 ampere scale DC ammeter in series between the alternator BAT terminal and the disconnected BAT (see illustration).
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|Charging circuit resistance test |
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4. Connect the positive lead of the test voltmeter to the disconnected BAT lead. Connect the voltmeter negative lead to the battery positive post.
5. Disconnect the FLD lead from the alternator.
6. Connect a jumper lead from the alternator FLD terminal to ground.
7. Connect an engine tachometer according to the manufacturer's instructions. Connect the battery ground cable.
8. Connect a carbon pile rheostat to the battery terminals. (See illustration.)
9. Start the engine and, immediately after starting, reduce the engine speed to idle.
10. Adjust the engine speed and rheostat to obtain 10 amperes (20 amperes for transistorized voltage regulators) flowing in the circuit. Observe the voltmeter reading. The reading should not exceed 0.3 volt (0.7 volt for transistorized voltage regulators). If higher voltage reading is indicated, you must inspect, clean, and tighten all connections in the charging circuit. A voltage drop test may be performed at each connection to locate the connection with excessive resistance.
11. When the test is completed, reduce the engine speed, turn off the rheostat, and switch off the ignition. Leave all of the other connections intact and continue with the current output test.
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