1. Before starting the test, check:
- installation of a generator;
- battery;
- alternator drive belt tension;
- fusible link;
- absence of extraneous noise from the generator when the engine is running.
2. Turn off the ignition.
Caution! The battery must be slightly discharged. The load created by a fully charged battery is insufficient to accurately perform this test.
3. Disconnect the cable from the negative terminal of the battery.
Fig. 9.2. Generator output current test diagram: 1 – battery; 2 – ignition switch; 3 – low battery indicator light; 4 – generator relay; 5 – voltmeter; 6 – ammeter; 7 – load
4. Disconnect the wire from the "B" terminal of the generator. Connect the wire from the "+" terminal of a DC ammeter with a measurement range of 0–100 A to the "B" terminal of the generator, and then the wire from the "–" terminal of the ammeter to the wire disconnected from the "B" terminal of the generator (Fig. 9.2).
Warning! Do not use clamps (crocodile clips) when connecting to an electrical circuit. Tighten the connections with bolts and nuts. Otherwise, a bad connection (using crocodile clips) may cause a serious malfunction or an accident due to high current.
Attention! It is recommended to use an ammeter with an inductive type sensor ("current clamp"), which allows you to measure the current without disconnecting the wire from the "B" terminal of the generator.
5. Connect the wire from the "+" of the voltmeter with a 0–20 V scale to the "B" terminal of the generator, and the wire from the "–" of the voltmeter to the "ground".
6. Connect the tachometer.
7. Connect the previously disconnected wire to the negative terminal of the battery.
8. Leave the hood open.
9. Check the voltage shown by the voltmeter. It should be equal to the battery voltage.
Warning! If the voltmeter shows 0 V, the probable cause is a break in the circuit (including the fuse) between the generator terminal "B" and the positive terminal of the battery.
10. Under the steering wheel exterior lighting switch, turn on the headlights, and then start the engine.
11. Immediately after turning on the high beam headlights and turning on the heater fan to maximum speed, increase the engine crankshaft speed to 2500 min⁻¹ and read the maximum value of the generator output current (shown by the ammeter).
The maximum permissible value is 70% of the rated output current.
Since the current generated by the generator drops rapidly after the engine is started, the test must be performed as quickly as possible in order to measure the maximum value of the output current.
The magnitude of the output current will depend on the electrical load and the temperature of the generator housing.
If the electrical load is low during the test, the specified value of the generator output current will not be achieved, despite the fact that the generator is in good condition. In such cases, to increase the electrical load (in order to discharge the battery), turn on the high beam headlights for a while or connect the external lighting of another car, and then repeat the test.
The specified value of the generator output current may not be obtained also as a result of overheating of the generator housing or too high ambient air temperature. In such cases, let the generator cool down and perform the test again.
The ammeter readings should be above the maximum permissible value. If the ammeter readings are below the maximum permissible value and the generator terminal "B" circuit is in good condition, remove the generator from the vehicle and test it on a bench.
12. After checking, let the engine idle.
13. Turn off the ignition.
14. Disconnect the cable from the negative terminal of the battery.
15. Disconnect the ammeter, voltmeter and tachometer.
16. Connect the standard wire to the generator terminal "B".
17. Connect the negative cable to the battery.