Charging Systems- Alternator Testing

Alternator output on car testing

Before working on any vehicle to do an alternator test you must do a check for safety and general preliminary checks before starting to test the charging circuit. These checks include

·         Is the park brake applied?

·         Is the vehicle transmission in park or neutral?

·         Does the charge warning light operate?

·         Are the ignition and all accessories turned off?

·         Have you carried out a visual inspection of the connections?

·         Have you checked the alternator mounting?

·         Check the condition of fuses and the fusible links

After inspecting these parameters you can start to carry out the circuit tests on the alternator. Firstly you must determine the condition of the battery by doing an OVC check on it. To check the OVC you place your voltmeter Positive and Negative to the batteries positive and negative terminals. The results you should be looking for are between 12.4v and 12.6v this is equal to 50% and 100% charge. Next, you have to determine the condition of the voltage regulator, the specifications for this is anything between 13.8v and 14.5v. to check the regulating voltage you attach he voltmeter to the battery again, turn the car on and rev to 3000RPM, what you are looking for in this check is a change in the voltmeters reading, as it should go up, if the regulating voltage is too high is would affect the charging system by blowing bulbs in the dashboard. Next you have to determine the ‘No load current’ the specs for this test is anything between 10amps-18amps for a fuel injected engine. To check the no load current you have to turn the car on and rev the engine to approximately 1500-2000RPM, clamp the ammeter to the B wire terminal coming off the alternator.

The next test is determining the voltage and output load; to perform a load test on the alternator you have to have the car running, connect the leads of the load tester to the positive and negative terminals, clamp the ammeter on the lead running from the battery to the alternator. Also the voltmeter must be connected to the battery as well. Turn on all accessories such as headlights, fans etc. What you are expecting to happen is the readings on the meters to increase from the no load test, as there is now load be introduced to the circuit. Lastly you need to perform a charging system voltage drop test. The voltage drops you need to carry out are

·         Positive side volt drop, the spec for this is <0.2v

·         Negative side volt drop, the spec for this is again <0.2v

To carry out the positive side volt drop, attach the positive of the voltmeter to the positive of the battery and the negative of the voltmeter to the alternator output (B+) while the engine is running. For the negative side attach voltmeter negative lead to the battery negative and the positive lead to the alternator body. The reading you would expect from a good system is less than 0.2v. a high voltage drop could affect the system by not letting it charge properly.

The alternator testing is now complete.