How does a technician measure the amperage output of an alternator

How does a technician measure the amperage output of an alternator

First, the mechanic will check the battery cables to make sure they are clean. Next, a voltmeter is used to check that the battery has the correct voltage, which is approximately 12.6 volts. Once a good battery voltage has been established, the battery is then subjected to a load test to see if it can withstand fifty percent of the rated load for fifty seconds without the voltage dropping below 9.6V.

Once the battery has been checked, the alternator charging system can be checked. During the test, the mechanic can use a voltmeter to measure the output voltage and an ammeter to measure the alternator amperage. Once the test equipment is connected as required, the mechanic begins testing the alternator. Start the engine and record the voltage and amperage at idle. The engine is then accelerated to between 1,500 and 2,000 rpm and another measurement of voltage and amperage is taken. All lights and accessories were now turned on and the same readings were recorded. The engine accessories were disconnected from the engine and the engine was stopped.

The measurements were analyzed to determine if the voltage and current were within vehicle specifications. At high idle, the reading under load should be around 13 volts and 85% of rated amperage. This is usually the value for most vehicles; vehicle specifications may vary. Some alternators are internally regulated, others are controlled by a computer module. Always follow the vehicle manufacturer's recommendations for checking the charging system. If the reading is below the specified voltage, the alternator is discharging. If the alternator voltage is higher than the maximum voltage, the system will be overcharged and the battery or components will be damaged.