ABYC Diesel Practice Exam

How can an indication of alternator output be evaluated?

1. Comparing engine temp when running

2. Measuring fuel consumption

3. Comparing battery voltage with engine running versus not running

4. Checking only the starter's performance

The correct answer is: Comparing battery voltage with engine running versus not running

Evaluating the output of an alternator is key to ensuring that it is functioning correctly and adequately charging the battery while the engine is running. One effective method to assess alternator output is by comparing the battery voltage when the engine is running versus when it is not running. When the engine is off, the battery voltage should typically be around 12.6 volts for a fully charged battery. When the engine is started and the alternator is operational, the voltage should increase, usually falling within the range of 13.5 to 14.7 volts, indicating that the alternator is generating sufficient voltage to charge the battery. This direct comparison provides a clear indication of the alternator's functionality. Other methods mentioned, such as comparing engine temperature or measuring fuel consumption, do not provide a direct insight into the alternator's performance. Engine temperature might indicate how well the engine is operating but does not relate to the alternator's output. Measuring fuel consumption may show the engine's efficiency or power requirements, but it does not reflect the electrical output of the alternator. Checking the starter's performance alone does not provide information about the alternator’s ability to generate power while the engine is running, as the starter draws power only during startup.