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The car generator is the main power source of a vehicle; its function is to supply power to all electrical devices (except the starter) while the engine is running, and at the same time charge the battery. The purpose of testing the current and voltage of an automotive generator is to evaluate its charging capacity, which is related to the electrical load applied to the battery. Any charge drawn from the battery must be replenished by the generator. The output of the generator is specified, and it must not be under-charged or over-charged. For the 12V series generators, the specified output voltage is 14V. For the 24V series generators, the specified output voltage is 28V. Channel 1 of the oscilloscope is connected using a BNC to banana plug cable; the red alligator clip is attached to the test wire and connected to the positive terminal of the battery, while the black clip is connected to the negative terminal. Channel 2 is connected using a current probe, with the probe set to a range of 100A. Click ZERO for automatic zeroing. Start the engine and turn on the electronic accessories (headlights, heater, etc.). Some cars may require the engine to run for 60 seconds or longer before starting to charge. Open the automotive repair testing package for the oscilloscope, select the charging/startup circuit, then choose either 12V or 24V for charging, and click OK to display the waveform. The measurement options below the oscilloscope will automatically display the high value and peak-to-peak value of the generator voltage on channel 1, as well as the peak-to-peak value, amplitude, and frequency of the generator current on channel 2. If the oscilloscope does not come equipped with automotive testing software, then we will need to make these settings manually. First, we set the oscilloscope’s time base to 100ms. Next, we set the attenuation ratio of probe channel 1 to 1X; also, make sure that the coupling mode is DC coupling and that the probe type is voltage. Channel 2 adjusts its attenuation ratio according to the current probe being used; the probe type is current, and the coupling method is also DC. Then, following the previous connection method, after connecting the probes, it is possible to observe the current and voltage waveforms of the car’s generator on the oscilloscope. Finally, we can open the oscilloscope’s measurement options and select the desired measurement items for observation. A good charging system sees an increase in charging current as the battery voltage drops, and vice versa. The rectified voltage can be measured with a multimeter, but when one of the diodes in the generator fails and causes the output to decrease by 33%, the multimeter still shows a normal reading. The only correct way to monitor the output of a generator is to use an oscilloscope to observe its voltage and current waveforms. The figure below shows the starting voltage and current of the Mazda vehicle, measured using a current probe with a 1KX attenuation ratio.