Automatic systems, such as the automatic start-stop system are installed to reduce the fuel consumption and emissions. There are different versions and requirements depending on the vehicle manufacturer. For this reason, highly efficient alternators with overrunning alternator pulley and starters with a reinforced structure for frequent starting processes are installed. The automatic start/stop function can only be guaranteed if all components of the start and charging system are operating correctly.
In this system, the charging system is intelligently controlled via the engine control unit (ECM). The central electronics module (CEM) sends a request about the desired charging voltage for the main battery to the engine control unit from where this request is forwarded to the alternator regulator. The charge signal lamp in the instrument cluster is controlled via the CAN network. At the same time, the engine control unit switches on the secondary battery via a relay for the charging process. The charging time of the secondary battery is calculated by the central electronics module and forwarded to the engine control unit.
The starter, also known as the starter motor , is required to start the internal combustion engine. Starters are electric motors that are briefly connected to the engine during the starting process via a ring gear that bring it to the desired starting speed. Depending on the design, the current consumption of the starter can be well over one hundred amperes. By reinforcing individual components, the starter has been designed for an increased number of start cycles over its entire service life.
Before starting the alternator test, the batteries must be tested first. A simple check of the state of charge can be carried out with a commercially available voltmeter. The open-circuit voltage of the battery can be measured directly at the battery terminals by establishing the voltage. However, for this purpose, all electrical consumers in the vehicle must be switched off first. A good battery must show a voltage of 12.4 to 13.2 volts.
If the measured value is below 12.4 volts, the battery must be charged and then checked again. In the event that the result after charging is still negative, check the battery with a battery tester and replace it if necessary.
In order to better assess the overall condition of a battery, it is advisable to test the battery with a suitable battery tester, such as the BPC-TOOL. After a short time, a statement about the state of charge (SOC) and the state of health (SOH) of the battery becomes available on this tool. If both batteries are OK, as is the case in our example, you can start the alternator test.
First check the belt drive's and the electrical connections' condition and functions.
Then check the power supply of the alternator. For this purpose, connect a suitable measuring device to alternator terminal B+ and the housing ground on the alternator. The measurement result must be equal to the battery voltage. The setpoint value in this case is the battery voltage with a maximum deviation of < 0.5 volts. If the voltage difference is greater, check the wiring for weak points, such as interruptions or contact resistance.
Checking the alternator charging voltage and charging current
Use a suitable measuring device and proceed as follows to measure the alternator output:
In this process, the control voltage must not drop below the setpoint value (13.7 to 15.0 volts) by more than 0.5 volts and the amperage must be higher than the total current consumption of all activated consumers.
In modern vehicles with battery management systems different functions can be opened to run tests in the vehicle, depending on the vehicle manufacturer and system. In our sample vehicle, any occurring faults in the charging system, engine control unit, and central central electronics module are recorded and stored in the fault memory. The alternator can be diagnosed either using the engine control unit as well as the central electronics module.
Many vehicle systems additionally provide digital measured values as parameters to enable fast diagnosis. Parameters indicate the current status or setpoint and actual values of the component. In this example, information about the IBS sensor and the battery's state of charge can be accessed
