How to run diagnostics and remove the cause of trouble of an alternator
Every vehicle is equipped with various electronic devices. In order to power them, it is necessary to organise the on-board network. This is the responsibility of the car alternator, which we will discuss here.
The car alternator works in conjunction with the battery, recharging it and powering the on-board network while the engine is running, converting the engine's energy into electrical energy.
To better understand the mechanism of the generator, we suggest to get acquainted first with its device:
No. 1– pulley;
No. 2– washer;
No. 3– front cover;
No. 4 – spacer ring;
No. 5 – rotor;
No. 6 – stator;
No. 7 – back cover;
No. 8 – casing;
No. 9 – rectifier unit with capacitor;
No. 10 – brush holder with voltage regulator.
A few words about how a car alternator works:
When the ignition key is turned, current flows to the field winding through the brushes and slip rings. A magnetic field is induced in the field winding. Torque is transmitted to the rotor from the crankshaft of the motor. The magnetic field acts on the stator winding and an alternating voltage is generated at the stator winding contacts. At nominal rotor speed, the alternator starts to operate in self-excitation mode.
The alternating voltage from the stator winding is converted to direct voltage by the generator diode bridge.
When diagnosing an alternator, you should pay attention to 2 key parameters:
1- The RPM when the alternator is excited and starts generating rated voltage. The nominal voltage for a 12 volt alternator is approximately 14.5V.
2- Current at maximum rpm. Approximately 3000 rpm of the crankshaft.
What faults may be:
- Intermittent shorting of the field winding;
- Stator winding intermittent short-circuit;
- One of the phases shorted to the chassis;
- Regulator relay malfunction;
- Diode bridge malfunction.
A variable component greater than 10 per cent of the load current will tell us that there is some fault in the alternator.
How to properly diagnose and troubleshoot – see our video on YouTube channel! The information will be useful for car service masters and those who are engaged in repair of automobile units and assemblies on their own.
The information will be useful for car service masters and those who are engaged in repair of automobile units and assemblies on their own.
