Alternator 101
Posted: 13 Feb 2018 09:32
There is a lot of talk about alternators on different pages on the forum with a lot of assumptions and some untruths.
Here I will share what I know about 12v automotive alternators and how they function. If my facts are wrong , please correct them with factual proof.
An alternator consists of a rotor , stator , rectifier and voltage regulator and a set of brushes.
Mechanical components are two end plates , each housing a bearing. At the drive end is a pulley with cooling fan.
The rotor is a fast spinning electro magnet that is powered with an energising dc current from the regulator. There should be resistance between the two slip rings and the wind should be completely isolated from the shaft body.
The stator has three long isolated copper wires wound inside a soft metal housing fitting tightly around the rotor. At one end , the wires are connected together(starpoint) and at the other end (output) it is connected to the rectifier. When the rotor (magnet)turns inside the winding , alternating current is generated.
There should be equal resistance between the three open ends of the wind and completely isolated from the metal core.
The rectifier has three positive and three negative diodes mounted on a positive and a negative plate. It converts the alternating current from the stator to direct current suitable for charging a battery. The diodes get damaged with incorrect jump starting or a bad connection on the earth/ positive wire to the battery. On most modern alternators , the diodes can not be separately tested and the complete plate is replaced if faulty.
The voltage regulator measures the system (battery) voltage and then increases or decreases the energising current to the rotor through the brushes and slip rings. This changes the intensity of the electromagnet and as a result , the output current. It is usually energised by the small current from the dash warning light at start up and then draws current from the output when operational. The light goes out because the energising point becomes a positive when the alternator is in operation. Pre set parameters will cause the alternator to produce maximum amperes when the voltage is at a low limit (11v) and gradually reduce output until the system maximum voltage (14.5v) is reached. These are sealed electronic units and are replaced when suspect. Different voltage parameters are available , but most units are set to standard.
The alternator base must be properly connected to the negative pole of the battery through the engine bonding cable.
The positive output terminal must be directly connected to the positive terminal of the battery. No current should run when the engine is turned off.
The warning light (energising) wire becomes active when ignition is turned on.
To properly test function , a dc voltmeter and a dc amp meter is needed. The charge rate amps must be close to max output when battery is depleted from starting or winch activity and should gradually decrease as the battery becomes charged. When volts reach battery maximum , only 2 to 4 amps output is correct.
As components in the vehicle requires energy , the alternator will react and match the draw with equal recharge.
Here I will share what I know about 12v automotive alternators and how they function. If my facts are wrong , please correct them with factual proof.
An alternator consists of a rotor , stator , rectifier and voltage regulator and a set of brushes.
Mechanical components are two end plates , each housing a bearing. At the drive end is a pulley with cooling fan.
The rotor is a fast spinning electro magnet that is powered with an energising dc current from the regulator. There should be resistance between the two slip rings and the wind should be completely isolated from the shaft body.
The stator has three long isolated copper wires wound inside a soft metal housing fitting tightly around the rotor. At one end , the wires are connected together(starpoint) and at the other end (output) it is connected to the rectifier. When the rotor (magnet)turns inside the winding , alternating current is generated.
There should be equal resistance between the three open ends of the wind and completely isolated from the metal core.
The rectifier has three positive and three negative diodes mounted on a positive and a negative plate. It converts the alternating current from the stator to direct current suitable for charging a battery. The diodes get damaged with incorrect jump starting or a bad connection on the earth/ positive wire to the battery. On most modern alternators , the diodes can not be separately tested and the complete plate is replaced if faulty.
The voltage regulator measures the system (battery) voltage and then increases or decreases the energising current to the rotor through the brushes and slip rings. This changes the intensity of the electromagnet and as a result , the output current. It is usually energised by the small current from the dash warning light at start up and then draws current from the output when operational. The light goes out because the energising point becomes a positive when the alternator is in operation. Pre set parameters will cause the alternator to produce maximum amperes when the voltage is at a low limit (11v) and gradually reduce output until the system maximum voltage (14.5v) is reached. These are sealed electronic units and are replaced when suspect. Different voltage parameters are available , but most units are set to standard.
The alternator base must be properly connected to the negative pole of the battery through the engine bonding cable.
The positive output terminal must be directly connected to the positive terminal of the battery. No current should run when the engine is turned off.
The warning light (energising) wire becomes active when ignition is turned on.
To properly test function , a dc voltmeter and a dc amp meter is needed. The charge rate amps must be close to max output when battery is depleted from starting or winch activity and should gradually decrease as the battery becomes charged. When volts reach battery maximum , only 2 to 4 amps output is correct.
As components in the vehicle requires energy , the alternator will react and match the draw with equal recharge.