Alternator - Stator - Generator differences.

The drawing above is to example what an AC wave looks like on an oscilloscope face screen. An oscilloscope is just another meter to measure voltages and frequencies. A frequency is based on any frequent occurrence, it could be electricity, unbalanced rotating weight, or the frequency of you drinking a cup of coffee. The waves coming onto the shore could be the frequency of the waves but then look and count all the waves 1 foot high and it becomes a specific frequency of a one foot wave in the sea of all the other possible wave heights. When I use the term frequency I will specify because frequencies need to be exact for the generation and commonly used household AC @ 120 Vac.

An electrical frequency is counted by the second, it is called Hertz or Hz in formulation. A frequency normally associated with the common 120 Vac in the U.S. is 60. At 120 Vac and 60 Hz a light will use a specific amount of current and dependent upon it's total resistance in Ohms (R). At twice the frequency the same light will draw twice the current. This would immediately blow out the light and it works the exact same with all AC appliances in the common household. On an AC alternator the speed of the rotation from the input power determines the frequency and that frequency is counted each time a magnetic field is crossed through by a coil of wire. In an alternator for example when there is one coil and one magnet passing one another it produces one frequency if the rotation speed is 60 RPM. At 60 RPM of the input rotation the magnet would pass the coil one time each second and that is 1 Hz. 

AC electricity has to be generated as it is used and inversely has to be used as it is generated and cannot be stored unless it is rectified with a diode and changed into Direct Current (DC). 

Here are some common varieties of alternators used to charge a 12 volt DC system. The reason they can charge a battery is due to the AC produced gets rectified by diodes and then regulated to go into the battery. An alternator can be used to produce AC voltage and run a light or drill motor. In the earlier years some mechanics used an alternator to power 120 Vac hand tools in the field, it requires small modification but will work fine. The point is that as the speed of the alternator changes as the engine RPM varies and that changes the frequency and voltage. It will ruin most AC devices because they need a specific frequency at a specific voltage continuously to operate efficiently.


So the modern automobile alternator generates AC voltage that needs rectified into a specific direction of travel within the wiring or electrical conduit. When a diode is used to slice (chop) a wave it takes the top half or the bottom half and then the AC becomes DC and can be put into a battery. The voltage in the alternator is high and when chopped in half, 120 AC volts as seen in the diagram becomes 60 Vdc which is to high to charge into a 12 volt battery so again the voltage gets changed to 14 and regulated into the battery.


An alternator has coils, diodes, & a regulator. It takes voltage to get an alternator to charge in an automobile or mobile piece of equipment and these are electromagnetic alternators. A stator alternator in a common small engine uses permanent magnets and can charge without having voltage in the beginning to start the charging.

Pictured above are four major parts to make electrical energy, they are found inside of an alternator (auto electromagnetic) and most all other electrical power generation known today. First we need a magnetic field (north & south polarity) and that is called the Rotor far left or picture 1. The rotor has no permanent magnets inside however has a coil of wire wound around that creates a magnetic field when electrical current is connected to it. For additional details on magnetic fields go to our Magnet page of this site.


In picture one the two bands of copper looking rings on the left end of the rotor is where dc electrical energy is applied and connected. Brushes are used to make that connection and rub on the rings, one is to the battery + and the other is attached to the battery -. When dc voltage is present at those two rings (brush contact) the coil of wire produces a magnetic field and the metal becomes saturated with magnetism (gauss). Depending upon the applied voltage at the brushes i.e. 1 Vdc produces 50 gauss and that is equal to magnetic pressure. Each volt added produces more gauss and for example 10 volts may produce 1,000 gauss which is a strong magnetic field. So now the rotor is rotated by the frictional attachment from the belt to the engine crankshaft pulley.

The magnetic field produced by the dc electrical current contains a north magnetic polarity on one end and a south magnetic polarity on the other end of the horizontal axis of the rotor. The metal triangle shapes on the left end of the rotor translate the magnetic polarity through them and the triangle shapes on the right end translate the opposite magnetic polarity. Go to the Power Generation page on this site to get deeper into the physics of making electrical energy.


Picture 2 is a stator for a three phase ac alternator, it has three coil leads and is not grounded to the metal they are wound around. Picture 3 is called a diode block which rectifies the ac into dc and the following picture is a voltage regulator IC (integrated circuit).


With these components alternating current can be produced and made to travel in one specific direction within the wiring of the equipment (dc) and then regulated at a safe battery level into the battery.

The schematic drawing on the left above is to example what a mechanic is interested in when repairing a 3 phase alternator. At the far left in the picture is called a field coil and when you apply an electrical current to it a magnetic field containing a North and South magnetic gauss (strength) becomes observable in the surrounding areas and is translated through the metal on the rotor. As seen in the drawing there is one wire in at ground and the electrons flow into the coil of the electro magnet. The more electrical voltage (E) that is applied and for example a volt at a time proportionally changes the gauss strength of the magnetic field. The coil strength goes by the number of turns around the core. A coil with 100 rounds around the core may have a potential of 100 gauss and when you add one more volt will add 100 more gauss to the strength and so on. The more gauss in strength the more current potentially can be generated to charge the battery. This rotor only produces a magnetic field and does not carry the charged current.