Does a Generator Generate DC or AC

There are two different ways to generate electricity in a rotating generator. One is to rotate a coils inside a magnetic field. The problem is to then capture the generated voltage from a rotating mechanism to bring it to the outside world. This is done by using brushes and slip rings. But the output is AC.

 

The rotating coils in a DC generator are called an armature There are usually many coils connected to commutator segments.

 

All rotating generators generate AC initially in the rotating armature. In a DC generator the conversion to DC is performed by the commutator and brushes. Capturing the energy output produced by using brushes is a rather inefficient method.

 

An alternator uses a magnetic field rotating inside a set of coils that are fixed in a housing. This means the energy can be simply connected by wires to the outside world. The output is AC. This method is much more efficient. The magnetic field is created by using brushes and slip rings to supply the power to the rotor coils. Much less energy is lost in this way because the current in the rotor is relatively low compared to the generated output. The output can easily be converted to DC by using rectifier diodes.

 

At the most fundamental level, a generator is a source. What is generated maybe be power or data, most any waveform you can think of. However, you are probably making the unsaid distinction that you want to talk about power generators.

 

The simplest power generator is a coil which is moved through a magnetic field. The simplest mechanical solution to that is to make a coil rotate through the magnetic field, alternately cutting magnetic lines of force in one direction and then cutting them again in the opposite direction on the “return” half of the revolution. This leads to a current being induced in the coil with one polarity and then an equal current induced in the coil with opposite polarity. If you view the voltage across the coil, you will see a sine waveform for every complete revolution of the generator, so we would call this device an alternator since it creates an alternating output.

 

If you would like the alternator to produce a DC output, you have two choices.

 

You could arrange a mechanical selector switch (called a commutator) on the rotating coil. This switch serves to reverse the coil’s output connections every half-rotation. The voltage output of this device (historically called a generator) is a series of half-sine waves with peaks at double the rotational frequency. (Think of the alternator’s positive and negative sine wave and then think that the commutator “folds” the negative half-cycles up above the zero level.) This does not create pure DC, but rather a common polarity with a big ripple content.

You could also apply an alternator’s AC output waveform to an electronic rectifier (no commutator needed), which would again create a half-sine pulsing DC.

In the automotive World, historical names for power generators have obscured their true function (just as automotive capacitors were long called “condensers” despite the fact that they have nothing to do with condensation). If you took an alternator and equipped it with a commutator, it created pulsing DC and was called a generator. If you took an alternator and equipped it with rectifiers, it created pulsing DC and was called an alternator.