What's the difference between an alternator and a generator?

Question

Just wondering.

Thanks.

Answer 1

An alternator makes DC voltage, a generator makes AC voltage.

Answer 2

"Alternators are used in automobiles to charge the battery and to power all the car's electric systems when its engine is running. Alternators have the great advantage over direct-current generators of not using a commutator, which makes them simpler, lighter, and more rugged than a DC generator. The stronger construction of alternators allows them to turn at higher speed, allowing an automotive alternator to turn at twice engine speed, improving output when the engine is idling. The availability of low-cost solid-state diodes from about 1960 allowed auto manufacturers to substitute alternators for DC generators. Automotive alternators use a set of rectifiers (diode bridge) to convert AC to DC. To provide direct current with low ripple, automotive alternators have a three-phase winding."

Read all about the topic at the link below.

Source(s):
http://en.wikipedia.org/wiki/alternator...

The key different between an alternator and a generator is what spins and what is fixed. On a generator windings of wire (the armature) spin inside a fixed magnetic field. On an alternator, a magnetic field is spun inside of windings of wire called a stator to generate the electricity. This allows the wires to be directly and easily connected to their outputs without the need for sliding contacts to carry the relatively high output current. The magnetic field is still generated via electro magnets mounted on a rotor, and the relatively small field current that powers them is supplied to the rotor by two small brushes that each ride on a separate and continuous slip rings. These smooth slip rings (unlike the comparatively rough contacts on a commutator in a generator) and the fact that the relatively heavy windings are fixed instead of rotating allows the alternator to be spun to much higher speeds. This allows it to reach it's maximum output sooner and to be spun fast enough at engine idle speeds to produce enough electricity to power most (if not all) of the needs of the car without relying on the battery.

http://www.rowand.net/Shop/Tech/AlternatorGeneratorTheory.htm

Answer 3

Alternator produces ac. Generator can be used as term for ac or dc.

Therefore an alternator is a generator.

Answer 4

Generators
First up is the generator, also known as a dynamo. I explain it first because it functions in a more basic way and is easier for many people to understand. These are the original electrical generation units used on automobiles - it was much later on that alternators were invented and car manufacturers switched over to them. To understand alternators, you should make sure you have a basic understanding of generators as many of the pieces and basic theory are the same.

The generator is like an electric motor in reverse. Instead of applying electricity to it to make it spin, when you spin it, it makes electricity. It does this by spinning a series of windings of fine wire (called the armature) inside of a fixed magnetic field by connecting them to a belt and pulley arrangement on the engine. As the armature is spun by the rotation of the belt and pulley, it gets a current and voltage generated in those windings of wire. That current and voltage will be directly proportional to the speed that the armature spins and to the strength of the magnetic field. If you spin it faster, it makes more and if you make the magnetic field stronger it makes more current. The speed of the spinning is controlled by the speed of the engine - that's why you need to rev the engine up to help charge the battery faster. The magnetic field is controlled by an electro-magnet, so by changing the amount of current supplied to the electro-magnets that make up the field you control the strength of the magnetic field. This current is referred to as the "field" current and it is controlled by the regulator in response to the electrical needs of the automobile at any given time.

The voltage of the generator is controlled by the number of windings in the armature. The current output varies widely from zero if the battery is perfectly charged and nothing is using any power up to the maximum rated output of the generator. The current output is controlled by the field current, but also by the speed at which the armature is spinning. This is important because a generator can only put out it's maximum rated current at or above some speed - at lower speeds the output drops off very quickly. This is why a generator-equipped car will not charge (or even maintain!) the battery at idle and this is one of the main reasons for the development of the alternator.

The current generated in the armature is AC - not DC. To get it converted to DC so it can charge your batter and run your headlights, a device called a commutator is used to "rectify" this situation. It is on the armature and has a series of contacts along it's outer surface. Two spring-loaded brushes slide on the commutator - one brush is connected to ground and the other is connected to the main output of the generator. As the armature and commutator assembly rotates, the brushes come touch the different contacts on the commutator such that the polarity of the current moving in the armature is always connected to the correct brushes. The net effect of this is that the generator output is always DC even though the current inside the armature windings is always AC.

A generator has to be "polarized" after the system is connected and before it is used. This is typically done by momentarily connecting the main output terminal of the generator to the battery with a jumper wire. This allows things to be set up so that the generator produces power of the correct polarity due to residual magnetism in the generator. For a simple visual image, imagine trying to jump start a car and reversing the jumper cables on one vehicle. It's not something you really want to do - unless of course you like sparking, arcing, and possibly burning out electrical components... This is important if you ever disconnect a generator or regulator - you must polarize it (follow the instructions in the manuals for your car!) before starting the engine.

A generator will have three connections - the field, the armature, and ground, although the ground is sometimes an "implied" connection because everything is metal and is bolted together. The field terminal is the smaller of the two main connections and is typically labeled "F". The armature is the bigger of the two main connections and is typically labeled "A" - this connections carries the main power output of the generator. Consult your manual for the specifics. All three connections go directly to the regulator and there will be a separate output on the regulator for the battery. The OEM regulator is almost always a mechanical device, although some aftermarket replacement units could be solid-state. (I don't know of any myself, but it is theoretically possible to build one.) A typical generator wiring diagram from a 1958 Buick is below for reference - click on the image to see a larger view.



Alternators
The more modern and more capable alternator is explained here. Every modern vehicle uses an alternator - and for good reasons. It is more complicated than a generator, but that added complexity brings a few very good features that you will most certainly want on your vehicle - mainly the fact that it will charge the battery at idle and can support the higher amperages needed to run all of the electrical equipment on a modern vehicle. Alternators tend to be more reliable than a generator and have fewer "hard to diagnose" problems as the system ages - particularly the internally regulated models. The internally regulated models are also very easy to service if something goes wrong - there is only one part to fail (the alternator itself) and replacing it is a simple 30 minute job. This all adds up to the performance and reliability that is expected in a modern vehicle.

The key different between an alternator and a generator is what spins and what is fixed. On a generator windings of wire (the armature) spin inside a fixed magnetic field. On an alternator, a magnetic field is spun inside of windings of wire called a stator to generate the electricity. This allows the wires to be directly and easily connected to their outputs without the need for sliding contacts to carry the relatively high output current. The magnetic field is still generated via electro magnets mounted on a rotor, and the relatively small field current that powers them is supplied to the rotor by two small brushes that each ride on a separate and continuous slip rings. These smooth slip rings (unlike the comparatively rough contacts on a commutator in a generator) and the fact that the relatively heavy windings are fixed instead of rotating allows the alternator to be spun to much higher speeds. This allows it to reach it's maximum output sooner and to be spun fast enough at engine idle speeds to produce enough electricity to power most (if not all) of the needs of the car without relying on the battery.

There are typically three separate windings of wire in the stator that are all set to so that the AC current that is generated is slightly out of phase in each one. The peaks and valleys of the rising and falling current do not happen at the same time, rather they are staggered a bit. This increases and smoothes the electrical output of the alternator much the same way that a 8 cylinder car runs more smoothly than a 4 cylinder one does - there are more power pulses happening in each revolution allowing more total power and better smoothness.

The process of rectifying the AC current into DC current is handled inside the alternator by something more complex than a commutator - diodes. A diode is a "solid state" device that allows current to flow in one direction only - "solid state" means it does this without any mechanical or moving parts. It relies on the different electrical properties of the materials it is made of to act as a one-way valve for current. By arranging diodes so that current from each of the three stator wires is only allowed to pass in one direction, and by connecting the three outputs together, you get a reasonably smooth and stable DC output without any moving parts. (This arrangement is typically manufactured as a single part and is referred to as the diode pack or diode trio.) This lack of moving parts makes the alternator not only very reliable - but also comparatively inexpensive to build and repair. That diode trio costs well something trivial like $1 to produce in large quantities.

Alternators do not need to be polarized after installation. You mount them to the engine, plug them in, and go. This is an advantage for not only manufacturing the car but for servicing it as well.

On externally regulated models, there are typically four connections on the alternator - the large output terminal (BAT), the ground terminal (GRD) which may be "implied" though the metal mountings of the alternator, the field connection (F), and terminal #2 on the regulator is a separate connection to one of the three poles on the stator (R). Unlike on a generator, the BAT terminal is directly connected to the battery and the rest of the cars wiring system, while only the F, R, and GRD connections will connect to the regulator. Also, terminal #3 on the regulator (if present) is connected to the main junction block for the wiring system and serves as a "remote voltage sensing" wire. Terminal #4 on the regulator will be connected via small wires to the charge indicator light on the dashboard of the car and the charge resistance wire. The regulator itself can be a mechanical or solid state device. A typical externally regulated alternator wiring diagram from a 1963 Buick is below for reference - click on the image to see a larger view.





On internally regulated models, there are also four connections on the alternator, but there is no separate regulator in the system - it is inside the alternator and constructed of solid-state components. The connections here are the large output terminal (BAT), the ground terminal (GRD) which may be "implied" though the metal mountings of the alternator, and two connections typically labeled simply 1 and 2. Terminal #1 on an internally regulated alternator is the same as terminal #4 on the regulator of an externally regulated system - it connects to a small wire that is goes to the charge indicator light on the dashboard of the car and the charge resistance wire. Terminal #2 on an internally regulated alternator matches terminal #3 on an external regulator - it is connected to the main junction block for the wiring system and serves as a "remote voltage sensing wire". If you are comparing to the externally regulated wiring, then you will note that the F and 2/R wiring connections are done inside the alternator. A typical internally regulated alternator wiring diagram from a 1973 Buick is below for reference - click on the image to see a larger view.