Yeah, because a generator will generate electricty by simply spinning it. Where an alternator needs an excitment charge to start generating electricity.

Also, a generator voltage output is variable based on its speed.

James

 

An alternator is a generator. It just needs a little bit of power to excite the field coils. Please explain to me the difference.

 

Generator makes DC driectly and an alternator makes AC which it rectifies to DC maybe?

 

Well, sort of. It's just two ways of saying the same thing. ALL generators/alternators produce AC.

...I'm having a hard time explaining it because theres little difference between the two, and in my mind, I must refer to an alternator as a generator since I come from an electronics background...

A typical automotive "generator" (or "dynamo") is simply a DC motor that is spun by the engine. AC is produced in the armature. This current is converted to DC by the commutator. Brushes ride along the commutator, connecting and disconnecting the output terminals from the windings in the armature. They are configured so that the output polarity (based on the position of the armature windings in relation to the magnets) is always correct. Hence, you get a dirty DC output.

An "alternator" is simply a (usually) 3 phase "induction" generator based on the designs of Nikola Tesla. The alternator spins the magnets inside the fixed windings, thus generating AC in the windings. It is then up to the regulator/rectifier assembly to output DC. You still get a dirty DC output though.

This dirty DC is why you should never run a car without the battery. The battery functions as a huge filter capacitor, smoothing out the pulsing DC.

Both the "generator" and "alternator" control their output with the field coil. This allows them to produce roughly the same voltage depending on how fast the engine is spinning. If you spin a generator/alternator faster, it will produce a higher voltage. Field weakening is also used on motors to produce a higher speed (but less torque) at a constant supply voltage. Everything about motors also generally applies to generators, but in reverse.

Really, it is proper to refer to an "alternator" as a generator, since they are both generators. But in automotive circles, it can be confusing because cars used to come with DC generators (though many old time techs still refer to them as "dynamos" or "gennies"). So most people make the distiction between an "alternator" and a "generator", even though they are both generators...

It's more confusing that way...

 

electronics background,.. that explains it,.. me = pwned,...


we were talking about cars though... where alternator and generator have there own automotive definitions.

 

Yeah, that's the problem. Too many terms that mean the same thing, yet mean different things in different contexts...

Motor vs. engine is one. It's technically correct to refer to a gasoline engine as a motor (according to the definition), but most engineers/EEs take "motor" to mean "electric motor". So whenever somoene here writes "motor" instead of engine, it gets on my nerves. Even worse are those people who say "electric engine". That's completely invalid, since "engine" generally means that output is made through chemical or heat energy....anyway....