# What is the difference between an alternator and a generator?

What is the difference between an alternator and a generator ?

• Utility and power station engineers distinguish between 1) the engine, the source of mechanical energy, i.e. a diesel engine; 2) the alternator, the device that converts rotational mechanical energy to AC electrical energy; and 3) the generator-set, which is the combination of an engine with an alternator, also including a fuel tank, control gear, and so forth. – Li-aung Yip Sep 27 '13 at 8:24

Realistically, not a lot. An electrical generator is any electro-mechanical device that converts mechanical energy (typically a spinning shaft) into electrical energy (a current). This is the exact opposite of the operation of an electric motor which converts a current (electrical energy) into mechanical energy. As such, some motors can also function as generators if the shaft is externally driven.

Generator is an umbrella term; there are various types of generators, but the only ones pertinent to your question are a dynamo and an alternator. A dynamo is a common generator used on bicycles to power lights, but it has been used for many other purposes as well. It incorporates a "commutator" which periodically switches the direction of the current flow from the rotor to the external circuitry to generate DC power.

If the commutator is removed, a dynamo is essentially an alternator producing AC power. The frequency of the resulting signal is determined by the windings of the generator and the rotational speed of the internal rotor. Technically, any generator that produces AC power is an alternator, but usually only the smaller AC generators driven by internal combustion engines (such as the one in a car) are known as such.

• Some reviews need to sleep a bit. The dynamo without the commutator is a Magneto, this should be included, and not called a dynamo. Also most of the bicycles generators are magnetos wrong called dynamos. – Diego C Nascimento Jan 11 '14 at 3:04
• @DiegoCNascimento A magneto is a type of alternator, and not a common one at that. I specifically said that a dynamo without a commutator is an alternator, hence, a magneto under certain circumstances (permanent magnets instead of coils, etc). And I didn't say "most bikes..." I said a dynamo is a "common generator" on bikes. I can't speculate what is used on "most bikes" just what I have seen. Your comment is misguided. – Kurt E. Clothier Jun 15 '14 at 22:27
• @KurtEClothier The message was directed to the reviews. Anyway, you said a "dynamo without a commutator" and I just added to your answer to better explain its just a didactic approach, so it be clear what I device like that is called if someone needs more information. I didn't say that you said "most bikes...", and the important point is the wrong identification of the two devices, not if it is or not used on most bikes. The comment is constructive, you are free to like or not, but the facts are one (just forget the bike part then). – Diego C Nascimento Jun 16 '14 at 23:27

A generator is a device for converting mechanical energy into electrical energy, either alternating current (AC) or direct current (DC).

An alternator is a specific type of generator that produces alternating current (AC).

• A generator produces direct current. What? NO! Alternator is a type of generator. – AndrejaKo May 8 '13 at 20:46
• @AndrejaKo I fixed my answer to make it more accurate – jwygralak67 May 8 '13 at 20:57
• Removed my downvote – AndrejaKo May 8 '13 at 21:08

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