Alternator or Generator? 1

[SEP87]

I'm sure this must have been covered somewhere but I can't find it.

I'm trying to find the exact engineering definition of a Generator and how it differs from an Alternator.

I am aware of two different definitions and I'm struggling to find which one is correct.

1) Generator is a generic term for any device which converts mechanical energy into electrical energy. Thus an Alternator is a type of generator.

2) A Generator is specifically a device which uses a static magnetic field to induce an AC current onto the rotor which then uses a commutator to produce a DC current. Whilst an Alternator uses a rotating magnetic field to induce an AC current in the stator?

If definition 2 is correct them I am content.

If definition 1 is correct, then I am happy that an Alternator is a type of Generator which uses a rotating magnetic field to induce an AC current in the stator. BUT... what is the technically correct term for device which uses a static magnetic field to induce an AC current onto a rotor which then uses a commutator to produce a DC current (as the term Generator is too generic to cover this exact application).

I hope this makes sense?

 

[Skogsgurra]

If you are talking Automotive, then your definition #2 is OK.

But there are other disciplnes where generator is used for both types of devices.

Then again, there are Light Machines, Exciters, Field Feeders and many other expressions.

What is true in Dallas may be a joke in Seattle. (OK, it was Jena and Heidelberg - you get the drift).

Gunnar Englund

http://www.gke.org

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Half full - Half empty? I don't mind. It's what in it that counts.

 

[SEP87]

Sorry, I was a little vague.

I'm referring to gas engine power generator sets.

 

[Skogsgurra]

Then I guess your #2 is still valid.

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[davidbeach]

In the strictest sense of the terms, a generator produces DC and an alternator produces AC. But most people will refer to an alternator as a generator and not be bothered by it at all.

 

[crshears]

In the strictest sense of the terms, a generator produces DC and an alternator produces AC.

Hello David,

I had to consult a dictionary to ensure I wasn't heading off into the weeds...and Webster's Universal College Dictionary, 1997 edition really didn't help as much as I thought it would!

"Generator: n: 1. a machine that converts one form of energy into another, esp. mechanical energy into electrical energy, as a dynamo."

The entry for "dynamo" defines it as "an electric generator, esp. for direct current." Perhaps this is the closest exact definition sought by the OP.

Like "most people," I will refer to an alternator as a generator and not be bothered by it at all. Upon further reflection, I have to admit that it's my standard practice; which makes me wonder why I only use the term "alternator" in the automotive sense - - where, perhaps ironically, the alternator's output is rectified to DC...

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[SEP87]

To further muddy the waters; take a generator (stator producing electromagnetic force, current being induced on the rotor). A commutator is usually used to turn the AC current on the rotor into DC current as it goes through the split rings. Now replace the split ring commutator with offset slip rings instead. The output current of the generator is now AC. Is this still a generator or has changing arguably the smallest component within the device turned it into an alternator?

As a side for my improved understanding: A Battery powered drill uses DC current, through a split ring commutator, to rotate the shaft. A corded drill takes AC current, is this rectified into DC and then uses the same motor as the battery powered drill. Or is AC current transferred directly to the rotor through slip rings therefore negating the need for the rectifier?

Thanks

 

[waross]

Google "universal motor" eg: AC/DC motors. Common for corded drills.

Alternator Versus Generator.
Automobiles historically used DC Generators to charge the batteries. In the 1950s, DC Generators in automobiles began to be replaced with AC Alternators. Hence the use of the terminology in the automotive industry.
Machines that produce DC by the use of a commutator are always called Generators.
A "Gen Set" that uses an engine to turn an Alternator may be called a Generator.
In large power installations the combination of a prime mover and an Alternator is often called a Generator.
DC Generators (with commutators) are always called Generators.
When there is a possibility of ambiguity, Alternators are called Alternators.
When there is no possibility of ambiguity, Alternators may be called Generators.


Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[davidbeach]

Machines that produce DC by the use of a commutator are always called Generators. ... DC Generators (with commutators) are always called Generators.

Except, of course, when they're called dynamos. ;-)

 

[Hoxton]

The history of all this is lost in the mists of time.

When I arrived in a generator design office in the early 70's the Chief Engineer explained the situation to me as follows.

Rotating machines that produced ac alternating current had been called alternators, but this term was no longer used in national standards as it was not precise enough. For example, a transformer could be called an alternator, because it produced alternating current....and the term alternator did not line up with the electric motor usage (AC motor and DC motor). A synchronous electric motor has similar construction to an alternator, but power flow is reversed.

Translation of these terms into other languages could result in inconsistencies.

So at a meeting (I think of British standards) it was decided that the correct terms would be

Generator
Motor


Preceded by AC or DC as appropriate.

Please Google shop.bsigroup and then search for "generator" - BS EN 60034 and it's predecessor BS5000.

Searching for "alternator" brings up devices in the automotive industry - we wait for them to catch up!

IEC60034.3 uses the term generator

So does ANSI C50.13 for the USA

The term alternator has got so far into the language, that it is so difficult to correct!

If anyone doubts me, look at a rating plate

 

[LionelHutz]

The alternator vs generator seems to be mostly from automotive use. A generator with a commutator was first used on every vehicle. Then, a new generator design was created with slip rings and diodes. They became common in or around the mid 60's. To promote how their new vehicles were equipped with this better generator design, the advertising departments needed a new name to promote so someone decided to use alternator and it's stuck ever since.

Industrial machines never really went through a design changed that required advertising. The only big promotional fight was the use of AC or DC but the public never really cared much what the machines behind the AC or DC electricity were called. So, people have just always used AC generator or DC generator or generator without worrying about the name much.

 

[squeeky]

Alternator is AC, generator is DC. In my world we constantly inter-change the two. The only time it seems to create problems is when we converse with people of other languages especially Chinese and Japanese as they learn Technical English and get confused. Diesel Generators are actually Diesel Alternators. But the TAs are Turbo Alternators and are steam driven alternators and thus fit the technical description. Automobiles have alternators with rectifiers. They are motor vechiles but are driven by engines not motors. Motors are elecrical driven machines.

 

[Hoxton]

Sorry, but I stand by my post which shows how the definitions were arrived at, precisely how to avoid confusion in translation.

Please read the international standards which I gave as reference.

To be blunt, engineers must no longer use the term "alternator".

We have to use international standards as our basis for definition. They have been produced by people much more qualified than us. ( well, more qualified than me, anyway)

 

[squeeky]

Unfortuanalty we use SANS and IEC. YOu will buy a TA, Turbo alternator, but we still buy a diesel generator which is an alternator. Coloquial expressions or not we need to define it. We have purcahsed machines from India and China and in e-mails we have to say alternator. When we work with the guy from Perkins he says Diesel Motor when it is an Engine. The main thing is that we speak engineering and make it work.

 

[ScottyUK]

The IEC 60034 'Rotating Electrical Machines' series of documents uses the terms: DC machine; induction machine; synchronous machine. Motor or generator / alternator is down to the way in which the machine is utilised, and in most cases the machine is capable of either mode of operation.

 

[Hoxton]

Squeaky
Mechanical engineers interchange motor and engine, originally gas engines were called motors. The Germans still often seem to prefer motor, this may be due to historically differentiating between steam engines and combustion engines.

For a long while we Brits called the compression ignition engine an "oil engine", since Dr Diesel did not invent the direct injection Diesel engine - this was a British development!

Scotty
Correct : the IEC 60034 series correctly, in my view, keeps the general series as Rotating Electric Machines, and uses motor etc for specifics.

It does not alter my argument that we have a definition, but even the standards committees have yet to have uniform policies.

As squeaky notes, the term alternator is well embedded and will take some time to disappear.

Have we exhausted this one now, or should we move it to the Engineering Grammar Skill Forum!

 

[Skogsgurra]

It is by no means exhausted!

There are also the Caloric Engine and the Stirling Motor. And, of cause, the Wind Motor or Wind Turbine - where terminology seems to be dependent on what the wing wheel is driving.

I don't think we need to add uncertainty to confusion. But exhausted - no way.

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[stevenal]

From IEEE 100:
"alternator (rotating electric machinery) An alternating-current
generator."

 

[Hoxton]

So even the IEEE cannot get it right?

Seriously, doing a google of "IEEE generator standards" shows that they use the term frequently, interestingly they worked on the harmonization of ANSI C50 with IEC 60034, both standards use the term generator.

Once again, googling "IEEE alternator standards" gives automotive style results.

I do not have access to IEEE 100, but I guess that revisions come fairly infrequently.

Could you ask them to amend their definition, in line with ANSI C50?

 

[stevenal]

IEEE 100 references IEEE 11, IEEE Standard for Rotating Electric
Machinery for Rail and Road Vehicles; last updated 2000.