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Alternators vs. Generators for wind power - Page 3

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Posted by Ulysses on July 9, 2008, 4:41 pm
 


I'm pretty sure that would be a big NO.  If it had commutators then it must
have produced DC directly.  I think the term "alternator" refers to
alternating current.

This makes me wonder if, since permanent magnet alternators do not use slip
rings, if it's possible to produce DC with permanent magnets and no physical
contact such as commutators.  I can't imagine how it could work but I think
I've seen PM DC generators advertised but I don't know if they were really
AC that was rectified.


ignorance |

to  |

ipal.net) |



Posted by phil-news-nospam on July 9, 2008, 5:55 pm
 

|>
|>> | silicon.  I suspect they were Germanium or some other such material.
|>
|> Maybe it is the case that long before the 1960's, cars had commutator type
|> generators/alternators, to get DC, and they migrated to rectified ones,
| when
|> that was practical, to make them more reliable.
|>
|> If they did have commutators, was it correct to call them alternators?
|
| I'm pretty sure that would be a big NO.  If it had commutators then it must
| have produced DC directly.  I think the term "alternator" refers to
| alternating current.
|
| This makes me wonder if, since permanent magnet alternators do not use slip
| rings, if it's possible to produce DC with permanent magnets and no physical
| contact such as commutators.  I can't imagine how it could work but I think
| I've seen PM DC generators advertised but I don't know if they were really
| AC that was rectified.

I presume you would consider the Faraday disk homopolar generator to be one
with slip contacts, with one on the axle and one (set) around the edges.  The
problem with this generator is that if you leave the disk stationary and just
rotate the magnets, you get nothing (because there is no representation of
rotation in a magnetic field, so rotating the magnets doesn't have any effect
on the field).  It would be great for generating DC is this were not the case.

--
|WARNING: Due to extreme spam, googlegroups.com is blocked.  Due to ignorance |
|         by the abuse department, bellsouth.net is blocked.  If you post to  |
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| Phil Howard KA9WGN (email for humans: first name in lower case at ipal.net) |

Posted by Johnny B Good on July 7, 2008, 4:43 pm
 from phil-news-nospam@ipal.net contains these words:


 True. The ones designed for wind turbine use are PM alternator designs
with the magnets on the rotor and power taken from the stator. This
avoids the need to consume part of the generated power to feed current
to excite the rotating field winding (and also eliminates the friction
of a slip ring assembly).


 This term was to distinguish between the modern alternator based DC
generator and the old fashioned dynamo it replaced.


 Yes, but it has a pair of slip rings with long life carbon brushes to
feed excitation current (maybe 4 or 5 amps max) to the rotating field
coil. The friction from these slip rings is a lot less than in the case
of the commutator used in a dynamo because of the low current allowing
less contact pressure against a totally smooth slip ring which need not
have as large a diameter as a segmented commutator.


 They did, it was called a "Dynamo".


 There are two basic types of electrical generator (leaving aside EHT
generators such as Van De Graaf and Whimshurst machines) for producing
electrical power. These are the Dynamo designed to produce DC current
directly via the built in commutation of the AC internally generated by
the rotating armature windings, and the Alternator, designed to generate
AC current (usually output from the stator windings, but there have been
designs which collected the output from the armature windings via two or
more slip rings).

 The automotive "Alternator" is a three phase AC generator with full
bridge rectifier pack and voltage regulator integrated so that it can
act as a drop in replacement for the older dynamo design.

HTH

--
Regards, John.

 Please remove the "ohggcyht" before replying.
The address has been munged to reject Spam-bots.


Posted by phil-news-nospam on July 7, 2008, 6:47 pm
 On Mon, 7 Jul 2008 17:43:04 +0100 Johnny B Good
| from phil-news-nospam@ipal.net contains these words:
|
|> On Mon, 07 Jul 2008 00:32:05 GMT Vaughn Simon
|> |
|> |> What I have long heard (and it is not necessarily correct; I'm just
|> citing
|> |> what I have heard) is that an alternator works from a magnetic
|> field produced
|> |> by a (usually) DC current, whereas a true generator works from a
|> permanent
|> |> magnet field.  Either design can be wired to produce AC or DC.
|> |
|> |   Either an alternator or a generator can be made with a permanant
|> magnet (PM)
|> | field.
|
| True. The ones designed for wind turbine use are PM alternator designs
| with the magnets on the rotor and power taken from the stator. This
| avoids the need to consume part of the generated power to feed current
| to excite the rotating field winding (and also eliminates the friction
| of a slip ring assembly).

It would be possible to avoid the slip ring by having a reversed PM
alternator feeding the field coils of main alternator.  Both would be
on the same rotor.  At one end 3 (or more) phase windings on the rotor
derive power from the magnets.  This multiphase power is recitified to
DC via rectifiers on the rotor.  This DC is then fed along the rotor
to the main alternator, powering its field coils from which the stator
windings get power.  No slip rings and no rotary transformer, either.


|> So what are the real definitions?  I've always been going on what
|> people called
|> them without really investigating.  I've primarily heard the term alternator
|> applied to the device inside a car, with very few exceptions.
|
| This term was to distinguish between the modern alternator based DC
| generator and the old fashioned dynamo it replaced.

OK

So it still is that "generator" is a broader term and "alternator" is a
subset of "generator", and includes both what we find in a car and in the
big power plant down by the river (actually, more than one of them where
I live).


|> So I did some Googling.
|
|> It seems there is a fuzzy boundary of usage, and perhaps a lot of it
|> is wrong.
|> No formal definitions are found.  But it seems the term generator is used to
|> describe all devices that convert mechanical/motion energy (and
|> possibly more
|> than that) into electrical energy.  The term alternator is a subset of the
|> term generator, mostly meaning a rotating electromagnetic generator that has
|> no commutator (and thus is producing AC, not DC).
|
|> So why do people call that device in cars that converts motion to DC
|> electrical
|> energy an alternator?  I've never dug into these.  Does it lack a commutator
|
| Yes, but it has a pair of slip rings with long life carbon brushes to
| feed excitation current (maybe 4 or 5 amps max) to the rotating field
| coil. The friction from these slip rings is a lot less than in the case
| of the commutator used in a dynamo because of the low current allowing
| less contact pressure against a totally smooth slip ring which need not
| have as large a diameter as a segmented commutator.

If there was AC available, they could have used a rotary transformer to
power the rotating field coils (with a full-wave bridge rectifier on the
rotor).

Another option might be a Faraday unipolar genrator (if it had enough
voltage) that has, instead of the permanent magnet normally seen from
Faraday's experiment, a DC field coil (can use battery power and can be
regulated).


|> and just convert the AC to DC?  Cars existed long before solid state
|> rectifiers
|> so how would they have converted AC to DC back then (I seriously doubt
|> the use
|> of vacuum tubes/valves in cars, aside from small ones in older car radios).
|> Surely they had to be using a device with a commutator.
|
| They did, it was called a "Dynamo".

OK, so if I step into my time machine (how many gigawatts do I need to drive
the flux capacitor?) and go back to say the 1920s and talk to car mechanics
about the generator, they would call it a dynamo.  OK, this is starting to
make some sense.


|> In any case, it seems the term alternator refers to a subset of devices that
|> the term generator refers to.
|
| There are two basic types of electrical generator (leaving aside EHT
| generators such as Van De Graaf and Whimshurst machines) for producing
| electrical power. These are the Dynamo designed to produce DC current
| directly via the built in commutation of the AC internally generated by
| the rotating armature windings, and the Alternator, designed to generate
| AC current (usually output from the stator windings, but there have been
| designs which collected the output from the armature windings via two or
| more slip rings).
|
| The automotive "Alternator" is a three phase AC generator with full
| bridge rectifier pack and voltage regulator integrated so that it can
| act as a drop in replacement for the older dynamo design.

Now it makes sense why they (auto mechanics) were calling it by the same
name as other people refer to in power plants.

Everything is a "generator" but some of them are "alternators", some are
"dynamos" (I had heard THIS term used in a power plant a couple times long
ago and I must conclude it was in error), and there are a few other kinds
of generators, as well.

--
|WARNING: Due to extreme spam, googlegroups.com is blocked.  Due to ignorance |
|         by the abuse department, bellsouth.net is blocked.  If you post to  |
|         Usenet from these places, find another Usenet provider ASAP.        |
| Phil Howard KA9WGN (email for humans: first name in lower case at ipal.net) |

Posted by Ken Maltby on July 7, 2008, 7:16 pm
 

  Before "alternator",  consider "magneto", ( and no, not the X-men guy).

Luck;
    Ken



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