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Posted by Vaughn Simon on July 7, 2008, 12:32 am
 


   Either an alternator or a generator can be made with a permanant magnet (PM)
field.

Vaughn





Posted by phil-news-nospam on July 7, 2008, 3:12 pm
 
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.

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.

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
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.

In any case, it seems the term alternator refers to a subset of devices that
the term generator refers to.

--
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| Phil Howard KA9WGN (email for humans: first name in lower case at ipal.net) |

Posted by Ulysses on July 7, 2008, 3:50 pm
 

alternator

electrical

commutator

A typical alternator in a car has slip rings and produces alternating
current (usually three-phase) which is rectified to DC.

Cars existed long before solid state rectifiers

radios).

I've never actually taken one apart but from what I've read DC producing
generators were in use in early cars.  I don't know just when solid-state
rectifers came into being but they existed in the '60s.  They were rather
large and had big heat sinks on them.  I don't know if they were made from
silicon.  I suspect they were Germanium or some other such material.


ignorance |

to  |

ipal.net) |



Posted by Johnny B Good on July 7, 2008, 5:29 pm
 


 An automotive dynamo is basically the same as a field excited DC motor
in construction. I've seen the armature from a 1930's Hoover vacuum
cleaner which looked remarkably identical to those used in today's
vacuum cleaners. The differences would all be hidden in that a modern
motor would use better steel and high temperature insulation materials.

 The principles of electrodynamics were well understood (and applied!)
over eighty years ago.


 You're probably thinking of the large plate Selenium rectifier stacks.
I've seen low voltage 1 amp ones in the early Triang Transformer
Controllers that replaced the dry cell 12 volt controllers. They were
about 5 or 6 cm square in a 2 cm stack and had a very characteristic
odour when overheated.

 A selenium rectifier capable of converting 25 amp AC to DC at 14 volts
would have probably been bigger than the car battery and the rectifier
losses would have been even greater than the losses in a dynamo
commutator of the same amperage rating, so would not have been used for
such service.

 The dynamo regulator box used a voltage sensing relay switching
technique to control the field current and would also have incorporated
a cut out/cut in relay to prevent the dynamo drawing current from the
battery at low revs or standstill.

 Until the advent of commercially available high amperage silicon
diodes, the best way to generate low voltage DC at 20 or more amps was
still the dynamo with its commutator/brush assembly.

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, 6:29 pm
 
| A typical alternator in a car has slip rings and produces alternating
| current (usually three-phase) which is rectified to DC.

[snip]

| I've never actually taken one apart but from what I've read DC producing
| generators were in use in early cars.  I don't know just when solid-state
| rectifers came into being but they existed in the '60s.  They were rather
| large and had big heat sinks on them.  I don't know if they were made from
| 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?

--
|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) |

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