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'[EE] Unusual alternator design?'
2005\10\03@174001 by Bob J

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On 10/3/05, Michael Rigby-Jones <spam_OUTMichael.Rigby-JonesTakeThisOuTspambookham.com> wrote:
>
>
> I managed to get it working (the rectifiers were toast), but I was
> interested to know if this is a common or well known alternator
> configuration? Does it have a name? Google isn't telling me anything, though
> I'm probably not asking the right questions.
>

I think its called a dynamo. An alternator produces a DC current.

Regards,
Bob

2005\10\03@183248 by Richard Prosser

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Not in NZ.
A dynamo is (usually - see below) DC, and alternator is AC, although
it may be rectified to DC subsequently (as in a car).
"Generator" is a more generic description which can encompass both
although it seems more DC orientated in automotive use & AC orientated
in power stations etc.

(& Then there were the old wheel driven bycycle dynamos - which were
AC, just to proove me wrong !)

RP

> I think its called a dynamo. An alternator produces a DC current.
>
> Regards,
> Bob
> -

2005\10\03@191001 by olin piclist

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Bob J wrote:
> An alternator produces a DC current.

No, it produces AC.  That's why it's called an "alternator".

*****************************************************************
Embed Inc, embedded system specialists in Littleton Massachusetts
(978) 742-9014, http://www.embedinc.com

2005\10\03@193242 by Spehro Pefhany

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At 04:40 PM 10/3/2005 -0500, you wrote:
>On 10/3/05, Michael Rigby-Jones <.....Michael.Rigby-JonesKILLspamspam@spam@bookham.com> wrote:
> >
> >
> > I managed to get it working (the rectifiers were toast), but I was
> > interested to know if this is a common or well known alternator
> > configuration? Does it have a name? Google isn't telling me anything,
> though
> > I'm probably not asking the right questions.
> >
>
>I think its called a dynamo. An alternator produces a DC current.
>
>Regards,
>Bob

I don't see the original question. I think modern automotive 'alternators'
typically include both a regulator (usually) to control the rotor current
and a 3-phase bridge rectifier (6 diodes) connected to the stator windings.

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
speffspamKILLspaminterlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com
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2005\10\04@053628 by Michael Rigby-Jones

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>-----Original Message-----
>From: Spehro Pefhany [.....piclist-bouncesKILLspamspam.....mit.edu]
>Sent: 04 October 2005 00:41
>To: Microcontroller discussion list - Public.
>Subject: Re: [EE] Unusual alternator design?
>
>
>I don't see the original question. I think modern automotive
>'alternators' typically include both a regulator (usually) to
>control the rotor current and a 3-phase bridge rectifier (6
>diodes) connected to the stator windings.

Oddly enough I didn't receive my original question either, though clearly some people did.

It was a bit of a long winded post on reflection so I'll shorten it:

Single phase alternator with no direct electrical connection to rotor.  Rotor has a coil, the ends of which are joined by a rectifier.  Stator has two coils, one for the output, one to provide field.  In this application (240v 50Hz 850W gas powered generator) the field was connected to the output coil via a simple current limiting capacitor.

It simply not a configuration I have seen before, and I was curious if it had a name.

Regards

Mike

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2005\10\04@140205 by Peter

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> It simply not a configuration I have seen before, and I was curious if it had a name.

FYI there seem to be a lot of these but without the wound rotor. That
wound rotor should help with starting under load. It was probably fried
by starting it under load.

There is a schematic on the web where someone built exactly such a
generator out of an old Briggs motor and a capacitor run ac motor
(capacitor run ac is usually squirrel cage - your wound rotor is like a
squirrell cage rotor but better).

Peter

2005\10\04@143102 by Bob J

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>From a purely technical standpoint yes you are correct. But I have yet to
see an alternator without a bridge rectifier built into it.

Regards,
Bob

On 10/3/05, Olin Lathrop <EraseMEolin_piclistspam_OUTspamTakeThisOuTembedinc.com> wrote:
>
> Bob J wrote:
> > An alternator produces a DC current.
>
> No, it produces AC. That's why it's called an "alternator".
>
> *****************************************************************
> Embed Inc, embedded system specialists in Littleton Massachusetts
> (978) 742-9014, http://www.embedinc.com
>

2005\10\04@160756 by Howard Winter

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Mike,

On Tue, 4 Oct 2005 10:36:26 +0100, Michael Rigby-Jones wrote:

> Oddly enough I didn't receive my original question either

Nor did I.


> It was a bit of a long winded post on reflection so I'll shorten it:
>
> Single phase alternator with no direct electrical connection to rotor.  Rotor has a coil, the ends of which
are joined by a rectifier.  Stator has two coils, one for the output, one to provide field.  In this
application (240v 50Hz 850W gas powered generator) the field was connected to the output coil via a simple
current limiting capacitor.
>
> It simply not a configuration I have seen before, and I was curious if it had a name.

I've certainly never seen or heard of it either - do you know how the coils are arranged (field on one side,
output on the other, or interleaved, for example)?  How many poles are there?  I think the capacitor is
probably for DC blocking rather than current limiting, or possibly give a bit of smoothing when the current /
magnetic field reverses...

I wonder if the rectifier is to provide a sort of reverse-commutation, so you get something like a sine wave
rather than half-wave rectified (I know this sounds counter-intuitive, but it's that sort of arrangement! :-)  
Was there some base excitation?  It must have either electrical feed or a permanent magnet somewhere, or it
sould never get started.

I don't suppose you put a 'scope on the output?  I'd be fascinated to see if it manages a sine wave.

Cheers,


Howard Winter
St.Albans, England


2005\10\04@163625 by Lee Jones

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>>> An alternator produces a DC current.

>> No, it produces AC. That's why it's called an "alternator".

> From a purely technical standpoint yes you are correct. But I have
> yet to see an alternator without a bridge rectifier built into it.

Even with the (commonly 3-phase) bridge rectifier, alternator output
varies to zero so frequently (more than once per revolution)  that
I would have to call it AC.  At a minimum, I'd call it folded AC.
The vehicle provides inductance (wiring harness) and capacitance
(battery) to smooth it out to usable DC.

Now an automotive generator(*) produced DC with some significant
commutator noise superimposed on the output.

                                               Lee Jones

(*) yes, I am (barely) that old; they had been phased out on new
  cars, but I had friends with older cars that still used them.

2005\10\04@163724 by Howard Winter

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Bob,

On Tue, 4 Oct 2005 13:31:02 -0500, Bob J wrote:

> From a purely technical standpoint yes you are correct. But I have yet to
> see an alternator without a bridge rectifier built into it.

Go to a power station - you'll see loads of them!  :-)

Cheers,



Howard Winter
St.Albans, England


2005\10\04@165428 by Bob Blick

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Lee writes:
> Even with the (commonly 3-phase) bridge rectifier, alternator output
> varies to zero so frequently (more than once per revolution)  that
> I would have to call it AC.  At a minimum, I'd call it folded AC.
> The vehicle provides inductance (wiring harness) and capacitance
> (battery) to smooth it out to usable DC.

Alternator output does not go to zero. The ripple current isn't even that
big, about 15%. Remember, it's a three-phase generator.

Ripple voltage is reduced by the battery and is much less than 15%.
Inductance from wiring is negligible at operating frequencies.

However if one or more diodes fail in the alternator, ripple shoots way up.

Cheerful regards,

Bob

2005\10\04@170651 by Lee Jones

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>> Even with the (commonly 3-phase) bridge rectifier, alternator output
>> varies to zero so frequently (more than once per revolution)  that
>> I would have to call it AC.  At a minimum, I'd call it folded AC.

> Alternator output does not go to zero. The ripple current isn't even
> that big, about 15%. Remember, it's a three-phase generator.

Oops.  I was visualizing one phase in my head.  I knew it was 3-phase
but didn't overlap the outputs in my head.  I stand corrected.

                                               Lee Jones

2005\10\05@035947 by Michael Rigby-Jones

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Vitualy any generator set use for portable "mains" power uses some form of alternator with unrectified output.  I suspect you are simply used to the term being applied to the device bolted to a car engine which will always have DC output for charging etc.

Regards

Mike

>{Original Message removed}

2005\10\05@075145 by Russell McMahon

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>From a purely technical standpoint yes you are correct. But I have
>yet to
see an alternator without a bridge rectifier built into it.

Any alternator intended to produce AC output, as the one which started
this discussion is, will not have any rectification in its main
output. There may be rectification in control circuits for fields etc
but these are auxiliary to the main intent.

Alternator, as Olin says, is traditionally meant to refer to something
which produces "Alternating Current" output = AC.


       Russell McMahon

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