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From: Michael on 11 Mar 2010 18:09
Why do vehicle alternators not employ permanent (Nd) magnets?
From: Jamie on 11 Mar 2010 19:05
Michael wrote:

> Why do vehicle alternators not employ permanent (Nd) magnets?
cost, heat, and size ?



From: Michael on 11 Mar 2010 18:48
On Mar 11, 4:05 pm, Jamie
<jamie_ka1lpa_not_valid_after_ka1l...(a)charter.net> wrote:
> Michael wrote:
> > Why do vehicle alternators not employ permanent (Nd) magnets?
>
> cost, heat, and size ?


Ah, so electromagnets have a larger magnetic field per unit volume?
From: sparky on 11 Mar 2010 18:52
On Mar 11, 6:48 pm, Michael <mrdarr...(a)gmail.com> wrote:
> On Mar 11, 4:05 pm, Jamie
>
> <jamie_ka1lpa_not_valid_after_ka1l...(a)charter.net> wrote:
> > Michael wrote:
> > > Why do vehicle alternators not employ permanent (Nd) magnets?
>
> > cost, heat, and size ?
>
> Ah, so electromagnets have a larger magnetic field per unit volume?

The output voltage can be regulated much easier.
From: Tim Wescott on 11 Mar 2010 18:56
Michael wrote:
> On Mar 11, 4:05 pm, Jamie
> <jamie_ka1lpa_not_valid_after_ka1l...(a)charter.net> wrote:
>> Michael wrote:
>>> Why do vehicle alternators not employ permanent (Nd) magnets?
>> cost, heat, and size ?
>
>
> Ah, so electromagnets have a larger magnetic field per unit volume?

No, but by the time you finish surrounding a permanent field alternator
with its supporting circuitry it may be bigger than current technology.

An alternator that uses DC magnets will have an output voltage that is
very strongly coupled to it's speed and that cannot be adjusted.
Instead, you'd need to have some sort of a switching power supply
circuit to take whatever happened to come off the alternator and feed it
to the battery.

Normal car alternators are regulated by adjusting the current to their
field coils; in effect their motor constants are changed by the
regulator circuit. This makes them fairly easy to control with very
little, and efficient, circuitry.

--
Tim Wescott
Control system and signal processing consulting
www.wescottdesign.com
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