Re: Permanent magnet alternators?

Michael wrote:

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

| 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.

I loath the amperes wasted by alternator's excitor circuit before
engines are started successfully. Does a brushless alternator
likewise waste amperes before an engine is started successfully ?

TE Cheah wrote:
> | 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.
>
> I loath the amperes wasted by alternator's excitor circuit before
> engines are started successfully. Does a brushless alternator
> likewise waste amperes before an engine is started successfully ?
>
>
You must hate 99.8 percent of all cars, or more likely
you are trolling.

On 2010-03-12, TE Cheah <(E-Mail Removed)> wrote:
>| 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.
>
> I loath the amperes wasted by alternator's excitor circuit before
> engines are started successfully.

have you measured it? typically it is exactly enough to light the
'altenator warning' lamp.

> Does a brushless alternator
> likewise waste amperes before an engine is started successfully ?

no, but it could make the engine harder to start.

I assume you mean a permanent magnet altenator, the are brushless
electromagnet field altenators.





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| > I loath the amperes wasted by alternator's excitor circuit before
| > engines are started successfully.
| have you measured it?
No.

| typically it is exactly enough to light the 'altenator warning' lamp.
Wikipedia says a 70 amp alternator uses 2 amp as exciter, so I
think exciter should be activated only after engine starts.

| > Does a brushless alternator
| > likewise waste amperes before an engine is started successfully ?
| no, but it could make the engine harder to start.
How ?

| I assume you mean a permanent magnet altenator
No, see http://en.wikipedia.org/wiki/Alterna...ss_alternators
, in 4-09 1 Toyota salesman said new Camry ( but not lower models
) has this.
I suspect rare earth magnets can't be used ; heat will ruin these
magnets.

On 2010-03-13, TE Cheah <(E-Mail Removed)> wrote:
>| > I loath the amperes wasted by alternator's excitor circuit before
>| > engines are started successfully.
>| have you measured it?
> No.
>
>| typically it is exactly enough to light the 'altenator warning' lamp.
> Wikipedia says a 70 amp alternator uses 2 amp as exciter, so I
> think exciter should be activated only after engine starts.
>
>| > Does a brushless alternator
>| > likewise waste amperes before an engine is started successfully ?
>| no, but it could make the engine harder to start.
> How ?

the last altenator I looked closely at an altenator it took the exciter
current from separate (positive side) rectifier diodes (D+ terminal) which
was fed back into the altenator exitation (DF terminal) by the regulator

with it's stopped or at low RPM the exciter current coming from the lamp
circuit is is only a few hundered millianps, once the speed gets up
the rectifier kicks in to supply the power.

>| I assume you mean a permanent magnet altenator
> No, see http://en.wikipedia.org/wiki/Alterna...ss_alternators

Those things still need power for the exiters stationary winding.
if that current is't taken mostly from the rectifiers then it's going
to cost the same,

if you're worried you could rig a horn relay (form C automotiver relay) to
cut the feed to the altenator when you activate the starter.


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