Martin,

On Mon, 06 Nov 2006 09:26:08 -0500, Martin K wrote:

> On most cars the alternator spins faster than the engine. The alternator 
> should be supplying energy to the battery at idle speed, 

As I remember it, this was the reason for going over from DC dynamos to Alternators - the commutator on a dynamo limited its speed because of the 
sparks it produces, so at low engine speeds it didn't generate enough to charge the battery, which was why the "Ign" light would come on at idle.  
Since alternators use slip rings they can turn faster, so they are "geared" higher by having a smaller pulley, and as you say will generate even at idle.

Cheers,


Howard Winter
St.Albans, England


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