"Fred Abse" wrote in message
news
On Sat, 03 Dec 2011 08:34:54 -0700, Jim Thompson wrote:

On Sat, 03 Dec 2011 07:28:05 -0800, Fred Abse
wrote:

On Sun, 27 Nov 2011 12:06:24 -0700, Jim Thompson wrote:

Well! Alternators _are_ current sources, but not for the reason Larkin
claims... no surprise ;-)

Are you referring to current limiting due to opposing flux cancellation?

No. An alternator is a transformer, just that the primary is
rotating. What do transformers transform? What is the mechanism?

...Jim Thompson

I would disagree. A transformer transforms electrical energy at one
voltage/current/impedance, into electrical energy at another
voltage/current/
impedance (or the same in the case of a 1:1 ratio transformer).

An alternator converts mechanical energy into electrical energy. It
requires
no source of electrical energy, if permanent magnet excitation is used. If
electromagnetic excitation is used, the energy consumed by the excitation
goes entirely in I-squared-R losses, and does not appear at the output.

The generated electrical energy comes entirely from the supplied
mechanical energy.

If the load current has harmonic components, it may be that they can be
reflected into the excitation windings, but that is a separate issue.

The discussion here is about permanent magnet alternators, where there can
be no ambiguity.

There are two possibilities for current limiting in a permanent magnet
alternator. Firstly when the volts per hertz of the generated EMF equals
the volts per hertz of the effective series inductance. Secondly, when
the opposing flux due to the generated current equals the flux provided
by the permanent magnet field.

To my mind the inevitable clearance gap between the armature poles and the
magnet/field winding poles must make some difference to a transformer with
its alternating magnetic field in a closed core.

Regarding the Sturmey Archer 'dynamo', the magnet is pretty crappy which
probably contributes to even more difference.