"John Larkin" wrote in message
...
On Thu, 1 Dec 2011 14:33:24 -0000, "Ian Field"
wrote:


"Martin Riddle" wrote in message
...

"Jim Thompson" wrote
in message ...
On Tue, 29 Nov 2011 16:50:02 -0600, John Fields
wrote:

On Mon, 28 Nov 2011 16:51:45 -0800, John Larkin
wrote:

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

On Sun, 27 Nov 2011 10:50:39 -0800, Fred Abse
wrote:

On Sun, 27 Nov 2011 10:28:17 -0800, John Larkin wrote:

Alternators like this are often designed with a lot of internal
series
inductance. As speed increases, open-circuit terminal voltage
increases, but the series inductance impedance increases too,
tending
to make them constant-current sources, ideal for driving light
bulbs
at sorta constant brightness at various speeds.

What I was going to say.

I think there is an ancient patent somewhere about just that.

Well! Alternators _are_ current sources,

Ah, so their terminal voltage must be infinite.

John

---
And, indeed, it would be, would not Mother Nature conspire against it
with the spoiler, resistance.

When Larkin sets out to put his foot in it he just can't resist
squishing his foot around to make sure it sticks.

Suggestion to Larkin: Set up loose connection at battery post...
connects but you can pull connector off easily.

With engine running at 3000RPM (you'll need a helper, maybe Ian Field
:-), right hand on car frame, left hand at battery post, take firm
hold of connector and pull quickly off of battery.

Unless you happen to have an alternator with built-in zeners to limit
voltage, you will be dead... or at least multiple broken bones... it's
a pulse. You do know what a "pulse" is? Then come back and talk to
me about "infinite" ;-)

Young bucks... DON'T try this... this instruction for Larkin-disposal
purposes only!

(Before zeners were added to alternators I had to design to a 400V
kick, and have the regulator survive. How did I do it?)

...Jim Thompson

My 95' GM alternator uses Avalanche diodes in it. It would not survive
that test.
Nor will it survive with a loose battery connection. Somewhere in the
manual it says not to use for welding.

Cheers

An interesting point about motorcycle alternators is that many are
permanent
magnet type with 3-ph windings, regulation is accomplished by adding 3
SCRs
in parallel with the 3 bottom diodes in the rectifier and using them to
short the alternator when the battery V gets too high.

A lot of aircraft alternator regulators do that, short the winding to
regulate. Probably to avoid huge terminal voltages that you'd get by
using some sort of series regulator.

I can't understand why more manufacturers haven't made quicker progress
toward field controlled alternators, it doesn't have to be about reliability
issues with slip rings and brushes, some of the later motorcycle alternators
have a kind of co-axial pole cage coupling to the interleaved pole fingers
mounted on the end of the crankshaft - the field winding is static as well
as the stator.

Wouldn't be surprised if car alternators went that way long ago.