Hi Greg,

On 05-Oct-03, Greg Mayman wrote to George White:

 GW>> One thing to remember is that _all_ dynamos needed a current
 GW>> limiter as they are not intrinisically self limiting. Most
 GW>> alternators intrinsically self limit the current output, so all

 GM> Hmmm... that doesn't sound right. It couldn't be the change of
 GM> which part rotates and which doesn't. So is it the impedance of
 GM> the diodes that makes an alternator self-limiting?

It's definitely not the diodes. It's to do with the internal design.
However, it is one of the factors that influenced the change to
alternators. The main factors were:

a) Higher output in the same frame size
b) Simpler regulators
c) Wider working speed range.

In a dynamo the field is static, and only two pole, and the output is
rectified by the commutator off the rotor.

In an alternator the field rotates, and is usually 6, 8 or 10 pole.
The output is a 3 phase static winding, can be either star or delta
wound (usually delta, from memory) that feeds the rectifier bridge.

I don't know the electro-magnetic design stuff involved, other
engineers did that, but it's to do with the fact the extra poles and
different magnetic circuit mean that the field reaches a limiting
value (field full on) and with appropriate design the output current
reaches a limiting value which can be handled by the stator windings.

George

--- Terminate 5.00/Pro