[TheForge] Re: Generators

[Charle B Vincent]

In autos alternators and generators are reversed.   Generator operates 
as you describe,  field windings on outside of case creat a magnetic 
field that  induce a current in the armature/rotor windings that then 
drives the load.  In an alternator, the rotating component creates the 
magnetic field that induces a current in the windings in the case.   
Additionally, a generator rectifies the current through the use of 
individual segements and brushes on the armature or rotating element.   
An automotive alternator creates three pahse AC and uses diodes to 
rectify the voltage to create DC.     The primary reason manufacturers 
went to alternators was that they can operate at higher rpm, due to the 
fact that the rotating assembly is simpler (no individual segments) and 
lighter.    This allowed it to be geared high enough to generate current 
at idle and not explode at full rpm.    All of the old home generators 
that I have worked on work as you describe ala auto generators, but they 
are all old.   I was not sure that newer home generators didn't work 
like an auto alternator.  Basically the concern that I had with the 
drill motor approach was that if you induced a current using the 110 
tap, that in either configuration ( rotating field or rotating load)  it 
would be energizing the wrong coil.   Old generators used relays that 
could stand a lot of experimentation like that maybe, but I would expect 
new units to be using solid state components with an SCR or something 
like it, that might not respond well to the wrong thing.   Who knows, 
maybe nothing has changed.

Charles


Paul Sperbeck wrote:

>Harking back to the generator question that began all this, zapping the
>field winding with a large current pulse will magnetize the core of the
>field magnets. How permanent that effect is depends on the steel. The
>armature core is the object of the magnetic fields that are created in the
>field windings, and the induced magnetic field in conjunction with the
>armature windings is the where the power is drawn off by the load circuit.
>The armature cores are not designed to retain magnetism and in many cases
>the field winding are either externally powered to provide control over the
>output voltage, as in your cars alternator, or the fields are comprised of
>permanent magnets. In the book, Alternator Secrets, available from Norm
>Larson I believe, their is an example of an electric motor used as a
>alternator. In this book the author speaks to possibly zapping one of the
>windings to generate a residual magnetic field until the unit begins
>generating power, whereupon the unit would self-excite...
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