alternators

In my book it says "a variation of the revolving armature ac generator is often used for very low power ( e.g. , Ann automobile alternator) where both windings are on interlaced on a stator and the field are coupled by a rotating soft iron (electromagnetic) armature without windings."

What do they mean by both windings? And interlaced? And why doesnt the armature need windings? What does electromagnetic in this case mean?

Linked is a typical wiring diagram of an automotive alternator.

The field (rotor) winding is attached to the shaft and spins,. It is fed via slip rings. Typical maximum excitation current (field current) is about 2A, so brushes last a long time.

The stator (stationary) windings are three-phase, 120 deg apart. The three-phase is rectified to DC using six to nine rectifiers. Stator currents can be from 50 to 150A, depending on alternator size. To a first approximation, at any given shaft speed, the output current of an automotive alternator is proportional to the field current Io=k*If, where K is about 25 to 75.

Small (motorcycle) alternators sometimes use a spinning permanent magnet to create the field. Their output current cannot be modulated by controlling field current, so they must be controlled by shunting excess current to ground...

gjoo said:

In my book it says "a variation of the revolving armature ac generator is often used for very low power ( e.g. , Ann automobile alternator) where both windings are on interlaced on a stator and the field are coupled by a rotating soft iron (electromagnetic) armature without windings."

What do they mean by both windings? And interlaced? And why doesnt the armature need windings? What does electromagnetic in this case mean?

Click to expand...

It means the field windings and the power windings.

Interlaced means that the field windings and the power windings are in the same part of the alternator.

When the armature is in one position, the magnetic field generated by the field winding will be linked, though the armature, to the power windings in one direction. As the armature moves to another position, the magnetic field is linked the other way, so that the field in the power windings is reversed. It's a bit like an electrical reversing switch, but using soft iron instead of the switch elements.

I think that "electromagnetic" means that the iron is soft as far as magnetic fields go, rather than being physically soft.

Diver300 said:

...When the armature is in one position, the magnetic field generated by the field winding will be linked, though the armature, to the power windings in one direction. As the armature moves to another position, the magnetic field is linked the other way, so that the field in the power windings is reversed. It's a bit like an electrical reversing switch, but using soft iron instead of the switch elements...

Click to expand...

You have described the Claw Pole Alternator