# are alternators AC motors with bridge rectifiers and/or diodes?

I've got these two motors that run on direct AC (120 V). I want to generate electricity with them. Will they produce AC electricity that i can then feed through a bridge rectifier? Could you explain how an alternator generates electricity?

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8 years ago
First off concept: moving a wire, or better, 'lots of wire' (a coil of wire, same wire, multiple passes) through a magnetic field induces a current in that wire. Inversely, Inducing a change in electrical current in a wire causes a magnetic field. These fields can interact with either permanent magnets or other electromagnets. A motor is a mechanism that converts electricity to physical motion by creating opposing magnetic fields between a coil and magnet, or 2 coils (Electromagnets). A generator (alternator) is pretty much the same, wired slightly different, to extract electrical energy from physical motion. "DC" generators (a misnomer, more properly permanent magnet generators) move a coil through a magnetic field created by a permanent magnet to induce current. They produce a sine wave AC that can be rectified with a bridge diode. Alternators have no magnets in them, instead they rely on a small amount of current to 'excite' one of the coils to create the initial electromagnet. The other (stator) coil is moved through this magnetic field, and the current is induced in the moving coil. Once the system is generating some power, it can self-excite the non-stator coil. Google 'AC motor generator' for how to make it work with your motors - it involves attaching a large capacitor to the motor's terminals to provide the exciting current and you can only generate at or just above the motor's rated rpm since it involves correctly timing the collapsing magnetic field with the movement of the stator.
8 years ago
REAL alternators DO have "magnets" in them, they are excitated by the magnet in the armature, which is driven by brushes. They may even have PM magnetic alternator armatures.
8 years ago
I dont doubt their existence, but its common for them to use (as shutter says below) an excitation current in a field coil. I like magnets. Everyone needs more magnets.
8 years ago
doh! that IS a magnet...remember? we calls 'em Electromagnets! ;)
8 years ago
you're making me use lawyer sp33k :P I do not believe they ever have permanent magnets as the sole source of magnetic field.
ShutterBugger8 years ago
They will probably generate some electricity. How much depends on their design and the speed that you turn the shaft. Induction motors have to be run at a higher speed than their normal motor RPM. Brush motors with field coils give very poor results. You would have to electrify either the rotor or the field coils to generate power. A car alternator has an electromagnetic rotor that excites 3 phase AC in the field coils. There are 6 diodes built in that rectify the output. The amount of current through the rotor is regulated to vary the output of the field coils. ~Bob~