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So, a friend brings a Honda generator to my son claiming it doesn't generate. Son checks the voltage at around 78 or so. SO he fashions an extension cord connected to the normal sized 9volt battery, plugs it into the running generator for a brief moment, rechecks the voltage to confirm....110! I need an explanation of this!
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The generator rotor [the part that spins] is consisted of a wound iron core. It terminates in two diodes connected to two slip rings through carbon brushes. The iron core is supposed to be magnetized at all times. When he measured the output, the core was partially magnetized. when he connected up the battery he was "polarizing" the core, that is "flashing" it with a DC voltage, which is what the rotor puts out. as the rotor spins, it makes and breaks magnetic lines of force which is what creates the ac or alternating current in the stator windings where the voltage is taken off. It is the same principle of any ac machine. in the case of a hydro machine, the prime mover is a water turbine connected to a dc excited rotor. same in a steam plant - the rotor is at a dc potential spinning within the stator.
In real early machines with a self excited rotor, merely hitting the iron core with a sledge hammer was enough to jolt the exciter into magnetizing it.Last edited by HayZee518; 05-22-2010, 04:41 AM. -
Exciting a generator
Good stuff, HayZee. Thanks again.Comment
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