Hi Rob, I'm not really sure what you mean when you say you have an AC generator rather than an alternator.
But heres an explanation of how it all works.. it will either inspire you, or put you to sleep.
An alternator and a generator both work the same way - wires are pushed through a magnetic field by the rotation of the engine.
Sometimes the magnetic field is created by fixed magnets, sometimes electromagnets (The field winding) is used. This is the same for alternators and generators too.
An alternator will produce AC electricity, which is rectified externally using semiconductor diodes. A generator also produces AC, but by a cunning arrangement of switches attached to the generator, the polarity of the AC is changed every 180 degrees. This gives you rectified AC directly - no external rectification is required. Generators were developed first, as the diode was not invented, so a mechanical system was the only way to go.
So, once rectified, you have a kind of DC - suitable for battery charging.
Voltage regulation.
The two main factors that control how much energy you are making with the wire you push through a magnetic field are (a) how strong the magnetic field is, and (b) how fast you push the wire through.
So, to control the output of your alternator (or generator) you have lots of methods. You could run it via a gearbox. And as the engine speed changed you could use the gears to speed up or slow down your alternator to change the output. I've never seen this done, but perhaps somewhere in Russia...
Or you could reduce the strength of the magnetic field. This is very common, and very easy if you have electromagnets creating your magnetic field. You just turn em off, and presto, job done.
But most motorcycles use fixed magnets. So the faster the engine goes, the more energy you produce, and an external regulator is required.
The series regulator simply disconnects the alternator from the battery when voltage gets too high. It works OK, but has a couple of problems. Firstly you have to be able to switch the entire full load current of your alternator. This requires quite big switches. Secondly, the ouput voltage of the alternator will get very high. As there is no current, there is no heat, but you have to build a very good alternator to withstand the high voltage that you might reach.
The shunt regulator works by diverting excess energy to heat. Effectively, a circuit is designed which simply detects battery voltage. As battery voltage gets too high, the circuit puts a load (like a resistor) across the battery. This resistor gets hot, but keeps system voltage in check.
Electronically its a very simple circuit, and vey cheap to make. It has a few drawbacks, and its regulation is not really that flash, but in practice, it works very very well.
Hope this helps !
David must play fair with the other kids, even the idiots.
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Originally Posted by SOHC
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