110V Generator

[Eviltail]

I have an old and very large 110V generator of which I know very little about, not even make and manufacturer. Recently, it stopped generating 110V AC. My theory is poor, however I understand that current is produced by the spinning of a permanent magnet within a coil of wire. Following dismantlement of the generator it was discovered that the rotor was not magnetic, going against what I had expected. So, my question is: do generators use permanent magnets? Is it possible for the rotor to become demagnetised? If so, is there anything that can be done to restore magetism? Or am I completely wrong?
Thanking you in advance,

John

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[aluijten]

I'm not an expert on the subject, but most generators (actually altenators), do not work on the principle of permanent magnets but on the principle of setting a field voltage to the rotator. This then acts as a (electro)magnet and because of the rotation the static coils deliver a alternating current (AC) that you can use. By regulating the field voltage you can regulate the output of the stator. I'm not sure how the initial field voltage for the rotor would be generated in your generator set.
Nevertheless it would explain why there is no magnetism to be found. My guess is that the regulator has died on you.

Arno

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[Graham_Wright]

I used to have this problem with the dynastarter on my engine.
Once the generator generates, the field becomes magnetic and is self-sustaining.
To kick it off, it relies on residual permanent magnetism in the frame or rotor.

I used to find that I could resuscitate my dynatstarter by flahing a battery briefly across the field winding. In desperation, with flat batteries I have even succeeded with torch baterries. Once there is a hint of magnetism, the output builds until it returns to normal.

Whether this is the problem with you genny, I wouldn't know.

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[William_H]

The magnetic field for generation of electricity is usually in the rotor and except for simple generators like bicycle gens the field is provided by a coil which is fed by brushes onto slip rings. In the case of a car or boat alternator the current is initially provided by the battery and is then when generating provided by rectifying the AC generated. Now in the case of a portable generator it is most likely that it relies on somer residual magnetism in the core of the rotor to provide some generator output which then provides popwer to increase this magnetic field and so output until the current in the field coil needs to be regulated to control the final output. I don't know if you can detect this residual field but you shouldn't worry if you can't. It can be replaced as already suggested by temporarily connecting a 12 vol;t battery to the coil (half a second is enough). If you are brave and can connect the 12 volts to the field coil via the slip rings when the gen is running you should find output at the AC connector possibly way more than 115V however any output will indicate the slip rings and field coils as well as the stator coils are working OK. In that case the problem is likely to be in the regulator which may be electronic but also may involve voltage sensitive relays. he most likely failure mode is in broken wires or spring connections due to vibration so you may find by inspection the problem. good luck will.

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[richardandtracy]

I had this problem myself with an old 110V genny. I just couldn't get it to generate.
With mine I found that it was a combination of poor brushes & not being used enough (the residual field in the alternator had decayed away below a starting stength). The cure was to clean up the brushes and put a 12V battery across them to sting it into action once the engine was running. I wore rubber gloves and wellingtons when doing this and removed the battery just as soon as the tell-tale 110V bulb lit (yeah, it's that old).

The genny now works a treat provided it's used weekly - consequently in winter I occasionally have to repeat the procedure.

Regards

Richard.


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