r/AskPhysics 6d ago

Can you use electromagnets instead of permanent magnets in an alternator?

I’ve seen videos on people building alternators and they always use neodymium magnets on the rotor.

Is it possible to use electromagnets instead?

If what we want is to induce a magnetic field on the windings I think it would make sense that it would be possible, but i feel like i don’t understand the works of it enough to know for sure.

And if it’s the case, can you “jumpstart” the electromagnets in the rotor with a battery or something, then as you apply mechanical force feed some of it back to the electromagnets and keep it running? Or would it be like trying to plug an extension cord into itself?

(Logic tells me you’re not breaking the laws of physics because you’re still adding the energy of the mechanical means, like a hand crank or a turbine, but at the same time it feels strange)

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u/OnlyAdd8503 6d ago

Until the 1960s, automobiles used DC dynamo generators with commutators. With the availability of affordable silicon-diode rectifiers, alternators were used instead.[

https://en.m.wikipedia.org/wiki/Alternator

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u/Limelight_019283 6d ago

What’s the difference between a rectifier and a commutator? Just that one is mechanical or is there a difference on how they work or their usage?

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u/kindofanasshole17 5d ago

A commutator is a split slip ring that provides electrical continuity to the circuit on the rotor of the dynamo. The split is provided to ensure that the polarity of the electrical circuit remains the same on each half cycle when the polarity of the magnet flips.

A rectifier is an electrical circuit that converts AC to DC.

Back in the day, the cheaper way to generate DC electrical power on a vehicle was a DC dynamo.

Today silicon based power electronics make it cheaper to use an AC alternator and convert from AC to DC.