Generator mystery

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cspirou
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Generator mystery

Postby cspirou » Thu Feb 05, 2009 1:38 am UTC

There isn't an engineering forum so science will have to do.

I've always been a little confused about how generators or alternators get started. I know that instead of a magnet they use an electromagnet which is also powered by the mechanical energy used to turn the generator. However when nothing is turning at all then there is no magnetic field and I would think if you start spinning it, it would just turn and not produce electricity at all. Am I missing something here? Is there actually a tiny magnet in the center of these just to start things until the electromagnet gets to full strength? Or when you start turning does a small current inevitably occur due to static or friction and it just build up from there?

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Goemon
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Re: Generator mystery

Postby Goemon » Thu Feb 05, 2009 2:10 am UTC

Most alternators and generators need a small source of electricity to get started. The alternator in your car, for instance, has a connection to the car battery which powers the electromagnet - cut the wire, and there's no output current.

It's of course possible to use permanent magnets instead of electromagnets, but then you can't control the output voltage and current independently.
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Solt
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Re: Generator mystery

Postby Solt » Thu Feb 05, 2009 2:53 am UTC

Think about it this way. If the output of the alternator can charge your car battery, and the electromagnet is powered by the output of the alternator...

Spoiler:
it is also powered by the battery!
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cspirou
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Re: Generator mystery

Postby cspirou » Thu Feb 05, 2009 2:55 am UTC

Ok, so the only way you can generate power without a magnet is if you've generated power before. Or you just have to defer the beginning to a smaller generator with a permanent magnet. This seemed like the common sense answer to me but for some reason I thought there was a pure way to convert motion into electricity since you can make electricity into motion without the use of magnets at all.

Edit: This also reminds me when I was reading up on programming and it blew my mind that GCC is programmed in C. The compiler for C is written in C. WTF?! Which came first? The compiler or the programming language? I realize that someone had to make a compiler from machine code a long time ago and then just go from there. But just because I understand it doesn't mean it isn't weird. Like e^(i*pi)=-1

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Sargon
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Re: Generator mystery

Postby Sargon » Thu Feb 05, 2009 3:05 am UTC

cspirou wrote:Ok, so the only way you can generate power without a magnet is if you've generated power before. Or you just have to defer the beginning to a smaller generator with a permanent magnet. This seemed like the common sense answer to me but for some reason I thought there was a pure way to convert motion into electricity since you can make electricity into motion without the use of magnets at all.

Edit: This also reminds me when I was reading up on programming and it blew my mind that GCC is programmed in C. The compiler for C is written in C. WTF?! Which came first? The compiler or the programming language? I realize that someone had to make a compiler from machine code a long time ago and then just go from there. But just because I understand it doesn't mean it isn't weird. Like e^(i*pi)=-1


Well, given the existence of hand-crank radios and flashlights and other such things that generate electricity from motion, you certainly have a generator that could be started in a similar fashion.
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cspirou
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Re: Generator mystery

Postby cspirou » Thu Feb 05, 2009 3:31 am UTC

@Sargon

True, but those all have tiny small permanent magnets inside.

Although now that I think about it. Couldn't you have an iron core of some sort in the middle of an alternator? It would be exposed to the magnetic fields while it is at work and then when you've stopped the core would be magnetized. It wouldn't be as strong as the magnetic field when it is in use but the residual field could be strong enough just to get it started. The problem I see with this is that the magnetic fields are constantly changing so I don't know how strong you could magnetize it.

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Charlie!
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Re: Generator mystery

Postby Charlie! » Thu Feb 05, 2009 8:06 am UTC

cspirou wrote:@Sargon

True, but those all have tiny small permanent magnets inside.

Although now that I think about it. Couldn't you have an iron core of some sort in the middle of an alternator? It would be exposed to the magnetic fields while it is at work and then when you've stopped the core would be magnetized. It wouldn't be as strong as the magnetic field when it is in use but the residual field could be strong enough just to get it started. The problem I see with this is that the magnetic fields are constantly changing so I don't know how strong you could magnetize it.

You couldn't, unless it was a superconductor, since any magnetizing done would mean that there was a circular current going on.
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cspirou
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Re: Generator mystery

Postby cspirou » Sat Feb 07, 2009 7:53 am UTC

Charlie! wrote:You couldn't, unless it was a superconductor, since any magnetizing done would mean that there was a circular current going on.


Superconductors don't have magnetic fields in them.

asad137
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Re: Generator mystery

Postby asad137 » Sat Feb 07, 2009 3:45 pm UTC

cspirou wrote:Superconductors don't have magnetic fields in them.


Type-I superconductors don't have magnetic fields in them. Type-II superconductors can.

Asad


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