An alternator

Discussion in 'General Science & Technology' started by Benson, Aug 24, 2019.

  1. Benson Registered Member

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    An alternator consists of moving a magnet within copper windings to generate electricity.

    I believe electricity is the flow of electrons.

    I also believe that you can't destroy or make matter and energy just convert one to another.

    So where do the electrons come from?
     
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  3. exchemist Valued Senior Member

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    The copper.

    Specifically, the electrons in what is known as the "conduction band" of the metal, which means the subgroup of electrons in any metal that are no longer bound to a single atom but are said to "delocalised" and are only bound to the metal as a whole. The presence of these delocalised electrons is the defining feature of a metal and is responsible for the common "metallic" properties: good thermal and electrical conductivity, shiny appearance, etc. A voltage applied across a metal can make these delocalised electrons flow through it.
     
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  5. DaveC426913 Valued Senior Member

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    Presumably, since the circuit is a closed DC loop, the electrons return to the battery, meaning it only requires a finite and limited number of electrons to function indefinitely. It's not like the copper eventually loses all its electrons.
     
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  7. exchemist Valued Senior Member

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    Indeed, for a current to flow there has to be a closed circuit, round which a fixed quantity of electrons circulates. But this is about an alternator, so no battery is involved in this case.
     
  8. DaveC426913 Valued Senior Member

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    Sorry, the alternator charges the battery.

    But yeah, OK, that's not the point, since it could just as easily power a light bulb instead.
     
  9. Janus58 Valued Senior Member

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    As already mentioned, the electron are already there in the winding of the coil and the conductor. Electricity is the flow of those electrons. If the alternator is connected to a closed circuit, the electrons flow in a loop through the alternator coils, the conductor, load, and back to the coils. The energy that, for instance, lights a light-bulb comes from that movement of electrons, and the energy in the movement of the electrons comes from the energy of the movement of the magnet.
    One other thing. Since current is flowing through the coils, this in turn causes the coils to be electromagnets themselves, and of a polarity such that the interaction between them and the magnet resists the motion of the magnet.
    The action of moving the magnet past the coils produces a counter electromagnetic field that opposes the motion of the magnet.
    The faster you move the magnet, the more current you generate and the stronger the counter electromagnetic field produced by the coils.
    If you have an alternator hooked up to a light-bulb as a load, turning the alternator at a greater rate produces more current, causing the light to glow brighter. However, the greater current also causes the alternator to "push back" harder against your attempts to turn it. The result is that the more energy per sec produced by the light, the more energy per sec you have to supply in order to turn the alternator.
    So the energy used by the light ultimately comes from whatever is turning the alternator. It is the conversion of mechanical energy to electrical energy, to, in the case of a light-bulb, light and heat energy.
     
  10. exchemist Valued Senior Member

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    I must admit I was thinking more in terms of this sort of thing:


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  11. DaveC426913 Valued Senior Member

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    I would have called that a dynamo.

    And then I would have immediately realized that I am not sure what the difference is between an alternator and a dynamo.

    And then I would have looked it up.

    And then I would have realized they're different, but not in the way I expected.


    Dynamos produce DC (unless they have a commutator).
    Alternators produce AC.

    http://www.differencebetween.net/bu...ems/difference-between-dynamo-and-alternator/

    "Power generation via alternators is the widely accepted practice around the world. Even vehicles like ships, cars, and motorcycles use alternators to charge their batteries and provide power to the accessories. On the other hand, dynamos are rarely if ever used to produce power but are still in widespread use as motors. Devices that use motors but rely on batteries for power use dynamos, since it can be run via DC. Toys, power tools, and other devices are some examples of things that use dynamos."


    And then I would still be confused. Is a dynamo with a commutator synonymous with an alternator?
     
  12. parmalee peripatetic artisan Valued Senior Member

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    Supplemental question: Is the function of the commutator analogous to inverting the phase at alternating zero-crossings, IOW is it essentially a rectifier in the mechanical domain?
     
  13. billvon Valued Senior Member

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    Sort of. For DC generators with commutators, that's effectively how it works. Note that commutators are also used with DC motors and other non-generator devices.
     
  14. billvon Valued Senior Member

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    No. An alternator uses slip rings for the field current. The stationary armature of the alternator generates AC current (hence the name - "alternator") then uses diodes to rectify the AC to DC.
     
  15. Benson Registered Member

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    And what happens when all the electrons are used up or is there an endless supply?
     
  16. exchemist Valued Senior Member

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    Read post 3. That addresses your exact question.
     

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