alternator

Discussion in 'General Electronics Chat' started by electronewb, Apr 5, 2013.

  1. electronewb

    Thread Starter Member

    Apr 24, 2012
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    I get the basics of an alternator but what makes it spins in the first place. Starting from the moment of ignition of the car.
     
  2. #12

    Expert

    Nov 30, 2010
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    A belt.

    Look under the hood of almost any car and you will see the rubber belt that drives the alternator.
     
  3. electronewb

    Thread Starter Member

    Apr 24, 2012
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    I though that the alternator was driving the belts!!!! So the pulleys move the belts and then "start" the alternator?
     
  4. tracecom

    AAC Fanatic!

    Apr 16, 2010
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    The engine provides all the power for everything under the hood. A belt is connected to the main crankshaft of the engine, and drives the alternator, the water pump, the air conditioning compressor, the power steering pump, etc.
     
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  5. crutschow

    Expert

    Mar 14, 2008
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    An alternator is a generator, converting rotary motion into electrical energy, not a motor. The only motor that drives the engine (in a non-electric/hybrid car) is the starter.
     
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  6. PackratKing

    Well-Known Member

    Jul 13, 2008
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    Alternators, are 3-Phase machines, converting the "alternating " current to charge the battery, to DC, via a set of 2 diodes per phase, configured as full-wave rectifiers.

    Re; "Lindsays technical books" for their dissertation on "Alternator Secrets" ... Very informative..

    For a fact, Lindsey puts out a library of very interesting reading for amateur and professional alike...
     
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  7. shortbus

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    Sadly Lindsay books are if not now, soon to be no more. He is retiring and not going to continue. A couple of companies will sell the books he had in stock until their gone. Lindsay was a great resource, I have a lot of his books on stuff I'm interested in.
     
  8. spinnaker

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    Oct 29, 2009
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    Hopefully I would be stealing the OPs thread just adding to i. Here is a good question. Why are alternators used in cars and not DC generators?
     
  9. PackratKing

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    Jul 13, 2008
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    Hi Spin... No hi-jack here -- just a very good question...

    If I remember right, the auto mfgrs. moved to alternators, mostly due to simplicity and efficiency over a DC Dynamo / Generator...

    An alternator, can be energized to output voltages based on what the magnet wire wound field variety can tolerate.

    The part I can never remember, is one requires a sight more torque to spin than the other... Alternators are amazingly hard to turn over once energized...

    Shortbus... That's bad news about Lindsay... Are any of the remaining books available to download, or just paper...??
    I suppose I should not be lazy here, but go and look :D
     
    Last edited: Apr 6, 2013
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  10. #12

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    No segments on the armature = cheaper to build, cheaper to rebuild, and the carbon brushes they do have in alternators last a lot longer.
     
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  11. crutschow

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    Mar 14, 2008
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    Three reasons that come to mind:

    1. Alternators can generate more output current at idle. Important when driving with the typical high electrical loads in city traffic.

    2. Alternators have no commutator that must carry the total output current, which is expensive to make, just slip rings that carry only the small field current, which are cheap.

    3. Alternators are cheaper to build and more compact.
     
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  12. YokoTsuno

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    Jan 1, 2013
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    They were actually used in the past, and you can still see them in vintage cars. They are longer and slender than alternators. The reason was that the only rectifiers available at the time were vacuum tubes and metal-oxide rectifiers, not really suitable for a harsh automotive environment. Both also had a limited lifespan and the latter was also quite bulky.

    Selenium rectifiers: http://en.wikipedia.org/wiki/Selenium_rectifier

    The alternative therefore was a DC generator which has a commutator for rectification.

    Alternators were introduced in the sixties when high power silicon diodes became widely available. These devices are small and have a very long lifespan.
     
    Last edited: Apr 7, 2013
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  13. shortbus

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    Packrat, far as I know, just the paper. The last catalog I got had the news.
     
  14. electronewb

    Thread Starter Member

    Apr 24, 2012
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    I'm reading a few things on 3 phase alternators. Are the 3 phase rectified from AC to DC? If so where do the 3 phase or cables end up in the car?
     
  15. gerty

    AAC Fanatic!

    Aug 30, 2007
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    The 3 phase is rectified in the "diode trio" and that is inside the alternator.

    http://www.bcae1.com/charging.htm
    Look aboutt halfway down the page
     
  16. electronewb

    Thread Starter Member

    Apr 24, 2012
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    And where does it go from there?Where are the 3 phase going to?
     
  17. gerty

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    When it's rectified it's turned into direct current, which means it's no longer 3phase.
     
  18. YokoTsuno

    Member

    Jan 1, 2013
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    Nowhere, they remain inside. If you want them you have to open up the alternator and connect 3 (or 4) wires to the windings.

    There's not much use for a 3-phase 9VAC grid though :D.
     
  19. strantor

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  20. PackratKing

    Well-Known Member

    Jul 13, 2008
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    The AC> DC rectifiers and regulation are internal, phases are also combined internally after rectification, with only one hot lead out to charge the battery, and run the rest of the electrical system while engine and accessories are in use...
     
    Last edited: Apr 9, 2013
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