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Mechanical energy to dc energy

  1. Jul 15, 2012 #1
    Hello world. Is there any way to convert mechanical energy into DC electricity energy WITHOUT using any magnets ? I know there is homopolar generator but it uses magnet and as I said I need something that doesn't use any magnets. I also know there are stuff that use friction (triboelectric effect), but they are very inefficient and waste a lot of mechanical energy input into heat. I need something fairly efficient, for example at least around 75%, you know what I mean. Also please don't say that I can do that by using self exciting ac generator then using rectifier to make it dc, I need direct DC generation. Any ideas ? *_*
     
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  3. Jul 16, 2012 #2

    vk6kro

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    There is the Piezo Electric effect.

    I have a flame lighter in my barbeque that delivers an awesome spark.

    What do you have against magnets? They are cheap and cost nothing to run.
     
  4. Jul 16, 2012 #3

    sophiecentaur

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    There are a number of electrostatic generators that generate DC without magnets. The Whimshurst Machine was a favourite in my School. Then it was decided that they are too dangerous and they now use the Van der Graaff (much less impressive in many ways).

    But to generate DC with low volts and high current is not possible without using magnets in one form or another, I reckon.
     
  5. Jul 16, 2012 #4

    jim hardy

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    no magnets.

    are electromagnets and DC generators excluded as well?
     
  6. Jul 16, 2012 #5
    You can generate heat with friction and then convert it with the thermoelectric or the pyroelectric effect.
     
  7. Jul 16, 2012 #6
    @jim hardy: no, electromagnets are not excluded, only permanent magnets are excluded. but even with electromagnets there is problem. you have to supply current to it to keep field and that itself would consume most of power from generator if not all.

    @DragonPetter: those effect are very inefficient, around 3-4%.

    Somebody knows please ? *__*
     
  8. Jul 16, 2012 #7
    @vk6kro: cheap ?! :D they are cheap but so tiny. I wanna make faradays disk ( homopolar generator ) and I think I need something with diameter at least 25cm with strong field so that I dont have to spin it at very high speeds. Any ideas ?
     
  9. Jul 16, 2012 #8

    jim hardy

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    All US automobiles prior to about 1959 used a self excited DC generator (Europeans called them dynamo) which required nothing but rotation to make 30 amps. No magnets just armature, field and brushes , with a clever electromechanical regulator for control. Unlike an alternator it'll bootstrap itself up and supply its own field with no external supply.

    read up on the simple dynamo , if it seems to do what you asked
    Peruse the junkyards for one of these:

    stude_gen.jpg

    I liked them because even with completely dead battery (or no battery) you could push-start the car.
    Chrysler went to alternators in 1959, Ford ~1964.

    old jim
     
    Last edited: Jul 16, 2012
  10. Jul 16, 2012 #9

    sophiecentaur

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    This is not correct. Car alternators have an electromagnetic field magnet which uses a very small proportion of the Power generated. Likewise, large scale Generating Sets use electromagnetic field windings. Power loss isn't an issue.
     
  11. Jul 16, 2012 #10

    jim hardy

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    and that '51 Studebaker generator pictured makes its own 2 amps of field current, delivering up to 30 amps for the vehicle .

    Reason they went to alternators is they are cheaper to manufacture (no big copper commutator) and alternator makes more current at idle speed - which was becoming an issue in stop & go traffic..
     
  12. Jul 16, 2012 #11

    vk6kro

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    Have a look at these:
    http://www.ebay.com.au/itm/5pcs-20m...0854284960?pt=AU_Supplies&hash=item27c7b57ea0

    (prices are given in Australian dollars which is about the same as US$.)

    Or look through these:
    http://www.ebay.com.au/sch/i.html?_...magnets&_osacat=0&_trksid=p3286.c0.m270.l1313

    The hole would be necessary so you could put screws in to hold the magnets in place. Glueing them would be a nighmare.
    If you had one every 40 mm on a flat surface, you could draw up a scale diagram to see how many you would need.
    I make it about 60 per side. 18 + 15 + 12 + 9 + 5 + 1 in concentric circles.
     
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