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Dynamo VS Motor

  1. Jul 17, 2013 #1
    I hope this post doesn't get deleted again.
    This forum moderator has something stuck up his you know what.
    Keeps deleting posts that I make that he considers speculative. So I guess every thing we know
    about our universe is all we'll EVER know. Because if you cant speculate you're stuck, indefinitely.
    Hope this guy is not a teacher. What a horrible thought.


    My question is only sort of speculation but not entirely. So maybe it will survive.

    Someone told me that an electric motor is the same exact thing as a dynamo.
    Now I understand they both use copper wire and magnets. With a spinning shaft down the middle. But a motor takes in electrical energy and converts it in to a spinning kinetic force or work? Not sure of the correct phrase sorry. The Dynamo does almost the exact opposite. So I understand the idea. But wouldn't a Dynamo be far more efficient at generating electrical energy then the motor? Don't motors excel at using power to create motion? Do you think a motor would be an equal to a dynamo in power creation?

    The reason I ask is I need a Dynamo. 1kw to be exact and im not finding them for a reasonable price. They are all very expensive. But the motor equivalent seems to be a bit more reasonable.
    So I can sub the dynamo for a motor and be satisfied? or will I be throwing away a lot in the way of efficiency?

  2. jcsd
  3. Jul 17, 2013 #2
    most of the mods are there because we want them there. This is a bad tactic to take if you want this to stay.

    If you have not studied the subject, speculating wildly is not scientific. This site explicitly considers only subjects that are within the realm of science and not metaphysics. Einstein is not not famous because he speculated, he is famous because he took his speculation and turned it into a scientific theory. If you do the same, you can publish your theory and then post about it.

    Now, as to your actual question, this might be better in an engineering forum since it is not a fundamental question, but rather one of construction. I would assume that a device designed to do something would do that job better than jury rigging some other device to do the same job. That is, however, just a guess.
  4. Jul 17, 2013 #3
    ok so from what you're saying it sounds as if you're not too sure about the Dynamo VS Motor thing?

    Anyone else?
  5. Jul 17, 2013 #4
    You can get an automotive alternator for $50. Standard ones produce about 700W. You can get bigger ones, or drive two of them. Is that in your budget?
  6. Jul 17, 2013 #5
    Oh my god your a genius. I never really considered an alternator. That's totally within my budget.
    Up to about 200$ was what I was willing to spend. But won't I need to buy a converter?
    I would like to eventually end up with 110-120 volt power so I can charge my cell phone, iPad, and laptop from it. I'm not sure 12-24v will do it. But you've givin my something to thing about.

    Do you have any idea if those are efficient?

    Thanks a lot
  7. Jul 17, 2013 #6
    Purchase one of those devices that allows you to charge phone/laptop etc. from cigarette lighter in car.
  8. Jul 17, 2013 #7
    Automotive alternators want to spin at ~4000RPM. What is your source of mechanical power?
  9. Jul 17, 2013 #8
    Oh wow. 4,000 rpm. Darn. I will have to use some gearing to help with that.
    I don't think I will be getting over 1,000 rpm so hmmm.
    Can't an alternator make power at lower rpm? How do cars work when they are at idle?
    Say 500-700 rpm. The alternator doesn't make power during idle? That doesn't seem right?
    Well I hope it's not. But thanks for the heads up.
  10. Jul 17, 2013 #9


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    Staff: Mentor

    An alternator makes power at idle RPM just fine, it just makes less of it. You'll easily be able to get enough out of an alternator turning at 700 rpm to charge a cell phone, laptop, iPad.

    You will need a transformer to step the alternator output voltage up to the 20 volts or so that those devices typically charge at... But look at your devices, they'll have labels telling what voltage and what amperage they want.
    Depending on the characteristics of the alternator you use, you may need to work out some way of getting voltage to the exciter circuit when you first start it.
  11. Jul 18, 2013 #10


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    Staff: Mentor

    So again: what is your source of mechanical power? What is going to make the alternator spin?
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