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Homework Help: Is it possible for DC alternator using inverter directl without accu ?

  1. Sep 24, 2013 #1
    Hello, i am new here, and i hope there is someone here that could help me with this :

    1. The problem statement, all variables and given/known data
    I have a DC alternator and i want using inverter to make AC.

    2. Relevant equations
    Is there possible without using ACCU ?

    3. The attempt at a solution
    I tried directly without using accu, but failed.
    I think because DC electric from alternator have a different kind from DC electric from accu.
    DC alternator is sinus current, are different with pure DC from accu.

    Is there any other reason ? and what should i do to make it working without using ACCU ?
  2. jcsd
  3. Sep 24, 2013 #2


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    Staff: Mentor

    Hi Antonius. Welcome to Physics Forums.

    Are you actually trying to build an AC power source for practical use, or is this an academic exercise (perhaps related to a course of study)?

    For advice on practical implementation you might find some knowledgeable people over in one of the Engineering forums such as Electrical Engineering or Mechanical Engineering (they have an Automotive section).

    My understanding is that the typical modern car alternator unit produces pulsating DC at its output. This is because it's basically an AC generator with built-in diodes for full-wave rectification, hence the pulsating DC output. In a car it's up to the voltage regulator + battery to filter this to DC for use by the car's electronics.

    Your inverter is probably not liking the pulsating DC, particularly if it is relying on this DC to power its internal circuitry such as an oscillator to provide the basic AC waveform.

    Depending upon how much current you need to draw from the alternator to power your inverter you may need to use a battery, or you might get away with a capacitor bank to provide the filtering and act like a virtual battery.
  4. Sep 24, 2013 #3

    Thanks Gneill, actually this is for my own research about the different kind of DC between from alternator and from battery. I will try that forum section too, thx.

    I tried using capacitor bank, and failed. It is because the car alternator that i using. I figured out that alternator don't have a strong enough magnet for its rotor, so it's need battery to ignited it.

    When i using battery, the output would become pure DC, and without battery the output become pulsating DC. And i cannot find inverter that could accept pulsating DC.
  5. Sep 24, 2013 #4


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    Staff: Mentor

    It sounds like the alternator is using an electromagnet for its field rather than permanent magnets, so it needs the battery to "bootstrap" its operation. Perhaps you can employ a small 12V battery to get things started (rather than a car battery), then the alternator can keep things going and supply its own power for its field. This assumes constant input of mechanical energy to keep the alternator turning under load, of course; no perpetual motion crackpots need apply :smile:

    I can't think of anything else to offer on a practical front. You'll have to seek out those who have tried similar things with similar equipment, or who have a good understanding of the operating characteristics of this type of alternator.

    Good luck with your investigations!
  6. Sep 25, 2013 #5
    Yes, i think so, thanks a lot. Of course it is not perpetual motion because input energy it greater than output energy.
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