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Discussion in 'General Electronics Discussion' started by davez, Oct 19, 2014.

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  1. davez

    davez

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    Oct 11, 2014
    I need help in my electronics projects I am making a mini wind turbine. If I used a DC motor do I still need rectifying diodes?
     
  2. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Nov 28, 2011
    You won't need diodes to rectify the supply from the motor, but if you're charging a battery from that motor, you will need some way of preventing the battery from back-feeding into the motor. If you're using some kind of charger (and you probably should), it probably includes that feature. You may also need some kind of smoothing circuit across the motor to keep a steady voltage at the input to the charger.

    This is just a provisional answer. I have no experience with wind turbines. Other people here can give you better, more specific advice, especially if you tell us more about the project, including part numbers and specifications for the parts of the system - the turbine, the charger, the battery, etc.
     
  3. davez

    davez

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    Oct 11, 2014
    howw can i prevent the battery from back-feeding into the motor?
     
  4. davez

    davez

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    Oct 11, 2014
    hmmm im just making a simple wind turbine using a 12v motor hehe but i think its not strong enough i dont have enough money to buy big dc motors :( :D
     
  5. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    You can start by telling us everything you know about your project. There are many answers to that question and lots of important variables that we don't know about. For example:
    • What is the battery voltage?
    • What is the battery capacity in amp-hours?
    • What is the power output of the turbine motor?
    • What is the power being used for?
    • What kind of charger do you have, or intend to use?
    And these are just the BASIC questions. Please don't just answer those ones. Tell us a LOT about your project.
     
  6. BobK

    BobK

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    Spinning a DC motor will produce a pulsating DC voltage. To get a steady voltage you will need a rectifier and a capacitor. Whether or not you need a steady voltage depends on the load your are powering. For example, if powering an incandescent light bulb, the pulsating voltage would work okay. But for a battery charger, as Kris already said, you would need a steady voltage so that the battery was not putting energy back when the waveform of the generator was at a point lower than the battery voltage.

    Bob
     
  7. davez

    davez

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    Oct 11, 2014
    so i just need to make a bridge rectifier and a capacitor? can you give mo some circuit design?
     
  8. Gryd3

    Gryd3

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    Jun 25, 2014
    If that's all you are planning on using, it is simple enough to make it yourself or google for an answer ;)

    Nothing against helping, but if we do all the work, what will you have learned?


    *** The purpose of a bridge rectifier is to redirect an AC current to a Pulsed DC current. (The result will still vary like the original signal, but it will only go one direction instead of two.)
    They typically have printing on them to show which 2 pins are input for AC, and which 2 pins are rectified with a + and -.
    After you figure that part out, the capacitor will be connected on the output side to help smooth things out. (Capacitor has a + and - side as well)

    Draw up your own schematic and we'll say if it's right or not and give you more tips.
     
  9. davez

    davez

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    Oct 11, 2014
    will these diagram be ok? im not really good at electronics its not my major subject :D
     

    Attached Files:

  10. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Nov 28, 2011
    That circuit would be right, but you don't need a bridge rectifier, because the motor already generates voltage with a fixed polarity. Just a series diode is enough.
     
  11. Mongrel Shark

    Mongrel Shark

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    Jun 6, 2012
    I have done a bit of experimenting with dc motors as generators. The big problem is you need to spin them really fast, and you still don’t get near the voltage they would need to run as motors.

    I hope your not trying to charge more than an AA with your 12v motor. ;) You might be able to charge a Lithium battery, but you'd really want a decent charge controller for that... Stick to ni-cad's. They are the least toxic when they burst...

    Cordless drill motors are good. I once got 7 watts (5a @ 1.1v using the 0.22 ohm current sense resistor in my DMM as a load) from a 18v drill motor. Cranking it with a handle from a fishing reel fitted in the chuck. Using the planetary gearbox of the drill helped crank the speed up. :D At the cost of some significant mechanical losses. Thinning the grease inside the gearbox helps, but I wouldn’t expect the gearbox to last as long. Still takes a lot of effort to crank with low resistance loads. I cant remember exactly what the voltage I got with higher resistance loads was. Somewhere around 5-6v I think. Cranking flat out with meg ohm resistor.

    Voltage was considerably lower with the 12v motors

    I did a video about it. Including how to modify the planetary gearbox so that you can crank the motor as a generator. Which is a necessary modification if the donor drill has variable speed.

     
  12. davez

    davez

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    Oct 11, 2014
    So I needed to create a series diode so it will prevent the electricity to flow back to the motor? right?
     
  13. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Right.
     
  14. davez

    davez

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    Oct 11, 2014

    In this video will any kind of diode work because I cant find a diode that he uses. Thanks
     
  15. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    What diode does he use? (I can't be bothered watching the video)

    But, yeah, probably any rectifier diode will work. I'd start with an 1N400x that you may already have on hand -- x can be anything.
     
  16. davez

    davez

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    Oct 11, 2014
    He uses BAT85 i have 1n4004 i will it be ok?
     
  17. Gryd3

    Gryd3

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    Jun 25, 2014
    The BAT85 seems like it would operate more efficiently, but your not squeezing water from rocks so I think you'll be just fine.
     
  18. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    BAT85 is a Schottky diode.

    Any Schottky diode rated at double the expected voltage (or more) would be suitable. As Gryd3 suggests, it's not too critical, but it would make a marginal improvement.

    I recommend at least double the PIV rating because Schottky diodes are very leaky and any gain you make could be negated by the leakage if you choose a device with too low a rated voltage.

    Incidentally Vf tends to rise with the PIV rating, so don't go to far overboard in the voltage either.
     
  19. davez

    davez

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    Oct 11, 2014
    so its ok?
     
  20. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Tell us what you've got. A 1N400x (or 1N540x) or a plethora of other diodes will be OK.
     
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