help

Discussion in 'General Electronics Chat' started by Maru1, Nov 20, 2013.

  1. Maru1

    Thread Starter New Member

    Nov 20, 2013
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    Background information: I'm designing a braking system for a mini wind turbine. My idea is to connect a low value resistor across the end terminals of the motor to increase current and torque. When not braking, there is a 10 ohm resistor connected across end terminals of the motor by default. I only need a basic idea for a circuit since this project is in early stages.

    [​IMG]

    Is this something I should be aiming for or is that stupid?

    Also this braking system should be activated once the wind speed reaches a certain speed, If I have a device that measures wind speed how would I create a circuit so that I get the 0.1 ohm resistor between the end terminals of motor instead of 10 ohm resistor automatically

    All help is appreciated.

    With thanks
    Maru
     
    Last edited by a moderator: Nov 21, 2013
  2. WBahn

    Moderator

    Mar 31, 2012
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    Is there any reason why the 10Ω resistor would need to be disconnected at all?

    Is there any reason why one side of the 0.1Ω resistor can't be left connected at all times?

    If the answers to both of the above questions are, "No," then you only have to manage a single connection, namely one side of the 0.1Ω resistor. You can do that with a relay that is appropriately sized for the voltage and current that you are dealing with.

    Then it becomes a relatively simple matter of taking the signal from your windspeed sensor and conditioning it into a suitable control signal for the relay.
     
  3. Maru1

    Thread Starter New Member

    Nov 20, 2013
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    What you said makes much more sense, thank you. Would it look something like that
    [​IMG] ? The relay being a SPDT
     
    Last edited by a moderator: Nov 21, 2013
  4. WBahn

    Moderator

    Mar 31, 2012
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    Is there any reason why the 10Ω resistor would need to be disconnected at all?

    Why can't it be left connected all the time? With the 0.1Ω resistor connected across it, only about 1% of the total current will go through the 10Ω resistor.

    Not only would that allow you to use a SPST relay, but it would keep from open-circuiting the motor/generator which could result in a pretty good inductive kick.
     
  5. Maru1

    Thread Starter New Member

    Nov 20, 2013
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    I suppose there isn't a reason to disconnect the 10Ω at all since the total resistance will be pretty much equal to 0.1Ω if 10Ω and 0.1Ω are in parallel. Thanks
     
  6. WBahn

    Moderator

    Mar 31, 2012
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    You're welcome.

    Oh, and in the future, try to use a meaningful thread title. "Help" just doesn't do it. You'll notice that there is another thread with that exact same title in the vicinity of yours. That makes it hard to keep straight which is which.
     
  7. Jaguarjoe

    Active Member

    Apr 7, 2010
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    Decades ago, I was gonna build one of these things. According to the book I had at the time, it said that controlling tip speed was the best way to go.
     
  8. Maru1

    Thread Starter New Member

    Nov 20, 2013
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    Ok, will remember. Now to back up a little bit, would this idea actually work? Would causing a higher current to run through the outputs of the Permanent Magnet DC motor make it so that a higher torque is required to maintain the same rpm so in effect it would brake.
     
  9. WBahn

    Moderator

    Mar 31, 2012
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    Basically, yes. The heavier load draws (or attempts to draw) more power at the same RPM, thus represents a heavier torque load on the motor shaft.
     
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