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Non-changing current with C-EMF

Discussion in 'General Electronics Discussion' started by XRZ, Jul 30, 2014.

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  1. Gryd3

    Gryd3

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    You should grab
    There is always a catch ;)
    In an ideal world, a multi-meter would have an infinite resistance when measuring voltage, 0 resistance when measuring current. Oscilloscope leads would have 0 capacitance...
    With many components, there are characteristics such as slew-rate http://en.wikipedia.org/wiki/Slew_rate that dictate how fast something will react.
    That of course could be used to your advantage to to prevent c-emf from propagating through certain components.
     
  2. Arouse1973

    Arouse1973 Adam

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    Every component is ideal. Remember in the real world every component has LCR.
    Adam
     
    Gryd3 likes this.
  3. XRZ

    XRZ

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    @Gryd3, @Arouse1973

    As long as current is constant 90% of the time(which I think it would be with a CCS) I think that's "idea" for me, nothing can be 100%.
    I know there are losses, and efficiency issues... But as long as current is constant most of the time that's great for this experiment. I know that the constant current source would react to maintain current, but how fast? I guess it's fast. Equal or a bit less than counter-emf's induction.
     
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    In theory there is no difference between theory and practice. In practice there is.
     
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  5. XRZ

    XRZ

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    "Practice = losses"
    Well most components nowadays are high in efficiency so I assume I can have the current constant like 95% and more possibly...?
     
  6. XRZ

    XRZ

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    So...how fast would the constant current source react to induced-counter emf?
    Also in both my example the range of voltage would be the applied EMF + counter-emf for the constant current correct? So for example if the applied voltage prior to counter emf was 2V and CEMF is 1V the voltage range would be 1V - 3V?

    @BobK @(*steve*) @Gryd3 @Arouse1973
     
  7. Gryd3

    Gryd3

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    I can't give you an answer, as it is heavily dependant on the components in the circuit, and in the constant current supply..
     
  8. XRZ

    XRZ

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    @Gryd3 Yea that's right... say you had such a system and you picked the components(by choosing the components you feel are right), could you guess/ or approximate it?

    I mean, I know we can't put a time frame here(could we guess it?), is it possible to have the constant current source change it's voltage fast enough to maintain current? Having it react fast enough to respond to the change in voltage due to the induced-counter emf?
     
  9. XRZ

    XRZ

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    Anyone know the price range of such power supplies, or how much the components could cost at the end(estimations anyone)? If I'm interested in building/buying them?
    @Gryd3 @Arouse1973 @(*steve*)
     
  10. Gryd3

    Gryd3

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    @XRZ, it's a lot of theoretical work that would most likely be useless... I think it's time for a real-world test.

    As far as buying them is concerned. They could be anywhere from $3-4 to $100s...
    Google is your friend mate ;)

    The biggest difference for you when you look at them is the current they are set to, and the upper limit of the input/output voltage.
     
  11. BobK

    BobK

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    "Fast enough" is a useless description. Any constant current source will track changes in the load and compensate within some amount of time. This might be 1uS or it might be 1S. Either of these are "fast enough" for someone's application. What is your requirement?

    Bob
     
  12. XRZ

    XRZ

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    One of the reasons I asked about "adding" voltage to a circuit(in another thread), is because I was wondering of an idea to just have a high voltage source(with exceptionally low current) aside from the constant current source that's purpose is just to cancel out with induced counter emf.

    So that now there are multiple power source, which I assume can add up? P1(constant current) + P2(voltage source) = total Power in the circuit?
     
  13. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Nope. What you say makes no sense.
     
  14. XRZ

    XRZ

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    Can't there be a secondary power source that just adds high voltage?
    A secondary power supply that has a high voltage and low current to deal with counter-emf.
     
  15. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Nope. What you say makes no sense.
     
  16. XRZ

    XRZ

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    What's wrong? What don't I understand that seems to make no sense?
    I'm pretty sure you understood what I meant, but to a circuit it's nonsense?
     
    Last edited: Oct 14, 2014
  17. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    There is no way to "add" a high voltage, low current source and a low voltage, high current source to get both high voltage and high current at the same time.
     
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  18. XRZ

    XRZ

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    How is this possible?
    A diagram:

    [​IMG]
    The first conductor and second, are in a changing magnetic field. From the diagram above it seems that they increase current in opposition while having the same induced counter EMF.

    Yet in this diagram without the PS, the cancel out:
    [​IMG]
    Of course both of them in a changing magnetic field.
     
  19. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    From your PM:

    The main issue that I see is that you absolutely want the current to vary in an electric motor.

    If you always had the stall current flowing, even when the motor was running with no load, you would be very sad.
     
  20. BobK

    BobK

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    Yes, that has come up before. People think back EMF is a bad thing. It is not, electric motors would not be practical without it.

    Bob
     
    Arouse1973 likes this.
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