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Is it possible to limit current with constant voltage?

Discussion in 'General Electronics Discussion' started by LEGEND383, Oct 9, 2014.

  1. LEGEND383

    LEGEND383

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    Oct 9, 2014
    For my raspberry pi project I would like to have just the one power lead coming in, then splitting off to the pi itself and a usb hub. I was wondering if it is possible to limit the current that would be sent to the pi to something like 1.5A at 5V (power supply would be something like 5A at 5V) to protect it from over-current, yet also limit the current drawn by the hub to the remaining amperage (eg. 3.5A) so as to make sure there is always enough power for the pi. Is this even possible? If it is, how?
     
  2. Colin Mitchell

    Colin Mitchell

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    Aug 31, 2014
    How much does the pi take?
     
  3. LEGEND383

    LEGEND383

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    Oct 9, 2014
    It's recommended to supply it with around 1.5A at 5V
     
  4. Colin Mitchell

    Colin Mitchell

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    Aug 31, 2014
    That is not the current taken by pi.
    It is recommended that my car be stored in a garage 15 metres x 30 metres.
    See what I mean? ????
     
    Bluejets likes this.
  5. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    The rpi will only draw the current it needs. You don't need to limit it. You could use a 1000A power supply. As long as the power supply can supply at least as much as is required, you're OK.
     
  6. LEGEND383

    LEGEND383

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    Oct 9, 2014
    @Colin Mitchell No, I don't see your point. If you need a garage that big to park a car, learn to drive and/or get your eyes tested.

    @(*steve*) Thanks for the help :)
     
  7. BobK

    BobK

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    Since no one answered the question in the title of the thread...

    The answer is no. You can limit either the voltage or the current but not both.

    For example, if you have a 5V supply and a device that needs 2A at 5V, there is no way to limit the current to 1A other than lowering the voltage.

    Bob
     
  8. Gryd3

    Gryd3

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    Jun 25, 2014
    You could always monitor the current @ 5V and turn off the power supply if the device exceeds the current rating you have set.
    The Pi will require more current when starting up, or when it is tasked with some CPU intensive tasks. At idle, it draws much less than 1.5A
     
  9. Bluejets

    Bluejets

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    Oct 5, 2014
    I understood the analogy...good one. o_O
     
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