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Help with current limit protection

Discussion in 'General Electronics Discussion' started by Bluewoolf, May 31, 2017.

  1. Bluewoolf

    Bluewoolf

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    May 31, 2017
    Hi all I am a newby at electronics so appologise in advance if my question is simple and obvious.

    I have a 12 volt source and wish to attach various loads to it none of which shoud draw more than 1/2 an amp 500ma. However any which of them could be short circuited. if that hapens I dont want the voltage drop to bring down the other loads or burn out the wires. I get the feeling that I could do this with a single component Linear voltage regulator or something similar but I don't know.

    Please help.
     
  2. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    The component you're looking for is commonly called a fuse. Use one fuse rated 500 mA per each load.
     
  3. Bluewoolf

    Bluewoolf

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    May 31, 2017
    Yes thank you, While this solution had occurred to me I was wondering if there was a component that would reset if the load returned. However you may be correct and the simplest solution is the best.
     
  4. Rixen

    Rixen

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    Feb 16, 2016
    There are self resetting fuses too, check out polyfuses.
     
  5. shrtrnd

    shrtrnd

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    Jan 15, 2010
    Google 'crowbar' circuit to understand what you're looking for.
    Heed Harald's advice about what your NEED, but the concept for what you're thinking about, is called a 'crowbar'.
     
  6. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    Sorry, I disagree. A crowbar will intentionally produce a short circuit in case of an event (e.g. overvoltage) to force a fuse to blow. This is meant to protect the attached circuit from overvoltage. It will not protect other circuits which are in parallel from undervoltage due to a short circuit in one of the circuits.
     
  7. shrtrnd

    shrtrnd

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    Jan 15, 2010
    Yeah, I guess Harald.
    I wasn't thinking about Bluewoolf's posted circuit question, I read his post thinking he was searching for the term or device used to protect power supply circuits. I probably read more into his question than what he actually meant.
    We in the Colonies, are often told we're wrong-headed thinkers.
    But thanks for clearing that up for Bluewoolf in the event I confused him.
     
  8. Bluewoolf

    Bluewoolf

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    May 31, 2017
    Thank you this looks exactly like what I am looking for. However, Ignorance pervades. Will these fuses cut out and then reset themselves? and having looked at them they are rated in mA and Volts. I am on 12V so will a 15V be good as they do not seem to be in 12V
     
  9. Harald Kapp

    Harald Kapp Moderator Moderator

    9,230
    1,861
    Nov 17, 2011
    1. These fuses will cut in when overcurrent flows and will be in the off-state as long as the load is present (these fuses work by self heating throughthe power dissipated). To reset the fuse you need to remove the load (short circuit) and let the fuse cool down for some time.
    2. The main factor is the rated current. This should match the application as well as possible.
      The rated voltage of teh fuse needs to as high as or higher than the nominal operating voltage of the circuit. This is to ensure the fuse will not burn through when in the off state as in that case the full operating voltage drops across the fuse. Therefore a 15 V fuse in a 12 V circuit is perfect.
     
    Rixen and Bluewoolf like this.
  10. Bluewoolf

    Bluewoolf

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    0
    May 31, 2017
    Thank you You have answered all my queries and I am most grateful. I can see I need a few 500mA 1A 15V polyfuses.
    Thank you, Thank you, and Thank you all who have contributed to this post. Even the 'crowbar' was interesting.
     
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