How to use PTC?

Discussion in 'The Projects Forum' started by rigers, Nov 10, 2014.

  1. rigers

    Thread Starter New Member

    Jun 14, 2011
    20
    0
    Hi,

    I am using a PTC fuse to protect against shorts but I believe I am using it wrong.
    What is the correct way to use a PTC? What I have now is this:
    12V-->PTC--> rest of circuit. When I plug it in the PTC gets really hot.
    From doing some more research I think I need to use it like this:
    12V-->PTC-------> rest of circuit
    |
    10K
    |
    GND

    Is the 2nd method correct or the 1st one and I may be doing something else wrong?

    Thanks
     
  2. BobTPH

    Active Member

    Jun 5, 2013
    789
    114
    Sounds like you have sized it wrong.

    Adding the resistor to ground in the second circuit will have no effect.

    Bob
     
  3. bertus

    Administrator

    Apr 5, 2008
    15,649
    2,348
    Hello,

    It looks like you are using the PTC at the boarder of opening.
    Have a look at the attached PDF for selecting the correct fuse technology.

    Bertus
     
  4. Dr.killjoy

    Well-Known Member

    Apr 28, 2013
    1,190
    156
    I could be wrong but you are using the PTC in series with circuit which is acting Like high impedance resistor hence why your PTC gets hot ... Oh if I am wrong please delete.. Check out Dave's Jones new vid on the repaired board with a blown PTC.. Also you could add a 1n4007 diode in order to prevent reverse polarity accidents .. Make sure the circuit can handle the voltage drop across the diode..

     
    Last edited: Nov 11, 2014
  5. rigers

    Thread Starter New Member

    Jun 14, 2011
    20
    0
    Sorry for taking too long to respond. The problem was entirely different. I had mixed GND and +12V, and the PTC was acting as it should have. When reversed everything worked correctly. Thanks for all the help.
     
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