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Resistor Wattage Question?

Former Member

Hello! I have a computer atx power supply thats about 700 watts that I never use so im using it to supply power to high powered devices I made. But I want to use a resistor to limit the current from my 12 voit line that gives off 23 amps from the power supply. Unfortaintly when I tryed using a 1/2 watt resistor, it burned out. So my question is how many watts a resistors rating has to be if im using a power supply giving off 12 vols and 23 amps? Thankyou! image

  • Using a  resistor to limit the current isn't usually  a very good plan with power supplies. If the resistor is a high enough value to seriously limit the short cicruit current it will also affect the on load voltage significantly.

     

    If you put  a 1R resistor in series with your 12V supply the short cicruit current will be 12A and the power in the resistor 144W (V squared)/R. If you try to draw as little as 2A from your supply the resistor will drop 2V so you will only have 10V on the load.

     

    You could just use a quick blow fuse rated for the load - most switching supplies have some kind of current limiting.

     

    You could also try a polyfuse like Farnell 1822239, this will trip at about 6A but unlike  anormal fuse it will reset itself when the load is removed.

     

    Fuses (either kind) take  afinite time to trip or blow so may not save your power supply if it isn't internally protected in some way.

     

    For experimenting a bench type supply with adjustable current limiting and meters is much better but it may be too expensive for you.

     

     

    MK