how can i find the watts of smd resistance

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  • Xristakis795
    Senior Member
    • Mar 2021
    • 162
    • Greece

    #1

    how can i find the watts of smd resistance

    hi
    in a pcb circuit of welding machine
    i have three resistances smd 4.7 ohm burnt in series with std2nb80t4 also burnt
    with hole on the middle
    this mosfet is connected on primary of an transformer and it seems take dc voltage
    how can i calculate the watts of smd resistances to be sure i have choice the right value
    can i take from an older pcb smd resistance with the same size?
    is right ?
  • stj
    Great Sage 齊天大聖
    • Dec 2009
    • 30997
    • Albion

    #2
    Re: how can i find the watts of smd resistance

    you can only try to guess from the physical size

    Comment

    • sam_sam_sam
      Badcaps Legend
      • Jul 2011
      • 6037
      • USA

      #3
      Re: how can i find the watts of smd resistance

      Or if there is a big enough pad you could external mount if you have any extra space in the enclosure ( just an idea )

      I have done this with surface mount LEDs before you do have to take your time doing and do not be in a hurry
      Last edited by sam_sam_sam; 05-30-2023, 05:50 AM.

      Comment

      • jiroy
        Badcaps Legend
        • Jun 2016
        • 2416
        • Lebanon

        #4
        Re: how can i find the watts of smd resistance

        That's a long story and needs lot of efforts and spare time . Each company makes its catalogue and put its own specs ; sometimes they follow international standards and sometimes they create their own .

        To add on difficulties , many small business companies do not even bother issuing catalogues , while some big companies on the other hand , make their catalogues discrete and difficult to get .

        That's said , a respected catalogue would put the whole specs of a smd resistor , with even its diameters , L x L x H , including the pins diameters and kind of package , wattage , etc ..

        If you know which company made the resistor and do have its catalogue , you're a king , otherwise Only a good knowledge and a high level understanding of Electronics study , plus a long experience , can fill all these gaps ..

        Comment

        • Xristakis795
          Senior Member
          • Mar 2021
          • 162
          • Greece

          #5
          Re: how can i find the watts of smd resistance

          ok
          i want to thanks all for your useful advices

          Comment

          • petehall347
            Badcaps Legend
            • Jan 2015
            • 4426
            • United Kingdom

            #6
            Re: how can i find the watts of smd resistance

            if you replace with one same size and ohms then you can measure volts across it and use ohms law to see if its ok for the circuit

            Comment

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