Is it possible to identify the wattage of resistors salvaged from circuit boards?

Discussion in 'The Projects Forum' started by Emare, Dec 9, 2017.

  1. Emare

    Thread Starter New Member

    Dec 8, 2017
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    Working on my LED lights for the RV and have been able to determine the resistance required to run the 6 volt LEDs on a 12 volt system. Is it possible to determine the wattage rating for resistors salvaged from a 6 volt radio circuit board? I found the Resistor colour code calculator to determine the resistance but not the wattage.
     
  2. dl324

    AAC Fanatic!

    Mar 30, 2015
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    There was a time when you could.

    Now there are resistors that are rated for higher wattage than in the past. For instance, some resistors the size of traditional 1/8W resistors are rated for 1/4W.
     
  3. Emare

    Thread Starter New Member

    Dec 8, 2017
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    You were able to recognize a resistor's wattage by measurement?
     
  4. dl324

    AAC Fanatic!

    Mar 30, 2015
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    We did it by eye, but you could also measure.

    Below is information for Yaego resistors. The "Normal" style MFR-25 is 1/4W and the "Miniature" MFR25S is also 1/4W, but is the size of a "Normal" MFR-12 1/6W.
    upload_2017-12-9_19-20-22.png

    Info for SEI:
    upload_2017-12-9_19-30-2.png
    Note that they consider the Yaego MFR-12 size to be 1/8W; as would I.
     
    Last edited: Dec 9, 2017
  5. Emare

    Thread Starter New Member

    Dec 8, 2017
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    The radio I took apart is 50 years old so t may conform to the old system you are referring to.
     
  6. dl324

    AAC Fanatic!

    Mar 30, 2015
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    If you're planning to reuse salvaged resistors, using the "normal" size would be conservative. If you were trying to replace damaged resistors, you'd need to analyze the circuit to see what power rating was required; unless you had a schematic or parts list that gave power rating.
     
  7. takao21203

    AAC Fanatic!

    Apr 28, 2012
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    you could somehow after a while, if the parts get hot and smoke is seen, they are underrated and need higher watts
     
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