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

Thread Starter

Emare

Joined Dec 8, 2017
23
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.
 

dl324

Joined Mar 30, 2015
11,861
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.
 

dl324

Joined Mar 30, 2015
11,861
You were able to recognize a resistor's wattage by measurement?
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:

dl324

Joined Mar 30, 2015
11,861
The radio I took apart is 50 years old so t may conform to the old system you are referring to.
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.
 
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