Electronics > Beginners
finding harvested resistors power rating
wraper:
--- Quote from: rsjsouza on November 29, 2019, 10:10:51 am ---
--- Quote from: wraper on November 29, 2019, 09:38:26 am ---
--- Quote from: rsjsouza on November 27, 2019, 03:35:20 pm ---Yes, anything near 60°C is already quite unbearable to touch. That is why I tend to have at least one cheap DMM with temperature around both my work and my home lab.
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And it's basically useless for measuring resistor temperature unless you will attach thermocouple with thermally conductive compound. And even then nearly useless for small resistors because thermocouple itself will sink a lot of heat. I feel like facepalming every time when someone touches heatsink or some part with junction on thermocouple end and thinks he is measuring it's temperature.
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Imprecise? Yes. Useless? Hardly.
It surely beats the finger test.
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If you measure something like half of actual temperature, I call it useless.
AVGresponding:
Yes, for measuring anything with such a small thermal mass, touching it with just about anything will skew the results so much as to make them nearly worthless.
You really need a non-contact thermometer, they're cheap enough these days (<£50) if you don't care much about brand names.
My personal preference is to not run anything at more than 75% of its rated values, but personal preference isn't scientific method.
schmitt trigger:
As someone else commented;
Assume the largest one is 1/2w, the mid sized ones 1/4w, and the tiniest one 1/8w, and call it a day.
In my much younger days I also harvested a lot of parts. Only used it for hobby stuff, though.
wraper:
--- Quote from: ThickPhilM on November 29, 2019, 02:30:57 pm ---You really need a non-contact thermometer, they're cheap enough these days (<£50) if you don't care much about brand names.
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Won't work on resistors unless it's something with size of at least as 5W ceramic resistor. You need thermal camera for smaller parts. Preferable with adjustable focus for working at close range. IR thermometer gun won't do the job. They capture too wide spot, and laser pointer is shifted from center of actual measurement spot quite a lot.
AVGresponding:
They do work, you just have to be mindful of the limitations, and adjust your measuring technique accordingly.
Full on thermal camera time is for the birds, and those with cash to burn. Even used (and useful) gear is well beyond the means of most hobbyists.
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