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| finding harvested resistors power rating |
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| T3sl4co1l:
Well, resistors of that style can operate at 150°C or so quite comfortably. Noteworthy that the finger method needn't be very accurate, not just because of the meat sensors and computer behind it (which, if adequately trained^Hcalibrated on various materials and temperatures, can be pretty accurate), but because the meaty finger has a lot more thermal mass than a tiny resistor, so you're more likely to feel a pulse of heat, and not its actual quiescent temperature. One "feature" of those kinds, the enamel is usually some kind of epoxy compound that smells funny as it heats up. This may not apply to old (salvaged) resistors, but it's true for new parts at least. When I'm breadboarding with them and notice the smell, that's a good hint I've wired something wrong, or used too low a rating. Tim |
| rsjsouza:
--- Quote from: T3sl4co1l on November 27, 2019, 05:51:17 am ---Well, resistors of that style can operate at 150°C or so quite comfortably. Noteworthy that the finger method needn't be very accurate, not just because of the meat sensors and computer behind it (which, if adequately trained^Hcalibrated on various materials and temperatures, can be pretty accurate), but because the meaty finger has a lot more thermal mass than a tiny resistor, so you're more likely to feel a pulse of heat, and not its actual quiescent temperature. --- End quote --- 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. --- Quote from: T3sl4co1l on November 27, 2019, 05:51:17 am ---When I'm breadboarding with them and notice the smell, that's a good hint I've wired something wrong, or used too low a rating. --- End quote --- That or when you realize the plastic hole of the breadboard itself became a bit wider... :-DD (this can also happen with power transistors) |
| james_s:
60C is about that point where I can touch it but I don't want to hold my finger on it for any length of time. I realize that resistors can safely operated at higher temperatures than that but unless they're power resistors I don't really like running them that hot. Even if the resistor survives, a lot of times the PCB will darken and the solder joints are prone to failing. |
| wraper:
--- 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. --- End quote --- 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. |
| rsjsouza:
--- 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. --- End quote --- 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. --- End quote --- Imprecise? Yes. Useless? Hardly. It surely beats the finger test. |
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