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| Capacitor brands? |
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| Zero999:
--- Quote from: WorldPowerLabs on November 22, 2017, 02:30:57 pm ---For electrolytics, I generally stick to Nichicon, Panasonic, or Rubycon. I did once have an issue with Panasonic, where I found a discrepancy between the negative mark on the shrink sleeve, and the negative as indicated by lead length on a part. At that point, quite a few boards had already been assembled and Panasonic was not terribly interested in either covering rework costs or developing a methodology to identify, in-circuit, if any of the caps were backwards (these boards were hand-assembled and the assembly personnel were using the body markings to tell polarity without double-checking the leads). They are still top quality parts and I still use and specify them -- I just wish Panasonic had shown a little more accountability in the matter. --- End quote --- It's usually fairly easy to tell the polarity of an electrolytic capacitor. It will behave like a poor quality diode junction. It should look like a capacitor when connected correctly and a diode with a relatively high voltage, about 1.5V to 3V, when connected backwards. I've just tested a capacitor using my meter's diode test function. When connected correctly, the voltage slowly increases, until it goes out of range >2V, but when connected backwards, it settles at around 1.7V. The test didn't work with all capacitors. Some will charge to a higher voltage, when reversed biased. Use a 5V power supply and a suitable resistor to limit the current, to a safe level. After reverse charging a capacitor, always reform it by recharging it to near the rated voltage. |
| bd139:
Interesting. Will try that here quick as well. |
| WorldPowerLabs:
I've definitely noticed the same behavior (usually when troubleshooting equipment), and I'd asked if a simple test like that would, in their opinion, be adequate to determine whether I had any reversed caps -- but the "official" reply was that they wouldn't "guarantee" any in-circuit test at all. --- Quote from: Hero999 on November 22, 2017, 03:57:44 pm --- --- Quote from: WorldPowerLabs on November 22, 2017, 02:30:57 pm ---For electrolytics, I generally stick to Nichicon, Panasonic, or Rubycon. I did once have an issue with Panasonic, where I found a discrepancy between the negative mark on the shrink sleeve, and the negative as indicated by lead length on a part. At that point, quite a few boards had already been assembled and Panasonic was not terribly interested in either covering rework costs or developing a methodology to identify, in-circuit, if any of the caps were backwards (these boards were hand-assembled and the assembly personnel were using the body markings to tell polarity without double-checking the leads). They are still top quality parts and I still use and specify them -- I just wish Panasonic had shown a little more accountability in the matter. --- End quote --- It's usually fairly easy to tell the polarity of an electrolytic capacitor. It will behave like a poor quality diode junction. It should look like a capacitor when connected correctly and a diode with a relatively high voltage, about 1.5V to 3V, when connected backwards. I've just tested a capacitor using my meter's diode test function. When connected correctly, the voltage slowly increases, until it goes out of range >2V, but when connected backwards, it settles at around 1.7V. The test didn't work with all capacitors. Some will charge to a higher voltage, when reversed biased. Use a 5V power supply and a suitable resistor to limit the current, to a safe level. After reverse charging a capacitor, always reform it by recharging it to near the rated voltage. --- End quote --- |
| bd139:
It does indeed work. Very handy. |
| Zero999:
Before there were electrolytic capacitors and silicon rectifiers, there were electrolytic rectifiers, which were pretty poor, even compared to the mechanical and mercury rectifiers of the day. Someone somewhere (anyone know?) realised that an electrolytic rectifier has a high reverse capacitance, which led to the development of the electrolytic capacitor. https://en.wikipedia.org/wiki/Rectifier#Electrolytic |
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