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| How to determine the voltage rating of an unknown capacitor? |
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| plazma:
I have the same problem. I got 3 component drawers for free. Full of 0805, 0606 and 0402 passives (RLC) and even a lot of semiconductor. Nice and compact drawers. Solves my component archive system :) The values are marked but no idea about cap dielectrics, inductor current rating or resistor construction. I'll probably just check digikey what rating the size usually has. |
| (In)Sanity:
Plazma , Nice collection of caps. AndyC and PA4TIM, love the ideas. I need to re-read everything a few times so I understand the concepts fully. I had an idea as well, what if using a micro with a simple 8 bit DAC + op-amp you charge a cap to say 1 volt, discharge it for a known time interval and then measure the voltage. Then charge to 2 volts, discharge for the same time interval and measure it's voltage, 3 volts...discharge for the same time interval and measure. This process would continue until the percentage of change during the pre determined time interval fell to some level. Now this approach might work better to determine the voltage coefficient then the max working voltage, I'm not sure on that one. The micro could also do a low voltage run to determine the time interval needed for the entire test. For example it would require a longer test period for larger capacitance. It would then use this exact same interval for each voltage range. Hope this makes sense, Ohh and by the way a tantalum cap will still catch fire regardless of the current limiting resistor. It makes for lots of excitement. Jeff Edit: I forgot to mention that the discharge process might need to use a constant current vs constant resistance. |
| PA4TIM:
Leakage ( for electrolytics most) will polute your reading. Possible also dielectric absorption. But for non electrolyts it could work. Why not use a 16 or 24 bit ADC for the micro. They cost allmost nothing ( i heard, i never do digital stuff but I have a 24 bit here for a auto reformer, leakage tester, VC tester, ESR, C meter project, a friend made it for me on a pcb together with guidelines to make the program on an arduino, a long term project but sub sections are finnished allready, the rest is still in my head and parts on paper, the C measurement will be done with a capacitance to voltage converter IC from AD) |
| (In)Sanity:
--- Quote from: PA4TIM on January 23, 2013, 02:10:07 pm ---Leakage ( for electrolytics most) will polute your reading. Possible also dielectric absorption. But for non electrolyts it could work. Why not use a 16 or 24 bit ADC for the micro. They cost allmost nothing ( i heard, i never do digital stuff but I have a 24 bit here for a auto reformer, leakage tester, VC tester, ESR, C meter project, a friend made it for me on a pcb together with guidelines to make the program on an arduino, a long term project but sub sections are finnished allready, the rest is still in my head and parts on paper, the C measurement will be done with a capacitance to voltage converter IC from AD) --- End quote --- Luckily electrolytic's tend to be well marked. No reason not to use a 16 bit or higher DAC, perhaps just do a rough run and then narrow in the final value. If the concept seams sound I may pursue it. Need to finish up my lab power supply project first. It's coming together well fortunately. Jeff |
| jimmc:
Should mention that not all ceramic capacitors have a significant voltage coefficient. Those using a Class 1 dielectric (NPO, COG) do not change significantly with applied voltage or temperature . This dielectric is used for lower value capacitors say less than 1nF give or take a decade. A quick blast with a hot air gun will show if you have a Class 1 dielectric - if the capacity doesn't change significantly with temperature, it won't change with voltage. For example see http://www.vishay.com/docs/23140/geninfo.pdf pages 6-8 The only way I can think of testing these is to apply a proving voltage of 3 times the voltage you want to use them at (through a current limiting resistor), if they survive for 60sec then you should be OK. e.g. If you apply 48v through 47k for 60 sec and no significant current flows then they should be safe at 16v. Jim |
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