| General > General Technical Chat |
| identifiing capacitors |
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| bob91343:
This being the real world, a capacitor isn't just a capacitor. It has many properties that often compromise its operation. There is no substitute for understanding what the circuit does and how ordinary parts behave under these conditions. Calling a part a capacitor is kind of like the blind men groping an elephant. With eyes open you can see much more. You many need to know about ESR, ESL, leakage, temperature drift, self resonant frequency, susceptibility to environment such as vibration, and so on. In the final analysis, actually running the circuit to see how it behaves is important. Capacitors are cheap unless improper selection causes consequential damage. |
| fixit:
thanks everyone and a special thanks to james_s. This simple circuit is something that I mostly understand, a 24v ac supply into a full wave bridge rectifier with a cap across the output to smooth the dc side out somewhat. The resultant dc is fed into a dc coil that opens the gas valve for the flow of gas to the furnace. In the past, these coils were all ac coils on the solenoid. I'm finding more and more of these dc coils on valves were in the past they were ac solenoids opening the valves, so they just put this little interface board on the gas valve to get the dc input they want. Seems to me like a lot of extra effort to change such a simple device that we have used for years and years in the 24v ac systems. Most of the failures I have come across with these dc interfaces are just soldering connection at the 24vac input, but this one actually has a bad diode in it and my meter isn't giving me good result with the capacitor, so I will change it also. Since this is my own, ill fix it for myself. A return trip to a customer after a fix like this is taking too many risks and just isn't worth it. Thanks a lot james_s for your very much down to earth reply to some one that knows a little but not enough to get it exactly correct. |
| S. Petrukhin:
--- Quote from: fixit on November 03, 2020, 05:14:33 am --- Electrolytic Capacitor, 220 µF, 50 V, M Series, ± 20%, Radial Leaded, 2000 hours @ 85°C --- End quote --- A capacitor of this capacity has a sufficiently large charge current that can damage the rectifier diodes or the output stage of the valve control. |
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