Capacitors

Capacitors hold a 'capacity' of electronics. You may want to take up Meditation if this is confusing.

List

• https://www.eevblog.com/forum/projects/how-is-a-motor-run-capacitor-sized/ - Motor run capacitors (e.g. HVAC fan motor capacitors)

Capacitor Testing List

There was a hackaday article on testing capacitors. It included steps such as looking at ESR, testing for a short, and a few other steps. I can't find it right now, but I'll leave this here, as the search engines may find it later. I think Charvat wrote it.

Tips/Techniques

AC Impedance

I put an article about this in my book of hacks. At AC frequencies, certain caps (usually around 1uf or lower) start to get higher impedance. This can be a problem if you want to, e.g. pass audio across a DC blocking cap, but you choose a small ceramic as opposed to a 10uf electrolytic.

Resonant Frequencies of (input/output filter) Caps

Capacitance will differ based on the frequency. One reason why LCR meters have two different frequencies to test at. You can take it a step further though, and setup something like an analog discovery to do a full frequency vs. reactance characterization. See: https://tahmidmc.blogspot.com/2024/03/electrolytic-caps-over-frequency-why-is.html per Hackaday: https://hackaday.com/2024/04/01/why-is-my-470uf-electrolytic-cap-more-like-20uf/ http://web.archive.org/web/20240402042237/https://tahmidmc.blogspot.com/2024/03/electrolytic-caps-over-frequency-why-is.html This has been discussed on the amp hour, referring to this article http://web.archive.org/web/20231208203302/https://www.signalintegrityjournal.com/articles/1589-the-myth-of-three-capacitor-values and if my memory isn't completely trashed, it came out to be: "most of the time you just throw a couple different values of caps on there and don't investigate unless necessary (but you should be aware of this trap)" or something like that. And that the signal integrity blog was 'technically correct' but for all practical purposes not correct (i.e. you won't have time to do a thorough analysis, although everything they wrote is true). I can't find the amp hour episode at the moment. Around 400. The impedance analyzer part (what you want) of the analog discovery is covered in detail here: https://digilent.com/reference/test-and-measurement/guides/waveforms-impedance-analyzer http://web.archive.org/web/20240303181454/https://wiki.digilent.com/reference/test-and-measurement/guides/waveforms-impedance-analyzer

Ripple on Input/Output Capacitors

A given switcher may have an input and output capacitor. There are acceptable values for input/output ripple (see Switchers#Calculators). This may be a hint of the capacitor failing.

Input Filter Capacitor Resources

For switchers

• https://www.eevblog.com/forum/renewable-energy/smps-input-filter-cut-off-frequency/

"As it is a bulk input cap, it has to be able to pass at least the average current of the load."

• https://www.eevblog.com/forum/beginners/bulk-input-caps-and-impedance/

With any LC circuit (either intentional or through parasitics) you can get oscillations. LC TANK.

• https://www.analog.com/media/en/technical-documentation/application-notes/an88f.pdf

LC Tank from 24V AC Adapter and Laptop DC-DC Supply. Avoiding overshoot. Comparison of different overshoot based on capacitors (perhaps it is possible to detect ESR failure with a close look at overshoot. I should test this.