Capacitors

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

From passivecomponents.eu blog (see link below)

dv/dt is the slope. The slope of the Capacitor charging depends upon input current. The blog also notes that ESR can be measured from a capacitor charging/discharging graph.

How ESR is measured from charging/discharge.

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.

Tantalums

• https://duckduckgo.com/?q=tantalum+with+fuse&t=h_&ia=web

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. See the book for more details.

Calculating Impedance / Reactance

Electrical Impedance (Z), is the total opposition that a circuit presents to alternating current.
Impedance changes according to the components in the circuit and the frequency of the
applied AC. Impedance can include resistance (R), inductive reactance (XL ), and capacitive
reactance (XC). It is not simply the algebraic sum of the resistance, inductive reactance, and
capacitive reactance. Inductive reactance and capacitive reactance are 90o out of phase with
the resistance, so that their maximum values occur at different times. Therefore, vector
addition must be used to calculate impedance. (from IET Labs LCR Measurement Primer)

Given you have an LCR meter and you put it to Z mode with a single capacitor, let's just consider it the impedance for now (though it is primarily reactive capacitance). If you do not have an impedance mode on your LCR meter, than you can calculate it from the capacitance reading as well as the frequency the LCR meter is using. Per EEVblog 137, with the BK Precision 879b, the formula is below.

• https://www.ietlabs.com/pdf/application_notes/030122%20IET%20LCR%20PRIMER%201st%20Edition.pdf - IET Labs LCR Measurement Primer 1st Edition, Feburary 2018
• https://bkpmedia.s3.amazonaws.com/downloads/guides/en-us/lcr_meter_guide.pdf - BK Precision LCR Meter Guide

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

This is an ongoing debate in electronics, much like tabs vs. spaces...

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.

Student Manual for Art of Electronics (ver 2.)

From the text:

MOhm and uF give time-constants in seconds
kOhm and uF give time-constants in milliseconds

1 RC is 63% (I need to remember this one)( I R C 6 3 : technically it rhymes. )

5 RC is 99% (or basically full) (note that 1RC and 5RC are for constant voltage, not constant current...)

t = RC

1millisecond = 1k and 1uF

1second = 1M and 1uF

0.1 second = 100k and 1uF

0.01 second = 10k and 1uF