What the heck is ESR?

[Jeffhs]

What is "ESR" and what does it have to do with capacitors? I worked with electronics as a hobby almost all my life (until I had to give it up, except for computer-aided amateur radio, when I moved to my apartment 20 years ago--long story and OT), and am completely baffled by this abbreviation. Is this something some electronics whiz kid in California came up with a few years ago, which eventually caught on and stuck (I say California because that state is where most trends, expressions, etc. in common use these days get their start, then eventually sweep the country), or just what the heck is it?

Thank you.

[MadMan]

I mean, isn't it electrostatic resistance? I don't even know myself, I just know that it's a measurement of a capacitor's... something. I think high ESR is bad, and low is good, but like, I think some applications need it one way or the other. And I believe it can change/degrade with age (hence waxy old paper caps going bad).

idfk google it.

[ppppenguin]

The wikipedia article is OK but not brilliant: https://en.wikipedia.org/wiki/Equiva...ies_resistance

This is better: https://www.meanwelldirect.co.uk/glo...esistance-esr/

[Tube TV]

I heard it was the same thing as power factor.
How much truth is in that, I don't know.

And like ManMan says low good high is bad.
I'll have to do some reading about it.

[Popester]

Equivalent series resistance. Back in the day you could hook up a VTVM to an electrolytic and see a deflection of the needle. If it read some sort of value of resistance the cap was deemed bad. If a cap has a high value of resistance that isn’t a desirable thing.

[lnx64]

I doubt ESR is a new thing since I have an old 1950's capacitor tester at my fathers place that tested impedance as well.

[Ed in Tx]

I'll take a crack at it.
Basically you are measuring the resistance to a AC signal passing through the capacitor. With a resistor you do that with an Ohm meter that passes DC through the resistor. But a capacitor blocks DC once it's charged up, then it should read infinity unless it's electrically leaky, so to test ESR you pass an AC current through the capacitor and measure the AC resistance. You want that to be as low as possible with a capacitor since it's either charges up and filters noise and high frequency ripple to ground through the cap, or passes a signal audio or video through the capacitor, with as little internal resistance as possible.

With my ESR meter I can calibrate it with a 47 Ohm resistor. High accuracy not necessary though to test the majority of electrolytic caps. You're just looking for close to as low as a new cap same specs. It measures Ohms like an Ohm meter, just very low Ohms like .1 or less at at a high frequency.