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How to measure ESR?

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OM222O:
I've done a lot of googling, but I've either seen schematics provided for an ESR meter with no explanation of how it works, or some videos which involved a signal generator and an oscilloscope ... I highly doubt the commercial products use the signal generator + scope technique as it would be very expensive to build into one small instrument  ??? please share your comments down below  :-+

Conrad Hoffman:
ESR is just Rs, usually measured at 100 kHz. Try my page here- http://www.conradhoffman.com/cap_losses.htm

You can convert loss, which can be in terms of Rs, dissipation factor or several other things, to any other form, if you also have value and frequency, so ESR is just a quick calculation away if you have the results from any LCR meter that also gives loss, but not all will do it at 100 kHz. That's why one-trick-pony ESR meters exist. Regardless, if you can set up to find the series resistance at 100 kHz, using a bridge or just current and voltage, you can get ESR. IMO, ESR isn't all that useful to anybody other than switching power supply designers. You need three things to evaluate a cap- value, loss and DC leakage at rated voltage. I realize that's contrary to the popularity of ESR meters, and they can be useful for a quick check, but they can also lead you astray or miss problems that you need to find. IMHO, it's so easy to build a bridge (or buy a cheap LCR board on eBay) that I'm surprised more people don't do it.

OM222O:
I have seen selectable frequency on a few designs so I might give that a try.'
To measure losses as you said, can I just use a known resistance in series with the cap and measure the voltage across it, hence getting the power it dissipates vs the input power. then calculate the difference which is power dissipated by cap  :-/O
I'm not sure what sort of values I should be expecting and if the difference is large or small.
maybe there is an easier way of calculating the difference in power?

Tek Tech:
Check out this project, with a nice explanation:
http://vk6tt.blogspot.com/2016/04/capacitor-esr-meter.html

Update:
http://vk6tt.blogspot.com/2017/03/esr-meter-update-and-pcb.html

MarkF:
Look here for a little project

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