cap esr question

[trem]

Could not copy an paste the whole conversation for some reason. I believe the guy was talking about lifting the ground sound of an Elytic, and putting a 100k resistor in series.
Then to measure ESR, he says to.......

"Then to measure ESR, just add small film 600V cap 0.1uF with low ESR across the 100k, then measure the AC voltage across the DUT. The ratio of applied AC to load AC is from C ratio. Any additional AC will be from ESR."

You guys probably follow what he is saying, but I am a bit lost. What is DUT...... C Ratio.?
Thanks

[Jazz P Bass]

DUT stands for "Device Under Test".

[trem]

Oh Jeez.....OK.
I had know idea, and a search turned up..... well, 3 letters have an endless Internet possibility I guess.
Thank You

[Malcolm Irving]

I think C ratio must be the ratio of the two capacitance values. Don't fully understand what is being proposed here, but two caps in series will act as a voltage divider for AC, giving a voltage across each cap in inverse proportion to the cap value. (The bigger cap gets a smaller proportion of the voltage.) If one of the caps has a significant ESR this will increase its impedance and give it more share of the voltage.

[MarkusBass]

If you search in google for "capacitor esr measurement technique" phrase, you will get detailed explanation how ESR is measured.
For example here: Geoff's Projects - Measuring Capacitor ESR
or here: Measuring Capacitor ESR and Inductance
or here: Measuring capacitance :: Electronic Measurements

Mark

[trem]

I think C ratio must be the ratio of the two capacitance values. Don't fully understand what is being proposed here, but two caps in series will act as a voltage divider for AC, giving a voltage across each cap in inverse proportion to the cap value. (The bigger cap gets a smaller proportion of the voltage.) If one of the caps has a significant ESR this will increase its impedance and give it more share of the voltage.

If I follow correctly.....using 1 Mic and a 10 Mic you would expect to see a 10:1 ratio.?
But if these are Elytics, in a rectified power supply, are the caps going to be seeing VAC across them.?
Thanks

[Malcolm Irving]

But if these are Elytics, in a rectified power supply, are the caps going to be seeing VAC across them.?

I see what you mean, but I suppose there would still be some AC ripple voltage across them. It is only the ripple current that is passing through the caps. But I have to admit I'm not sure what test is being proposed exactly.