Voltage loss of capacitor

[belkzak]

Hi Guys,

One of the tests that i have been requested to do by my manager in order to validate a capacitor is to measure the voltage loss across the capacitor,

does anyone have an idea how to do that?

thank you in advance

 

[rjenkinsgb]

You read the data sheet for the range of leakage specified by the manufacturer.
Or use the formula for capacitive reactance if you mean AC signal loss in a coupling application.

End. No more silly question answered.

 

[crutschow]

One of the tests that i have been requested to do by my manager in order to validate a capacitor is to measure the voltage loss across the capacitor,

Do you mean the loss in voltage of an open circuit capacitor due to leakage resistance of the capacitor?

What type of capacitors?

One way might be to use a CMOS op amp in a follower-configuration, which would have a very high input impedance, to monitor the voltage change with time.

 

[danadak]

Was the question V or real Power loss in a capacitor or reactive Power dissipated in a capacitor ?

Regards, Dana.

 

[crutschow]

reactive Power dissipated in a capacitor

That's something you don't have to measure, is it?

 

[JimB]

While everyone is postulating what is required, it would be a good idea if belkzak would let us know just what he means by:

the voltage loss across the capacitor,

Because I have no idea what he means.

JimB

https://www.electro-tech-online.com/admin.php?users/attoutagesus.310841/delete

 

[belkzak]

I mean by voltage loss, the one caused by ESR of the capacitor.

 

[danadak]

Capacitor ESR, Dissipation Factor, Loss Tangent, Q | Electronics Notes

Important parameters associated with capacitors include: ESR– equivalent series resistance, dissipation factor, loss tangent, Q: what they are, formulas . .

www.electronics-notes.com

Regards, Dana.

 

[ChrisP58]

I mean by voltage loss, the one caused by ESR of the capacitor.

In which case the question should have been "what is the ESR of the capacitor."

Since ESR (Equivalent Series Resistance) is fundamentally a resistance, the voltage drop (not loss) of a device is a function of the current through the device. So you need to specify that current. Since DC does not flow through a capacitor, you may also need to specify the frequency of the AC current.

 

[The Electrician]

Look here: https://github.com/lorf/transistortester/blob/config/T4-Li-Ion/Doku/trunk/pdftex/english/ttester.pdf
on page 99 (section 5.3.8). If anyone can understand exactly what the test does, please explain to the rest of us.

 

[Pommie]

Since ESR (Equivalent Series Resistance) is fundamentally a resistance, the voltage drop (not loss) of a device is a function of the current through the device. So you need to specify that current. Since DC does not flow through a capacitor, you may also need to specify the frequency of the AC current.

I've always assumed that the ESR was an actual resistance and is the leakage (DC) current through a capacitor. Is this wrong?

Mike.
Edit, google tells me I'm wrong!!! Oh well.

 

[Nigel Goodwin]

I've always assumed that the ESR was an actual resistance and is the leakage (DC) current through a capacitor. Is this wrong?

Mike.
Edit, google tells me I'm wrong!!! Oh well.

I would imagine so, what you were thinking would be a parallel resistance, not a series one.

You never see EPR mentioned

 

[The Electrician]

I would imagine so, what you were thinking would be a parallel resistance, not a series one.

You never see EPR mentioned

The reason you never see it mentioned is because meters that can measure it don't call it EPR (equivalent parallel resistance), they call it Rp. They also call ESR by the name Rs. Even the low cost currently available LCR meters like the DE-5000 can measure both Rs and Rp.

It should be noted however that the value Rp of a capacitor measured by an LCR meter is not what one would measure by applying a DC voltage about equal to the rated voltage of the capacitor and measuring the small (hopefully) DC current (the leakage current) that results. To properly measure the leakage current, a DC voltage must be applied. Since LCR meters measure Rp using a small AC voltage, the measured value of Rp can't be used to calculate what leakage would be if the rated DC capacitor voltage were applied, by dividing the applied DC voltage by Rp.

 

[danadak]

The physical nature of ESR -

Equivalent series resistance - Wikipedia

en.wikipedia.org

ESR losses in capacitors explained

source: Capacitor Faks blog Simon Ndiritu from General Dielectrics explains some basic capacitor losses principles and mechanisms on Capacitor Faks

passive-components.eu

Regards, Dana.

 

[KeepItSimpleStupid]

You have to remember that there are ideal components and real components. Real components have what's called parasitics.
Even a simple wire has inductance.
A wire moving in the Earth's magnetic field generates a current. A very small one. I had to worry about it.

Components have models. Typical capacitor model is a series resistance (ESR), a parallel conductance and an ideal capacitor.

It does sound like homework though,

LCR meters have modes to measure these things at various frequencies.

There are times where three 1K resistors in series works in a circuit and a 3K resistor won't.

Look at some LCR meters from Keysight and others to get a feel.

Each application requires different characteristics. A capacitor for a sample and hold is a lot different than one for RFI supression.

An LCR meter may apply a DC bias and some low amplitude AC signal to make these measurements.

 

[belkzak]

LCR meters have modes to measure these things at various frequencies.

Do you mean that measurements are affected by frequencies? in fact i was wondering about that many times when using my LCR meter to measure ESR, each time i change the frequency i get a different value, so which one is the real ESR !!?

 

[danadak]

ESR Frequency dependency -

What are impedance/ ESR frequency characteristics in capacitors? | Murata Manufacturing Articles

Find Murata's technical articles.

article.murata.com

Regards, Dana.

 

[belkzak]

ESR Frequency dependency -

What are impedance/ ESR frequency characteristics in capacitors? | Murata Manufacturing Articles

Find Murata's technical articles.

article.murata.com

Regards, Dana.

Thank you,

What's your comment on the following please,
it's saying ESR is not a frequency dependent !

 

[Nigel Goodwin]

Thank you,

What's your comment on the following please,
it's saying ESR is not a frequency dependent !

It is - end of story.

The 'standard' frequency for testing ESR is usually 100KHz, so this is what is normally used - although some expensive units might allow different frequencies.

 

[The Electrician]

Do you mean that measurements are affected by frequencies? in fact i was wondering about that many times when using my LCR meter to measure ESR, each time i change the frequency i get a different value, so which one is the real ESR !!?

ESR does vary with frequency, but sometimes it doesn't vary much, and sometimes it varies a lot.

We can use an impedance analyzer to measure several different types of capacitor and see just how ESR varies with frequency. The following images show the impedance magnitude |Z| and ESR of a capacitor with the frequency swept from 100 Hz to 5 MHz. The two curves are shown with the vertical scale ranging from .001 ohms at the bottom to 1000 ohms at the top; that's 6 orders of magnitude. The impedance magnitude is the green curve and ESR is the yellow curve. There are two markers, A and B at 100 Hz and at approximately 100 kHz. The values of the parameters at those frequencies are shown in the upper right of the graphs.

The first graph show the results for a sweep of a Rubycon 1800 uF small electrolytic. The ESR at 100 Hz is 41.3 milliohms decreasing to 16.44 milliohms at 100 kHz. The variation of the ESR is about 3 to 1 over the swept frequency range:

Next here is the result for an older "Bumblebee" paper capacitor. The ESR at 100 Hz is 413 ohms decreasing to 364 milliohms at 100 kHz and finally to about 90 milliohms at 2 MHz. The total variation is about 3.5 orders of magnitude.