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Not understandable ESR value of the capacitor.

Discussion in 'General Electronics Discussion' started by caps, Nov 17, 2018.

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  1. caps

    caps

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    Jul 29, 2018
    I checked the electrolytic capacitors during the repair of the old audio center. When checking the capacitor 0.1uF 50V, my ESR meter shows more than 10 Ohm. I looked at different ESR tables, but I did not find such a capacitor there.
    What is the allowed value of the ESR of this capacitor?
     
  2. The Electrician

    The Electrician

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    Jul 6, 2012
    Probably the reason you didn't find that value in tables is that 0.1 uF is an uncommonly small value for an electrolytic capacitor. Are you sure it's an electrolytic? You could just replace it with a 0.1 uF film capacitor.

    I have some 0.1 uF electrolytics only because they were part of a full assortment I bought; I would never use one in a project.

    However, I got one out of the box and measured its ESR with a DE5000 LCR meter. At 1 kHz the ESR was about 27 ohms, at 10 kHz the ESR was about 7 ohms, and at 100 kHz the ESR was about 3 ohms.

    What kind of ESR meter did you use to make your measurement? The typical meter that is an ESR only meter makes its measurements using a 100 kHz square wave, but can't get an accurate ESR measurement for a 0.1 uF capacitor because the reactance of such a capacitor at 100 kHz is already about 15 ohms, and the meter can't measure an ESR less than that.
     
  3. caps

    caps

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    Jul 29, 2018
    Yes, electrolytic.Nichicon.For the first time I met this, so the result caused doubts. It is strange that there are no small capacitors in any ESR table, because they are sometimes found in different devices.
    My tester measures at 100 kHz and the waveform doesn’t matter much here.
    Found datasheet.Nichicon.0,47uF-50v. The maximum impedance at a frequency of 100kHz-23 Ohm. Means 0.1uF-50v according to the logic should be even greater.
    http://products.nichicon.co.jp/en/pdf/XJA043/e-pm.pdf
     
    Last edited: Nov 17, 2018
  4. The Electrician

    The Electrician

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    Jul 6, 2012
    If the measurement you got for your 0.1 uF was around 10 ohms then it must be ok, since extrapolating from the data you found of a 0.47 uF max impedance at 23 ohms, 0.1 uF max allowable would be much more than that.
     
  5. caps

    caps

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    Jul 29, 2018
    The search for the datasheet for the maximum impedance of an electrolytic capacitor of 0.1uF-50V, at a frequency of 100 kHz, ended without result.
    It seems to me that the maximum impedance of this capacitor at a frequency of 100 kHz will be approximately 40 ohms.
    Following the logic, my ESR meter measures this capacitor correctly.
    This principle can be periit and for other capacitors.
     
    Last edited: Nov 17, 2018
  6. The Electrician

    The Electrician

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    Jul 6, 2012
    What is the model of ESR meter you're using?
     
  7. The Electrician

    The Electrician

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    Jul 6, 2012
    The 0.1 uF capacitor I have in my assortment is marked with the manufacturer--it's Jwco.I found the manufacturer's list of capacitor models here: http://www.jiaweicheng.com/en/productlist/products.html

    They show several models whose capacitance range goes down to 0.1 uF. My capacitor doesn't have the series designator marked on the capacitor, so I chose the LF series to look at: http://www.jiaweicheng.com/Data/jiaweicheng/upload/file/20151126/LF(1).pdf

    For some reason they only show down to 0.47 uF at 50 volts even though the first web page says that the LF series goes down to 0.1 uF. They do show the maximum impedance for the 0.47 uF 50 volt capacitor as 5.4 ohms. This is much less than the 23 ohms for the Nichicon data that you found.

    Here is a list of various ESR information, including descriptions of how ESR meters work. The link you gave for the meter you constructed also describes how it works. All of these simple ESR meters actually measure the impedance magnitude, not the actual ESR. As explained here: https://www.midwestdevices.com/pdfs/Tnote3.pdf
    this technique only works if the capacitance to be measured is large enough that its reactance is significantly less than its ESR at the measurement frequency. This means that as a practical matter the capacitance should be larger than 1 uF if the measurement frequency is 100 kHz.

    However, if a small 0.1 uF capacitor is very bad, meaning that its ESR has become much higher than its reactance, the simple ESR meter will show this, and a truly defective capacitor will be detected.

    You said that your capacitor measures more than 10 ohms, but you haven't said how much more. If the capacitance of your capacitor is exactly 0.1 uF, its reactance would be 15.9 ohms, and if its ESR is much lower than that, its impedance would be almost the same as its reactance--just a little more than 15.9 ohms.

    But another complication is that the capacitance of electrolytic capacitors decreases at high frequencies. Manufacturers specify the capacitance at a frequency of 120 Hz (or possibly 100 Hz). But ESR meters measure at 100 kHz; if the capacitance is lower at 100 kHz than at 120 Hz, the reactance will be higher. Your capacitor is probably less than 0.1 Hz at 100 kHz. Since the ESR meter can't give a reading less than the reactance, it is to be expected that the reading for your capacitor (even if it's not defective) will be greater even than 15.9 ohms.

    A reading for your capacitor somewhat greater than 15.9 ohms would be indicative of a good 0.1 uF capacitor.

    Using an impedance analyzer we can see how the impedance of my new 0.1 uF capacitor varies with frequency. Here is an image showing the impedance (green curve) and ESR (yellow curve) for a frequency range from 100 Hz to 5 MHz. The bottom of the graph is 1 ohm, and the top is 1000 ohms. There are two markers, marker A at 100 Hz, and marker B at 101.7 kHz (essentially 100 kHz). The values of impedance and ESR at those two frequencies are shown in the upper right of the image. The impedance magnitude of my 0.1 uF capacitor is 19.7 ohms at 100 kHz, and its ESR is 3.77 ohms at 100 kHz:

    Point OneCap.png

    I have a commercially available ESR meter, Model MESR-100, which uses the impedance measuring technique just like your meter. For this capacitor it gives a reading of 21 ohms, which is close to the value 19.7 ohms the impedance analyzer got, and quite different from the true ESR of 3.77 ohms.

    But just knowing that the impedance is not many times greater than the reactance suggests that the capacitor is not defective.
     
  8. caps

    caps

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    Jul 29, 2018
    12ohms.
    MESR-100.
    Wide Measurement Range: >1uF (for 0.1uF the error will be larger on equation 1/(2*pi*F*C) @ 100Khz )
     
    Last edited: Nov 18, 2018
  9. caps

    caps

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    Jul 29, 2018
    The Electrician
    Yes, it completely coincides with my worldview.
    Thank
     
  10. Harald Kapp

    Harald Kapp Moderator Moderator

    10,817
    2,438
    Nov 17, 2011
    Impedance is not equal to ESR.
    This is a standard model for a capacitor (from Wikipedia):
    [​IMG]

    If we neglect Rleakage and LESL, the the model simplifies to a series RC combination, the impedance of which is Z = RESR + (j*w*C)-1
    The term (j*w*C)-1 introduces the frequency dependence seen in post #8.

    A more detailed analysis will reveal a resonance with LESL and a rise in impedance above the resonant frequency. See e.g. this report.
     
  11. caps

    caps

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    Jul 29, 2018
    Z,ESR.png At 100kHz, the impedance loses its meaning.
     
    Last edited: Nov 23, 2018
  12. caps

    caps

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    Jul 29, 2018
    What did the Electrician try to tell in his post? In real measurements one can clearly see the difference between different ESR meters.
    In expensive and complex instruments, the measurement process has a complex form of calculations, many formulas and Fourier are used.
     
  13. caps

    caps

    183
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    Jul 29, 2018
    For example.
     

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