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Capacitor ESR ??

Discussion in 'Misc Electronics' started by Jim Thompson, Feb 11, 2004.

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  1. Jim Thompson

    Jim Thompson Guest

    I'm having trouble tracking down typical Capacitor ESR values for
    Aluminum and Tantalum electrolytics.

    Can someone point me to a page?

    Or some rules of thumb I can use in simulations?

    Thanks!

    ...Jim Thompson
     
  2. James Beck

    James Beck Guest

    I did a quick look at some of our suppliers websites and I think this
    has some references to Al Cap ESR in it.

    http://www.nichicon.com/english/lib/alminium.pdf

    Jim
     
  3. The ESR is a matter of technology.
    Have a look at the manufacturer's pages, eg
    http://www.epcos.com

    Rene
     
  4. Jim Thompson

    Jim Thompson Guest

    Thanks, At least that gives me some ball-park numbers.

    ...Jim Thompson
     
  5. Just look up in LTspice's capacitor list to see what
    voltage/capacity/ESR ranges are viable?

    aha
     
  6. Jim Thompson

    Jim Thompson Guest

    Wouldn't that mean you need DF given at a specific frequency so that
    you can work back to ESR (which should(?) be fairly constant)?

    ...Jim Thompson
     
  7. At 0Hz, the ESR of a capacitor will be darn high. It drops as one goes
    up in frequency until inductance takes over.

    When you do find specs for ESR in capacitor data sheets, they specify at
    which frequency (usually 120Hz in the US) they are providing the ESR for.

    According to
    http://www.cooltron.com/component/technical/library_of_capacitor.shtml

    7. Equivalent Series Resistance (ESR)

    It's the sum of all the internal resistances of a capacitor measured in
    Ohms. It includes:

    - Resistance due to aluminum oxide thickness
    - Resistance due to electrolyte / spacer combination
    - Resistance due to materials (Foil length; Tabbing; Lead wires; Ohmic
    contact resistance)

    The lower the ESR the higher the current carrying ability the capacitor
    will have. The amount of heat generated by ripple current depends upon
    the ESR of the capacitor.

    ESR is both frequency and temperature dependent, increasing either will
    cause a reduction in ESR. The ESR is an important parameter in
    calculating life expectancy as the power dissipation (internally
    generated heat) is directly proportional to its value.
     
  8. I think dissipation factor includes several factors, one of which is
    ESR. The bigger factor at higher frequencies is a fairly constant per
    cycle loss. Your formula looks like it is interpreting those per
    cycle losses as ESR. Not very useful, I suspect.
     
  9. You may be right. My formula was provided by the engineer at ASC, and
    I've also seen it on some online sites as well. I'll bet that the
    formula is useful for line-frequency based power supplies, though.
     
  10. qrk

    qrk Guest

    Jim, if you tell me what style capacitor (el cheapo, low-esr, ...), I
    might be able to measure the Z on our network analyzer. Z data varies
    quite a bit depending on capacitor construction. ESR can vary quite a
    bit over frequency, perhaps over 100 to 1 for some ceramic caps (as
    reported by AVX's SpiCap program.

    FYI, AVX <http://www.avxcorp.com/ProdInfo_Listing.asp> has good data
    on their ceramic and tantalum caps.
    Aloha, Mark
     
  11. Leeper

    Leeper Guest

    I've tried some of these AO caps, the A700 series, and one
    nice thing, unlike alot of tantalums and some niobium, is they
    don't go up in flames....ran a 4V version to 14V and held it
    there, and then back down, it nearly recovered all its original
    characteristics.
     
  12. DarkMatter

    DarkMatter Guest

    Nice catch!
     
  13. If you want to interpret all losses as if they were a result of an
    actual series resistance, and the total losses are low, the formula is
    fine. If you want to know what the parallel losses, the series losses
    and the hysterisis losses are, it is not much use. I think the best
    way to measure the actual series resistance is to subject the cap to
    its series resonant frequency and and measure its impedance.
     
  14. Jim Thompson

    Jim Thompson Guest

    [snip]
    Are you saying that the best model would be a series R-L-C evaluated
    at resonance?

    ...Jim Thompson
     
  15. Yes. I think ESR shows up most clearly under those conditions.
     
  16. Jim,
    Maybe I should interject here that the equivalent circuit
    of an AL electrolytic is really a ladder network:

    ---/\/\/\---o---/\/\/\---o---/\/\/\---o...
    | | |
    --+-- --+-- --+--
    --+-- --+-- --+--
    | | |
    ------------o------------o------------o...

    LTspice's capacitor database just uses 1 R and 1 C
    as an quick and effective approximation. But if you
    use 2 R's and C's, you can model the phase angle of
    the impedance correct within a few degrees over many
    decades of freq. Three 3 R's and 3 C's should let
    you model more accurately than you can measure with
    any component analyzer I know of.

    --Mike
     
  17. Mike Engelhardt wrote...
    Do you know of a good way to obtain the values of the
    3 R's and 3 C's, given the component-analyzer data?

    Thanks,
    - Win

    whill_at_picovolt-dot-com
     
  18. Win,
    For 2 R's and 2 C's, a good initial guess was each C
    was half the cap's "DC" capacitance and each R was
    equal to the cap's ESR. So my initial guess for 3 R's
    and 3 C's is each C is 1/3 the total cap an each R is
    equal to the nominal ESR.

    --Mike
     
  19. I read in sci.electronics.design that John Popelish <>

    You can separate parallel and series losses by measuring at more than
    one frequency; two if inductance is negligible, three if it isn't. I'd
    need to think about hysteresis loss: it isn't something that is normally
    significant in capacitors.
    That still gives you a lumped 'equivalent series resistance' figure, and
    often not a useful one, because you won't be subjecting the capacitor to
    frequencies anywhere near the resonance.
     
  20. I read in sci.electronics.design that Mike Engelhardt
    If you use more than one R and C, you need to add inductors as well.
     
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