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Where are all the ESR meters?

Discussion in 'Electronic Design' started by Fred Bloggs, Jul 21, 2007.

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  1. Good idea for some applications, but how are you going to maintain
    contact resistance? We are talking about readings of hundreds or
    thousandth of an ohm.


    --
    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida
     
  2. Robert Baer

    Robert Baer Guest

    Not electrolytics..use the old-fashioned power line caps (not exactly
    light).
     
  3. Robert Baer

    Robert Baer Guest

    ...by at least a few orders of magnitude!
     
  4. Terry Given

    Terry Given Guest

    by doing this:

    Ckt ---------+
    o |
    o<--o-+-- to DUT
    |
    Gnd ---+-------- to DUT

    Cheers
    Terry
     
  5. Maybe a power resistor in there so it doesn't go bang when you short
    out that 400V electrolytic.
     

  6. Why would you expect the ESR to change in those type of capacitors?
    Any defect in the inner connections would be obvious, because the cap
    would disintegrate.


    --
    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida
     


  7. So, you want to flash the silver off the contacts to metalize the
    insides of the switch's body, or even weld them together?


    --
    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida
     
  8. Fred Bloggs

    Fred Bloggs Guest

    I know where you're coming from with that statement and it is not true.
    I am far enough along to know for sure whether something will work or
    not. All you have thought of so far is measuring the in-phase component
    of voltage developed by a current pulse. And your typical white board
    brainstorming is largely used for the how and not the what. The idea
    within the original Italian hobby circuit was not too bad, the execution
    was lacking, and the outputs of interest were sort of compressed, but
    the idea of a bridge driven by a reasonably *low* impedance current
    source, resulting in short transient recovery from the ESL and limited
    peak response, is not bad at all.
     
  9. Fred Bloggs

    Fred Bloggs Guest

    It is more than apparent from your posts that newsgroup is on the whole
    a disturbing influence for you and may not be the best thing for your
    health. You should abandon it and put that time into a support group.
     
  10. Winfield

    Winfield Guest

    A better idea, I think, is to use a proper higher-impedance
    current source, and drive with a 100kHz sine wave, thereby
    greatly reducing the ESL problem, which can otherwise be a
    killer for the 1 to 30 milliohm region. Using a sine wave
    also means the measured ESR can be compared with laboratory
    meter readings. Otherwise, how would one compare sets of
    square-wave readings with accurate lab instrument readings?

    I'm thinking of using a 2-volt peak sine wave with a 200-ohm
    resistor (10mA peak test current) delivered from a rail-to-
    rail opamp with a slew rate exceeding say 2V/us. I'll break
    the resistor into three parts and add two sets of protection
    diodes to the rails. The outermost resistor can be a 100-ohm
    10-watt high-thermal-mass part to discharge the capacitors.
     
  11. 2-volt P-P is too high to do in-circuit testing in all cases as it
    could cause Si junctions to conduct. 0.2V or 0.3V would be a lot
    better.
    Some of the designs out there don't bother with discharging the
    capacitor- they put a low (and stable) -ESR cap of a few uF in series
    with the DUT. That way you have an upper limit on the energy to be
    handled (given an upper limit on the voltage of (say) 400VDC or 500VDC
    to handle off-line filter caps).


    Best regards,
    Spehro Pefhany
     
  12. Winfield

    Winfield Guest

    Michael, I'm sorry to hear your health problems have become
    so severe. I was hoping the VA would get you back on track,
    but now I wonder if they've diagnosed you properly? Could
    it be that at this point you're suffering more from the cure
    (medications) than the illness?
     
  13. MooseFET

    MooseFET Guest


    If the DUT is a large capacitor charged to several hundred volts, that
    would have to be one heck of a switch.

    I think it would be far better to make a current source and voltage
    preamp that can both withstand several hundred volts.

    Neither the current source nor the voltage preamp needs to be super
    good they just have to not crosstalk. Assuming we have well regulated
    +/- 12V supplies, the current source can be just a rail to rail output
    driving a resistor. For a measurement current of 1mA, a 12K resistor
    would be required. Assuming we have to withstand 500V, we need a
    resistor that can take a 21W pulse.

    Operating at 1mA results in about a 1uV measurement requirement. This
    would let us use a resistor on the order of 100K on the input of the
    preamp without getting swamped with noise.
     
  14. Winfield

    Winfield Guest

    Do some of you readers have a suggestion for a low-
    power 5-volt opamp with specs like: 2MHz or higher fT,
    2V/us or faster slewing, rail-to-rail output that can
    deliver 10mA or more while within 500mv of the rail,
    and of course, low cost? Should be easy to find. :)

    How about a low-power low-cost 5V instrumentation amp?
     
  15. Jim Thompson

    Jim Thompson Guest

    [snip]
    I'm with you on that, even the frequency.
    I've been thinking along the lines of an AC _current_source_, and
    using the cap UT as the filter to keep it queued. Then you get a
    linear reading of ESR.

    But I've been lacking time to put pencil to paper... I'm up to my
    gills in (paying) projects... and, in my business, one must make money
    while it's available ;-)

    ...Jim Thompson
     
  16. Jim Thompson

    Jim Thompson Guest

    [snip]
    One has to wonder.

    I've been thru all kinds of shit tracing my leg pain to crushed disks,
    only to finally have someone say, "Why don't we take an X-ray of your
    hip".

    Looks like that's the culprit :-(

    ...Jim Thompson
     
  17. John Larkin

    John Larkin Guest

    10 mA won't make much voltage across an electrolytic cap!
    The other possibility is to just limit the current, not instantly
    discharge the cap,

    John
     
  18. John Larkin

    John Larkin Guest

    Synchronous detector?

    John
     
  19. Jim Thompson

    Jim Thompson Guest

    Without pencil to paper, synchronous _may_ allow separation of real
    and imaginary terms.

    ...Jim Thompson
     
  20. John Larkin

    John Larkin Guest

    If the drive is a sine wave, ESL peaks go away.

    And what is a "*low* impedance current source"?

    John
     
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