Electrolytic Tester

Discussion in 'The Projects Forum' started by grant1842, Sep 1, 2011.

  1. grant1842

    Thread Starter New Member

    Aug 21, 2010
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    I am looking at this Electrolytic Tester circuit I found on the net and can not get it to simulate in Circuit Wizard.

    Can someone look at it and tell me should it work as is, or what I am doing
    wrong.
    Here is the one I am trying to get to work in Circuit Wizard.
    [​IMG]

    Here is the original schematic .
    [​IMG]



    Thanks for any help.
     
  2. t_n_k

    AAC Fanatic!

    Mar 6, 2009
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    You haven't wired in anything for RA0. Was RA0 specified? Plus you've mixed up your schematic around R4, D1 & D2 in relation to the original.
     
  3. SgtWookie

    Expert

    Jul 17, 2007
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  4. grant1842

    Thread Starter New Member

    Aug 21, 2010
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    0
    Thanks for your help :)
     
  5. SgtWookie

    Expert

    Jul 17, 2007
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    I don't know how valid that leakage tester is; seems that they're only using low voltage, and I don't know if they're taking voltage rating and capacitance into account. They have to be factored in to decide if the leakage rate is acceptable.

    Before using electrolytics that have been sitting around for awhile, it's a good idea to re-form them. Charge them up to their rated voltage using very low current (a few mA) over several hours.
    The general formula for maximum permissible leakage current is:
    Capacitance in uF * Working Voltage * 1.5 / 10,000
    So, for a 1000uF cap, 16wv, max permissable leakage would be 2.4mA.

    Have a look at this thread:
    http://forum.allaboutcircuits.com/showthread.php?t=36743
    In my reply, I attached file "ReformerNo1.pdf" from back in 1957. Leakage tables are on the very last page. You'll find that the formula I posted above very closely agrees with the tables.
     
  6. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    RA0 and RA1 are the names of PIC microcontroller pins, the ones that have digital and also ADC functions.

    The circuit probably uses a PIC to charge and discharge the cap and measure charge times.
     
  7. SgtWookie

    Expert

    Jul 17, 2007
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    Hello The_RB,
    Exactly right; that's what is on the pages I linked to. The source code for the PIC is also included.

    As I mentioned above, I have doubts about the validity of the results unless the PIC program can take into account not only the capacitance value of the DUT, but the voltage rating as well. I just don't have the time to build/program/verify the results.

    Maybe you'd be interested in checking it out? :)
     
  8. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    I had a look on the Talking Electronics site you linked to in post #3. It talks about using the 2 LEDs as a "zener" voltage reference, and (in my understanding) the PIC can measure time very accurately and has ADC inputs that can measure the voltage quite accurately. So there is probably enough hardware there to measure capacitance quite well and even the capacitor ESR, although (like you said) "good" ESR will depend on the cap voltage rating so that must be interpeted by the user.

    Like you I don't have the time (or the desire) to verify their results, but if someone wants a good PIC based cap meter I made one earlier that will measure 50uF down to 0.01pF and with very high resolution (although it does not measure ESR or caps in-circuit);

    http://www.romanblack.com/onesec/CapMeter.htm

    [​IMG]
     
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