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Esr Meter Build

Discussion in 'General Electronics Discussion' started by pete g, Apr 14, 2016.

  1. pete g

    pete g

    79
    2
    Sep 14, 2010
    hi forum members, ijust completed a build of an esr meter. it is the ludens design by Manfred M. I would like to use this meter to check caps in circuit. the basic requirement for this is to keep the test voltage under .6v as to not bias on any semis in the area. i'am seeing about .5v at the present time. my question is how can I drop the test voltage down to .2v

    http://www.py2bbs.qsl.br/esr_meter.php
     
  2. pete g

    pete g

    79
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    Sep 14, 2010
    adam, where are you?
     
  3. HellasTechn

    HellasTechn

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    Apr 14, 2013
    I would like to point out that you can not test components on their boards. That will give you false readings for sure.
    You will have to remove your capacitors from the boards and then test them with your ESR meter.
     
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010

    True, but if the value is high, the capacitor is bad. A normal or low reading tells you nothing
     
  5. Alec_t

    Alec_t

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    Jul 7, 2015
    Try increasing the value of R3 to ~220k. This will reduce the test voltage, but a side-effect is a change in oscillator frequency, which will require re-calibration of the meter.
     
  6. pete g

    pete g

    79
    2
    Sep 14, 2010
     
  7. pete g

    pete g

    79
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    Sep 14, 2010
    thanks, alec, i'll try that. I guess a voltage divider won't work. actually. if your aware of the limitations, esr meters work quite well. service techs have been using them for years to find bad caps in on board circuits.
     
  8. Alec_t

    Alec_t

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    Jul 7, 2015
    I don't see why not, but I thought changing just one resistor might be simplest. Either method would require re-calibration.
     
  9. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    True, but if you're probing a board that you don't have some understanding of the circuit my comment stands.

    Low readings can be caused by things other than a good capacitor.
     
  10. pete g

    pete g

    79
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    Sep 14, 2010
    steve, your right. but like all test equipment it has its limitations.
     
  11. 73's de Edd

    73's de Edd

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    Aug 21, 2015
    .


    Sir pete g . . . . . . .

    Ayyyyyyyyy Caramba !
    ¿ parece que las instrucciones están en un idioma diferente?

    The test voltage level is partially "carved in stone" in that circuitry by the back to back 1N4xxx shunting diodes.
    Initially, sub in some 1N5817's to see if you can live with that yet slightly lower testing threshold.
    Probably, don't want to go the " power germanium " route . . . due to touchy leakage and temperature tantrums.
    Of course that will necessitate higher loop gain in the following op amp to bring up your amplified detection level.
    I have continually used an ESR bridge for " in circuit " testing . . . just a matter of knowing when shunting circuits
    adjunct parts and conditions preclude its use.

    73's de Edd



    .
     
  12. pete g

    pete g

    79
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    Sep 14, 2010
    hi 73s, are you referring to the diodes across the test leads? I agree with the last sentence of your post. rarely do you probe a circuit that you have no concept of how it works. btw, can't read Spanish, should I ask for a translation?
     
  13. 73's de Edd

    73's de Edd

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    Aug 21, 2015
    .



    YES . . . . .those bi phased shunting diodes Vf thresholds are exactly what establishes the test level that reaches your capacitor being tested.

    Ayyyyyyyyy Caramba !
    ¿ parece que las instrucciones están en un idioma diferente?

    HEY MAN ! those instructions are in Portuguese !
    I no speak-a-da . . . speak a-da


    .
     
    Last edited: Apr 21, 2016
  14. pete g

    pete g

    79
    2
    Sep 14, 2010
    yes, they are in Spanish. thank god for babel fish. those diodes are there to discharge any charged caps you inadvertly test. are the diodes your suggesting have a high enough prv rating? I could delete them. I noticed the length of the test leads has a definite effect on the test voltage. I noticed the author used a different op amp. I used the tl062 as in the original design.
     
  15. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    for back to back diodes the required PIV is probably around 2V.

    the actual value depends on the forward voltage at whatever current is passing through its pair.

    a practical consideration is the leakage (reverse current) and forward current at the operating voltage.

    if you look at the graphs of voltage vs current (both forward and reverse) you'll find some surprising behavior at values close to zero for low voltage devices.

    practically this means you should be looking at a silicon (non-schottky) rectifier diode with a moderate piv rating of about 50V.
     
  16. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    oh, another thing is that you should also pick a diode with low capacitance. These are often listed as fast rectifiers.
     
  17. pete g

    pete g

    79
    2
    Sep 14, 2010
    hi steve, good morning from sunny s. florida. I have some fast diodes I could use. will that drop the test voltage. btw, for anyone wanting to build this circuit, you can use a radio shack audio transformer( google modified ludens by dennis hill) I suspect that's why the test voltage is higher, different turns ratio.
     
  18. pete g

    pete g

    79
    2
    Sep 14, 2010
    hi members, can someone explain what happens if you vary r6?
     
  19. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    most likely it's resistance changes.

    I suspect that r5 should be equal to r6 and probably double the secondary impedance of the transformer.

    reducing r5 and r6 will increase the load on the op amp. If it can supply the additional current, the test voltage will remain largely unchanged but the rest current will increase. Since the output of determined by the test current rather than the voltage, this will require changes elsewhere to recalibrate the device.

    reducing the voltage swing on the primary of the transformer would be a better option.
     
  20. 73's de Edd

    73's de Edd

    2,678
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    Aug 21, 2015
    ..


    Sir peter g . . . . . . .

    If R6 is decreased in value it will produce a lower meter reading . . .if increased in value it will produce a greater meter reading.
    Optimally, you want it to be same value as R5.

    BUT I initially need to know about your transformer sub and how you installed it .
    Is it being the Radius Shackimus audio output transformer . . . . 8 ohm to 1k # 273-1380 transformer . . . . a la . . . .
    [​IMG]



    it will have more than the 20 to 1 ratio specified.

    AND did you install it using the 8 ohm Z winding and use either the full 1K secondary or use the centertap to get a 500ohm winding . . . .and was the high impedance wired to the op amp side or possibly the 8 ohm winding was erroneously connected to the op amp side ?


    73's de Edd
     
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