Odd effect when measuring cap

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  • Tom41
    Badcaps Veteran
    • Oct 2005
    • 336
    • England

    #1

    Odd effect when measuring cap

    I got some old Fuhjyuus out of the SUNTEK PSU I mentioned in the other thread, and decided to test them with a multimeter. With resistance (ohms) setting, I noticed a value on the display which was slowly increasing until it reached a certain point, then did not go up any further. I assume the cap is charging up from the battery inside the multimeter, but what exactly am I measuring here? General resistance? ESR? Capacitance?
    You know there's something wrong when you open your PC and it has vented Rubycons...
  • kc8adu
    Super Moderator
    • Nov 2003
    • 8829
    • U.S.A!

    #2
    Re: Odd effect when measuring cap

    meter voltage is trying to charge it.it should go infinite but since it a known badcap its likely leaky.electricly and physicaly.

    Comment

    • whiz
      Member
      • Aug 2006
      • 48

      #3
      Re: Odd effect when measuring cap

      Really? can we messure leakage with the ohm meter??
      i have some caps that going almost infinite and some other that are totally
      infinite does this shows they are leaky?

      P.S some capacitors when you connect them with the ohm-meter they go up to 1Kohm and they slowly fall...if we have 2 identical caps and there is a difference (at which point the ohm-meter goes and then falls) can we understand something about the caps?!

      thanx!
      Last edited by whiz; 08-21-2006, 04:16 PM.

      Comment

      • gonzo0815
        Badcaps Legend
        • Feb 2006
        • 1600

        #4
        Re: Odd effect when measuring cap

        Ypur cords are a powers ource, if in ohm messuring mode. So if the caps is ok, the cap will sink all current untill it is charged. this will result in a low reading wich will go higher till open. If the cap is bad, the leakage current could get high. Thus the cap won`t charge and the reading would not go infinite. If the cap is open, then now low reading would occure, hence the cap isa dried up.
        Any way, this is very basic and rough testing. Untill the problems are obviouse, there is not mutch won. The only exact messurment is IMHO an ESR meter and a caΓΌacitance checker. But for SMPS i think ESR meter is all what it needs to find faulty caps.

        Comment

        • willawake
          Super Modulator
          • Nov 2003
          • 8457
          • Greece

          #5
          Re: Odd effect when measuring cap

          hmm i thought it would be the cooling down from the desoldering. i didnt know the meter woud charge the caps.
          capacitor lab yachtmati techmati

          Comment

          • whiz
            Member
            • Aug 2006
            • 48

            #6
            Re: Odd effect when measuring cap

            Originally posted by willawake
            hmm i thought it would be the cooling down from the desoldering. i didnt know the meter woud charge the caps.
            You probably don't play alot with your analog multimeter!


            @gonzo0815 thank you for your answer! could you please explain me better this?

            When we connect a capacitor to the ohm-meter the first indication we get shows low ohm resistance and then starts to fall slowly or fast to infinite resistance...
            I understand that if the cap does not fall to infinite, then this shows it is leaky...The first indication (low ohm resistance) what indicates? and how low is it good to go?

            do we need our capacitors to touch infinite? if it is slightly higher is it problem?


            P.S i understand that this is not the bes method to test caps but why you call it rough test?

            Comment

            • gonzo0815
              Badcaps Legend
              • Feb 2006
              • 1600

              #7
              Re: Odd effect when measuring cap

              Originally posted by whiz

              do we need our capacitors to touch infinite? if it is slightly higher is it problem?


              P.S i understand that this is not the bes method to test caps but why you call it rough test?

              With inifnite i mean there should be an open reading, eg. a resistance far beyond the usuall 20Mohm range of standard DVM. It should the same reading if the cords are on air not conected to anything. it is obviousely, that there is nothing wich can go higher than infinite. But ok, if there would be a lower reading e.g. 20Mohm it could be tolerated may be....

              Well, with that testing, you can meay be deterime on an old hifi amplifer that the big Al caps would have ben worn out, or are totaly dry, but you can`t decide on a normal behavior in this test, that the caps has a suitable ESR or if the capacitance is in the range. And that basically is the question, wich is important for SMPS circuits, wich is my background for the above stated.
              If you messure the time and the voltage during the test with a second DVM, you can may be calculate the rough capacitance, but nothing said about ESR.
              I have some very old Jptur caps from an old Enermax, it was shuting down with any seriouse load. But if i tested them like above stated, i would have taken them as good.

              Keep in mind, that even new caps or long stored ones could fail tho this test, and could be ok after some time under voltage. i hope you can get my view, why tist test is not good for a definite answer, if the cap is ok for the applikation or if it is worn out.

              The ESr meter is different. If the ESr is to high, you know fore shure, if this is a problem (and hence the cap is bad) or not.
              Capacitance meter will at least give an idear, if the cap can be used in some circuits, where ESR isn`t that important, but again not good or exact for SMPS.

              @willawake

              hoock a LED to an DVM and in most cases it would lite a bit (only low power types...normaly only about 3v). You need voltage to measure the current and hence be able to calculate the resitance.
              Last edited by gonzo0815; 08-23-2006, 03:03 PM.

              Comment

              • whiz
                Member
                • Aug 2006
                • 48

                #8
                Re: Odd effect when measuring cap

                I looked on the internet and i can't find ESR tester...

                Comment

                • dood
                  Deputy dood
                  • Mar 2004
                  • 2462
                  • USA

                  #9
                  Re: Odd effect when measuring cap

                  Originally posted by whiz
                  I looked on the internet and i can't find ESR tester...
                  Then it must not exist!!!
                  Ludicrous gibs!

                  Comment

                  • trodas
                    Badcaps Veteran
                    • Jan 2006
                    • 770
                    • Czech republic

                    #10
                    Re: Odd effect when measuring cap

                    It does exist, however

                    Google - ESR meter:

                    http://members.ozemail.com.au/~bobpar/esrmeter.htm






                    PS. to stay on topic, the charging cap is visible on DMM too, if it got the analog gauge and simply by looking how the resistance increasing. But in real life, most recapped Vcore caps (all in parallel) does start at about 8 ohms and swiftly move to about 28 ohms, where is slowly then increasing the resistance to a little above 30 ohms, where it stop. Who can explain me that...?
                    "It is dangerous to be right in matters on which the established authorities are wrong." - Voltaire
                    "I believe that all the people who stand to profit by a war and who help provoke it should be shot on the first day it starts..." - Hemingway my config - my caps

                    Comment

                    • willawake
                      Super Modulator
                      • Nov 2003
                      • 8457
                      • Greece

                      #11
                      Re: Odd effect when measuring cap

                      I looked on the internet and i can't find ESR tester...
                      https://www.badcaps.net/forum/showthread.php?t=1287

                      they shipped this to me in greece fine, nice meter. ask them though if they supply the leads cos chilli_sauce said they did not supply them anymore, though they did when i purchased it.
                      Last edited by willawake; 08-25-2006, 11:59 AM.
                      capacitor lab yachtmati techmati

                      Comment

                      • whiz
                        Member
                        • Aug 2006
                        • 48

                        #12
                        Re: Odd effect when measuring cap

                        Thanks guys!

                        @Trodas i found it on Google too...and some other home made ESR meters! i said that i can't find any, because i thought is is a meter widely used and i expected to find dosens from known brands (or unknown) like any ordinary multimeters...

                        possibly there is something that i haven't understood!

                        @Willawake do you think i can order via paypal? i have heard many bad things about paypal...

                        http://www.paypalwarning.com/

                        do you think it is safe to make so "big" transaction?

                        Comment

                        • kc8adu
                          Super Moderator
                          • Nov 2003
                          • 8829
                          • U.S.A!

                          #13
                          Re: Odd effect when measuring cap

                          Originally posted by trodas
                          It does exist, however

                          Google - ESR meter:

                          http://members.ozemail.com.au/~bobpar/esrmeter.htm


                          ROFLOL!

                          Comment

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