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    capacitor in circut, powered up

    On a energized power supply will a capacitor voltage read the same on both leads? I have a dead power supply and I m trying to locate the bad area.

    #2
    Re: capacitor in circut, powered up

    Why not open a thread for it in a relevant section - post pictures and we will suggest
    some tests
    Please upload pictures using attachment function when ask for help on the repair
    http://www.badcaps.net/forum/showthread.php?t=39740

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      #3
      Re: capacitor in circut, powered up

      Just seeking some general knowledge. With a capacitor just conditionig voltage I was thinking that the voltages would be the same and wanted to find out if I was wrong about this.

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        #4
        Re: capacitor in circut, powered up

        Originally posted by 13919 View Post
        On a energized power supply will a capacitor voltage read the same on both leads?
        I'm not quite understanding the question. Are you asking if the voltage will be the same if you reverse the probes on your multimeter?

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          #5
          Re: capacitor in circut, powered up

          Taking the probe and contacting the capasitor leads one after the other while leaving the ground lead on the frame.This is on a hot circut. What kind of reading should I expect.With my 40 yr old training my basics really suck.

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            #6
            Re: capacitor in circut, powered up

            It theoretically could on the primary side of the supply, but most likely will not.

            Voltage across an individual primary cap could be as low as 170VDC, or up to about 400VDC if the PSU has active power factor correction.
            Last edited by Uniballer; 01-25-2014, 05:46 PM.

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              #7
              Re: capacitor in circut, powered up

              Would the voltage be the same in and out????12v in 12v out or would they differ. 12v in nothing out ,I would assume would be bad.

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                #8
                Re: capacitor in circut, powered up

                The capacitors have a negative side and a positive side.

                If you want to measure voltage on capacitor, you can put the probes either way, the multimeter will measure the voltage difference between the two terminals. So, if you put the probes the other way around you'll just see the voltage with a negative sign on the multimeter screen.

                You can't test if a capacitor is good by checking voltage on each side, it's not working like a resistor in the circuit.

                In electronics electrolytic capacitors are almost all the time connected between the + and - of a power supply to store energy. They're not "in series" like a resistor. If you put a capacitor in series, that capacitor will only let AC move through it and DC will be blocked.

                See this for something that will make you understand easier : http://electronics.stackexchange.com...citor-block-dc

                later edit as you added a few posts while writing this:

                Would the voltage be the same in and out????12v in 12v out or would they differ. 12v in nothing out ,I would assume would be bad.

                On the secondary side, most power supplies tie the negative side to ground... the power supply is earth referenced. So if you put one probe on earth or chassis and the other on the negative side of the capacitor you would measure 0 or close to 0, with the probe on + you would measure the output voltage.

                On the primary side, where those large capacitors are, it's a bit tricky. Often, that section is "floating" or in other words, not referenced to ground. The two AC wires from the socket come in a bridge rectifier and get converted to DC and you get a virtual ground (the -) and the virtual plus (the +) ... there may be no connection between the chassis and that - on the primary side.
                Last edited by mariushm; 01-25-2014, 06:17 PM.

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                  #9
                  Re: capacitor in circut, powered up

                  OK Now I get it,took a while. Thanks for the remedial electronics lesson. I needed it.

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