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Re: [loopantennas] Oil filled capacitor

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  • toddroberts2001@aol.com
    In a message dated 11/16/2008 8:25:46 A.M. Eastern Standard Time, fast.electrics@ntlworld.com writes: I have read that it is possible to significantly increase
    Message 1 of 8 , Nov 16, 2008
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      In a message dated 11/16/2008 8:25:46 A.M. Eastern Standard Time,
      fast.electrics@... writes:

      I have read that it is possible to significantly increase the voltage
      rating and capacitance of an air spaced variable capacitor by
      immersing it in mineral oil. Would this approach work on a loop
      antenna capacitor?

      Neil G7AQK

      ___________________________________________________

      I think it would work but don't know how well. It will be
      extremely messy unless you have the capacitor well-sealed
      inside a leakproof container. Also I believe the capacitance
      would not be as stable as an air-variable because the
      mineral oil expands and contracts with heat and cold.
      Someone will just have to try it and let us know if it
      works!

      73 - Todd WD4NGG

      **************Get the Moviefone Toolbar. Showtimes, theaters, movie news &
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    • Jim Miller
      If possible check the Q of the antenna before and after doing the immersion to see if the mineral oil causes additional dielectric loss. The dielectric
      Message 2 of 8 , Nov 16, 2008
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        If possible check the Q of the antenna before and after doing the
        immersion to see if the mineral oil causes additional dielectric loss.

        The dielectric constant of mineral oil is 2.1 so your capacitance should double.

        73

        jim ab3cv
      • Jim Dunstan
        ... Hi Neil I guess it depends on the kind of oil used .... e.g. not the infamous PCB type hi hi. I am no expert on the subject ... but many years ago we used
        Message 3 of 8 , Nov 16, 2008
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          At 09:35 AM 11/16/2008 -0500, you wrote:

          >In a message dated 11/16/2008 8:25:46 A.M. Eastern Standard Time,
          ><mailto:fast.electrics%40ntlworld.com>fast.electrics@... writes:
          >
          >I have read that it is possible to significantly increase the voltage
          >rating and capacitance of an air spaced variable capacitor by
          >immersing it in mineral oil. Would this approach work on a loop
          >antenna capacitor?
          >
          >Neil G7AQK

          Hi Neil

          I guess it depends on the kind of oil used .... e.g. not the infamous PCB
          type hi hi. I am no expert on the subject ... but many years ago we used
          oil-immersed high voltage power switches (in the Arctic) for switching high
          line power sources. They of course shielded the contacts from wx and
          limited contact sparking and burn. They worked down to -40 deg C without
          difficulty. I am not sure whether they increased voltage rating ...
          however they seem to seal the switches from wx corrosion and burning (in
          the presence of oxygen).

          Jim, VE3CI

          [Non-text portions of this message have been removed]
        • gplynas
          Hi Neil, Oil filled capacitors do work very well for high voltage. I work with these every day, with some up to about 40,000 volts. The major reason it does
          Message 4 of 8 , Nov 16, 2008
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            Hi Neil,
            Oil filled capacitors do work very well for high voltage. I work with
            these every day, with some up to about 40,000 volts. The major reason
            it does work is the elimination of corona in the air between the
            plates. So the first thing to do is removal of all air. For large
            plate spacings, this can be done by vibrating the capacitor to let the
            bubbles go to the top. For close spacing, putting a vacuum on the
            capacitor and then filling while under vacuum is necessary. The oil
            needs to be clean and pure, and moisture free. We use special
            transformer oil, which you might be able to get from your local
            utility. Multiply the capacitance of the air gap capacitor by about
            2.2 when you add the oil. Breakdown in air is about 3000 volts per
            mil. In mineral oil, such as Shell Diala Oil B, it can be as high as
            80,000 volts breakdown in 0.1 inches. At high frequencies breakdown
            characteristics get a bit more complex. Another consideration with
            loop antennas would be the dielectric losses in the oil, which will be
            greater than in air, so the Q of your loop might go down, reducing the
            sensitivity.
            Regards,
            Paul
            WA5LFY



            --- In loopantennas@yahoogroups.com, Jim Dunstan <dunstan@...> wrote:
            >
            > At 09:35 AM 11/16/2008 -0500, you wrote:
            >
            > >In a message dated 11/16/2008 8:25:46 A.M. Eastern Standard Time,
            > ><mailto:fast.electrics%40ntlworld.com>fast.electrics@... writes:
            > >
            > >I have read that it is possible to significantly increase the voltage
            > >rating and capacitance of an air spaced variable capacitor by
            > >immersing it in mineral oil. Would this approach work on a loop
            > >antenna capacitor?
            > >
            > >Neil G7AQK
            >
            > Hi Neil
            >
            > I guess it depends on the kind of oil used .... e.g. not the
            infamous PCB
            > type hi hi. I am no expert on the subject ... but many years ago we
            used
            > oil-immersed high voltage power switches (in the Arctic) for
            switching high
            > line power sources. They of course shielded the contacts from wx and
            > limited contact sparking and burn. They worked down to -40 deg C
            without
            > difficulty. I am not sure whether they increased voltage rating ...
            > however they seem to seal the switches from wx corrosion and burning
            (in
            > the presence of oxygen).
            >
            > Jim, VE3CI
            >
            > [Non-text portions of this message have been removed]
            >
          • Andy
            The oil filled capacitors I ve seen were used for HV supply filtering, where dielectric losses don t matter. Are they also commonly used in other applications?
            Message 5 of 8 , Nov 16, 2008
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              The oil filled capacitors I've seen were used for HV supply filtering, where
              dielectric losses don't matter.

              Are they also commonly used in other applications? With either pulses or RF
              power where dielectric losses are important?

              Andy
            • Bob Warren
              Hi Neil Wouldn t it be simpler to use a vacuum variable capacitor? They are reasonable easy to obtain. Bob VK7KRW 2008/11/16 Neil McGrath
              Message 6 of 8 , Nov 16, 2008
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                Hi Neil
                Wouldn't it be simpler to use a vacuum variable capacitor?
                They are reasonable easy to obtain.

                Bob VK7KRW


                2008/11/16 Neil McGrath <fast.electrics@...>

                > I have read that it is possible to significantly increase the voltage
                > rating and capacitance of an air spaced variable capacitor by
                > immersing it in mineral oil. Would this approach work on a loop
                > antenna capacitor?
                >
                > Neil G7AQK
                >
                >
                >


                [Non-text portions of this message have been removed]
              • gplynas
                Hi Andy, We do use the oil filled capacitors in RF applications for very high power transmitters (up to 2 MW), although the frequencies are generally under
                Message 7 of 8 , Nov 16, 2008
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                  Hi Andy,
                  We do use the oil filled capacitors in RF applications for very high
                  power transmitters (up to 2 MW), although the frequencies are
                  generally under about 200 kHz. In this application, dielectric
                  heating has not been a problem. We also use oil filled capacitors and
                  transformers in high voltage pulse applications.
                  Best regards,
                  Paul
                  WA5LFY

                  --- In loopantennas@yahoogroups.com, Andy <Andy.groups@...> wrote:
                  >
                  > The oil filled capacitors I've seen were used for HV supply
                  filtering, where
                  > dielectric losses don't matter.
                  >
                  > Are they also commonly used in other applications? With either
                  pulses or RF
                  > power where dielectric losses are important?
                  >
                  > Andy
                  >
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