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Re: [loopantennas] High voltage in Microwave caps.

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  • sonicxcove@aol.com
    The issue with many of these units is that they are made as cheaply as possible and in countries that have few or no standards. UL listings only apply as to
    Message 1 of 5 , Aug 5, 2007
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      The issue with many of these units is that they are made as
      cheaply as possible and in countries that have few or no
      standards. UL listings only apply as to case grounding
      and the likes on many things.

      Eric

      In a message dated 8/5/2007 9:22:24 P.M. Eastern Daylight Time,
      theboyd@... writes:

      Hi all: I would think that good manufacturing practice dictates the use of
      bleed-off resistors on these caps to eliminate, or at least reduce the
      danger posed by this high voltage that may be stored in said caps. Good
      listening: theboyd








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      [Non-text portions of this message have been removed]
    • Keith Browning
      The use of screw drivers etc, to discharge capacitors can be dangerous. Use a high resistance resistor to blead off the voltage in an orderly fashion. Ground
      Message 2 of 5 , Aug 6, 2007
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        The use of screw drivers etc, to discharge capacitors can be dangerous.
        Use a high resistance resistor to blead off the voltage in an orderly fashion. Ground end first ..
        Some microwave ovens do have bleed resistors. But never rely on such as working.
        Life is short enough already.

        I think the transformers are used by Hams for ht supplies on tubed amplifiers .

        Keith

        ----- Original Message -----
        From: "c e boyd" <theboyd@...>
        To: <loopantennas@yahoogroups.com>
        Sent: Monday, August 06, 2007 1:20 PM
        Subject: Re: [loopantennas] High voltage in Microwave caps.


        Hi all: I would think that good manufacturing practice dictates the use of
        bleed-off resistors on these caps to eliminate, or at least reduce the
        danger posed by this high voltage that may be stored in said caps. Good
        listening: theboyd



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      • Chris Fleming
        I repaired a microwave some years back cica 1988 (replaced the HV diode). My brother dropped it off after having been sitting around for few days. I shorted
        Message 3 of 5 , Aug 6, 2007
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          I repaired a microwave some years back cica 1988 (replaced the HV diode). My
          brother dropped it off after having been sitting around for few days. I
          shorted the cap with a long piece of wood and an earth strap it and made
          quite a bang, zap! Guess they do not make caps like that anymore. Oil filled
          5KV I seem to recall. .
          Cheers
          Chris

          There was no bleeder resistor in this unit.
          -----Original Message-----
          From: loopantennas@yahoogroups.com [mailto:loopantennas@yahoogroups.com]On
          Behalf Of c e boyd
          Sent: Sunday, August 05, 2007 2:21 PM
          To: loopantennas@yahoogroups.com
          Subject: Re: [loopantennas] High voltage in Microwave caps.


          Hi all: I would think that good manufacturing practice dictates the use of
          bleed-off resistors on these caps to eliminate, or at least reduce the
          danger posed by this high voltage that may be stored in said caps. Good
          listening: theboyd






          [Non-text portions of this message have been removed]
        • Len Warner
          ... And possibly damaging to the capacitor. As well as the obvious risk of arc damage to the terminal, which may be only of trivial importance, there is the
          Message 4 of 5 , Aug 7, 2007
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            At 12:42 pm ((PDT)) Mon Aug 6, 2007, in Digest 887 Keith Browning wrote:

            >The use of screw drivers etc, to discharge capacitors can be dangerous.

            And possibly damaging to the capacitor.

            As well as the obvious risk of arc damage to the terminal,
            which may be only of trivial importance, there is the risk of
            internal damage to the capacitor through the high current
            in the connecting foils. Remember the capacitor is only
            intended to provide the magnetron current, not an
            instantaneous arc discharge.

            >Use a high resistance resistor to blead off the voltage in an orderly fashion.
            >Ground end first ..

            Good advice. What you need is a discharging stick consisting
            of a long insulating handle ending in a metal probe, the probe
            connecting via a chain of resistors (to share the discharge
            voltage) to a stout alligator clip for grounding. Apply the ground
            clip firmly first, you don't want it to fall off.

            When the capacitor is discharged it is prudent to leave a
            permanent discharge link during a repair, since dielectric
            relaxation can cause a newly-discharged capacitor to
            recharge to a considerable (and painful) voltage level.

            >Some microwave ovens do have bleed resistors.
            >But never rely on such as working.
            >Life is short enough already.

            If you have a HV voltmeter probe you can make several
            measurements as the circuit self-discharges to prove
            the working of a bleed-off circuit. But it's probably not
            worth the bother. Just discharge it and strap it to ground
            with components you know and trust.

            >And please trim all this when replying!

            Please...


            Regards, LenW
            --
            A: Because it destroys the flow of the conversation
            Q: Why is top-posting bad?
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