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Re: [lcwn] measurement problem

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  • multiplx@athenet.net
    The magnetron s filament doesn t have be from the transformer s secondary. You can run the filament off a 3.6 V battery pack from a cordless drill or similar.
    Message 1 of 4 , Jun 29, 2009
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      The magnetron's filament doesn't have be from the transformer's
      secondary. You can run the filament off a 3.6 V battery pack from a
      cordless drill or similar. That also reduces the insane AC input
      current. Also be sure to isolate the transformer's secondary winding
      from the case ground if you are using a non-standard voltage doubler
      circuit.

      You might try a snubber circuit on the transformer's primary. Use an
      AC-rated 0.1 uF and 100 ohm resistor in series across the primary
      winding to suppress any back-EMF surges. Also try something like a
      high-voltage 1000 pF capacitor across the transformer's secondary.


      Quoting Dean von Germeten <germeten@...>:
      > I'm working on way to run a magnetron from a 12V car battery.
      > (I know I could use an inverter for this but trying to go with
      > something simpler and cheaper.)
      >
      > Basically the battery powers a relay wired as a buzzer, to
      > drive the primary winding (about 130 turns) of a MOT. That part
      > works well enough, i.e. the buzzer buzzes and the MOT delivers
      > an output.
      >
      > But when I try to measure the output from the 3 turns of heater
      > coil windings on the MOT, I get a whole range of bizarre readings
      > that don't make sense, depending upon the meter settings. (I'm using
      > a cheapie cen-tech multimeter from harbor-freight.)
      >
      > For example, in the 20V range, the voltages vary between 12 - 17V.
      > In the 200V scale, from 100 to 170V, and HV range, 1200 to 1750V!
      > These all from a step-DOWN winding! The AC & DC readings are similar.
      >
      > On circuits with fewer harmonics, the meter works normally.
      >
      > Until I can get some stability in the power supply, my maggie
      > experiments can't progress.
      >
      >
      >
      > ------------------------------------
      >
      > Yahoo! Groups Links
      >
      >
      >
    • Dean von Germeten
      Thank you for the suggestions. I ll take your word that what you advise would possibly help the measurement problem, but I really can t afford to reduce
      Message 2 of 4 , Jun 29, 2009
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        Thank you for the suggestions. I'll take your word that what you
        advise would possibly help the measurement problem, but I really
        can't afford to reduce current, as I think the capacitor, and know
        the resistor will do that. The transformer primary has an R of 1.2
        ohms so a 12V battery will only pass 10 amps through it. That's only
        120 watts to power maggie and doesn't even consider her heater R,
        which is low (.5 ohms) but further reduces output power.

        The transformer is isolated from ground. And my measurements were
        taken without the doubler circuit hooked up. In other words, 12V
        from the buzzer into the MOT primary was generating hellacious
        voltages in the step-down heater winding, while the HV winding could
        well have been shorting to the steel core, I don't think most MOT's
        have enough insulation to function as ignition coils.

        I suppose I could use a voltage divider to power the maggie off the
        12V battery, but that would waste power, and I still need a HV source
        to fire her up. I just thought someone might have something simple
        vs. the inverter route.

        ---------------------------------------------------------------------

        --- In lcwn@yahoogroups.com, multiplx@... wrote:
        >
        > The magnetron's filament doesn't have be from the transformer's
        > secondary. You can run the filament off a 3.6 V battery pack from a
        > cordless drill or similar. That also reduces the insane AC input
        > current. Also be sure to isolate the transformer's secondary winding
        > from the case ground if you are using a non-standard voltage doubler
        > circuit.
        >
        > You might try a snubber circuit on the transformer's primary. Use an
        > AC-rated 0.1 uF and 100 ohm resistor in series across the primary
        > winding to suppress any back-EMF surges. Also try something like a
        > high-voltage 1000 pF capacitor across the transformer's secondary.
        >
        >
        > Quoting Dean von Germeten <germeten@...>:
        > > I'm working on way to run a magnetron from a 12V car battery.
        > > (I know I could use an inverter for this but trying to go with
        > > something simpler and cheaper.)
        > >
        > > Basically the battery powers a relay wired as a buzzer, to
        > > drive the primary winding (about 130 turns) of a MOT. That part
        > > works well enough, i.e. the buzzer buzzes and the MOT delivers
        > > an output.
        > >
        > > But when I try to measure the output from the 3 turns of heater
        > > coil windings on the MOT, I get a whole range of bizarre readings
        > > that don't make sense, depending upon the meter settings. (I'm using
        > > a cheapie cen-tech multimeter from harbor-freight.)
        > >
        > > For example, in the 20V range, the voltages vary between 12 - 17V.
        > > In the 200V scale, from 100 to 170V, and HV range, 1200 to 1750V!
        > > These all from a step-DOWN winding! The AC & DC readings are similar.
        > >
        > > On circuits with fewer harmonics, the meter works normally.
        > >
        > > Until I can get some stability in the power supply, my maggie
        > > experiments can't progress.
        > >
        > >
        > >
        > > ------------------------------------
        > >
        > > Yahoo! Groups Links
        > >
        > >
        > >
        >
      • multiplx@athenet.net
        Yes, I didn t think of that. The MOT is only designed to operate at 2,000 VAC so it is possible there was internal arcing to the transformer s core, even if
        Message 3 of 4 , Jun 30, 2009
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          Yes, I didn't think of that. The MOT is only designed to operate at
          2,000 VAC so it is possible there was internal arcing to the
          transformer's core, even if isolated. I usually look out for big,
          heavy older transformers which have better winding insulation.

          Quoting Dean von Germeten <germeten@...>:
          > Thank you for the suggestions. I'll take your word that what you
          > advise would possibly help the measurement problem, but I really
          > can't afford to reduce current, as I think the capacitor, and know
          > the resistor will do that. The transformer primary has an R of 1.2
          > ohms so a 12V battery will only pass 10 amps through it. That's only
          > 120 watts to power maggie and doesn't even consider her heater R,
          > which is low (.5 ohms) but further reduces output power.
          >
          > The transformer is isolated from ground. And my measurements were
          > taken without the doubler circuit hooked up. In other words, 12V
          > from the buzzer into the MOT primary was generating hellacious
          > voltages in the step-down heater winding, while the HV winding could
          > well have been shorting to the steel core, I don't think most MOT's
          > have enough insulation to function as ignition coils.
          >
          > I suppose I could use a voltage divider to power the maggie off the
          > 12V battery, but that would waste power, and I still need a HV source
          > to fire her up. I just thought someone might have something simple
          > vs. the inverter route.
          >
          > ---------------------------------------------------------------------
          >
          > --- In lcwn@yahoogroups.com, multiplx@... wrote:
          > >
          > > The magnetron's filament doesn't have be from the transformer's
          > > secondary. You can run the filament off a 3.6 V battery pack from a
          > > cordless drill or similar. That also reduces the insane AC input
          > > current. Also be sure to isolate the transformer's secondary winding
          > > from the case ground if you are using a non-standard voltage doubler
          > > circuit.
          > >
          > > You might try a snubber circuit on the transformer's primary. Use an
          > > AC-rated 0.1 uF and 100 ohm resistor in series across the primary
          > > winding to suppress any back-EMF surges. Also try something like a
          > > high-voltage 1000 pF capacitor across the transformer's secondary.
          > >
          > >
          > > Quoting Dean von Germeten <germeten@...>:
          > > > I'm working on way to run a magnetron from a 12V car battery.
          > > > (I know I could use an inverter for this but trying to go with
          > > > something simpler and cheaper.)
          > > >
          > > > Basically the battery powers a relay wired as a buzzer, to
          > > > drive the primary winding (about 130 turns) of a MOT. That part
          > > > works well enough, i.e. the buzzer buzzes and the MOT delivers
          > > > an output.
          > > >
          > > > But when I try to measure the output from the 3 turns of heater
          > > > coil windings on the MOT, I get a whole range of bizarre readings
          > > > that don't make sense, depending upon the meter settings. (I'm using
          > > > a cheapie cen-tech multimeter from harbor-freight.)
          > > >
          > > > For example, in the 20V range, the voltages vary between 12 - 17V.
          > > > In the 200V scale, from 100 to 170V, and HV range, 1200 to 1750V!
          > > > These all from a step-DOWN winding! The AC & DC readings are similar.
          > > >
          > > > On circuits with fewer harmonics, the meter works normally.
          > > >
          > > > Until I can get some stability in the power supply, my maggie
          > > > experiments can't progress.
          > > >
          > > >
          > > >
          > > > ------------------------------------
          > > >
          > > > Yahoo! Groups Links
          > > >
          > > >
          > > >
          > >
          >
          >
          >
          >
          > ------------------------------------
          >
          > Yahoo! Groups Links
          >
          >
          >
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