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measurement problem

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  • Dean von 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.)
    Message 1 of 4 , Jun 29, 2009
      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.
    • 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 2 of 4 , Jun 29, 2009
        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 3 of 4 , Jun 29, 2009
          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 4 of 4 , Jun 30, 2009
            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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