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280V motor on 230V circuit

Discussion in 'Electronic Repair' started by Deodiaus, Apr 26, 2008.

  1. James Sweet

    James Sweet Guest


    Get UK/commercial appliances, they're out there.
     
  2. Yes like my Amana commercial RadarRange which is 4KW in 2.2KW out and has 3
    HV magnetrons along with 3 each of the other necessary items (cap, diode,
    etc.). It even has a current transformer that tells the control board via
    current draw when the magnetrons are warmed up so that the timer doesn't
    start counting down until it is actually cooking. It has a standard NEMA
    6-20 plug on it now and will pop a bag of popcorn in roughly 75 seconds
    without scorching it. I can tell you it sure beats the hell out of regular
    microwave ovens for most things. The only thing I still use the regular one
    for are items that involve liquids as the Amana tends to make them either
    boil over or boils out all of the water before the food is cooked.
     
  3. Guest

    | Yes like my Amana commercial RadarRange which is 4KW in 2.2KW out and has 3
    | HV magnetrons along with 3 each of the other necessary items (cap, diode,
    | etc.). It even has a current transformer that tells the control board via
    | current draw when the magnetrons are warmed up so that the timer doesn't
    | start counting down until it is actually cooking. It has a standard NEMA
    | 6-20 plug on it now and will pop a bag of popcorn in roughly 75 seconds
    | without scorching it. I can tell you it sure beats the hell out of regular
    | microwave ovens for most things. The only thing I still use the regular one
    | for are items that involve liquids as the Amana tends to make them either
    | boil over or boils out all of the water before the food is cooked.

    Will it operate on single phase power, like I have in my home?
     
  4. David Lesher

    David Lesher Guest

    A Lucas snowblower? It would leak oil, not work when damp,
    and plow down the wrong side of the driveway...

    And want 50Hz...
     
  5. Still thinking of the British Rail trains that
    wouldn't work because (to quote their PIO)
    "It was the wrong kind of snow"?
    They'd be drooling over 60 Hz.
     
  6. Guest

    |
    |> writes:
    |
    |>>| I envy EU houses. If we had regular 240V/30A+ outlets, I'd be able to
    |>>| buy a snowblower with real guts. The [email protected] ones are wimpy.
    |
    |>>So put one in.
    |
    |>The issue is not the outlets available in my house [but I sometimes wish
    |>for 3 phase..].
    |
    |>Rather, it's the ready market of consumer appliances that would take
    |>advantage of them. That would require many houses to have them.
    |
    | Yes the inability to go to the nearest WallyWorld and buy a 240V 4kW
    | cooker/microwave/whatever is a big problem. European appliance could be
    | got, but I'd worry about anything with a motor (50 Hz), clock (do their
    | electronic clocks operate off the line frequency like some in the US?),
    | microwaves (don't they use frequency-dependent constant voltage
    | transformers?).

    It's all chicken and egg.

    People don't usually go to the added expense of installing a 240V outlet when
    there are hardly any (and none at WallyWorld) 240V appliances.

    Appliances are not generally made at power levels requiring 240V, at least for
    homes, because there is nowhere to plug it in by default.

    BTW, one appliance I am interested in is an electric induction wok. Normally
    a wok just doesn't work right used over an electric burner surface. So most
    wok cooktops are gas based. However, the induction technology with the right
    kind of work actually does work fine on electric power. The catch is it needs
    a lot of power. Only the smallest version can run on 120V. All the rest need
    240V. Here is the smallest 240V version:

    http://www.selectappliance.com/exec/ce-product/ck_mwg-2500

    And from this, it indicates world plug options for the 240V versions, which
    suggests to me the lowest wattage unit isn't marketed outside of 120V parts
    of the world (and hence is probably considered a wimpy model intended to at
    least work where 240V isn't available).

    http://cooktek.com/product_info.php?c=3&s=24&p=12
     
  7. David Lesher

    David Lesher Guest


    Yes. Note the primaries are broken by insulators, and there is no
    secondary [240/120] service on the pole. [The lowest run is TV coax, then
    neutral above it.]

    I've never heard of such as manual regulators so I assume they are
    automatic.


    It's somewhat unusual to see all three on one pole; it must be a BIG
    one. Generally I see them staggered on 3 adjacent poles; or two poles
    hold a platform between them.
     
  8. David Lesher

    David Lesher Guest

    I don't know if microwave ovens still use ferroresonant transformer
    supplies. I'd heard that they'd moved to switchers but have not
    worked on any with same. It would make sense: good transformer iron
    & copper ain't cheap... and a switcher would also save shipping weight.

    And yes, the clock would run fast.
     
  9. James Sweet

    James Sweet Guest


    Some use switchers, they'll be much lighter and say "Inverter"
    prominently on the front of the unit.

    I've never seen one with a ferro-resonant transformer. They use a
    standard laminated core power transformer with a pair of magnetic shunts
    to regulate the current. Every one that I've ever worked on has exactly
    the same circuit, 2KV RMS transformer feeds a charge pump doubler
    consisting of a diode and capacitor, feeding 4KV pulsed DC to the
    magnetron. Heater voltage is obtained from a tap at one end of the
    secondary, usually physically it's several turns of much heavier wire
    next to the HV winding wired in series with it.
     
  10. David Lesher

    David Lesher Guest

    [Johnny Carson voice] "I did not know that...."

    All I've ever had to a u-w power supply was to replace the rectifier
    stack; or junk the oven because it was clearly smoked...

    Someone one mentioned they were F-R, and a casual look seemed to confirm
    that, so I never questioned it. A F-R is also current limited; short the
    output and it delivers rated current, period..
     
  11. Never seen an FR uwave. :) Why would they use that when the basic
    circuit is adequate and reliable (more or less!)?

    --- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
    Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
    +Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
    | Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

    Important: Anything sent to the email address in the message header above is
    ignored unless my full name AND either lasers or electronics is included in the
    subject line. Or, you can contact me via the Feedback Form in the FAQs.
     
  12. Fiat Sparks

    Fiat Sparks Guest

    Mostly less! :) My Panasonic inverter unit just released the magic
    smoke. First the magenetron died, and then after I replaced that, an
    IGBT in the switcher shorted and did a fair bit of collateral damage.

    I finally did find a service manual...in spanish (which I read
    poorly,) but it did at least tell me what all the small resistors and
    diodes were supposed to be (before they melted.)

    So, $100 in parts later, I now have a working microwave again. And, if
    I get tired of it, I can sell it on Craigslist for at least $35! :-/
     
  13. Sorry, I was referring mostly to the normal transformer/capacitor/diode
    circuit. :)
    :)

    --- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
    Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
    +Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
    | Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

    Important: Anything sent to the email address in the message header above is
    ignored unless my full name AND either lasers or electronics is included in the
    subject line. Or, you can contact me via the Feedback Form in the FAQs.
     
  14. A motor designed for 50 Hz would run fast on 60 Hz, which might
    overload something like a fan motor. A clock would run fast. On the
    other hand, more iron is needed for 50 Hz motors (at a given voltage
    and number of turns), so the motor is actually overbuilt for 60 Hz
    operation. Same goes for ordinary transformers.

    I've taken a number of microwave ovens apart over the years, and none of
    them used constant-voltage transformers. They do have a magnetic shunt
    to give them somewhat of a constant *current* characteristic, and that
    might reduce the magnetron current some when operated from 60 Hz.
    The magnetron itself operates from half-wave rectified DC, so it
    shouldn't care.

    Some Panasonic microwave ovens use an inverter to generate the HV supply
    for the tube. Feeding it 60 Hz instead of 50 Hz should not be a
    problem; it will just reduce the ripple at the output of the initial
    rectifier.

    Dave
     
  15. They look similar. Both transformers have magnetic shunts, and there's
    a big capacitor near the transformer. But the circuits are different.

    The FR transformer puts the capacitor across the secondary winding, or
    two secondary windings in series, and the windings plus capacitor
    resonate at the designed line frequency. This causes the voltage to
    rise above what you'd expect from the turns ratio alone, but the voltage
    is limited by the portion of the core that the secondary is wound on
    going into saturation. Sometimes the secondary voltage waveform looks
    pretty square because of this peak clipping, but sometimes there's a
    third winding that (somehow) reduces the second harmonic and gives
    something closer to a sine wave.

    There's a magnetic shunt between the primary and secondary windings so
    that the primary current doesn't go through the roof when the iron in
    the secondary saturates. It limits the shorted output current to about
    *twice* the rated current, not equal to the rated current.

    Still, the FR transformer runs hot with no load, dissipating about 20%
    of its full output rating as heat.

    In comparison, the capacitor in the microwave is wired as part of a
    voltage doubler; it doesn't resonate with the transformer secondary.
    The transformer iron is not designed to saturate (though, as an
    intermittent-duty transformer that is fan-cooled in use, it is
    apparently designed to operate close to saturation to minimize the
    amount of iron).

    Dave
     
  16. Ouch. We have one that's only a few months old; I hope it does better
    than that. I love it because all of the power settings from "3" to "10"
    actually vary the magnetron RF output while keeping it on continuously.
    At "3", I can cook a single egg in the oven without it exploding.

    Conventional microwaves set to "3" run the magnetron about 4.5 seconds
    at full power followed by about 10.5 seconds off, and 4.5 seconds of
    full power into a single egg generates enough steam for an explosion.

    (On the Panasonic, settings of "1" and "2" actually run the magnetron at
    30% power, using 1/3 and 2/3 on time).
    For that much, I'd be tempted to scrap it and buy a new oven.

    Dave
     
  17. bz

    bz Guest

    (Dave Martindale) wrote in @swain.cs.ubc.ca:
    Saw something in a catalogue: a plastic 'Egg' shaped chamber that holds 4
    eggs and some water. I am guessing that it is a 'plastic pressure cooker'.
    Anyway, they claim you can hard boil eggs in it in a microwave oven.



    --
    bz 73 de N5BZ k

    please pardon my infinite ignorance, the set-of-things-I-do-not-know is an
    infinite set.

    remove ch100-5 to avoid spam trap
     
  18. Fiat Sparks

    Fiat Sparks Guest

    Mine lasted about eight years with daily use for a family of 5. So,
    hopefully you've got a ways to go. I agree, it does cook nicely, which
    is why I even bothered to repair it.
    You know, that's what the wife said! :)

    Had I known it was going to go out again after the magenetron died, I
    probably would have. But, my pride was at stake!
     
  19. David Lesher

    David Lesher Guest

    I know mine [which look to be very similar to the picture..] are
    automatic -- after my PSC complaint, the PEPCO phone droid read off the
    trouble report where the lineman went out, found higher-than-wanted
    voltage on my phase and set it to manual until the correct person could
    fix the regulator.

    Alas, the first repair didn't work, as a week later, I was awoken
    again....

    Later conversations with lineman in the area confirmed both that detail;
    and the fact their standard pole-pigs do NOT have a choice of taps.
    [They replaced the pig serving me with a larger one a few years back.]
     
  20. Do you actually use a setup like that? I'd think that for any sort
    of current, the filament windings would be melting down even though
    they are made of fat wire. For example, at 300 VA of output, you're
    looking at ~100 A in the filament winding.

    --- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
    Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
    +Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
    | Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

    Important: Anything sent to the email address in the message header above is
    ignored unless my full name AND either lasers or electronics is included in the
    subject line. Or, you can contact me via the Feedback Form in the FAQs.
     
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