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220V to 110V adapter without transformer?

Discussion in 'Electrical Engineering' started by peter, Jun 13, 2008.

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  1. peter

    peter Guest

    Most 220V to 110V travel adapter use a transformer, making it very heavy.
    Is there something that is transformerless? Perhaps some sort of switching
    circuit?
     
  2. Palindrome

    Palindrome Guest

    What do you want to power? There are lightweight "hi power" travel
    adapters - which just have a rectifier and a fuse inside. They are
    suitable for a lot of 110v kit, eg electric frypans, waffle makers, etc.

    If what you are powering is an external power supply, it is often
    lighter (and cheaper) to replace it with an 110v equivalent.

    One thing to consider is to travel with a 12v inverter, which can
    produce mains voltage from a car socket. You could add a lightweight 12v
    SMPSU to suit. Thus giving you a few hundred watts of the appropriate
    mains voltage, wherever you are.
     
  3. James Sweet

    James Sweet Guest


    They're a triac light dimmer circuit with a fixed, they work only for
    resistive loads.
     
  4. Unfortunately, that doesn't work. Usually it will result
    in some combination of smoke, sparks, and a bang;-)
    If you take 240V RMS and half-wave rectify it, you will
    end up with an RMS voltage of 240/sqrt(2) = 170V. This
    will run a 120V appliance at exactly twice it's power
    rating, and whilst overloading it in this way, also stress
    its insulation to twice its design voltage.

    To get the power rating right, you would need to half-wave
    rectify and then let only alternate pulses through by some
    other means. You still have the peak voltage problem, and
    a peak current which is 4 times the design rating.

    I built a switcher to solve this problem some years back.
    I use a pair of MOSFETs to switch the mains. What I do is
    switch off during the middle portion of each positive and
    negative going cycle. (IIRC, the switching angle is 43/137
    degrees to produce 120V RMS from a 240V RMS sine wave,
    but that's actually quite a bastard to work out with
    integral calculas, although going the other way is easy.)

    This has a number of benefits. The higher voltage part
    of the sine wave is removed, reducing the excess stress
    on the insulation of the 120V product (although it's still
    higher than when running on 120V RMS sine wave). It also
    keeps the instantaneous peak current as low as possible,
    although the power factor will only be 0.5. It also draws
    power only from the portion of the sine wave which is under-
    utilised by the very many power supplies which only draw
    current near the peaks, so although it generates a nasty
    harmonic current, it's cancelling out the nasty harmonic
    currents most other loads generate!

    In my case, this runs a 1050W 120V frying pan on 240V
    mains, and is a big improvement over the transformer which
    we used to lug around.
     
  5. Palindrome

    Palindrome Guest

    Erm, IME, it works rather well - I've got a US waffle iron in the
    kitchen that has run for well over 10 years on an adapter that consists
    solely of a power rectifier in a box (I opened the box to see what was
    inside, out of curiosity..).

    Of course I don't make waffles all that often ;)

    I did modify things a little by running an earth wire to the metal case
    of the thing. As supplied, it was two pin.

    I'd replace it with a UK one, if I could find one that made such large
    waffles. It heats up quickly, too. ;)

    Doubtless, in time, the thermostat contacts will burn out, or the
    element fail.
    Yep, I'm not disputing any of that. But all that is in this particular
    "hi power travel adapter" is a rectifier. I even checked its part number
    to make sure that is wasn't something special.

    I'd assumed that all these "hi power" adapters had the same arrangement.
    However, I have only opened this one to see.
     

  6. That is the current norm in modern switcher manufacturing practice.

    Also, I would add that most auto switch through that entire range just
    fine. In the past, one would have to set a switch depending on the
    region.
     
  7. peter

    peter Guest

    What travel appliance does not work on both 110 V and 220 V?
    I had a AA charger that says 110 to 240 V. It works perfectly in the USA.
    Last time I traveled to a 220V country, the charger overheated and the
    plastic shell started to warp. The batteries were damaged -- their plastic
    covers peeled off. Good thing I noticed it before it did more damage.
    Amazingly, it still worked when I bring it back to the USA.

    Even though it was out of warranty, I asked the manufacturer to replace it,
    and they did. Since then I am afraid to plug anything bought in USA into
    220V, even if it says 110-220V. Admittedly, that charger was not a very well
    known brand.

    This time I'm bringing a panasonic camera (usa version) to europe. The
    charger also says 110 to 220V. I suppose it should be safe to use, and I
    don't want to carry a 50W 220V to 110V transformer. But if there is a light
    weight device to step down 220V to 110V, I would feel safer using it. Maybe
    I can also bring my scary AA charger for other use...

    BTW, the high wattage voltage reducer all say "resistor network" in their
    product descriptions, but people responding to this thread say they use
    diodes, which make sense. Could it contain a diode and a resistor? Light
    dimmer (triac) also sounds feasible, but it would produce spikey waveform,
    probably not suitable for transformer use.
     
  8. charles

    charles Guest

    I use a Panasonic camera battery charger (supplied with the camera)
    regularly here on 235v. I've never had overheating problems - and it
    worked on 110v in the USA last summer.
     
  9. James Sweet

    James Sweet Guest


    Modern stuff with switchmode power supplies is usually designed to cover
    the full range from 120 to 240V. This wasn't nearly as easy to do with
    magnetic transformers common in the past.
     

  10. Most modern switchers work from about 85V up to 265V. Most run easily
    down to 90V, and that is the goal since Japan uses 90 Volt system, AND
    the end of the line voltages can be lower than that.
     
  11. Guest

    | On Sat, 14 Jun 2008 21:25:40 GMT, James Sweet <>
    | wrote:
    |
    |>
    |>charles wrote:
    |>> In article <[email protected]>,
    |>>
    |>>> This time I'm bringing a panasonic camera (usa version) to europe. The
    |>>> charger also says 110 to 220V. I suppose it should be safe to use,
    |>>
    |>> I use a Panasonic camera battery charger (supplied with the camera)
    |>> regularly here on 235v. I've never had overheating problems - and it
    |>> worked on 110v in the USA last summer.
    |>>
    |>
    |>
    |>Modern stuff with switchmode power supplies is usually designed to cover
    |>the full range from 120 to 240V. This wasn't nearly as easy to do with
    |>magnetic transformers common in the past.
    |
    |
    | Most modern switchers work from about 85V up to 265V. Most run easily
    | down to 90V, and that is the goal since Japan uses 90 Volt system, AND
    | the end of the line voltages can be lower than that.

    Japan uses 100 volts. End if the line can be 90 volts.
     
  12. Don Kelly

    Don Kelly Guest

    ----------------------------
    I used a Sanyo automatic 120/240 VAC NiMH charger in the UK recently
    with no problems.
    Cheers,
    Roger

    I have used a Panasonic 120/240 NiMH battery charger on 240V (New
    Zealand ) with no problems.
    I took it to Italy as well.
     
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