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Discussion in 'Electronic Basics' started by Jim, Aug 10, 2003.

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  1. Jim

    Jim Guest

    I know this may sound stupid but I have recently relocated to the
    untied states from Australia I am just wondering if I bring a couple
    of table Lamps that are 240volts Can I use them as they are in the
    United States with 110volts or do I need to rewire them. Can you
    please send any replies to me directly at


  2. John G

    John G Guest

    For lamps and other small loads the Aus wiring will be adquate but the plug
    will have to be changed.
    The lamp bulbs will have to be changed for 110 volt versions but if the lamp
    sockets are the common (in AUS) bayonet type you may have trouble gettting
    lamps to fit, most US lamps are Edison screw base.
    Explore a lighting shop in your new location.
    NG replies should go to NGs and not email direct so everyone can share the
    replies or comment if needed.
  3. Terry

    Terry Guest

    Jim: I was partly wondering if this was a serious enquiry!
    What kind of lamp (bulb) sockets do the Australian table lamps
    Are they bayonet type, like in the UK or are they Edison (medium
    size I think?) screw in as used in North America (US and Canada).
    So change the bulbs to 110 volts and change the plug to fit into
    North American duplex two or three pin outlets and they should
    work OK.
    I presume that the wiring would be heavy enough to carry the
    current required; that is a 100 watt bulb in Australia requires
    approx. 0.4 amps at 240 volts. A 100 watt bulb at 120 volts
    requires 0.8 amps. That's still less than one amp so the gauge of
    the copper wires in the lamp plug in lead/cord would normally be
    more than adequate to carry that higher current. And voltage
    should be OK too since the wire is insulated for at least 240
    However having said all that does the worth of a couple of table
    lamps justify the amount of effort. There may be other appliances
    that you will need in North America that you will have to buy.
    Few if any microwave ovens for example are 'dual voltage'.
    If you could plug the 240 volt lamps into 110 volts (say by
    changing the plugs but leaving the lamps otherwise the same) they
    would be very, very dim, giving less than one quarter the amount
    of light!
    Also you can buy kits of the parts that people use to make lamps
    out of found objects such as big glass bottles, pieces of
    driftwood etc. for a few dollars, and provided you are handy and
    have a few tools convert your lamps to 120 volts using North
    American bulbs and plugs, fairly easily.
  4. Terry

    Terry Guest

    I agree with your comment; I did send a copy of my comments
    direct to Jim in this instance but my top posting was back here,
    where he asked the question.
    I have learned much from reading the questions, responses and
    discussion on this and other news groups.
    Often the answers alone spark other ideas and IMHO that is one of
    the good things about internet news groups such as this. And
    often it's "That's good info.". Or; "Why didn't think of that!".
    Most technical news groups try to avoid personal criticism;
    hopefully presenting opinions and information on it own merits.
    What I refer to is the sort of "Well I've been in this business
    for 25 years and only a moron wouldn't know ... etc. etc. etc.!"
    And then, in some cases it turns into a battle of egos!
    many thanks and my apologies for being a little off the topic.
  5. Dan Fraser

    Dan Fraser Guest

    Lamps are so cheap here, they are not worth bringing with you when you
    move. At a place like Fryes in LA, and at Wal Mart, who are everywhere,
    you can but 6 great lamps for under $50.00. Unless it is an heirloom,
    don't bother. I can't even give away old lamps here because new ones are
    so cheap now.

    Dan Fraser

    From Costa Mesa in sunny California
    949-631-7535 Cell 714-420-7535

    Check out my electronic schematics site at:
    If you are into cars check out
  6. The Captain

    The Captain Guest

    totally agree. Been there, done that, got the scars. It's going to
    cost you more to ship the lamps than they're probably worth. Until
    such time as we get a worldwide standard for electrical power and
    appliances, its going to be a lot cheaper and simpler to buy new where
    you are going.

    My advice: take them to a car boot sale and get a few bucks for them.
    Buy beer.

  7. John Fields

    John Fields Guest

  8. John G

    John G Guest

    Please do not answer questions
    a. 6 weeks after the thread died and has disappeared from some servers and
    b. When you have not got a clue what you are talking about.
    Yes you can series 2 lamps to run 110 volt lamps on 240 but it is very
    unwise for safety reasons and would be frowned upon by the various
    But NO connecting 2 240 volt lamps in parallel will not make them work
    correctly on 110 volts. They will not com to any harm but will be very dim.
    The proper thing (and fairly inexpensive.) is to change the bulbs for the
    correct voltage and change the plugs for the correct type.
    As they were 240 volts to start with and only lamps then the wire will be
    rated for 240 volts and the double current will not be a problem.
  9. John Fields

    John Fields Guest

    If I don't know which servers have disappeared then someone might still
    be out there waiting for a late answer. Better late than never say
    never I always say.
    Oh really? Well I'll have you know that the only reason I suggested
    that he wire them in parallel is because it's very hard to shorten the
    filament. Not only that, changing the lamp socket is a job best left to
    a qualified electrician type not to mention the plug.
    Hahaha you're wrong trying to run two 110 volt lamps in series is only
    220 volts and connecting them to 240 volts would only leave 20 volts
    unaccounted for, not very dangerous because of the amps. From home's
    law, since the difference in voltage is 20 volts and the resistance of
    the two in parallel is 1/2 of what it would be normally, 20
    volts/(1/2)ohms = 40 amps, which is very low impudence.
  10. John G

    John G Guest

    I never suggested changeing the socket but if the Untied states do not have
    bayonet plug lamps then that's their loss.
    I did not say the OP should change the plugs himself but many people are
    capable of doing it .
    110, 220, 240, most people see this as within the range of supply variations
    and would not argue about it in the case of lamps.
    No , the total resistance is half what it would be with only one lamp and so
    the total current will be twice that of one lamp. Absolutely nothing to do
    with volts/(1/2)ohms = 40 amps or 4.4kilowatts.
  11. Fred Abse

    Fred Abse Guest

    I don't think he saw the smiley, John.
  12. John Fortier

    John Fortier Guest

    If you wire two 240 volt lamps in parallel, the voltage applied across each
    is still 110 volts. So each lamp will glow, but dimly.

    P=E^2/R, so the power generated in each lamp, which in an incandescent lamp
    is used to cause the filament to glow, will be, relative to the power
    generated when connected to 240 volts, 110^2/240^2 or 12100/57600 which is
    approx 0.21. So your two lamps connected in parallel to 110 volts will
    develop 42% of the power of one lamp connected to 240 volts.

    I'm afraid that John Fields' answer is very misleading.

  13. John Fields

    John Fields Guest

    Well, John, I'm afraid you've missed a couple of things, the first being
    the tongue-in-cheek smiley at the end of my post and the second being
    the effect of the temperature coefficient of resistance of tungsten on
    the power dissipation of the lamp with a 110VRMS input.

    Just for grins, I hooked up a couple of 120V 100W lamps in series and
    ran them using a 240VRMS 60Hz source. I measured the current through
    them and got 0.81A. 240V*0.81A = 194.4W, pretty close to what it
    should be.

    Then I reduced the voltage to 110V and got 0.53A, so the lamps were
    dissipating a total of 58.3W.

    Bottom line? A 240V incandescent lamp with 110V across it will
    dissipate 58.3W/194W ~ 30% of what it would with 240V across it, so two
    240V lamps in parallel connected to 110V mains will dissipate about 60%
    (not 42%) of what a single 240V 200W lamp will when connected to 240V

    If you care to pursue the matter further, here's a pretty good link:
  14. The Captain

    The Captain Guest

    deals with the temperature co-efficient of hot wires in a convective

    "you will have to wire your 240V lamps in parallel to get them to work
    here. ;^)" With or without "smiley" this is misleading.

    And I think John, that with or without the details of resistance
    change with tremperature, you, yourself, have proved the silliness of
    connecting the lamps in parallel.

    Actually, Jim, the simplest and most pragmatic solution, which I have
    had to use myslef, is to change the lamp fittings. They aren't
    permanent installations, since manufacturers know they may get bent or
    broken. So a quick trip to your local hardware store for screw in
    sockets and bulbs and the necessary American style plugs is really the
    simplest, easiest solution.

    I have one lamp which has had a 220 volt screw in socket in Germany
    (where I bought it) a 240 volt bayonette socket in England and now a
    further 110 volt screw in socket in the States. It hasn't exploded

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