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Idle Step-Down Transformers consume electricity?

Discussion in 'Electronic Basics' started by Opticreep, Oct 29, 2004.

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  1. Opticreep

    Opticreep Guest

    For the past six months, I have been using a cheap step-down
    transformer (220v to 110v) rated at 500W. Even when all the
    electronics connected to it are on stand-by, the transformer gets
    pretty hot. As hot as hamburgers typically served at McDonald's.

    Any idea how much electricity it might be consuming on such an idle
    state? If it's a negligible amount (10 or 20 watts) I wouldn't mind.
    But if it's chugging down sixty, seventy watts, I'll have to
    disconnect it.

    Also, how "safe" is it to use such a transformer, and leave it on
    24/7? I haven't been able to find a decent one in this 3rd World hell
    hole that I find myself in. The only one I found costs an equivalent
    of $7 USD. It's hooked up to electronics worth well over $1700 USD.
    Needless to say, I'm a little uncomfortable with that. Is the design
    of a step-down transformer basic enough that even cheap generic ones
    pose little hazard?

    Any advice would be appreciated. TIA.
  2. That sounds normal. If you can touch it for one second or two without
    getting blisters on your fingertips it is probably okay.
    (When it has been running for hours)
    It can use as much as 60-70 Watt in idle state, transformers do that.
    They use 5-10% of the rated wattage when in idle state.
    There are, of course, fire hazards to think about, but it should be
    pretty safe. If you have used it for several hours with a load without it
    catching fire it should be safe when in idle state, because it is a
    little cooler without a load.
    The risk for your electronics is very small, nothing to worry about.
    You could tell us more about this transformer. Is it encapsulated in some
    way, inside a sheet metal casing? When you say it is hot, do you mean the
    metal box it is in, or the transformer itself?
    Is the transformer the common type, rectangular shape, and very heavy?
    Are the input and output windings completely separate electrically, or
    does it have a common connection for the input and the output side?

    If you worry about the heat and the fire hazard you can mount a fan to
    cool it. The power used by a fan is very small compared to the power
    it uses in idle state. A fan does a lot to keep the temperature down, and
    that prevents shortcircuits developed by heat melting the isolation
    between wires.

    To prevent a fire in case something goes wrong it should be mounted
    inside a sheet metal box, with very good ventilation, preferably a fan,
    and of course not be placed close to flammable stuff.

    It should/must be protected by a fuse between the mains and the
    transformer, to prevent fire in case of short circuit in the transformer.

    If you cannot use a fan you can mount it on a wall, vertically, to allow
    the air to move upwards around it more easily than if it is placed on a
    horizontal surface.

    If you mount it inside a vertical metal tube there will be a stronger
    flow of air around it, without a fan, because of a kind of chimney
    effect. Warm air flows upwards, and the effect becomes stronger if there
    is a chimney, say a meter long or so.
  3. BobGardner

    BobGardner Guest

    Transformers are supposed to be 90+ percent efficient, unless they are
    saturating... A 1st cut is the VA 'apparent power'.... stick a multimeter in
    series with the primary and see how much current its drawing.... 10
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