# Idle Step-Down Transformers consume electricity?

O

#### Opticreep

Jan 1, 1970
0
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.

R

#### Roger Johansson

Jan 1, 1970
0
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.

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)
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.

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.
Also, how "safe" is it to use such a transformer, and leave it on

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
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.

The risk for your electronics is very small, nothing to worry about.
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.

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.

B

#### BobGardner

Jan 1, 1970
0
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
watts/120V=83ma

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