How much electricity an AC transformer (220v->115v) spends when it is merely plugged to the wall?
Answer:
Under no-load conditions, a transformer will still consume a small amount of electric power. This power loss comes primarily from eddy current losses and magnetization current losses.
These two sources of power loss are often assigned values as transformer equivalent circuit parameters. In the textbooks and literature I have seen, eddy currents is (Rc) and magnetization current is (Xm).
Anyway, I am a TA for an electric machinery laboratory course at The Ohio State University and one of the experiments that I have conducted with my students is to measure/calculate the equivalent circuit parameters for a small 220V (primary) transformer.
So... I can only give you an estimate of transformer loss when it is merely plugged into the wall, since every transformer is a little different.
Nevertheless, my students and I generally got a few kilo-ohms for both Rc and Xm (referred to the primary side). This would come up to about 10-15 Watts of power loss. These were pretty crappy demonstration transformers, though, and I would imagine the core material and core laminations would be far better in your average outlet transformer. So, a reasonable guess would be on the order of a few Watts for an outlet transformer.
Final Answer: I estimate about a few Watts from my experience with transformers, but it would be interesting if someone measured this for a typical outlet transformer.
Depends on time,it does use some in form of eddy current(s).
Depends on the size of the transformer. Most household types probably about 2 to 4 Watts max ~
Just enough to keep it warm.
Losses thru hysteresis of the core and heating of the copper coils, plus reactance.
A small one will only burn a watt or 2, at say 10 cents per kilowatt-hour, that's about
$0.10 * 2watts *24hr * 30days in month/1000 = $0.14 per month
If the secondary of the transformer is an open circuit (there is no load on the transformer), then the amount of current allowed through the transformer is equal to (ACvoltage) divided by (2(pi)(ACfrequency)(L Tprimary)).
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