power loss in battery chargers...USB

a transformer, being a pair of electromagnets, such that it reduces the voltage of household power to whatever voltage your battery powered device needs, will cost you somethin if its plugged into the wall, even if yoour phone, laptop, etc isn't plugged in.

but it seems that these 5v usb chargers are too small to contain a transformer. I dont think they get warm when they are idly plugged in.  I imagine they may just have a rectifier and zener diode. Is that the case?  Do they waste power when left in an outlet?

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Toga_Dan (author) 2 years ago

Here's are 2 pictures of a transformer with 1 end cut off of the core. In 1 pic, it is holding up a 4 lb plate while running on 110v AC. In the other pic, it is holding a 15 lb weight while running 110V DC. Although the coil burned out shortly after that, it shows that a transformer is electromagnetic.

transformer 4 lb plate.jpgTransformer 15lb weight.jpg
Toga_Dan (author)  Toga_Dan2 years ago

Should've changed "here's" to "here" Ah, well.

A transformer has nothing whatsoever to do with electromagnets.

The little supplies you are talking about now draw less than 0.1W when they are not on load. Left on for a year, they'd draw less than a unit of electricity.

steveastrouk: "A transformer has nothing whatsoever to do with electromagnets".

What? Ammm. Yes they do.

electromagnetc coil is an electrical conductor, such as a wire, in the
shape of a coil (or spiral or helix). It is a device that when a
time-varying current (AC power) is passed through the coil winding will
induce a time-varying magnetic field along the axis of the coil. When we
reverse this and place a time-varying magnetic field along the axis of
the coil, it will induce a time-varying current through the coil

An electromagnet is nothing more than a electromagnetic
coil with a time-varying current (AC) passing through it. If the core of
the coil is made up of just air, it will be very weak. If we wind the
coil around iron or another magnetic material it concentrates the
magnetic field and increases the strength of the electromagnet.

The reverse is also true. The iron core will cause a time-varying magnetic field to induce a larger time-varying current (AC).

transformer is nothing more than two electromagnetic coils placed in
close proximity to each other. We place a time-varying current (AC) on
coil1 . It induces a time-varying magnetic field. When coil2 is placed
within the magnetic field, that field will induce a time-varying current
(AC) on the second coil. This is called mutual induction.

If the
two coils are wrapped around an iron core, and an AC power supply is
connected to coil1, a magnetic field is generated and passes through the
inside of the iron core. Since coil2 has been wrapped around the same
iron core, the magnetic field varies inside of coil2.

Bottom line is that a transformer is made of up two coils. One acting an an electromagnet to drive the second coil.

Ammm. No. An electromagnet is not an "electromagnetic coil", it is SPECIFICALLY an electromagnet coil driven with DC. A good electromagnet design is a crap transformer.

Bottom line is that a transformer is made of at least two coils, and runs on AC. An electromagnet has one and runs on DC. That doesn't make them "the same".

Toga_Dan (author)  steveastrouk2 years ago

i disagree on transformers and electromagnets. What is the primary winding but an electromagnet? It's just a winding of wire around an iron core. it is essentially switched on and off 60x per second.

at 1 point i had a device similar to the kill-a-watt. some power supplies drew more power than others.

Try getting something to stick to a transformer, or even be rattled by it. A transformer HAS no flux leakage.

It is not a matter of "disagreement".

Toga_Dan (author)  steveastrouk2 years ago

My point in describing a transformer as an electromagnet was that the primary coil is connected, and drawing power, regardless of whether there is a load on the secondary.

A transformer has very _little_ flux leakage. It can be detected by an audio pickup coil. Essentially the transformer is an electromagnet in a closed box. A cat in a closed box is still a cat.

The primary draws virtually no power when there is no load, at least for a decent transformer. Cheap transformers leak. Toroidal transformers pretty well do not.

A cat in a closed box is not a dog because you choose to think of it like that.

Toga_Dan (author)  steveastrouk2 years ago

Steve Astro: "try getting something to stick to a transformer" ok. I openned the "box" of a small 12v wall wort. (cutting the core) The unmodified primary coil lifted a 4 lb steel plate. When i switched to dc, it lifted 15 lb. I'd say that this cat has claws. I was not surprised when i burned out the coil shortly after that. Explaining _why_, however, is something I would appreciate help with. I think this could be an " understanding transformer fundamentals" instructable. Care to collaborate?

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