[Hussar]

There I was, reading the newspaper, which was talking about how to save electricity and help stop global warming.

The National Society of Whatever said I should unplug my cell phone charger when the phone is not charging.

I'm like... what the heck?? If my cell phone is not plugged into the charger, how can it be drawing power?

Someone want to take a stab at this?

Thanks!

[NeedKarma]

Makes very little sense, I agree.

[BTA]

Most electronic devices these days have what's called "standby" mode. It is very likely that your cell phone charger, even when its not charging your phone, is drawing some power from the outlet it is plugged into. Your TV, VCR, DVD player, video game console and computer are also doing this.

Cell phone chargers contain lots of components for power conditioning including transformers, AC/DC converters (which is composed of solid state electronics in many cases) - the power draw is probably a very small amount, but over time it adds up...

[Lowtax4eva]

A lot of cell phone chargers have small transformers, they take the wall current and transform it into a lower voltage current the cell phone can use. This transformer is the piece that makes your charger get hot and continues emitting heat when plugged into the wall, even without the cell phone being connected.

The heat it emits is electricity being transformed into heat and is essentially wasted without the phone using the electricity... it can't be very much but its something.

[Hussar]

Okay, I can accept that now... but what is the technical hurdle that keeps the manufacturer from developing a charger that doesn't draw power when the phone is not connected?

[Lowtax4eva]

Physics.

An open circuit will always have power loses due to heat, it's unavoidable. In the future improved circuit designs may make these losses even smaller, perhaps so small they are inconsequantial but there will always be heat generated by electronics and the heat is wasted electrical current.

[BTA]

Okay, I can accept that now ... but what is the technical hurdle that keeps the manufacturer from developing a charger that doesn't draw power when the phone is not connected?

The technical hurdle? Well, I suppose that would be the voltage of the battery and the nature of the electricity used in our households. Typical North American households are supplied with electricity at 120/240V alternating-current. Typical cell phone batteries are in the 3-4 volt range, direct-current.

So the hurdles are converting the power from AC to DC and from a high voltage to a lower one. This requires electrical components like transformers, capacitors, resistors, triacs, etc, all of which result in losses in the form of heat and/or signal chopping.

How to avoid this?

Well, I suppose if someone were able to make an AC battery (not possible) at 120V for cellphones then there would be no hurdle and we could just plug them directly into the wall with no power conditioning. It is possible to charge a DC battery from an AC source without converting the electricity to DC first - it just takes longer and isn't as efficient since the charging would only occur when the AC waveform is at a higher voltage than the DC voltage; as the battery charges, less and less of the AC waveform would contribute to charging.

So as long as we want cell phone batteries that charge quickly and aren't huge then I'm not sure we can avoid these hurdles.

[Hussar]

Okay, then let's extend this further... to a simple lamp.

The fact that there is a lamp pluged in, yet not turned on... it is drawing power?

[BTA]

Okay, then let's extend this further.... to a simple lamp.

The fact that there is a lamp pluged in, yet not turned on ... it is drawing power?

Simple answer: No.

Not-so-simple answer: Maybe. When a lamp is turned off there is usually a physical break in the connection between line and neutral. If the physical distance between line and neutral is relatively small, however, there may be some ionization of the atmosphere between the two 'terminals' and an extremely small current may flow, hence drawing power. If the gap is small enough where the ionization causes an arc to form, then yes, power is being drawn.

But, for most intents and purposes, no. A regular old 120V, 60W incandescent lamp that it plugged-in but not turned on is not going to draw power.