Leaving an AC charger plugged in

[BespinReactorShaft]

If, say, we leave a mobile phone charger plugged into the wall socket without the phone being attached, do we still consume electricity? If so, how do we work out the power consumption? Will it be negligible for all practical purposes (i.e. saving up on power bills)?

 

[Torched]

Yes it will consume power. Only milliamps though. Will you save money on your power bill if you unplug it? probably pennies. Best hing to do if you are concerned about this is to get one of those devices that can measure stand by power... Want to save money on your power bill, Put all of your entertainment center on a power strip with a on off switch... Turn your pc completely off when not in use ond most of all turn your fridge temp to a higher setting and run your A/C at 3 to 5 degrees hotter than normal.

 

[Bassyhead]

For a small wall wart or charger, being idle won't consume more than a few watts of power so for your practical purposes, the energy consumption will be negligible. However, there are many other devices that you may have that also still consume power when "off" or in standby, such as TVs, DVD players, stereos, etc and combined they add up significantly over the whole population. It's estimated that Americans spend billions annually to power idle or "standby" devices that aren't even being used. Take a look at this link.

 

[DrPizza]

I actually have a wall switch which controls all the electronic components in my living room. But, at least at the moment, everyone else in my family feels its far more convenient to be able to just turn on the tv, dvd player, receiver, and start watching. If the power is shut off, it takes a slight bit longer for everything to start up. But, more significantly, turning off power to the satellite receiver/decoder box means that we have to wait 3 or 4 minutes while it reloads. Quite a pita.

 

[Mark R]

It depends on the type of charger really - specifically, whether it is an electronic converter or a transformer. You can tell because the transformers are heavy, whereas the electronics are light.

I've checked several of my transformer based chargers - and they use about 5W each when idle. That's works out at about $.30 per month per charger. Sure you won't notice 1, but if you've got one in each room - then things can add up.

OTOH, a charger like this would use about 10W when charging. If charging takes 2 hours, every 2 days - then the actual charging would cost about $.03 per month per phone. So you're using 10x as much electricity leaving the charger plugged in idle, than you are actually charging your phone.

Electronic chargers are much better. They can use virtually no power when idle, and are more efficient when charging.

 

[RemyCanad]

On a related note, leaving your phone on a charger when the battery is full is actually bad on the battery and will reduce it's life time. I only charge when I am either going to be away for a long time or my battery is almost dead.

 

[Bassyhead]

Originally posted by: RemyCanad
On a related note, leaving your phone on a charger when the battery is full is actually bad on the battery and will reduce it's life time. I only charge when I am either going to be away for a long time or my battery is almost dead.

Depends on the battery type. Most cell phone batteries nowadays, like laptops, have lithium ion batteries which require intelligent chargers (for more complex charging) that sense how much and the rate of charge has been put into the battery and what the temperature of the battery is, etc. They will pretty much completely shut off when a lithium ion battery finishes charging. For other types of rechargeable batteries, overcharging can be detrimental.

 

[PowerEngineer]

Parasitic Loads

 

[BespinReactorShaft]

Originally posted by: Mark R
It depends on the type of charger really - specifically, whether it is an electronic converter or a transformer. You can tell because the transformers are heavy, whereas the electronics are light.

Any links or details on how transformer converters are different from electronic converters? I've always thought that converters were all based on transformer theory.

 

[djhuber82]

Mark: It was my understanding that EVERY AC-DC converter needs a transformer for isolation. A power supply connected directly to the mains would be extremely dangerous, wouldn't it?

 

[Mark R]

Mark: It was my understanding that EVERY AC-DC converter needs a transformer for isolation. A power supply connected directly to the mains would be extremely dangerous, wouldn't it?

Yes, I was inaccurate in my wording. Technically an electronic converter does have a transformer, but electronic switching is used to allow a very much smaller transformer than would otherwise be necessary.

Essentially, a conventional AC-DC converter has a block diagram like this:

Mains AC -> Transfomer -> Low voltage AC -> Rectifier -> Smoothing

An electronic converter looks something like this:

Mains AC -> Rectifier -> Smoothing -> High voltage DC -> Inverter -> High voltage, high freq AC -> Transfomer -> rectifier -> smoothing

There are some minor differences in the way the 'Inverter/transformer' section work e.g. some supplies do not actually use a transformer, but a 'flyback' inductor (which is very similar, 2 seperate windings on a magnetic core - the difference being that the transformer core doesn't store (much) energy, while the inductor core does).

Actually, the flyback circuit is somewhat simpler than a transformer based circuit - so I think these are the usual type for electronic wall warts.

 

[bobdole369]

I think what Mark is getting at is the difference between a "linear" power supply (what he calls a "transformer based" or conventional AC-DC converter), and a "switching" power supply (what he calls an electronic converter).

Every device besides simple light bulbs, heating elements, and such that plug into the wall require at the very least: "isolation". Simply because it is much safer. Essentially it makes it safer because if the transformer is rated at a certain power level will break when that power level is surpassed, as is what could happen in a dead short. See if you shorted the hot and neutral wires (the two slots) with a conductor, you are looking at 120V (in the USA) / 0.5 ohms (the wire) = 240 amps of current. That 240 amps X 120V = 28,800W available instantly from the wall. Your talking about half a second or longer until your mains breaker or fuse melts. That much power will melt your house wiring, and quite likely cause a serious fire, not to mention can kill you. The purpose of isolation is to make sure that it is much less likely to happen. Any shorts beyond the isolation transformer cannot supply more than the rated power of the transformer. There are other reasons as well, including reducing the likelihood of radio frequency interference.

That said, the block diagram for a switching supply looks something like this.

mains -> transformer (most are step down, every one uses some kind of isolation)-> rectification -> smoothing -> high voltage DC -> PWM (pulse width modulator) (a small transformer is almost always here) ->output transistors -> high frequency high voltage AC -> rectifier -> smoothing. The output voltage is fed back to the PWM to determine the PWM duty cycle. higher duty cycle means more available current to develop across the load to maintain voltage.

Switching is very rarely used in your typical wall wart box plug. It is very common to see a switching supply in laptops and every computer has a switching supply.

Back on point - Every wall wart will use a few milliamps of power. There are almost always "bleeder" resistors that drain the output capacitors when there is no load. These are across the output caps, and sometimes also the input caps. They are high value and as long as its plugged in, will consume power.

In a switching supply, you use very VERY little power, since as long as there is no load, the PWM is essentially off. The only losses are leakage on the input circuit, and whatever power it takes (microamps) to keep the PWM on.

 

[Witling]

The subject of battery life was raised by RemyCanad with a reply from BassyHead. For an article on the various types of batteries and how to baby them, see Squeezing more life out of batteries. I'd characterize this article as "Everything you wanted to know about batteries plus a lot more."

 

[Mark R]

mains -> transformer (most are step down, every one uses some kind of isolation)-> rectification -> smoothing -> high voltage DC -> PWM (pulse width modulator) (a small transformer is almost always here) ->output transistors -> high frequency high voltage AC -> rectifier -> smoothing. The output voltage is fed back to the PWM to determine the PWM duty cycle. higher duty cycle means more available current to develop across the load to maintain voltage.

The whole point of a switching supply is that the transformer (which provides isolation) comes after the PWM and output transistors. The PWM allows you to use a highly efficient, small and light transformer, instead of the bulky, inefficient and very heavy transformer which is needed if you want to connect directly to the mains.

Switching is very rarely used in your typical wall wart box plug. It is very common to see a switching supply in laptops and every computer has a switching supply.

Technically, "switched mode power supply" is the correct term, however, "electronic" is quicker and simpler to understand by most people. It is also the way power supplies for low voltage, or fluorescent lighting are described (e.g. you can LV halogen lights with a transformer or "electronic transformer").

Switching is very common these days. Without exception, every mobile phone, digital camera and PDA I've seen in the last 3 or 4 years uses an electronic converter. Aside from the improved efficiency of an electronic converter, it's extremely easy to make an electronic converter "universal voltage" - i.e. it will run on any input from 90 - 270V and from 50-60 Hz so will operate in all countries.

Back on point - Every wall wart will use a few milliamps of power. There are almost always "bleeder" resistors that drain the output capacitors when there is no load. These are across the output caps, and sometimes also the input caps. They are high value and as long as its plugged in, will consume power.

The bleeder resistors are negligable. Almost all the loss comes from using a conventional transformer. I've tested several of mine, and a 5 W charger will typically use 5W at idle, and up to 15W while charging. Yes, they are that bad! Of that, less than 0.1% is lost in the bleeder resistors.

My electronic converters, OTOH, have idle currents so low that I cannot measure them (they just read 0 with my multimeter and AC power meter).

Increasing legislation (particularly in Europe) about standby power has prompted many manufacturers to switch from production of transformer based wall warts to electronic ones. It would simply be impossible to comply with conventional transformers. Additionally, the demand for portable electronics devices to be multi-voltage compatible has also driven this market.