Power Consumption Query

[BernardsWatch]

I was thinking about something the other day and I was wondering if someone could enlighten me. Basically, if I?ve got a laptop power pack/charger (I guess that contains a step down transformer and rectifier) and I plug it into the mains, will I still be charged for power consumption even if my actual laptop isn?t plugged into the charger. As I understand it, the magnetising reactance, core losses, primary leakage reactance and primary winding resistance will be supplied even without the laptop connected? I understand that the utility company don?t directly charge for the reactive power, but what about the real power drawn?

 

[kingpb]

Resistive losses will draw real power, although low for the device in question, there will be a charge from the utility.

This goes along with all the other devices in your house that are on standby.

 

[fmtjfw]

chicken feed

chicken feed

1) It is most unlikely that you have a linear power supply for a laptop. It is most likely that it is a non-linear power supply. The non-linear ones convert the incoming power to "dc", then uses a solid state circuit to raise it to an HF frequency, use a tiny hf transformer to raise the voltage, a rectifier back to dc, and a voltage regulator to set the proper output voltage.

I've been in the computer business since before PC and laptops. I have never seen a linear [transformer -- rectifier] brick power supply for a laptop.

2) These power supplies are usually voltage and frequency agile: 50-60Hz, 100-250VAC inputs without any manual adjustments, so they can be used on "mains" power in virtually any place on earth.

3) I took a 1/2 dozen different laptop supplies of different companies and a WattStopper? plug in meter.
All six read 0.00 W, 0.00KwH. and 0.00VA on 124.5V. They had an inrush current of .5A ? .05A as registered on the meter. They had a steady state reading of 0.01A.

This high inrush current versus unloaded current is indicative of non-linear power supplies. Transformers have a higher inrush than unloaded current but not at this high a ratio.

The wattage, assuming unity power factor would be 1.25W, at 10?/KwH, it would take 80 hours to waste a penny.

Hope this helps!

[This is all based on the 100% accuracy of the meter]

 

[gar]

140310-1206 EDT

Virtually all laptop and cellphone 120 V AC to device power supplies manufactured in recent years are of the switching type and have very little standby power consumption by themselves.

My IBM Thinkpad power supply is less than 0.3 W when not connected to the Laptop. When the computer is off, the supply is connected, and charging the battery about 30 W. When the battery is fully charged and the computer is on, but the screen is not backlighted, then about 11 W.

My power meter increments by 0.1 W, but reads 0 somewhat below 0.3 W.

At 120 V 0.3 W = 48,000 ohms.

.

 

[Besoeker]

I was thinking about something the other day and I was wondering if someone could enlighten me. Basically, if I?ve got a laptop power pack/charger (I guess that contains a step down transformer and rectifier)

fmtjfw is correct. It is a Switched-Mode Power Supply. Or SMPS. Pretty much all the electronic gadgets use them.
A crude test of how much energy it wastes when unloaded is how hot it gets. The charger for my phone, for example, doesn't get detectably warm even on load. Nor does the one for my Kindle. The cable modem, printed, router, laptop, are just very slightly above ambient and all are on load.

Chicken feed as the man says.

 

[Jraef]

I have seen several "papers" written expounding on the energy wasted by un-used "wall wart" power supplies left plugged in with nothing connected to them. When it comes down to it though, those "papers" all seem to be written by people somehow associated with the power strip industry, espousing the use of a switched power strip being used to plug those things in to so that you "save" all that energy. the thing is that if you paid even $10 for that power strip, the energy savings would not pay for it in 10 years...

 

[broadgage]

Agree, the power supply for a laptop is virtualy certain to be a switched mode type, if plugged into the utility but not supplying any load, then some power is wasted but very little and it is unlikely to matter much.

As posted above, the wasted energy appears as heat and if the unit remains cool then the losses must be very small.

 

[Besoeker]

I have seen several "papers" written expounding on the energy wasted by un-used "wall wart" power supplies left plugged in with nothing connected to them. When it comes down to it though, those "papers" all seem to be written by people somehow associated with the power strip industry, espousing the use of a switched power strip being used to plug those things in to so that you "save" all that energy. the thing is that if you paid even $10 for that power strip, the energy savings would not pay for it in 10 years...

Agreed.
I post on a forum which is primarily about going green, being efficient, and using renewable energy.
I've seen quite a few claims about how power strips have drastically cut energy bills. I get routinely castigated for supplying numbers and facts that quite simply ought to disabuse people of that notion.
Rose tinted comes to mind.

 

[broadgage]

Agree, a solution looking for a problem in most cases.
Years ago, most plug in power supplies used a copper iron transformer and a linear regulating circuit.
These units DID waste significant energy if left plugged in needlessly, as may be proved by them getting warm.

A loss of from 2 to 5 watts was typical, and that is significant for a long hour load.
4 such units could in total could be 15 watts, or say 120 KWH a year. Depending on electricity prices that could be in the region of $12 to $20 a year. Not a fortune but worth saving.

Note however that virtually all modern power supplies are switched mode and the standby losses though not totaly eliminated are very much reduced.
The losses are often a fraction of a watt, and whilst money would be saved by turning them off, the amount is trivial. Less than $1/?1 a year typicly.
Taking a shower for 599 seconds instead of 600 seconds might save more !

 

[Jraef]

...
Taking a shower for 599 seconds instead of 600 seconds might save more !

Nah, I use gas to heat my water...

Agreed.
I post on a forum which is primarily about going green, being efficient, and using renewable energy.
I've seen quite a few claims about how power strips have drastically cut energy bills. I get routinely castigated for supplying numbers and facts that quite simply ought to disabuse people of that notion.
Rose tinted comes to mind.

My wife and I go to bed at different times, so I am having to stumble around in the dark. I bought a few electroluminescent night lights to put in receptacles near the floor in order to save my toes. They each take 0.1W and have a light sensor so they automatically turn off when the ambient light is higher, so they are on for no more than about 8 hours per day. My wife still complains about "wasting energy" by leaving them on all night. I've told her that if she turns her 1500W hair drier off just 1 second earlier every week it will save over a years worth of night light power, for all of them combined. Still falls on deaf ears.

 

[Besoeker]

Somewhat related, our main television takes 0.9W on standby - less than 8kWh a year.
Not worth unplugging.

 

[gar]

140311-1719 EDT

Adding to my post #4 of yesterday.

I have had the Thinkpad off for a day and the power supply connected. In the off state the battery has been charged. Now in a fully charged state, power supply connected to laptop, and the computer off, the power input to the power supply is 0.6 W.

.