I have a laptop with a recharger (also known as an AC adapter), this is how it looks like:

enter image description here

When I disconnect my laptop from the charger, does it (the charger) still consume (waste) electricity?


I am trying to do math, how many kW I waste every year to keep my adapter plugged in the whole time. I tried to read how much watts does it take, but I am not good with that kind of stuff, so here is some info:

INPUT : 100-240V~50-60Hz 1.5A(1,5A)

OUTPUT: 19.5V(19,5V) --- 4.62A(4,62A)

Does this info help to do the math?

There is 8760 hours in year.

migrated from physics.stackexchange.com Sep 26 '11 at 19:23

This question came from our site for active researchers, academics and students of physics.

  • Apple provides some information about its power adapters in its environmental reports. The power adapter of a 2013 Macbook Pro 13 inch uses between 0.004W (100V) and 0.019W (240V) without load. – Daniel Beck Jan 28 '14 at 14:13

Yes. Generally anything with a transformer in it will draw at least some power when plugged in. See here for more details on the types of devices that will typically use power even when off. The only thing that will keep a device from drawing standby power is if you actually break the circuit that the device is plugged into.

  • But how much? I added some text from the adapter, I am not sure if those are right numbers, since I only found volts. – Jaanus Sep 27 '11 at 5:01
  • 2
    @Jaanus you'd need to measure it. The exact amount of idle current is dependent on the the implementation details. Mostly in that cheaper devices will draw more power for the save level of functionality. Unfortunately for consumer level hardware this is easier said than done because idle power levels are similar to both the base error level and granularity of inexpensive power meters like a killawatt. – Dan Neely Sep 27 '11 at 12:58

Yes, not a whole lot but over time it does add up. It can also wear out the transformer sooner.

See http://electronics.howstuffworks.com/everyday-tech/plug-in-transformer.htm for more info.

  • 2
    modern laptop power supplies are switching power supplies – Journeyman Geek Sep 26 '11 at 22:46
  • But how much? I added some text from the adapter, I am not sure if those are right numbers, since I only found volts. – Jaanus Sep 27 '11 at 5:01
  • The article I refer to shows you how to calculate it. – bryan Sep 27 '11 at 5:06

I just did a test with my P3 watt meter. One old DELL adapter (10+ years, for Latitude P3 650) uses 1.3W while the laptop is not connected. However, a recent HP adapter (2+ years) uses 0 W (at least from P3 watt meter reading).

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.