I have a laptop and I leave the AC adaptor plugged into the wall but not plugged into the laptop. Is this consuming electricity? How much compared to when it’s plugged into the laptop? Is there any danger of fire?
It’s not using electricity if no current is passing through. If it’s a fire hazard it likely wouldn’t have passed UL inspection. I wouldn’t worry about it. Our AC’s for the cell, notebook, and Nintendo DS are always left plugged in. No problems at all.
There will be some electricity used due to the resisitance of the winding in the transformer (and also due the magnetostriction of the core, IIRC). This would be significantly less than if the computer were plugged in. You probably will be able to feel a temperature difference between an adaptor that’s only plugged into the wall vs. one that’s not plugged in at all.
Duffer is not quite correct regarding the electricity consumption, if you want to be picky (and of course I do!) Although he’s correct for practical purposes, and bang-on regarding safety.
Most AC adapters contain a transformer, which will consume a small amount of electricity even when the adapter isn’t connected to anything. That’s why they’re always slightly warm.
The electricity consumption is piffling compared to when they are connected to the laptop, and they are safe to leave plugged in. There isn’t a bunch of power being drawn with nowhere to go - it doesn’t work that way.
The adapter is probably using electricity. It has a power transformer in it which runs without the computer being on. TVs and VCRs also have transformers (built in) and consume energy when they are turned off. Google “phantom loads” and there are all kinds of sites that discuss the collosal amount of electricity thereby wasted. This
alternative energy site, for instance, discusses “phantom load” energy consumption.
That’s not quite true. If the cat gets ahold of the plug end, and knocks it into a box of steel wool, the 9-12 volt potential is enough to start a blaze. It’s not likely, but not impossible either.
Sounds about as likely as Cecil’s explanation of how you would get a disease from a paper towel.
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- No, current is passing through. More current in fact than would normally flow, with a device connected.
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- Not having any of the secondaries of a transformer plugged into anything is called an “unloaded transformer” and causes it to heat up more than usual. There’s at least two windings on any transformer. The primary constitutes an inductive load in itself, and any secondaries each reflects an inductive load on the primary winding as well, which is the one connected to the wall electricity. Induction requires current flow–so if you take the secondary winding and open it, then it cannot conduct current at all, and its inductive resistance on the primary [essentially] vanishes, and then all of the inductive resistance that the primary was designed to operate against is not present. So a greater than normal amount of current flows through the primary winding, and so the transformer heats up MORE than normal.
… - There are some types of electrical equipment where running a transformer unloaded will damage the equipment–however–common wallblocks are not one of them. It very-probably won’t get hot enough to start a fire, but it does shorten the life of the transformer unit. Do it if you want.
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It is often true that in a linear power supply (i.e. power transformer operates at 110V/60Hz, 220V/60Hz, or whatever the local mains supply is), the transformer will run warmer when the downstream device is disconnected, but that doesn’t mean that the overall currents flowing through the transformer are lower.
All this is irrelevant for the OP anyway, since all modern laptops use switching power supply units (PSUs). These not only improve efficiency and decrease bulk compared to the equivalent linear PSUs, but they are also (in the case of laptop PSUs, which are often left plugged into the wall as in the OP) designed to have very low leakage currents when the target device - the laptop - is unplugged.
Switching PSUs rectify the incoming 100-240Vac line voltage, then use controlled switching MOSFETs to “chop” the raw dc at frequencies of tens of kHz and up. A high-frequency transformer (much smaller and lighter than its 50/60Hz counterpart) is used to step down the voltage and provide isolation. Feedback from the secondary side changes the MOSFET switching duty cycle to keep maximum efficiency. When the laptop is disconnected, this is detected by the switching PSU and the MOSFETs are essentially turned “off” (except for a very low duty-cycle waveform to keep the load-detector circuits powered). The current in a laptop PSU when the laptop is disconnected is essentially leakage due to the input filter capacitors and the (very low) “off” current of the MOSFETs. These can be kept to well under a milliamp on the primary side, or under one-tenth of a watt of power consumed.
If a modern laptop PSU gets warm when the laptop is unplugged, it’s either poorly designed or malfunctioning.
Phantom loads, such as plugged-in TV sets with remote-control “on” switches and “instant-on” tubes (as in leroy_the_mule’s link) are an entirely different issue.
As explained above, this is not true in the case of a laptop (or any similar switchmode) PSU designed for unpluggability.
[NB: Older switch-mode PSUs did used to complain under “no-load” operation if they weren’t designed for such conditions (e.g. for the PSU inside a desktop PC, which isn’t intended to be run with the motherboard, disk drives etc, unplugged).]
Thanks Antonius, consider me edumacated!
I could do with some clarification on this though:
"It is often true that in a linear power supply (i.e. power transformer operates at 110V/60Hz, 220V/60Hz, or whatever the local mains supply is), the transformer will run warmer when the downstream device is disconnected, but that doesn’t mean that the overall currents flowing through the transformer are lower."
Isn’t it the case that the primary current is higher under the no-load situation? It’s just that resistive losses aside, the energy is just going back and forth - basically creating and collapsing a magnetic field at twice the AC frequency?
Someone give a cite for these horror stories. I’d like to have some evidence before , um, using a cite of never having a problem with this.
In 20 years.
Fear lives I guess.
Now give me a cite?
What problems are documented with notebooks? I’ve had notebooks since 1993, and have never seen a problem with AC adapters. Should I run to unplug everything?
Horror stories?
That there’s a slight chance your wall wart is poorly designed, gets slightly warm, and uses a fiftieth of a cent per day of electicity if you’re not using it?
Someone please think of the children.
A few quick errata for my post #9:
[ul]
[li]I meant to say “110V/60Hz, 220V/50Hz” instead of “110V/60Hz, 220V/60Hz”, although one of the advantages of a switchmode PSU is that it’s very tolerant of variations in input voltage and frequency (which makes it perfect for a laptop).[/li][li]IGBTs (Insulated-Gate Bipolar Transistors) are often used as the high-current switching elements (instead of MOSFETs) in modern switchmode PSUs. For this particular purpose, IGBTs combine the best features of MOSFETs and regular bipolar junction transistors (BJTs).[/li][li]The line “Switching PSUs rectify the incoming 100-240Vac line voltage…” should read “rectify and smooth…”. The ac line voltage is converted to [dc + ripple], and that is what is chopped by the MOSFETs/IGBTs to provide the primary voltage for the transformer.[/li][/ul]
One has to consider both in-phase (which will cause heating) and quadrature (which won’t) components of the primary current; a lot is going to depend on the precise nature of the transformer and any input filtering. I deliberately didn’t go into more detail because it’s totally irrelevant for the OP’s case, since the transformer in a switchmode PSU is downstream of the primary switching elements (MOSFETs or IGBTs), and is thus almost completely isolated from the wall power when a “disconnected load” condition is detected and the switching elements are predominantly in the high-impedance state.
Actually, a modern laptop PSU will have “crowbar protection”, which means that it should shut down when faced with a dead short such as your steel wool (I have to admit that I haven’t tested this experimentally). Since laptop PSUs are designed to deal with various “unusual” load conditions (they recharge the batteries as well as powering normal operation), they have sufficient intelligence to deal with a wide array of load conditions.
Older-style “linear” PSUs (for things like answering machines – which you’d want to leave on anyway!) have a small but perhaps non-negligible leakage current when unloaded. If you’re counting every penny, unplug them to save those few cents per year. They do not represent an appreciable fire hazard, however (unless you are visited by Squink’s cat with its beloved box of steel wool).
In the case of a switchmode PSU for a laptop (as in the OP)? Leave it plugged in. It will consume negligible power and provide no measurably greater risk of fire. [I’d say that there is almost a greater likelihood that a would-be arsonist might break into your home, trip over the plugged-in laptop PSU, and knock himself out on the coffee table, in which case the PSU would have **saved** your home from an impending conflagration!]
Basically, if it’s a Dell - YES
As far as documented issues, in just in the last year, Dell (twice actually) and IBM have both had recalls of notebook power cords.
Oh, in the first Dell recall, the number cited by the Consumer Products Safety Commission (and, by extension, the first article) only indicates the number sold to individual US consumers. According to this article, the number is actually closer to 4.4 MILLION.
And, while not a laptop, Microsoft is not immune to poor power adapter design.
If you really want some pleasant thoughts for bedtime, go to the CPSC’s website and Search for “power adapter”…sleep tight! 