Wall wart current draw

A while back there was a discussion about why wall wart transformers that were not under load would draw no current. Anyone recall that thread? As I recall there were some references to the induced currents created by collapsing magnetic fields etc.

Anyway, I'm trying to either prove or disprove the statement that unplugging wall warts when not actually using them to power or re-charge your device will save electricity. My recollection is that it doesn't matter. Right or wrong?

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It will save a little, but you won't notice it. Manufacturers usually recommend unplugging them when not in use, for safety reasons, as they can be a fire risk if they develop a fault.


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Iron losses are constant for all loads including none. Copper losses are proportional to the load.

You will save the energy used by the iron losses. Whether this is enough to make more than a few cents difference in a year is the question.

Assume 1/4 watt loss and $.20/kw.

(1/4 / 1000) * 24 * 365 * .20) = $0.438 per year.

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Jim Stewart

Just put your hand on a plugged in wall wart; it will be warm. that is the power it's wasting; some but not much.

Reply to
Nick Hull

Does it get warm whel left plugged in with no load? If so, it IS wasting electricity. It may not be a whole lot, possibly you can feel loss of less than a watt. And, it can't be a whole lot, as those little plastic cases can't dissipate more than a couple watts without getting VERY warm.

A very high quality transformer can be very efficient. But, the stuff they put in a wall wart is NOT going to be high quality. So, if it gets warm, that is absolute proof energy is being wasted.


Reply to
Jon Elson

It does matter. Just put your hand on an energized wall-wart which isn't plugged into anything and you'll feel warmth- losses which are typically in the 1-4W range. The Asian wall-wart sweatshops use about the cheapest of materials, particularly the laminations, and push them to the limits of saturation (meaning they don't use any more material than absolutely necessary), so there is substantial loss. Using better magnetic alloys would push the cost up perhaps 10-20%, so it's not done.

California is supposed to be enacting a regulation mid-this year wot prohibits sale of new gadgets with losses of more than 500mW, which will knock out most linear AC adapters (also the active mode losses are limited). It's already voluntary in China, Canada and the EU, and mandatory in Oz. Manufacturers will probably more go to switchers rather than improving the linear adapters**, which has advantages in shipping weight and size, and allowing 'universal' input voltage which can be used anywhere in the world, from 100VAC in Japan to 240VAC in Europe etc. Also less losses in regulation.

Anyway, if the losses are 2.5W and you're running it 24/7, you're wasting 22kWh/year, which is probably worth more than the adapter cost to make, but it's still only a couple dollars, so not really a big deal for one. But if you made all of them in the US twice as efficient you could save energy equivalent to the output of a nuclear power plant or two, IIRC.

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** Or maybe just hire lobbyists..

Best regards, Spehro Pefhany

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Spehro Pefhany

I just used my "Kill-A-Watt" power meter to take a look at several wall warts. All the samll ones were slightly warm to the touch, at no load used less than 1 watt (limit of resolution) on the power meter, and had a power factor down in the .15 range. I tried a bigger one used for charging my big cordless drill, it ran 4 watts and .47 power factor.

As a side note, I got a "Kill-A-Watt" power meter

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about $30 to $35, used it to track down about 3/4 of my total household power useage. The wall warts were NOT an issue, the freezer, the refrigerator, and my wife's reading lamp were heavy hitters. The reading lamp got a 40 watt florescent, saves about $6 a MONTH on that item alone!!

I took a read> A while back there was a discussion about why wall wart transformers that

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I knew Malcolm Coleman at Motorola. He was head of the power group in Area D. We were neighbors and amateur photographers. We both had Canon EF cameras.

Bob Swinney

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Robert Swinney

One household won't notice much difference, but if everyone unplugged their wallwarts and turned off (instead of let sit on stand-by) their computers I bet there would be quite the loss in consumption.


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Bob -

I knew Malcolm Coleman at Motorola - well - I did custom designs for him at his request - and they were approved by the divisional Engineering in Ill. I flew all over the U.S. with members of Malcolm's Dallas team and the Sch. Ill. Team. Sadly, some friends were on a plane in the fateful day in Chicago - another missed that plane and lived. The system was a computerized Utility Load Controller - monitoring power substations .... and shedding loads (hot water, well pumps, air conditioners...).

I lost track of him when the small company I was working for got smaller. I went to work for SLB and a long string of home moves.

Fond memories of the local Motorola office and memories of our trips.


Martin Eastburn @ home at Lions' Lair with our computer lionslair at consolidated dot net NRA LOH & Endowment Member NRA Second Amendment Task Force Charter Founder IHMSA and NRA Metallic Silhouette maker & member

Robert Sw> Martin,

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Martin H. Eastburn

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Robert Swinney

Even more so with TVs left on standby, there are more of them in use than computers.


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Yeah. :)

All my stuff like that is hooked up through a "power strip" and turned off with one switch. One for the computer and its stuff and another for the TV and its stuff.

My antenna pole has been stuck by lightning at least 3 times (that I was here to witness) and since I'm about as high as anything around here, during that season the antenna is disconnected too and only connected when it's being used. It was disconnected the first time it was stuck and so only burned up the house wiring and out-building wiring.

That first bolt was a whopper and some of the electricity "spilled over on me". I woke up laying on my back with my arms and legs in the air like a dead cockroach. All my muscles were frozen and as tight as they could posibly be, even my diaphram. I couldn't move and I couldn't breathe. "shear terror"

It was cool! :)

No, I don't want to be struck again, thank you, once was enough.

I'm a retired railroad signal ape and can say, that bolt that got me wasn't anywhere near the strongest, but was a good solid stike anyway, the next two were more typical. There's been several times I opened a signal case full of relays and lightning arrestors, to "hunt down the signal trouble" and "couldn't see anything in the he case" because it was -all- one flat-black color. It looks creepy as anything.

Anyway, I figure I only -got- about 1%.

It -felt- like the whole friggin thing tho! :) Believe it? ;)

Alvin in AZ

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This computer, the on I'm running right now (750Mhz AMD K7 T-Bird),

net ID lazarus, was struck by lightning about three years ago (2003).

Well, it actually hit outside on the driveway, but a lot of my electronics got fried - including this computer!

Power had just gone off, but the cpu was on battery - shutting down - when it hit.

When the lights came back on (reset all the breakers) the VCRs and TVs (2) were all gonzo, but the computer tried to start up - and then Smoked! Badly! Stinky Black power supply smoke! Along with a bright yellow glow from the back of the box!

I remember being dumbstruck thinking "It normally doesn't do that...", before swatting the switch off.

Which did cause the "glow" to go out immediately, but it just rolled smoke!

A few days later, figuring "what the heck" I swapped out the power supply, and the machine came up an ran, sort of. Cad was no problem, but it would hang up on things it used to do just fine... couldn't dial!

I did a careful visual exam of the motherboard and found every one of the small electrolytic capacitors had the tops blown off. Little round tops hinged over to one side and the stuffing's oozing out - like tiny spinach cans in a Popeye cartoon.

So I made a list, found all the right caps (which all looked a lot better quality than the originals, btw) and very carefully replaced them one at a time.

And finally replaced the modem to get back on line.

And it rocks on... But under a new name: lazaruz

For what it's worth?

That was out in the country - local shore power not exactly always stable.

I had a battery backup on the cpu/monitor (with surge suppressers) Surge suppresser on the master power switch box. Surge suppresser on the printer power outlet strips (2). Surge suppresser on the laptop circuit (Laptop not connected at the time) All in one room.

And the phone line physically disconnected.

Yet it still somehow fried the modem...

Now somebody explain that one!


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True. Any transformer has slight losses, even when idling. Just FEEL a 'wall-wart' ... they get warm, even when NOT under significnt load. That heat comes from resistive losses in the wire and magnetic losses in the core. Even when NOT under external load, there are short-term internal current flows in the coils (or there would be NO magnetic field). Current in a wire is always a resistive LOSS, no matter which way it flows. For a well designed transformer, those losses are slight, but never zero. It's doubtful that you'd ever SEE a difference in your electric bill from letting ONE idle, however.

Dan Mitchell ============

Reply to
Daniel A. Mitchell

"could come up with a thousand senarios and none of them would be exactly right" ...is my typical answer, just before I procede to speculate my ass off. ;)

Easy. ;) The dangged lightning can jump miles outside and jumps from one thing to another (at-will;) inside. BTSeenT when looking at the evidence of it and it sometimes makes no sense at all why it chose that particular path (other than lightning has no sense and makes no choices?;).

The bolt that got me had -at the very least- jumped 1+1/4" between metal objects, then through me to ground. It was the first bolt from two clouds that came together at about a 90 degree angle... I was watching them hoping it'd rain. It was late June in the desert and the first rain is a big deal for us born here.

Alvin in AZ

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