Phone chargers and power consumption

[Mr__Bill]

Has anyone with the power consumption meters plugged in the power adapter for their cell phone to see if it draws the same when no phone is attached? I had a salesman swear ti only drew power when the phone was attached but it seems to me that as a transformer it should draw the same all the time and be on the list of vampire devices.

Just wondering.

Bill
On the left coast

[LCHIEN]

I haven't measured one lately. But a phone typically takes a half amp at 5V or about 2.5 Watts when charging. The phones control the charging current closely and shuts it off when the battery is full.

When there's no battery the current of modern chargers with switch-mode power supplies will be way lower than those with just a transformer and rectifier. You can tell the SMPS they will be marked with Universal input like 110 to 240V AC, instead of just 110-120V. The SMPS waste a whole lot less power than the old transformer warts. It won't be zero but it will probably be 1/20th as much. In total dollars its really, really small. If you're really tight for pennies, unplug it when not in use. I don't worry about it, myself and I've been an electronics engineer for 40 years.

[atgcpaul]

OK, I just checked this out with my Kill-o-watt using three different chargers--one for my wife's iPhone, one for my HTC phone, and a generic one. They are all USB out.

With no device connected, all three showed a momentary draw of 1-2 watts, then quickly went to 0. I didn't plug her iPhone in, but when I connected a tablet to each of the other two devices, I was pulling 6 watts.

[LCHIEN]

its not zero but its below the minimum resolution of the Kill-a-watt.
Close to zero.

Question: How much money is too much money to leave it plugged in 24/7 for convenience sake?

Tell me that and I'll tell you how much it costs to do so.

[Mr__Bill]

Thanks guys. Just looked at the Samsung warts and they do say 230 to 240 v. I wasn't really worried more wondering. I look around and I have 4 plugged in all the time. Perhaps it's time for another cfl to offset the electricity. <grin> Hard to have to admit the sales man was right.
Thanks
Bill

[tfischer]

Yeah this is true of most any "wall wart" power supply. It will use a tiny bit of wasted power when the device it powers isn't in use, but nothing approaching the full rating.

[woodturner]

Yeah this is true of most any "wall wart" power supply. It will use a tiny bit of wasted power when the device it powers isn't in use, but nothing approaching the full rating.

As LCHIEN noted, switching supplies essentially turn off when disconnected and draw nearly zero current.

Older style wall warts are transformers with an AC output or transformers with a rectifier circuit to provide DC output. Line current will be load current/turns ratio. For a 12 VDC output and 120 VAC input, line current will be about 1/10 load current. The diodes use a little current, so figure 50 mA or so disconnected, the line current will be in the range of 5 mA, and the transformer will draw 0.6 W or Wh. Electricity is commonly billed in KWh at a cost of $0.06 - $0.15 per KWh, so even at the higher rate, you can run the transformer for something like 1666 hours (69 days) for $0.15, or around $0.78 per year.

So, as a practical matter, you can plug them in and not worry about the cost of operation.

A greater concern may be fire - there are some reports of wall transformers catching fire, and there have been some recalls. This is always an issue with cost sensitive electrical components connected to power full time - and why I unplug nearly everything when not in use. As an electrical engineer for many years, I have dealt with marketing trying to squeeze the last penny out of a consumer product, and have also heard the customer horror stories.

It really gets down to your comfort level, and I probably lean a bit toward the paranoid side ;-)

[LCHIEN]

FWIW, I left a Kill-a-watt meter plugged in for 24 hours logging KWH on a unloaded iPod charger (same as would be used for an iPhone) recorded .01 KWH which is the minimum resolution. (after 10H it still read 0.00 so I know it was accumulating at a higher resolution than the display).

That's a bit inaccurate because of the limited resolution but assuming its right then I would use 3.65 KWH for plugging it in a year unloaded (not charging anything) which would cost me 36 cents for the year.

OTOH, its about 1-2 lbs of CO2 per KWH (range depends on natural gas or coal) so you could be saving 5 or 6 pounds of CO2 from being created if you are green.
But you also generate ~20 lbs of CO2 for each gallon of gas you burn in your car. It would be easier to save 6 lbs of CO2 by not driving 6 or 12 miles.