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[Phys-L] Wall warts and other Green devils



On 2012, Dec 21, , at 08:28, Josh Gates wrote:

We all know about the losses caused by leaving wall warts plugged in when not in use (and TVs, etc.), but do these outlets have the same issue?
http://www.homedepot.com/buy/leviton-15-amp-tamper-resistant-combo-outlet-usb-charger-white-r02-t5630-00w.html#.UNSNc2me78M
http://www.homedepot.com/buy/u-socket-15-amp-ac-standard-wall-duplex-outlet---white-with-built-in-usb-charger-ports-ace-7169.html#.UNSOHmme78M


There are several different types. This one references built-in electronics to sense this and that, which presumably requires some power. Does anybody know the comparison? Along the same lines - does my new phone charger (small block, usb connection to mini usb) have the same issues as the old ones? There doesn't seem to be enough room for a large transformer in there. I don't know if they're smaller or if it's a new technology.

First, let me assure everyone that there is no problem with leaving a modern wall-wart (SMPS) plugged in.

It's a new technology to a physicist (me) who quit teaching more than a decade ago, but it shouldn't be since it has been around since the 70's. Only today did I bother to look into it in some detail. Fortunately I knew that the technology is called "switching mode power supply" (SMPS) and everyone who travels with a laptop computer has one. There is a transformer inside, but it is a higher frequency transformer (for isolation purposes) making it much smaller and lighter. An example can be found at <http://media.digikey.com/photos/rdl/evlvip17_5wchg_schematic.jpg>. There are a couple of "bugs" shown in the diagram, and the diode-transistor pair with double arrows is an opto-isolator. Fortrunately it's Christmastime and our oldest son is home, so he explained the circuit to me. Pretty clever, and with Google at hand any physicist with some electronics experience can understand it. (Or perhaps bc could write an explanation.)

These SMPS's and their heftier wall-wart predecessors make it possible to get DC powered appliances to market rapidly and more cheaply, avoiding the necessity of getting Underwriters Laboratory (or CSA) approval of a new 110 VAC powered device with a DC supply built in. Only the power supply needs to be approved, and it can be used for many different appliances.

Our electric utility BC Hydro sets up "information" tents at many public events such as fairs. I always annoy the attendants by questioning them about what they are doing (e.g. telling people they will greatly reduce their carbon footprints by remembering to unplug their cell phone chargers when not in use). I also inquire about what physics courses they have been exposed to. None I have met could discuss anything physical intelligently. I ask them "What does BC Hydro sell?" I have done this more than ten times in recent years, and until a month ago no one had ever answered correctly, but that time the girl (who had not taken any physics course) answered "Energy". I was appropriately pleased and told her so. The more common answers are "power" and "electricity". I can then inquire about the price of electricity, or the quantity, and confirm the vacuity of their preparation to meet the public.

The public has been evangelized and converted; there are many Greenies out there. As a particularly dramatic example of how bad it has become, see <http://www.theregister.co.uk/2012/05/27/human_powered_electricity_please_make_it_stop/>. I have little hope that this Green disease will abate any time soon. The Enlightenment failed to destroy Christianity, so I have little hope that teaching the masses some physics will make them any smarter.

Merry Christmas,

Leigh