אנציקלאפעדיע

How many of those little Power Cube thingies do you have around your house? Here's how many I found around mine:
The answering machine
The cordless phone
The cell phone
The digital camera
The nicad battery recharger
The video camera battery replacer/recharger
The digital clock in the bedroom
The electric toothbrush
The electric razor
The electric screwdriver
The electric drill
Both sides of the baby monitor
The laptop computer
The office phone
The ink jet printer
The speaker system on the computer
The tape recorder that records notes in the office
The calculator recharger
The 9-volt battery replacer for the radio
The radio shack univeral power cube
22 of them! (remember, the baby monitor has 2) And they are all different - they have different plugs, different voltage ratings and different amperages.
So let's take one of these apart and see what's inside. Here's the transformer we will be exploring today:


Under the cover

[Figure 1.1]

This transformer came with a rechargeable electric screwdriver. This particular transformer is rated at 3 volts and 240 milliamps. Once you convince the cover to come off here is what you find inside:

[Figure 1.2]

What you can see here are two windings. The purpose of a transformer is to convert one AC voltage to another AC voltage. In this case the transformer converts the normal 120 volt AC current in your house down to three volts. The 120 volts comes in on the primary winding on the left. Running down the middle of that winding (as well as around the outside) is an iron core. The AC current in the primary winding creates an alternating magnetic field in the iron just as it would in an electromagnet. The other winding, known as the secondary winding wraps around the same iron core. In the secondary winding the magnetic field in the core creates current. The voltage in the secondary is controlled by the ratio of the number of turns in the two windings. So if the primary and secondary windings have the same number of turns, the primary and secondary voltage will be the same. If the secondary winding has half as many turns as the primary then the voltage in the secondary will be half that of the voltage in the primary. You can see in the following figure that the primary in this particular transformer uses very fine wire while the secondary uses much thicker wire. To drop down to 3 volts, there needs to be 40 times more turns in the primary than in the secondary.


Turning the AC current into DC current

[Figure 2.1]
On the other side of the transformer you find two diodes wrapped in rubber insulation. The diodes act as a rectifier, turning the AC current into DC current.

[Figure 2.2]




Most transformer cubes that you find around the house produce a low-voltage DC current (3 to 12 volts, and less than an amp of current). DC current is necessary because rechargeable batteries store DC current, because most electronics require low-voltage DC current and because small DC motors run directly from batteries and are the least expensive motors available.

The big question remains, however - why can't somebody standardize all of these little cubes?!



Tons of products use transformers. Walk around your home and you probably see them everywhere. In my house, I found them attached to my printer, scanner, speakers, answering machine, cordless phone, electric screwdriver, electric drill, baby monitor, clock radio, camcorder… You get the idea. A typical home probably has five to 10 of these little transformers plugged into the wall at any given time.

It turns out that these transformers consume power whenever they are plugged into the wall, whether they are connected to a device or not. They also waste power when powering a device.

If you have ever felt one and it was warm, that is wasted energy turned to heat. The power consumption is not large -- on the order of 1 to 5 watts per transformer. But it does add up. Let's say that you have 10 of them, and they consume 5 watts each. That means that 50 watts are being wasted constantly. If a kilowatt-hour costs a dime in your area, that means you are spending a dime every 20 hours. That's about $44 every year down the drain. Or, think of it this way -- there are roughly 100 million households in the United States. If each household wastes 50 watts on these transformers, that's a total of 5 billion watts. As a nation, that's half a million dollars wasted every hour, or $4,380,000,000 wasted every year! Think of what you could do with 4 billion dollars…

Where these small loads really take a toll is in remote locations powered by things like solar cells and wind generators. In these systems, you are paying something on the order of $10 to $20 per watt (once you add up the cost of the solar cells, the batteries to store the power, the power regulators and inverter, etc.). Fifty watts at $20 per watt means that you have to spend an additional $1,000 just to power the transformers. In these kinds of systems, small loads are something you avoid by unplugging the transformers when not in use or by eliminating the transformer and powering the device straight from the battery bank to improve efficiency.

However, the added electricity expense is offset by the manufacturing cost savings passed along to the customer, hopefully, as a lower product selling price. For example, it costs a manufacturer considerably less to manufacture and stock one universal "flavor" of printer that runs on 12 volts DC. The manufacturer then packages the printer with a country-dependent voltage AC wall transformer for the country it's being sold in. When a new version of the device comes out, the manufacturer doesn't need to retool the power supply.