So inexpensive (although recently it seems difficult to obtain short supply), I tried to make things with the same functionality and current transformers. When I went to Osaka on business, I found a junk shop in Nihonbashi. I think it was one of a few hundred yen. It may be your own luck too.

In principle, the current transformer is to say the same thing as a normal transformer. "Hollow" There are 3,000 enameled wire wound iron core shape. This is the secondary winding. The primary winding is not anything original. As shown in the figure and the AC windings wound temporarily while twice the iron core of the line leading from the plug outlet. The ratio of current flowing through the primary side and secondary side is the inverse ratio of the number of turns. Linearity will be worse and the secondary load resistance is large. Half-wave rectified capacitor low germanium diode forward voltage drop with a 100μA Rajiketa smoothed C (1556Ω internal resistance) is measured at DC current. D2 is the current in the opposite direction let out a half-wave rectified, if it does not indicate the correct value. 1000W and 100W is a full-scale switch is for but more. As shown below, to calculate the smoothed dc current relationship after the half-wave rectified AC rms current, shunt resistors R1 and R2 to calculate the value of Yarimasu. Resistance because it is an odd number, or combination of resistors having a few on hand, use a semi-fixed resistor. In fact, 100W incandescent bulb or, 500W showed the correct value by connecting the appliances do you know in advance, such as power, electric stove.

This measured the various things at home. For example, the PC operates at about 80W, standby (standby) at about 35W, the liquid crystal display operating at about 35W, 5W standby was about. This is a CRT display and power, not so much a house is more Remasen. Then, the AC adapter will depend on various things as well, such losses are surprisingly low, they stuck to the outlet side without using any DC 1W or less.

Now, Do not keep your computer on standby for 10 hours at night when my family
(35W + 5W) × 10h = 400Wh be. 1kWh from approximately 22 yen, 270 yen is a waste of about 10 yen per month in one night. Last night decided to turn off the computer.
Note: You may damage the large current and a current transformer primary side Secondary side left open current transformer. Please be careful. This is a short break with an ordinary voltage transformer secondary side is exactly the opposite phenomenon.