Most sold in Russia electrical appliances designed for a voltage of 220 volts. Those that have impulse power supply units – for example, many TVs and portable computers, working at a voltage from 110 to 220 V. sometimes, However, to power a device requires low voltage.
To lower the voltage, use an auto-transformer. You can purchase as a modern auto, and look on the markets are cheap and quite reliable autotransformers Soviet production. Due to the presence of the adjustment handle you can change the voltage in a fairly wide range. Remember that the power of the autotransformer should not be lower than the power plug of the appliance.
Lowering the supply voltage is twice as possible by including in the circuit a powerful diode. This option is especially convenient when used with a lamp having a filament. Putting a diode, you will cut off one half wave of the alternating current than lower voltage to 110 volts. The lamp will burn weaker, but will significantly increase its service life.
For smooth tension adjustment, use thyristor controller. You can assemble it yourself using one of the existing schemes. For example, this: http://sovmasteru.ru/125/
Lower the voltage by using transformer, including homemade. With decreasing voltage the number of turns in the secondary winding should be less than the number of turns in the primary winding. For the exact calculation of transformers are relatively complex formulas, but for simple household transformer you can use a simplified formula n = 50/S, where n is the number of turns for 1 volt, voltage, S is the cross – sectional area of the magnetic circuit. If you use for manufacturing of transformer W-shaped plates, the area of the magnetic circuit is determined by the product of the thickness of the plate pack to the width of his middle of the reed, in inches.
Lower the voltage by using a powerful damping resistor, but this method is uneconomical, so the resistor will dissipate significant portion of power. Instead of damping resistor in some situations, you can use the included sequentially in the network of the incandescent bulb. Changing the power of incandescent bulbs, you can change the output voltage.