If you need to lower the voltage two times, for example for powering low voltage incandescent lamps that turn on in a chain of powerful diode. He will cut off one half wave, the voltage is 110 V. what it will be permanent, lamp filament does not matter. This method of incorporation is useful where you want low power consumption and long lamp life.
To increase tension use autotransformers. Their design allows you to set the level of the output voltage, increasing it in the range of 50 volts. Autotransformers are normally used in networks with a low voltage , for example, in rural areas, where the voltage drop is fairly commonplace. With the help of autotransformer it is possible to lower the voltage in the same range. But keep in mind that a large decrease or increase in voltage of the autotransformers is strongly heated. Using them, always consider the load power, for which they are intended.
To maintain a voltage of 220 volts enables the voltage regulators. Most often they are used at reduced voltage, they can increase it by a few tens of volts. When the stabilizer do not exceed the load for which it was designed.
To raise the voltage by using multiplier circuit is a special device consisting of diodes and capacitors. Such multipliers are used in power supply circuits anodes of the tubes, increasing the voltage to about 25-27 thousand volts. Read more about the tubes you can read here: http://radioskot.ru/publ/spravochnik/umnozhitel_naprjazhenija/2-1-0-363.
If you need to raise or lower the voltage you can wrap a homemade transformer. The exact formula of its calculation is quite complicated, so use the approximation formula: n = 50/S, where n is the number of windings per 1 volt of voltage. S – area of the magnetic circuit. When using W-shaped plates, the area is equal to the product of the average width of the tongue plate, the thickness of the package in inches.
Calculation example: if the width of the middle tongue 4 cm, thickness of the package is 5 cm, then S=20. Dividing 50 by 20, you will receive the 2.5 coils on 1 volt. Then the primary winding will have a 220 x 2.5 = 550 turns. If in the secondary winding you need to, for example, 300 volts, then it will need 750 turns (350 x 2.5). This calculation method is most applicable for low-power transformers designed for power electronics and other low power devices.
Advice 2: Why 220 Volts
Voltage 220V used in home power, is dangerous to life. Why not begin to organize in the homes of the 12-volt network and produce the corresponding electrical appliances? It turns out that such a decision would be very inefficient.
The power allocated to the load equal to the product of voltage on it and passing through it current. It follows that the same power can be obtained using an infinite number of combinations of currents and voltages - the main thing to work every time was the same. For example, the power output of 100 W can be obtained by 1 V and 100 A or 50 V and 2 A, or 200 V and 0.5 A, and so on. The main thing - to make a load with so much resistance that when the desired voltage is passed through it the required current (according to Ohm's law).
But the power stands out not only on load but also on the lead wires. This is detrimental because this power is lost useless. Now imagine that for the power load capacity of 100 watts uses conductors with a total resistance of 1 Ohm. If the load is supplied with voltage of 10 V, to obtain such capacity through it will have to pass a current of 10 A. that is, the load must have a resistance of 1 Ohm, comparable to the resistance of conductors. So, they will have lost exactly half of the supply voltage, and therefore power. So in this scheme, the power load developed at 100 watts, you will have to raise the voltage from 10 to 20, and in heating the conductors will be of no use to save even 10 V * 10 A = 100 watts.
If 100 watts are obtained when the combined voltage to 200 V and current 0.5 A, the conductor resistance of 1 Ohm will drop the voltage of only 0.5 V, and the capacity allocated to them, will be only 0.5 V * 0.5 A = 0.25 W. Agree, such a loss can be neglected.
It would seem that when 12 volt power is also possible to reduce losses by using thicker conductors have less resistance. But they will be very expensive. Therefore, low-voltage power is used only where the conductors are very short, and so they can afford to make thick. For example, in computers such conductors located between the power supply and the motherboard, in vehicles - between the battery and the electrical system.
What if, on the contrary, to apply in home electrical lot of tension? Because then the conductors can be made very thin. It turns out that this solution is also unsuitable for practical use. High voltage can penetrate the insulation. In this case it would be dangerous to touch not only exposed wires but also isolated. Why do only the high-voltage transmission lines, which saves a huge amount of metal. Before serving in the house this voltage is lowered to 220 V via transformers.
A voltage of 240 V, as a compromise (one side, not piercing the insulation, and on the other, allowing to use for household wiring is relatively thin wires), proposed the use of Nikola Tesla. But in the US, where he lived and worked, this proposal was not heeded. There are still applied voltage 110V - too dangerous, but to a lesser degree. In Western Europe the voltage is 240 V, that is, as much as Tesla suggested. In the USSR there are primarily two voltage: 220V in rural areas and 127 in the cities, it was then decided to transfer to the first of these stresses and the city. It is now widely used in Russia and the CIS. The most low is the Japanese grid. The voltage it is only 100 V.