• # How voltage is reduced from 220 to fewer volts?

Curious to know whether or not it is possible to reduce the general voltage of electric power cables from 220 to fewer volts? The answers at this Ask Expert page will explain the mechanism that functions behind the power supply voltage and how it can get reduced.

The electric power that we receive from the power line is either 220 volts or 110 volts supply in general. How we get less power technically via an adapter or connector? How does its mechanism generally work? Is it possible to split the power from high to low and if so, is there any special technique?

• We can do it in many ways. But the simple technique is to use resistors.

If you want to divide voltage to half you have to use 2 resistors of equal value in series. Then a jumper wire is to be placed in between these two resistors. At the point where the jumper is placed the voltage will be half of the input.

Based on the input voltage and the required voltage we have to use the resistors. The resistor voltage can be obtained using a formula as given below.

R2= (V)(R1)/(VIN - V) V is the voltage wanted, R1. First resistor voltage. V IN is the Voltage input. Then we should connect it to another resistor of R2,

Say R1 is 10KO. Say VIN is 5 V. Say V is 3V. Then R2= 3X10/5-3 =30/2=15KO. So to reduce 5V to 3V we have to use two resistors of 15KO and 10KO.

drrao
always confident

• This is a technical query which many people ask time to time and before going into the detailed answer let us go through the basic science behind the electrical energy flow. I will take the example of an ordinary electrical battery or cell that we use in our watches, wall clocks or torch. A battery used in the common torch is rated as 1.5 Volts. This is the electro motive force that is available in the battery. Now if we use it to glow a LED which is rated for 1.5 Volts then LED will glow and some current of the order of only 10 milli ampere will flow through it. If we connect a filament type of torch bulb to the battery then it will also glow but current will be about 300 milli ampere. It means that from the source of 1.5 Volts different currents can flow depending upon what we have connected to it. This is the basic principle that we have to understand. More current flows in the filament type bulb means that more power of the battery will be consumed and the battery will be discharged in less time. Same battery will go for a long time if LED is used as current flowing through LED is very less. So, this more current and less current is actually the power and we say that more power is used in the filament bulb while less is used in the LED type bulb. Actually power is equal to the multiplication of voltage and current ( P = V * I ) and depending on the current it will decrease or increase.

After understanding the concept of electrical power and its relation to the voltage and current now let us try to understand what type of electricity is connected to our houses generally called 220 Volts or 110 Volts coming as domestic supply. In India we have 220 Volts so we will talk of that only. This domestic supply of 220 Volts is AC (alternating current) and not DC which is what a dry cell/ battery gives. The difference is that the DC flows in one direction while AC flows in both direction with a frequency known as line frequency. In India we have line frequency of 50 cycles/second (known as Hertz (Hz) also, where 1 Hz is equal to 1 cycle/ second). There are advantages in having AC as it can be taken to long distances without the much loss of power in the electrical wires as compared to the DC. Another thing is AC is much safer than DC.

Now we will learn how this AC voltage is reduced for our various usage in electrical appliances or battery /AC operated toys etc. So, reduction of voltage is carried out with the transformers or resistors or certain semiconductor assemblies which are used to convert the 220 AC to the desired level say 12 Volt. Now this 12 Volt is again AC only and for use in a toy or some other appliance we have to convert it to DC for which there are some electronic circuits which are known as rectifiers. They will change the alternating direction of AC to uni-directional DC. Now all these circuits are concealed in the gadgets, toys and other items which run on 220 Volt AC. So, apparently we will not be able to see these components and electronic circuits from the outside but they are in built to the appliance. For example if there is an electronic circuit inside our washing machine which requires 5 Volt DC for its working then the manufacturer will integrate a step down mechanism for the mains voltage (220 Volt AC) and a rectifier there itself so that the electronic circuit can function properly. You will find everywhere these low voltage power supplies. Remember, everything we are deriving is from the 220 Volts AC electrical line only.

One last thing I want to add is to understand the power concept is that the mains voltage which is coming to our house is 220 Volts. The question comes how much power I can take from it? The answer is that it is limited to the electrical fuse wire or strip that has been installed in your main electrical board fitted in your house adjacent to your electrical meter. If that fuse is 32 Ampere then the total current in your house should not exceed 32 Amperes as the electrical fuse will blowout to prevent damage to the electrical lines as more current than that will start heating the electrical lines themselves which will be a safety hazard.

Knowledge is power.