Do you know the difference between AC and DC? Or what is Watt? And who was Ohm?

Join us in this crash-course in power supply and check out what these abbreviations and technology terms really mean!

Absolute power

Since the late 19th century, electricity has had a tremendous impact on humankind and life on earth, with inventions like the light bulb, telephone, phonograph, generator, motor, and motion pictures. And that is all thanks to Thomas Alva Edison, inventor in the US and Nikola Tesla, a European scientist who is often seen as the inventor the AC power.

Watt and Voltage and Ampere – how do I know the difference?? In electricity there are some basic units to be aware of; voltage (U), current (I),watt (W) and resistance (R).

Power is measured in watts, voltage is measured in volts, current is measured in amps and resistance is measured in ohms. A common analogy to help understand electricity is water falling in a river. In this case the current (I) is like water flow rate, the voltage (U) is equivalent to the water fall height, resistance (R) is the rugged surface in the flood bed and power is “water fall height” times "water flow rate".

DEFINITIONS First of all, it can be good to know that the total sum of energy is always constant, energy only change its shape. It may change from something moving (electrons or cars or computers), to heat when the object is slowed down. As the sum of energy is constant, the energy that is not used for the purpose is converted to another form, for instance heat. This additional heat must be transferred to a place where it is not doing any harm and this requires more energy. So, cooling something is just an expression for the function of transferring the unwanted heat away from the equipment ultimately to the outside air, where the heat does not cause a problem. Power & Watts Electrical power is measured in watt - a unit that tells you what the power output will be, from a 100W light bulb for instance. Watt is used to specify the rate at which electrical energy is dissipated, or the rate at which electromagnetic energy is radiated, absorbed, or dissipated. The watt symbol is W. Examples of amount of Watts required for various applications • 10's of Watt = power supply for light bulbs or a portable PC's • 100's of Watt = Printers, faxes and other small office machines • Kilo Watt = Stoves, telecom systems or other large industry systems. Current & Ampere The more “techy version” of energy is that electricity, or current, is the result of an electrical charge, as electrons moving through a wire, often made of metal such as copper. Current (I) is measured in AMPERES (Amps or A). Ampere is a unit to measure the rate of electron flow – the current output – in an electrical circuit. Or to use the water analogy – to measure the amount of water flowing in a river – more force (U) pushes more water (I) faster through to generate more power (P). Ampere is named after Andre Marie Ampere, French physicist (1775-1836). Voltage & Volts Voltage is the electrical force that makes current (electrons) flow in a circuit or through a wire. To continue the water analogy, voltage can be compared with the height of a water fall. The standard unit is Volt, symbolized by a non-italic uppercase letter V. Voltage can be direct or alternating. A direct voltage maintains the same polarity at all times. In an alternating voltage, the polarity reverses direction periodically. The number of complete cycles per second is the frequency, which is measured in hertz (one cycle per second), kilohertz, megahertz, gigahertz, or terahertz. Resistance & Ohm’s Law To be a full fledge expert in the power ABC, you also have to know about resistance. Resistance can be anything that causes an opposition to the flow of electricity in a circuit, and can be compared with the rugged surface in the flood bed. Resistance is used to control the amount of voltage and/or ampere in a circuit. Resistance (R) is measured in Ohms or (Ω).

Ohm’s Law “The amount of current flowing in a circuit made up of pure resistances is directly proportional to the electromotive forces impressed on the circuit and inversely proportional to the total resistance of the circuit” – easy, right?! Ohm's Law – named after German scientist Georg Simon Ohm - is the mathematical relationship among electric current, resistance and voltage. By using Ohm's Law you can determine one value by knowing the other two, for instance to figure out the Current by using Voltage and Resistance values: I = U/R. If the current in amperes is represented by I, the voltage (or potential difference) in volts is represented by U, and the resistance in ohms is represented by R, then the following equations hold for power in watts, represented by P: P = U*I As mentioned about Resistance, the resistance consumes power in electrical wires, and the power consumed increases as the current going through the wires increases. You can see how this happens by doing a little rearranging of the two equations. What you need is an equation for power in terms of resistance and current. Let's rearrange the first equation: I = U/R can be restated as U = I*R. Now you can substitute the equation for V into the other equation: P = U*I substituting for U we get P = I*I*R, or P = I2R. What this equation tells you is that the power consumed by the wires increases if the resistance of the wires increases (for instance, if the wires get smaller or are made of a less conductive material). But it increases dramatically if the current going through the wires increases. So using a higher voltage to reduce the current can make electrical systems more efficient. The efficiency of electric motors also improves at higher voltages. AC-DC – Rockband, or... No, AC and DC is short for Alternating Current (AC) and Direct Current (DC) and the difference is the way the water flows. DC – Direct Current Direct Current (DC) is when the current, or water, flows in only one direction, from point A to point B. DC power was the first current technique used, and a common source of Direct Current are DC generators and batteries. DC can be either positive or negative, but it never alternates. Industry applications/areas using DC power are telecom system equipment and automotive applications such as cars and buses. However, DC is today seldom used in household outlets. DC power is used internally in almost all electronic equipment. AC – Alternating Current If the current instead moves back and forth – it is called Alternating Current (AC). AC means that both voltage and current alternates. AC is the electricity we use in our homes, to power our TV and radio, armatures and computers. In a standard household outlet the electrical current changes direction, from positive to negative and back, 50 (in Europe) or 60 times (in USA) each second.