Tag Archives: electricity

Peltier Cell Generates Electricity from a Lamp

The early 20th century saw the end of the use of candles and oil lamps as electric lighting became more common. Earlier, candles were made from various items such as natural fat, wax, and tallow. However, most manufacturers make candles from paraffin wax, a substance obtained from refining petroleum.

Compared to an incandescent bulb, a candle produces nearly a hundred times lower luminous efficacy. The luminous efficacy of a modern candle is about 0.16 lumens per watt, and it produces nearly 80 W of heat energy. Another form of the candle, tea lights, come with a smaller wick and produce a smaller flame. However, a standard tea light produces about 32 W, depending on the wax it uses.

The Peltier cell makes it possible to convert a small fraction of the heat energy from tea light into electricity. This can be used to drive a highly efficient LED light. This arrangement helps to boost the total luminous efficacy of the tea light and we can get a larger amount of light.

The Peltier element is really a solid-state active heat pump. Electricity applied to the element causes it to transfer heat from one side of the device to the other. Therefore, a Peltier element can be used for heating or cooling. If one side of the Peltier element is heated to a temperature higher than that on the other side, the Peltier element works in reverse, generating a difference of voltage between the terminals. This reverse effect is known as the Seebeck effect and the device works as a thermoelectric generator.

As the efficiency of a typical thermoelectric generator is only around 5-8%, the heat from a tea light should be capable of generating about 1.6-2.56 W of electrical power from the Peltier element. In practice, the Peltier element gives only about 0.25 W with the heat from the tea lamp. The reason being the inability of the Peltier element to capture the entire heat produced by the tea lamp to generate electricity—some heat is lost in transmission, and some in heating up the Peltier element. However, the energy generated by the Peltier acting as a thermoelectric generator is capable of running a small fan and drive an LED lamp satisfactorily.

A thermoelectric generator can be built around two 40×40 mm TEC1-12706 Peltier elements, mounted between two heat sinks, and connected in series to boost the voltage output. The smaller heat sink at the bottom serves to spread the heat from the tea light to heat up the Peltier elements evenly. The larger heat sink at the top has a fan to cool it and maximize the temperature difference between the two sides of the Peltier elements.

Although the fan draws power from the Peltier elements, it also helps to improve the efficiency of the system and make more energy available for the LED light. The fan also helps to keep the Peltier elements from overheating. Peltier elements are internally soldered with a bismuth allow solder melting at 138°C. Therefore, no Peltier element should operate above this temperature.

How Do Wind Turbines Work?

Wind turbines generate electricity from moving winds. You can see them in large numbers on wind farms both onshore and offshore. The blowing wind turns their blades, and rotates the shaft on which the blades are mounted. The shaft in turn, operates an electric generator and the resulting electric output is sometimes stored in a battery. A swarm of wind turbines can generate a substantial amount of energy. Wind turbines are often called a renewable source of energy, as they generate power from natural renewable sources, and do not consume fossil fuel, a source that cannot be replenished.

Inside the wind turbine, there are several control systems at work. These include its ability to turn the face of the turbine into the wind, called yawing, and its ability to control the angle of its blades, called pitch. Yawing and pitch extract the maximum amount of power from the blades rotating in the wind and require motors and controls. However, the yawing of a wind tower may actually twist the cables inside. The wind turbine usually has electronic intelligence built inside to untwist the cables.

The wind actually propels the blades, which are designed using the laws of physics and vectors to extract the maximum from the wind driving them. Speed analysis shows the maximum efficiency the wind turbine can achieve is about 59%. The laws of physics, especially Betz’s limit prevents the wind turbine from achieving efficiencies any higher.

As mentioned earlier, the main parts of a wind turbine are the blades mounted on a shaft. As the blades turn with the wind, the shaft rotates and spins a generator to make electricity. Most designs of wind turbines use electronic controls to generate the 60 Hz AC sine wave, although there are wind turbines that generate DC as well.

Typically, a doubly-fed induction generator is used to generate three-phase power. As this requires capacitors and a DC link, workers need to monitor the systems periodically to prevent failure of capacitors. Most of the control is similar to that used for controlling bidirectional motors, using IGBTs, and rectifier diodes in a full bridge arrangement. These components are rather large, considering the voltage generated is nearly 690 volts, and the power is in megawatts. Transformers step up the voltage from the generator to the grid power line, and there is built-in protection to limit the spikes as the speed of the wind increases.

The rotation speeds for wind turbine blades are 5-20 rpm, while a generator needs to rotate at speeds between 750 and 3600 rpm to generate power. Therefore, a gearbox in between translates the speeds. When maintenance time comes around, a combination of yawing and proper pitch is used to stop the rotation. Workers then insert pins into the shaft, locking the blades to prevent them from spinning.

Workers servicing and maintaining the blades have to dangle from ropes hundreds of feet above the ground in the air. Other parts, being within the tower, can be maintained more easily. In general, the maintenance and servicing for a wind turbine is similar to that required by any other turbine in a power generating station.

Can Electrocution Really Kill You?

Although cartoons tend to show a person being fried due to electrocution as the body flashes like fireworks with the bones visible to everyone, in reality, things do not work that way. Electricity does not actually fry you – unless you are struck by a thunderbolt. However, only a frighteningly miniscule amount of electricity is enough to snuff out your life.

At the beginning, it is necessary to get some facts clear. Some major units used by electrical engineers are – volts, amperes, watts, and ohms. Volts describe the difference in potential across two points, while amperes describe the amount of current flowing between the two points. Watts is a measure of the power flow between two points, and is the product of volts and amperes related to the two points. Ohm measures the resistance of a substance to the flow of current through it.

Plumbing offers a suitable analogy. Volts can be equated to the water pressure between the two ends of a pipe. Current is the same as the flow rate, while resistance is similar to the inner diameter of the pipe. As you increase the volts or the pressure, current, or water flow increases, assuming the diameter or resistance of the pipe has remained the same.

Scientists have conducted experiments on healthy humans to find an answer to “How much electricity is needed to kill a human?” The surprise answer is, only seven milli-amperes, for three seconds. Heart is an electrical pump and electricity reaching the heart interrupts its rhythm. The human heart goes arrhythmic and stops working when a current of seven milli-amperes passes through it continuously for three seconds. After that, the other parts of the body begin to shut down as well. Skin-penetrating Tasers do not kill, as the electric pulses they generate are of much shorter duration than that from three seconds.

However, our bodies have their own defenses against electric shock and that is why millions of people do not drop dead every minute with ultra-tiny shocks from the different electrical and electronic gadgets they always use. The major defense comes from the skin – it has a resistance of about 5,000 to 15,000 ohms. The clothes people wear add to the resistance of their skin. To break through such a formidable resistance, the static shock necessary just only to sting your skin is about 20,000 Volts. However, a person may not die from high-voltage electric shock if the electricity did not pass through the heart. If it traveled along the outside of their body, they would live, but likely with a scorched skin. This happens mostly when the skin is wet.

A lightning bolt is a different game altogether. One bolt of lightning can hit with over a billion volts. The resistance air offers to electricity is about 10,000 volts per centimeter. Therefore, for electricity simply to move current through 10 cm of air, the voltage required is 100,000 volts, and this is between the cloud generating the electricity and the earth below our feet. As high-voltage electricity or lightning takes the path of the least resistance when passing to the earth, it passes through the outer surface of the body, scorching the skin.

Wing Waves Can Generate Electricity

Scientists around the world are working to perfect technology for generating cost effective electricity from oceans and seas using wings waves. Stephen Wood, an assistant professor of marine and environment systems at the College of Engineering of Florida Institute of Technology is building up on the expertise available to exploit it in a more efficient way.

A set of wing waves, also called sea fans comprise two metal structures shaped like wings. The fans are installed on the floor of the sea. There are some basic requirements for putting up the wings. The sea bottom must be sandy and about 50 feet deep from the water surface. The metal wings must be resilient enough to withstand the constant buffeting of the waves around them. At the same time, they must be flexible so that they can flap back and forth along with the seawater’s swells. The constant motion of the wings is harnessed to produce electricity eventually by rotating a coil of an AC generator in a magnetic field.

The fans are trapezoid shaped with a height of 8 feet and a width of 15 feet. They are manufactured in plants near the ocean or sea to facilitate transportation.

Like wind turbines and windmills, wing wave technology makes for a greener option for production of electricity compared to that provided by thermal power plants using fossil fuels. Clean and Green Enterprise, a firm based in Tallahassee and dealing in renewable energy choices, originally conceived this technology. Terence Bolden, a chief executive of the firm explains that the ocean swells cause the fans to swing by as much as 30 degrees from on either side of their mid positions. The fans take about 10 seconds to complete each sweep. The mechanical energy produced by the wings is passed on to the generator coil. The coil rotates at great speed in a magnetic field to produce electric current.

Wood asserts that wings strategically placed in a square mile can generate close to 1000 units of electric power. This is adequate for lighting up 200,000 homes.

Apart from being an environmentally clean option for generating electric power, wing wave technology affords several other advantages. They can be operated in any seaside area. The fans are designed to perform when the sea is calm and the swells are moderate. When there is a storm and the sea is rough, an automatic locking system renders the fans inoperable. A reasonable level of maintenance ensures that they can be in operation for as long as 20 years. Unlike wind turbines, they do not spoil the natural beauty of coasts as they are submerged under water. The structures do not cause any harm to marine life. It is crucial however, that they are not placed near coral reefs.

The current prototype, installed on offshore Florida coast, is constructed with aluminum. The research group at the university uses it to collect data related to wave motion and other issues regarding power production. The team now plans to replace it with a version made from a composite material that will be less prone to corrosion.