Rechargable Batteries: A Lifesaver?

Have you wondered why the 12-volt battery that is in your car is so much heavier and larger than the 12-volt battery in a small portable radio? The answer is that the power rating of a battery is a measure of how much amperage or electric current the battery can provide over a period of time. An automobile requires extremely large amounts of current flow in a short amount of time.

A portable radio consumes very little current compared to many other large electric appliances like a large stereo or big a screen TV. The battery that powers a small radio can be smaller in size because the radio does not consume large amounts of electricity.

The science of batteries is a very complex science. It has always been a challenge to build a small battery that can deliver large amounts electrical energy over long periods of time. The electrical energy in a battery is created by the reaction between different types of chemicals and metals. The chemical reaction that takes place forces the atoms in the metals to give up some of their electrons. These electrons are stored as potential energy or EMF (electromotive force). When the battery is connected in a circuit to a device the EMF causes the current to flow through the circuit.

For many years lead has been used as a metal in batteries. However, lead is a very heavy material and is not good choice for rechargeable battery construction. Recently scientists have developed batteries using different types of materials. These new materials like Nickel Hydrogen have better electrical output characteristics than the traditional lead materials used in battery construction. They are also lighter and provide more energy per volume than lead acid batteries.

The ISS is equipped with Nickel Hydrogen battery assemblies. The batteries in the ISS are fully rechargeable battery assemblies connected to the Photovoltaic arrays of the space station. The batteries on the ISS must have enough capacity to supply 78 kW of continuous power to the station while it is behind the earth and unable to generate its own electricity. This has been a very challenging problem for the NASA scientists due to the weight and size restrictions of items on the ISS.

If the ISS batteries are typically fully charged when going into the eclipse portion of the orbit in the earth’s shadow. They will be drawn down to a 65% charge level during this 30-minute portion of the orbit. If the PV arrays of the ISS become damaged there is only enough power in the batteries to complete one full 90-minute orbit around the earth.

















 

Electromotive Force
The amount of force that causes electrons to flow in a conductor is called electromotive force, which is abbreviated “emf”. This force can be created in several ways. One way is a chemical reaction between different kinds of chemical solutions and metal. This chemical reaction produces many free electrons. This type of emf is called a cell. A group of cells together are called a battery.

The amount of current flow that can be produced by a cell is limited. As the electrons in the material that the cell is made from are depleted, the amount of emf is reduced proportionally. That is why we need to replace batteries in flashlights and other electronic devices. Some batteries are made up of materials that are not eaten away as the electrons are given up. The depleted electrons in these cells can be replaced with new electrons. These batteries are called rechargeable batteries and are the types of batteries we find in cars, in computers, and in many electronic devices.

The measuring unit of emf is called the volt. An ordinary “D” size flashlight cell battery generates an emf of about 1.5 volts. This is the force that pushes the electrons through the circuit or conductor. If we again compare electricity and current flow with water flow, the emf would be the amount of water in a mountain lake that supplies the water in the stream.

Most electric devices require much more energy or emf than a small flashlight cell or battery can create. Larger cells or batteries are necessary to provide enough emf to power electric devices. The ISS (International Space Station) is equipped with many batteries to supply its electrical power, and these batteries are rechargeable batteries that are charged by light energy from the sun. The light energy or rays from the sun are changed into electrical energy by a photovoltaic cell.

Drawing of light rays hitting a device out-putting electrons