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About battery and batteries suppliers
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About battery and batteries suppliers
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County Battery Services UK Home
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ABOUT BATTERIES |
All batteries have two terminals. One battery terminal is marked (+), or positive, while the other battery terminal is marked (-), or negative. In normal torch batteries such as an AA, C or D cell - and watch batteries, the ends (top and bottom) of the battery are the terminals. In large batteries like a car or truck battery, there are two lead posts terminals. . Within the battery a chemical reaction produces the electrons, electrons gather on the negative terminal of the battery. The speed of electron production by this chemical reaction (the internal resistance of the battery) controls the quantity electrons which flow between the terminals. Electrons flow from the battery into a cable, and must travel from the negative to the positive terminal for the chemical reaction to take place. That is why a battery can be stored for up to a year or more and still have ample power -- unless of course electrons are still flowing from the negative to the positive terminal, in which case the chemical reaction does not happen. Once a cable is connected the reaction will start.
The very first battery was created by Alessandro Volta (Volts, Voltage) in 1800. To make the battery, he built a stack of alternating layers comprising; zinc, absorbant ( blotting) paper soaked in salt water and silver.
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This formation is known as a "voltaic pile." each end or top and bottom of the stack must be different metals. If we place wire to the top and bottom of the voltaic pile, we can measure a voltage and a current from the voltaic pile. The voltaic pile can be stacked as high as managable, each and every layer will increase the voltage by a certain amount. We can recreate a voltaic pile with coins and kitchen towel. With salt with water, add as much salt as the water will absorb and soak the paper towel in this solution. Then make a stack of alternating pennies and five pences - or two pences and ten pences. See what kind of voltage and current the pile produces. Try a different number of layers and see what effect it has on voltage. Try aluminum foil and steel, each metallic combination should produce a slightly different voltage. |
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To do these experiments accurately, you may want to buy an inexpensive (£10 to £20) volt-ohm meter contact County Battery Services UK. Another simple experiment involves a baby food jar or fish paste jar, lemon juice or vinegar , wire and nails. Fill the jar with lemon juice or vinegar (dilute acids) and place a nail and a piece of copper wire in the jar so that they are not touching. Try galvanized nails and ordinary iron nails. Then measure the voltage and current by attaching your volt meter to the two pieces of metal. Replace the lemon juice with salt water, and try different coins and metals as well to see the effect on voltage and current. In the 19th century, before the invention of the electrical generator (invented in the 1870s), the Daniell cell also known by three other names ; the "Crowfoot cell" due to the shape of the zinc electrode, the "gravity cell" because gravity keeps the two sulfates separated, and a "wet cell," as opposed to the modern "dry cell," because it uses liquids for the electrolytes. The Daniell cell was extremely common for operating telegraphs and doorbells. The Daniell cell is a wet cell consisting of copper and zinc plates and copper and zinc sulphates. To make the cell, the copper plate is placed at the bottom of a glass jar. Copper sulphate solution is poured over the plate to half-fill the jar. Then a zinc plate is hung in the jar and a zinc sulphate solution poured very carefully into the jar. Copper sulphate is heavier than zinc sulphate, so the zinc sulphate "floats" on top of the copper sulphate. Obviously, this does not work very well in a torch, but it works okay for items that are stationery. If you have access to the sulphates, zinc and copper, you can try making your own Daniell cell.
Battery Reactions Imagine that you have a jar of sulfuric acid (H2SO4). Place a zinc rod in it, and the acid will immediately start to eat away at the zinc. You will see hydrogen gas bubbles forming on the zinc, and the rod and acid will start to heat up. Here's what is happening: The acid molecules break up into three ions: two H+ ions and one SO4-- ion. The zinc atoms on the surface of the zinc rod lose two electrons (2e-) to become Zn++ ions. The Zn++ ions combine with the SO4-- ion to create ZnSO4, which dissolves in the acid. The electrons from the zinc atoms combine with the hydrogen ions in the acid to create H2 molecules (hydrogen gas). We see the hydrogen gas as bubbles forming on the zinc rod.
If you now stick a carbon rod in the acid, the acid does nothing to it. But if you connect a wire between the zinc rod and the carbon rod, two things change:
The electrons flow through the wire and combine with hydrogen on the carbon rod, so hydrogen gas begins bubbling off the carbon rod.
There is less heat. You can power a light bulb or similar load using the electrons flowing through the wire, and you can measure a voltage and current in the wire. Some of the heat energy is turned into electron motion.
The electrons go to the trouble to move to the carbon rod because they find it easier to combine with hydrogen there. There is a characteristic voltage in the cell of 0.76 volts. Eventually, the zinc rod dissolves completely or the hydrogen ions in the acid get used up and the battery "dies." The cell has one plate made of lead and another plate made of lead dioxide, with a strong sulfuric acid electrolyte that the plates are immersed in. Lead combines with SO4 to create PbSO4 plus one electron. Lead dioxide, hydrogen ions and SO4 ions, plus electrons from the lead plate, create PbSO4 and water on the lead dioxide plate. As the battery discharges, both plates build up PbSO4 (lead sulfate), and water builds up in the acid. The characteristic voltage is about 2 volts per cell, so by combining six cells you get a 12-volt battery.
Normally, when you buy a pack of batteries, the package will tell you the voltage and current rating for the battery. For example, my digital camera uses four nickel-cadmium batteries that are rated at 1.25 volts and 500 milliamp-hours for each cell. The milliamp-hour rating means, theoretically, that the cell can produce 500 milliamps for one hour. You can slice and dice the milliamp-hour rating in lots of different ways. A 500 milliamp-hour battery could produce 5 milliamps for 100 hours, or 10 milliamps for 50 hours, or 25 milliamps for 20 hours, or (theoretically) 500 milliamps for 1 hour, or even 1,000 milliamps for 30 minutes. However, batteries are not quite that linear. For one thing, all batteries have a maximum current they can produce -- a 500 milliamp-hour battery cannot produce 30,000 milliamps for 1 second, because there is no way for the battery's chemical reactions to happen that quickly. And at higher current levels, batteries can produce a lot of heat, which wastes some of their power. Also, many battery chemistries have longer or shorter than expected lives at very low current levels. But milliamp-hour ratings are somewhat linear over a normal range of use. Using the amp-hour rating, you can roughly estimate how long the battery will last under a given load. If you arrange four of these 1.25-volt, 500 milliamp-hour batteries in a serial arrangement, you get 5 volts (1.25 x 4) at 650 milliamp-hours. If you arrange them in parallel, you get 1.25 volts at 2,600 (650 x 4) milliamp-hours.
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Contact Information Unit F1, Field Industrial Estate Lowmoor Road, Tel: 01623 757 377 Fax: 01623 757347
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News Release By Peter Yexley Telephone 01707 646457
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