Battery. Student booklet

Transcription

1 Battery Student booklet

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3 Battery - INDEX :51 Battery Batteries are all over the place, in our cars, our PCs, laptops, portable MP3 players and cell phones. A battery is essentially a can full of chemicals that produce electrons. Chemical reactions that produce electrons are called electrochemical reactions. In this module, you'll learn all about batteries, from the basic concept at work to the actual chemistry going on inside a battery. You will also experience all the ways you can test a battery in a workshop, including the battery analyser. Contents The battery's function Battery types Battery plates & electrolyte Discharge Charging Connection of batteries Safety - Warning symbols Help starting Environmentally hazardous Service and maintenance The Volvo battery analyser Charging using a battery charger Charging by alternator Excercise - Volvo Battery analyser Exercise - Acid density measuring Exercise - Battery load tester Sum up Assessment INDEX -

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5 Battery - BasElbattery01.swf :49 The battery's function The battery is one of two voltage sources supplying the trucks electrical systems with current. The other is the generator. The battery stores chemical energy, which is transformed into electrical power when charge is drawn from the battery, meaning connected to an electrical load. When the engine is switched off and the generator is not charging, the battery supplies current to a number of components, such as the parking lamps. When the engine is started the battery supplies current to the starter motor, the ignition and the fuel system. When the engine is running the battery acts as an energy reserve for the generator when generator capacity is not sufficient. For instance, heating the rear window could require more current than the generator can provide at that time. 1

6 Battery - BasElbattery02.swf :49 Battery types The type of battery in most trucks is called a lead accumulator battery. It is so named because the battery contains plates made from lead and it is designed to accumulate energy. There are three main types of starter battery, low maintenance, semi-maintenance free and maintenance free. Low maintenance A low maintenance battery needs regular maintenance such as topping up the battery water. It has a number of holes sealed by plugs. Semi-maintenance free A semi-maintenance free battery needs even less maintenance than a low maintenance battery, but it still needs be topped up regularly. It has less antimony on the plates. Maintenance free A maintenance free battery does not need be topped up, and therefore it does not have any holes. It has a lead-calcium alloy on the plates. 2

7 Battery - BasElbattery04.swf :49 Battery plates & electrolyte Each plate is composed of a grid coated with a surface layer of an active material. The plates are immersed in a conductive fluid consisting of electrolyte, also known as battery acid. Because the plates consist of different materials a voltage is produced between the positive and the negative electrodes. The active materials take part in the electrochemical process when the battery is charged and discharged. When the battery is charged the active material on the positive electrode consists of porous lead oxide (PbO2). When the battery is charged the active material on the negative electrode consists of porous lead (Pb), also known as spongy lead. Electrolyte is a mixture of concentrated sulphuric acid (H2SO4) and battery water (H2O). Battery water is distilled or deionised water. When the battery is charged the electrolyte contains approximately 26 % concentrated sulphuric acid and 74 % distilled water. Acid density is 1.28 g/cm3 at +25 degrees Celsius. 3

8 Battery - BasElbattery05.swf :50 Discharge When charge is drawn form the battery, that is when it is connected to an external electrical load, a chemical reaction starts between the electrodes and the electrolyte. The stored chemical energy is transformed into electrical energy and current flows through the circuit. This process is called discharging. During the discharge process the active material on the negative and the positive electrodes (lead (Pb) and the lead oxide (PbO2) is transformed into lead sulphate (PbSO4). During this reaction the active material on the plates use up the sulphuric acid (H2SO4) and water (H2O) is formed. This results in a decrease in the electrolyte density since water has lower density than sulphuric acid. During discharge this density continues to decrease. After discharge the electrolyte is almost completely transformed into water. Then acid density is 1.12 g/cm3 at +25 degrees Celsius. 4

9 Battery - BasElbattery06.swf :50 Charging While charging the battery the process is reversed. There is a reversed chemical reaction and the battery's capacity is restored. During the charging process the active material on the electrodes is transformed from lead sulphate (PbSO4) into porous lead (Pb) on the negative electrode and into lead dioxide (PbO2) on the positive electrode. Water (H20) is consumed and sulphuric acid (PbSO4) is formed. This results in the density of the electrolyte increases again. At the end of the charging process there is formation of gas. The water in the electrolyte begins to disassociate and forms oxygen (O2) and hydrogen (H2). Note that explosive oxyhydrogen can form. Oxyhydrogen is highly explosive which means that there is a high risk of explosion in the vicinity of the battery. 5

10 Battery - BasElbattery08.swf :50 Connection of batteries Trucks in most countries have two batteries connected in series. They can also be connected in parallel, but this is not as common. By connecting the two batteries in series, the voltage is doubled. Batteries connected in series must be equivalent, that is they must have the same nominal capacity and voltage, and they must be the same age. When charging the batteries, each battery receives the current produced by the charger. The total voltage must not exceed the charger's stated voltage. Example: If you connect two 12 V batteries with the capacity 170 Ah in series, the total voltage becomes 12 x 2 = 24 V and the capacity 170 Ah. By connecting the two batteries in parallel, the capacity is doubled. Batteries connected in parallel do not need to be equivalent in age and capacity, but they must have the same nominal voltage. When charging the batteries, each battery receives only half of the current produced by the charger. Example: If you connect two 12 V batteries with the capacity 170 Ah in parallel, the total voltage becomes 12 V and the capacity 2 x 170 = 340 Ah. 6

11 Battery - BasElbattery09.swf :50 Safety - Warning symbols To prevent accidents it is very important to understand the warning symbols on the battery. Remember that the battery positive and negative terminals consist of lead or material containing lead. These materials are carcinogenic and can affect the human reproductive system negatively. Always wash your hands after working with batteries and battery accessories. Use protective goggles when handling batteries. When batteries are charged, highly explosive oxyhydrogen forms. Avoid sparks or open flames in the vicinity of batteries as these may ignite the explosive oxyhydrogen gas that is formed when charging a battery. Smoking, welding, grinding or the use of open flame in the vicinity of a battery could cause the battery to explode and cause personal injury and serious damage to the car. Charge batteries in a well-ventilated area. Batteries contain sulphuric acid that can cause serious corrosive injuries. If sulphuric acid comes into contact with your eyes, skin or clothes, flush with copious quantities of water and seek medical advice. Contact a doctor immediately if acid splashes into eyes. Always keep batteries out of the reach of children. Additional information about batteries can be found in the trucks instruction manual. 7

12 Battery - BasElbattery10.swf :50 Help starting If the battery is discharged you can take current from another battery or vehicle using jumper cables. Connect the positive lead from the positive terminal on the auxiliary battery to the positive terminal on the battery that needs charging. Always connect the lead to the auxiliary battery first. Connect the negative lead from the negative terminal on the auxiliary battery to ground on the vehicle with the battery that needs charging. Connect the lead away from the battery to prevent sparking near to the battery. Connect this lead last to avoid short-circuiting. Always connect the lead to the auxiliary battery first. 8

13 Battery - BasElbattery11.swf :50 Environmentally hazardous A lead battery contains environmentally and health hazardous substances such as lead and sulphuric acid. Recycle old batteries so that dangerous materials are not disposed of in the environment. Always handle used batteries as hazardous waste. Follow your country's handling guidelines. 9

14 Battery - BasElbattery12.swf :50 Service and maintenance A battery requires care and maintenance to work efficiently over a long period. It is important to clean the battery. Dirt on a battery can cause creep currents between the battery terminals. Check the battery for loose or dirty terminals. Check that battery leads are not worn, oxidised or damaged. If the battery is cracked, is leaking or if a terminal is loose or bent, discard it. Check that the battery is properly secured. Otherwise, the positive terminal can come into contact with the frame and cause a short-circuit. Check the battery acid level regularly as the water in the electrolyte is consumed during charging. Measure the acid density using a battery hydrometer or a refractometer. Always take readings at room temperature. Check the density in all cells. If the density is low the battery needs charging. 10

15 Battery - BasElbattery13.swf :50 The Volvo battery analyser To test and check Volvo batteries (and to some extent other batteries) use the Volvo Battery Analyser. This instrument provides information about battery status and suitable corrective action. This instrument can be used to test the performance of an individual battery, balance several batteries with similar capacity or test new batteries. The analyser can also be used to test the start system and/or charging system, such as generator, charging regulator and diode ripple, which saves a great deal of time. You can transfer the test results from the Volvo Battery Analyser to a PC using the instrument's IR link. An IR link is a wireless link using infrared light to transfer data. Then you can print the results from your PC and show the customer the battery status. Read the service literature to get more information. 11

16 Battery - BasElbattery14.swf :50 Charging using a battery charger Always charge the battery in a well-ventilated space so that oxyhydrogen is removed. Maintenance charging Maintenance charging can be used to compensate for the self-discharge of batteries that are already charged. Maintenance charging means that you use a very low charging current, ma. Set the charging current to 0.1 ma for each A of the battery's CCA number or 1 ma for each Ah of the battery's Ah number. Maintenance charging is a continuous process and has no specified charging time. Long-term charging Long-term charging is used for charging batteries that have gone flat. Long-term charging means that you set the charging current to approximately 1% of the battery's CCA number or 10% of the battery's Ah number. The charging time is approximately 20 hours. This depends on the battery's charge when the charging process starts, the charging current and the battery's CCA or Ah number. Ensure that temperature during charging does not become too high. A temperature above +50 degrees Celsius is not good for the battery. The battery is fully charged when its acid density reaches 1.28 g/cm3 and gas begins to develop in the cells. 12

17 Battery - BasElbattery15.swf :50 Charging by alternator When the battery is in the truck the generator charges it. The generator transforms the engine's mechanical energy into electrical energy. When the engine is switched off the generator is not charging the battery. However, the battery does supply a number of components with power. This means that the battery is discharged when the engine is switched off. This discharge depends on how much power the components connected use. When starting the engine the battery is subjected to a heavy load that discharges it rapidly. When the engine is running the load decreases and the generator begins to charge the battery. Once the battery is fully charged the charging stops. If the generator's capacity is too low, the battery will supplement the generator when many large power-consuming components are connected. This means that the battery discharges until the load decreases. 13

18 Battery - BasElbatteryexcer16.swf :50 Excercise - Volvo Battery analyser Perform the following tests with the Volvo battery analyzer: 1) Batteries only (balance battery pairs) 2) Charging system 3) Full system 4) Transfer the obtained test results to a computer using the IR transfer kit. Go through the results together in the group. 14

19 Battery - BasElbatteryexcer16b.dcr :51 Exercise - Acid density measuring Perform measurements on the battery acid density. The value read from the instrument should be around 1.28 g/cm3 at +25 degrees Celsius. That is to say, if the battery is Ok. 15

20 Battery - BasElbatteryexcer16c.swf :51 Exercise - Battery load tester You use this tool to be able to put load on the battery. In this way you can get a good picture of how it bahaves under pressure. If the battery is weak or not. Perform measurings with the battery load tester. Perform the measurings on several batteries. Also on batterie pairs. 16

21 Battery - BasElbatterysumup17.swf :51 Sum up The root cause is poor maintenance i.e. to less recharging during the time the trucks gets into full operation. It is no problem with the batteries them self. A tool to measure the batteries will highlight the NEED of recharging but will never solve the discharging so this is a matter of handling and maintenance and not a component failure. The density of the electrolyte is measured with an air gauge-type densimeter. The density depends on the concentration of sulfuric acid and it varies with the temperature. Density increases when the temperature goes down and it decreases when the temperature goes up. The electrolyte of a fully charged battery has a temperature of + 27 C and a density of 1.25 g/cm³. 17

22 Battery - BasElbatteryassess18.swf :51 Assessment 1) What happens in a battery when it is discharged? 2) Can you read out what battery performance the battery should have just by reading the specifications? 3) How many volts do you get if you connect two batteries in series? 4) How should you do when you need to help start a vehicle where the batteries have gone flat? 5) Why is it important to clean the battery? 18

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