Batteries

The task that had to be done was on an automotive battery and it was to check the condition of the battery by testing many different parts of the battery and checking the condition of the battery such as corrosion around the terminals and battery posts. This is just one of the basic checks that were done.

We started working on batteries in pairs in the unitec workshops as a practise session before we worked on batteries in cars but the checks are done in exactly the same way, we started by noting down the make of the battery which was a Lucas battery and the battery number which was 46G, we then noted down the cold cranking amperage (CCA) and the type of battery which is convetional.

We then carried out a visual check of the battery this is done by checking things like how tight the terminals are on the batteries positive and negative posts, whether there is any corrosion around the terminals which is seen as a yellowish or blue powder that builds up around the battery posts and can even rust metal on car body work if the battery area has not been well maintained by neutralising the acid, we then described what needs to be done to fix the problems which in the case of our practice session work there was some corrosion on the positive battery post. The way to fix corrosion is by mixing baking soda in warm water, this neutralizes the acid and prevents the acid or corrosion from spreading and effecting other areas of the car body or doing damage to the battery by creating a weaker connection at the terminals and thus creating resistance.

We then checked the electrolyte level this is another visual check in which you remove the battery cell covers on a conventional battery and check how high the level of electrolyted is, electrolyte is a mixture of 34% sulphuric acid and 66% distilled water. The level of the electrolyted should be around 1-2mm above the battery cell in our case all the cells were above the level that they should have been by about 1cm this means that there is weaker solution and could produce less voltage as the electrolye mixture is weaker than what it should be. This can also effect the life of the battery and shorten it.

We then did a open circuit voltage (OCV) test in which we test the voltage level of a battery, this is done by making sure there is nothing switched on that can drain power like a radio or interior light, as these will affect the results, you then get a multimeter set it to direct current voltage (DCV) set the multimeter to 20volts and take a reading by puuting the red probe on the positive battery post and the black probe on the negative battery post you will then get a reading which should around 12.8 volts which is what you get from a fully charged battery. If the voltage is higher than that it is known as surface charge and can be cleared by switching on the headlights of the car for 1 minute or in the case of working in the unitec workshop getting a battery load tester and setting it on 50 amps for 30 seconds to remove the surface charge as there is no other way to remove surface charge in this case. If the battery is below 12.4 volts which is classified as 50%charged then it is to discharged to carry on testing you must slow charge the battery for 10-12 hours at 4 amps and then let it settle for 24 hours.

We then did a hydrometer test which measures the specicfic gravity of the electrolyte in the battery cells, this gives and indication to the condition of each of the cells in the battery. The hydrometer test is done by removing all of the battery cell caps then getting a hydrometer and put the end of it into the electrolyte then gently squeezing the rubber bulb at the other end, now slowly release the rubber bulb and electrolyte will begin to fill the glass chamber at the point that the float inside the chamber is floating you take the reading off the float which has a scale on the side of it. Then note down the number given from the test and the cell being tested. Whilst doing this take note of the colour of the electrolyte it should be clear if it is murky then it shows the cells are disintergrating and the battery will need to be replaced soon. But if it is clear then there is nothing wrong with the cells. After taking down the readings from the hydrometer test minus the highest reading by the lowest reading to get the specific gravity variation a perfect battery should have no variation at all, but the variation is allowed to go up as high as 50 points if it is any higher than that then the battery needs to be replaced. If the specific gravity reading was low in one of the cells which it was in the pracitical session this would indicate that the cell is struggling to retain a charge and the battery would have to be replaced.

We then did a high rate discharge test, in which you get a battery load tester making sure that the loader is fully switched by turning the nob to the off position. Then hook up the tester,positve lead to positive terminal, negative lead to negative terminal. Then turn the tester up to half the the cca's of the battery which our battery was 410cca's so you turn the load tester up to 205 amps and leave it there for 10 seconds, The needle on the load tester should not move off of 205 amps and the voltage of the battery must remain above 9.5volts, The multimeter is hooked up to the battery during the test to get the voltage reading. If the tester cannot maintain 205 amps or the battery does not stay above 9.5 volts this could indicate that the battery is not charged enough to carry on testing or the battery cells are struggling to maintain charge if this is the case then the battery needs to be replaced as its life expectancy would be very short.
Then we measured parasitic draw which was not done in the assesment, this is done by setting the multimeter to milliamps then put the negative probe of the multimeter on the negative post of the battery and put the positive probe on the negative terminal of the battery now holding the negative probe in place lift up the negative terminal and a reading should appear on the mulitimeter this is the parasitic draw caused by other electrical components in the car, below 50 milliamps is an acceptable reading.

We then used a digital battery tester to test the battery this was not done in our assesment either, connect up the digital tester postive lead to positive on battery negative lead to negative on battery this will provide power to the tester and it will switch on, SAE will flash up very quickly on the screen then a number will appear make sure this number matches the CCA's of the battery. Then press test and either pass or fail will appear in our case the battery passed, then press test again and the OCV of the battery will come up then press test again and the tester will give you the calculated cold cranking amperage of the battery and in our case it came up 10 amps less than what the battery specicfied.

These were the steps that we went through to test the condition of the battery and the steps that we had to do in our assesment except for the ones that I mentioned that were not tested which was using the digital battery tester and measuring parasitic draw. In both the practice and the assesment the battery passed the test. And both were in good condition nothing needed to be done to the batteries.