Automotive Batteries

In this section of the course we learned about the automotive batteries. What they are, How they work and how to check them for faults.
There are two types of batteries:
Primary cells - such as a torch battery once used throw away.
Secondary cells - such as a car battery (can be recharged but do wear out over time).

The purpose of an automotive battery is to convert chemical energy into electrical energy. A battery is an important component of the car. It supplies electrical energy to the components in the car when the car is turned off. When the engine is starting the battery provides current to the starter motor, alternator, ignition (spark plugs), fuel systems of the car etc. So without a battery a car would never work. But batteries do need to be maintained.

A battery has to be regularly inspected visually. To make sure that there is no corrosion building up on the terminals and to ensure that the terminals are attached firmly. Corrosion can build up around the battery terminals due to oxidation. This corrosion can restrict the contact surface of the wires to the battery terminals, which can result into a small voltage drop. This is bad because the components of the car wont get the full amount of voltage that they require to operate. This corrosion can then be cleaned of using a solution mixture of baking soda and warm water. This solution will neutralize the acid and allow it to be cleaned off. Loosely attached terminals can also cause voltage drop as the surface contact area to the battery is reduced. Therefore the terminals should always be attached firmly to the battery. Another thing to check for is battery swelling. Battery swelling is caused by overcharging. When a battery is being overcharged it produces hydrogen which can be explosive.
Another check that can be done is to check the electrolyte levels over each cell of the battery. In theory the electrolyte levels in a battery should only be about 1 to 2mm above the cells. Its easy to perform this check. All you have to do is remove the battery cell covers (caps on top of the battery) and check the levels visually. Low electrolyte levels can mean that the battery is leaking. If no evidence of the leaking is found it can indicate a high charging rate, or faulty cells.

Practical Class
We performed three tests on the battery of our own cars to check and see if they were in good working order. These tests were Checking electrolyte levels (explained above), Testing electrolyte specific gravity and a High rate discharge test.

Testing electrolyte specific gravity
This test shows us the strength of the acid in each individual cells of the battery. Electrolyte specific gravity test should be performed on a battery before it is topped up. If the test is done after it has been topped up the specific gravity off the acid will be low. This is because by topping it up you will be diluting the acid which means the acid is now weaker, hence the specific gravity is now lower. This test is done using a tool called the hydrometer. A hydrometer is a open ended test tube with a rubber bulb at one end and a point at the other end. It also has a float with readings inside it. To perform this test you undo the cell cap, introduce the hydrometer into the electrolyte and slowly squeeze the rubber bulb. Release the bulb slowly and watch the electrolyte rise up in the tube until the float is floating. (Note: if you release the bulb too quickly then you will cause air bubbles into the electrolyte in the tube. These air bubbles will then cause you to get a false reading of the float). You now check the color of the acid (it should be clear, if its murky then that means that the battery plates are disintegrating. 'Signs of wear') and then take the reading of the float at the top of the electrolyte level. Record your results. You then continue this processes with each individual cell. The variation between the specific gravity readings should not be more then 50 points. If its more then that means that your battery has a fault or is worn out. Here's what the hydrometer readings mean 1265 = 100% charge ... 1250 = 95% charge ... 1230 = 75% charge ... 1200 = 50% charge and 1175 = 25% charge.. If the readings for your battery are lower than the spec here or below 25% charge, then that means that your battery is flat and needs to be charged. The best way to charge a battery is to slow charge it. Using 4amps for about 10 to 12hours and then letting the battery sit for 24hours. When you let the battery sit, it lets the acid settle down and rise up to its state (charge level). Perform the test again. If your readings are higher than the spec, that means that the battery is carrying extra charge (surface charge) or that your battery acid strength is stronger. This is not a bad thing.

High rate discharge test
The high rate discharge test is a load test which shows you your battery's ability to supply cranking voltage. The battery has to be at least 50% charged, any lower will mean that the readings you'll get will be unreliable. If battery charge is lower than 50%, then the battery should be recharged (as explained above). The load applied to the battery is going to be half the battery's CCA. (E.G: if the CCa is 400 then the load applied is going to be 200Amps). The load should be applied for 10secounds and the battery must hold a voltage above 9.5V when the load is being applied. The load is applied using a load tester. Before you connect up the load tester make sure that load controller is off. If its not off and you connect it to the battery, it could cause a spark. Which can result in the battery exploding. After that you connect the positive lead to the positive terminal of the battery and then the negative lead to the negative terminal of the battery. Apply the specified load by turning the load control knob. Wait for the specified time and take the voltage held and load current readings. Turn of the load tester and disconnect the load tester's leads in the reverse order (negative first then the positive). If the voltage held reading was above 9.5V it means that the battery is in good working order. But if the reading was below 9.5V. That would mean that the battery is not capable of supplying the voltage required. This is bad in your car as it means that the electronic components in the car wont get the voltage they need to operate properly. It is advisable then to discard the battery.