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.
Thursday, March 31, 2011
Sunday, March 27, 2011
Electricity Circuits
In this section of the course we looked at simple electrical circuits that would be found in the automotive electrical industry. Within this topic there were a few new terms and tests to do. These tests were done on four different types of electrical circuits: Individual, Series, Parallel and compound circuits. The results were then analyzed and compared with eachother to get an unerstanding of how each circuit works. A few terms to remember: Voltage, Ampere, Ohms, Wattage, Voltage drop, Available voltage.
What do these terms mean?
Voltage: Voltage is the force or pressure that is required to move the electrons (current) in a circuit.
Ampere (Amps): Ampere is the measure of current. The more current in a circuit the larger the reading and vise
verse.
Ohms: Ohms is the unit of resistance. This is the resistance to the flow of electrons (current).
Wattage: This is a measure of the power that is being used by a consumer to produce an output.
Voltage drop: This is a reading that shows how much voltage is being used up (consumed) by a component in the circuit.
Available Voltage: This is a reading that shows how much voltage is available to use at different points in the circuit.
Individual Circuits
An individual circuit is a very simple circuit. It has only one consumer. Only one path for the electricity to flow through. This circuit was used to understand simple laws of electricity. The power supply was set to 12.73V. One law of electricity sates that the voltage supplied must be used within the circuit. In this case the voltage drop over the bulb was 12.71V. This means that the bulb was using this voltage to produce an output (work done), and in this case the output was light. The remaining voltage (0.02V) is being used up by the wires in the circuit to push the current through. This is caused by the internal resistance of the wires. In this circuit most of the resistance was caused by the bulb we used. This then affected the amperes (current flow) in the circuit (0.36A). By using a bigger bulb like we did in the following circuit the ampere reading changed to 0.77A. the reason being is the bigger bulb offers less resistance as it allows more current to flow through it. Since its the only consumer and a majority of the resistance holder, the overall resistance of the circuit is reduced. Therefore the current flow increases.
Series Circuits
A series circuit is the same a individual circuit except it has more than one consumer. Both the consumers are wired one after another. Meaning there is still only one path for the electricity to flow through. This creates a flaw because if one consumer doesn't work or shorts out then the entire circuit wont work as the circuit is now open and electricity doesn't have a clear path to flow. There are two rules we follow when it comes to series circuits. The first rule is that the overall resistance of the circuit is the sum of each individual resistance the circuit has. E.G: If a series circuit has two light bulbs each with the resistance of 5ohms. The overall resistance of the circuit will be 10ohms (5ohms + 5ohms). The second rule is that the voltage is shared equally depending on the resistance of each individual component in the circuit. E.G: If there are two bulbs both with the resistance of 5ohms, the voltage used by each bulb will be 6V (12V supply). But if there are two bulbs with different resistance 5ohms and 7ohms the voltage used by each bulb will be different. (5ohms uses 4V and the 7ohms uses 8V). The ampere reading (current flow) in a series circuit will be lower to that of the individual circuit. This is because the overall resistance in a series circuit will be higher than the overall resistance of the individual circuit as the series circuit has more consumers (more load on the circuit). The more number of consumers in a series circuit the lower the current flow (ampere reading) as each extra consumer adds to the total resistance of the circuit.
Parallel Circuits
In a parallel circuit each consumer has its own power supply (positive) and its own earth (negative). This is good as it means that the circuit will still work even though one consumer shorts out. This is because electricity has more than one path to flow through and if one path is closed (short circuit) electricity will just flow through the other components, as there still is a circuit. There are two rules we follow when it comes to parallel circuits. The first rule is that the voltage over each individual consumer (each link of the circuit) is the same as the voltage supplied. E.G: If three bulbs are in a parallel with a power supply of 12V, the voltage drop over each bulb will be 12V. This is because each bulb will have its own power (positive) and earth (negative). The second rule is that the overall resistance in a parallel circuit is lower than the lowest resistance. E.G: If there were three light bulbs in parallel with different resistance (5ohms, 3ohms and 9ohms). The overall resistance of that circuit will be lower than 3ohms. Lower resistance means more current flow. That's why the current flow in a parallel circuit is higher than the current flow in the series circuit. The overall current flow is higher but the current flow over each individual component is determined by its resistance. Electricity is lazy and will always try and take the easiest path. That's why you'll find that the current flow through a bigger bulb will be greater than the current flow through a smaller bulb. The bigger bulb offers less resistance than the smaller bulb and therefore more current flows through the bigger bulb. The more number of consumers in the circuit the greater the overall current flow, as the overall resistance of the circuit decreases.
Compound Circuits
A compound circuit is made up of part series circuit and part parallel circuit. Both the rules from the series circuits and the parallel circuits apply here. The parallel part of the compound circuit acts as one unit or one consumer. Since its in parallel the overall resistance of that part of the circuit will be low. Most of the resistance of the circuit will come from the components that are wired up in series (resistance = sum of all individual resistance). Since the parallel side of the circuit has lower resistance, the voltage drop (volts used) over that part of the circuit will be low and voltage drop over the components in series will be greater. The current flow in a compound circuit will be higher compared to the current flow in a series circuit. But the current flow will be lower compared to the parallel circuit. This is because the parallel side of the circuit acts as one consumer with a low resistance to flow. This affects the overall resistance of the circuit as it will be lower than a series but still higher than a parallel circuit.
What do these terms mean?
Voltage: Voltage is the force or pressure that is required to move the electrons (current) in a circuit.
Ampere (Amps): Ampere is the measure of current. The more current in a circuit the larger the reading and vise
verse.
Ohms: Ohms is the unit of resistance. This is the resistance to the flow of electrons (current).
Wattage: This is a measure of the power that is being used by a consumer to produce an output.
Voltage drop: This is a reading that shows how much voltage is being used up (consumed) by a component in the circuit.
Available Voltage: This is a reading that shows how much voltage is available to use at different points in the circuit.
Individual Circuits
An individual circuit is a very simple circuit. It has only one consumer. Only one path for the electricity to flow through. This circuit was used to understand simple laws of electricity. The power supply was set to 12.73V. One law of electricity sates that the voltage supplied must be used within the circuit. In this case the voltage drop over the bulb was 12.71V. This means that the bulb was using this voltage to produce an output (work done), and in this case the output was light. The remaining voltage (0.02V) is being used up by the wires in the circuit to push the current through. This is caused by the internal resistance of the wires. In this circuit most of the resistance was caused by the bulb we used. This then affected the amperes (current flow) in the circuit (0.36A). By using a bigger bulb like we did in the following circuit the ampere reading changed to 0.77A. the reason being is the bigger bulb offers less resistance as it allows more current to flow through it. Since its the only consumer and a majority of the resistance holder, the overall resistance of the circuit is reduced. Therefore the current flow increases.
Series Circuits
A series circuit is the same a individual circuit except it has more than one consumer. Both the consumers are wired one after another. Meaning there is still only one path for the electricity to flow through. This creates a flaw because if one consumer doesn't work or shorts out then the entire circuit wont work as the circuit is now open and electricity doesn't have a clear path to flow. There are two rules we follow when it comes to series circuits. The first rule is that the overall resistance of the circuit is the sum of each individual resistance the circuit has. E.G: If a series circuit has two light bulbs each with the resistance of 5ohms. The overall resistance of the circuit will be 10ohms (5ohms + 5ohms). The second rule is that the voltage is shared equally depending on the resistance of each individual component in the circuit. E.G: If there are two bulbs both with the resistance of 5ohms, the voltage used by each bulb will be 6V (12V supply). But if there are two bulbs with different resistance 5ohms and 7ohms the voltage used by each bulb will be different. (5ohms uses 4V and the 7ohms uses 8V). The ampere reading (current flow) in a series circuit will be lower to that of the individual circuit. This is because the overall resistance in a series circuit will be higher than the overall resistance of the individual circuit as the series circuit has more consumers (more load on the circuit). The more number of consumers in a series circuit the lower the current flow (ampere reading) as each extra consumer adds to the total resistance of the circuit.
Parallel Circuits
In a parallel circuit each consumer has its own power supply (positive) and its own earth (negative). This is good as it means that the circuit will still work even though one consumer shorts out. This is because electricity has more than one path to flow through and if one path is closed (short circuit) electricity will just flow through the other components, as there still is a circuit. There are two rules we follow when it comes to parallel circuits. The first rule is that the voltage over each individual consumer (each link of the circuit) is the same as the voltage supplied. E.G: If three bulbs are in a parallel with a power supply of 12V, the voltage drop over each bulb will be 12V. This is because each bulb will have its own power (positive) and earth (negative). The second rule is that the overall resistance in a parallel circuit is lower than the lowest resistance. E.G: If there were three light bulbs in parallel with different resistance (5ohms, 3ohms and 9ohms). The overall resistance of that circuit will be lower than 3ohms. Lower resistance means more current flow. That's why the current flow in a parallel circuit is higher than the current flow in the series circuit. The overall current flow is higher but the current flow over each individual component is determined by its resistance. Electricity is lazy and will always try and take the easiest path. That's why you'll find that the current flow through a bigger bulb will be greater than the current flow through a smaller bulb. The bigger bulb offers less resistance than the smaller bulb and therefore more current flows through the bigger bulb. The more number of consumers in the circuit the greater the overall current flow, as the overall resistance of the circuit decreases.
Compound Circuits
A compound circuit is made up of part series circuit and part parallel circuit. Both the rules from the series circuits and the parallel circuits apply here. The parallel part of the compound circuit acts as one unit or one consumer. Since its in parallel the overall resistance of that part of the circuit will be low. Most of the resistance of the circuit will come from the components that are wired up in series (resistance = sum of all individual resistance). Since the parallel side of the circuit has lower resistance, the voltage drop (volts used) over that part of the circuit will be low and voltage drop over the components in series will be greater. The current flow in a compound circuit will be higher compared to the current flow in a series circuit. But the current flow will be lower compared to the parallel circuit. This is because the parallel side of the circuit acts as one consumer with a low resistance to flow. This affects the overall resistance of the circuit as it will be lower than a series but still higher than a parallel circuit.
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