Thursday Tip: How Does My Car Generate Electricity?

& What can go wrong?

Your car’s electrical system consists of the battery, starter and alternator. The battery provides the power to the starter in order for the start to literally start your car. Then, once the car is started the alternator provides the battery with the power that it needs to charge and the battery gives the charge to the electronic control module (ECU) which in turn controls the power going to the electrical items in the car such as lights, power steering, sensors, comfort module etc. Thus, if one of these chains in the system is not working as it should that the whole system will not run properly and as such the car is not running efficiently if at all.

Let’s have a look at each of these components in turn.



Before the engine starts, the battery provides the car’s entire electrical current until the vehicle starts, including current to the starter, ignition, and fuel systems responsible for creating the combustion necessary for your engine to function.  As a result, the power that the battery generates to crank the starter motor is far greater than in running conditions. As the battery needs to produce enough output to move the starter, the battery has to have a rating capable of doing this. Thus, each battery has a raking that shows the maximum current to crank the starter. If a smaller battery is used or one with the wrong rating, this affects the battery’s longevity and could also damage the whole electrical system.

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While the battery supplies the power to start your vehicle, the starter is, as we have seen, the component that gets the engine started. So, first, the battery delivers a certain amount of power to the starter motor. The starter then rotates the flywheel, which turns the crankshaft and begins the movement of the engine’s pistons.  This causes the compression that ignites the fuel in the top of the chamber, allowing power to be generated to continue this process automatically and provide mechanical power from the engine to produce the car’s motion. This intricate process is why it’s key to make sure the starter works.

However, it is virtually impossible to know when a starter will fail.  That said, there are many warning signs that you can look out for as prevention is far better than a roadside breakdown. These include the draw from the current that the starter is taking, as an excessive current draw will indicate a worn starter, while a low current draw points to corroded cables or connections. Slow to start or to take several attempts to start can also mean starter problems and, of course, the wrong or a worn battery can damage the starter. This is especially true of Stop/Start systems, where the battery provides numerous high-power charges each time the car starts.  

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After the starter has started the car and the engine is now running, the alternator takes over, keeping the battery charged and ensuring that the current produced is in keeping with the system’s electrical requirements. As such, cars can start with a faulty alternator, but it will not keep the car running over some time. More than likely, the battery will have drained flat before the car was stopped with a faulty alternator and so even though it is feasible to start the car, it will not start. If the alternator requires replacement, the vehicle’s electrical system will perform erratically, the battery will discharge, and eventually, the engine will lose power.

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Electronic Control Unit (ECU)


The vehicle’s ECU is a micro controller that controls one or several electrical systems in the car. It monitors and informs the electrical systems of what, when and how to operate.  There can be over 100 ECU’s in some vehicles, each controlling different elements like engine performance and power steering, control comfort, and security features, such as parking assistance, memory seats, and airbag deployment. Therefore, any change to the electrical input to these devices can have catastrophic results on the vehicle they are in.

To function correctly, the ECU needs to receive inputs from one or several parts of the vehicle and takes steps on the information provided.  For example, an airbag ECU receives information from crash sensors and seat sensors. When there is a crash, the ECU decides which airbags to deploy depending on where people are located within the vehicle. Then it tells the actuators to deploy them. Then the actuators convert the electrical signal into the physical value needed, using valves, injectors or relays. Thus, to work correctly, the ECU needs to receive current from the electrical system. An incorrect or inadequate current and the system might not work, making the car dangerous to drive.

Alternator / Fan / Drive Belt


The loop between the engine and the alternator is made via the belt. The belt is driven by the crankshaft pulley that runs from the engine’s crankshaft and another pulley that is forced to turn on the end of the alternator. The belt has a series of teeth that run along one side of the belt, which generates traction, allowing the belt to grip the shafts it connects to and keep it from slipping off at any point. The belt transfers rotational power from one place to another in the engine.

The belt’s wear signs are usually detected by the belt’s loud squeaking noise when it starts to slip. In addition, as it wears thinner, the texture of the belt changes to cause a loud squeaking as it makes contact with engine shafts. This is a clear sign that you need to have your fan belt replaced, as decreasing friction in the engine will increase the engine’s overall performance. It will also mean that the belt will last longer and will have to be replaced less often.

Get it Checked!


As we have seen, a car’s electrical system is critical. Therefore, car drivers must understand what the electrical system in a car does and how it operates.  As with anything, if problems are left unchecked, no matter how big or small they are, they can wreak havoc on other parts of the electrical system, like alternators and starters.

Read more tips on Batteries and Car Electronics

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