Starter vs alternator: Know the secrets differences.

You might be wondering which between these two key components plays a major role in the vehicle’s starting system, starter vs alternator? Furthermore, which one between the two is responsible when the car won’t start?

Which are the roles of the starter and alternator in the combustion engine starting process? Such information is crucial for any car owner or enthusiast.

So, explore the importance of as we distinguish between these two essential electrical components. When you turn the key (or push the start button) to start your car, it’s not just a simple spark that ignites the engine.

Several elements work together seamlessly in coordination to facilitate the combustion process. The starter motor is responsible for initiating this process by engaging with the flywheel and cranking over the engine.

Afterwards, the alternator generates electrical energy and keeps all systems powered once your engine is running. You’ll be better equipped to diagnose issues and ensure smooth operation after this article.

Because you’ll get an understanding of how these vital components function within your automobile. So let’s take a closer look at starters and alternators and unravel their significance in your vehicle’s starting system.

The starting system: Overview.

The starting system plays a crucial role in initiating engine operation. It consists of various components, including the battery, starter motor, ignition switch, and more.

The primary function of this system is to crank the engine for ignition. Here’s a breakdown of the key components and their functions:

1. Battery.

The starting system relies on the battery to provide enough power to initiate engine cranking. Battery voltage flows to the starter solenoid.

Afterwards, the solenoid transfers that electric current to the starter motor. The battery stores electrical energy for use during engine startup.

2. Starter motor.

The primary role of this component is engine turn over. The starter design is for engaging with the flywheel or flex-plate to rotate it and facilitate engine cranking.

The starter converts electric current flow into mechanical energy since it causes the starter to start spinning. When you turn the key or press the start button, it activates the starter motor.

3. Starter solenoid.

It’s usually mounted on the starter motor housing. The starter solenoid facilitates electric current transfer to the motor when you hit the start button.

Low electrical current flow from the solenoid activates and pushes the starter gear into the flywheel. This is the role of the solenoid as an electrical switch and a mechanical actuator.

However, a faulty starter is unable to facilitate this process. That’s why you’ll notice a clicking sound when you try to start the car.

4. Ignition switch.

The role of an ignition switch is to be a control mechanism for starting and stopping the engine. The ignition switch in older vehicles uses a key while modern models use a button.

A key ignition switch has various modes including; Off, on, accessories, start. All allow different activities to take place in the electrical system. However, sometimes, the key may get stuck in the ignition.

Hence hindering normal operation. It allows you to engage or disengage the starter motor when needed. A signal is sent to the starter motor when you engage the vehicle ignition.

5. Electrical system.

The starting system is part of a larger electrical system in your vehicle. All the electrical current flow begins with the starter hence its importance.

The car electrical system connects various terminals, gears, and parts to ensure smooth operation. There are several electrical system problems that may interfere with the smooth operation.

Combustion engine starting process.

The starting process is a coordination of different parts of the vehicle’s electrical system. When you want to start your vehicle’s engine, here’s what happens:

  • You insert and turn the key or press the start button.
  • The ignition switch sends an electrical signal to activate the starter motor.
  • The starter motor engages with either the flywheel (in manual transmissions) or flexplate (in automatic transmissions).
  • As a result, it cranks and rotates the engine until combustion occurs.

If you encounter any issues with your vehicle not starting properly, there are several things you can check:

  • Ensure that your battery has enough power by performing a voltage check.
  • Check if any component within the starting system is faulty or requires replacement.
  • If your battery is weak or dead, jump-starting it using jumper cables can help get your vehicle running.

Starter vs alternator.

Open Car engine hood

Both the starter and alternator play crucial roles but have distinct functions. While the starter gets things moving initially, the alternator ensures a continuous supply of electricity when the engine is running.


The starter is responsible for initiating engine rotation. It kickstarts the engine by turning the crankshaft, allowing fuel combustion and power generation to begin.

The crankshaft is responsible for creating the motion that drives car wheels. It changes the pistons up-and-down motion into a rotation motion.

However, people often confuse between the crankshaft and the camshaft. While the camshaft opens and closes the engine’s valves, the crankshaft controls engine pistons.

The timing belt is responsible for synchronizing the motion of these two engine components. Back to our discussion about the starter.

The starter begins its operation when the ignition is engaged. This engagement causes the starter motor to engage with the engine flywheel or flex-plate.

Afterwards, the flywheel or flex-plate turn to crank the engine. The flywheel is found in manual transmissions while the flex-plate is found in automatic transmissions.

The main difference between the flywheel and flex-plate comes in their design and function. Flex-plate connects torque converter and engine crankshaft, however, the flywheel connects the clutch to crankshaft.

Flywheel and flex-plate are usually a contact between the starter motor and the engine’s crankshaft. Once the starter motor engages the flywheel or flex-plate, they turn and cause the engine’s crankshaft to rotate.

Hence cranking the internal combustion engine. Afterwards, the engine starts running until the disengaging of the starter by turning it off. This is where the alternator comes in.


Alternatively, the alternator generates electrical power once the engine is running. It converts mechanical energy from the engine into electrical energy.

The alternator connects to the crankshaft and it’s belt-driven by serpentine belt or V-belt. The crankshaft rotation allows for the turning motion of the belt which drives the alternator.

Alternator belt charges the battery and power various electrical components in the vehicle. The engine’s mechanical energy converts to electrical current called alternating current.

The alternator main role is to preserve the car battery life by keeping it charged at 12 volts. The alternator voltage regulator ensures that the electrical output doesn’t exceed a constant voltage.

Understanding these differences between starters and alternators helps in recognizing their individual contributions to a vehicle’s operation.

Understanding the differences.

Starters and alternators play crucial roles in a vehicle’s electrical system. However, they work together harmoniously to keep your vehicle running smoothly throughout its life.

These remarkable components do their job with precision to facilitate turning on your car or working electrical components. For example, headlight bulbs and other interior car accessories.

Let’s dive into the key differences between these two components. We are going to categorize the differences for better understanding.

1. Consequences of failure.

A failing starter will have different symptoms. However, a main symptom is that the vehicle will not start. Furthermore, you’ll notice a whirring sound, clicking sound or even smoke and burning electrical smell.

A faulty alternator has different causes as well consequences. It causes battery discharge and electrical system issues.

However, the vehicle will still run but for a short period of time. Because the car battery charge will be depleted and this will cause the car to stall mid-journey.

2. Replacement intervals.

The starter has a long lifespan and its replacement within the car maintenance schedule only takes place after it’s worn out. However, intervals of replacing the starter are longer than for an alternator.

Alternator replacement also takes place after the accumulation of a lot of mileage. For example 100,000 mileage. However, when you notice that the battery keeps dying, it could indicate a failing alternator.

Therefore, at this point, a replacement is necessary for continuous operation. Furthermore, there will be more symptoms that point to a failing alternator.

3. Activation process.

The starter is activated by the ignition key or button. Afterwards, it turns the flywheel or flex-plate which start the engine by cranking it.

Alternatively, once the engine starts running after cranking, the alternator is activated. It is driven by the alternator belt to convert mechanical energy into electricity called alternator current.

4. Power supply.

The car battery is responsible for power distribution to the starter. After power reaches the starter solenoid, it goes to the starter motor which engages the flywheel or flex-plate.

The alternator relies on the motion of the crankshaft to produce electric power. When this power is produced it goes to the car battery and the other electrical components.

5. Location.

The starter location is close to the flywheel or flex-plate which connect to the crankshaft. This facilitates its function of cranking the engine during ignition.

The alternator is driven by a belt and it is located near the front of the engine. It connects to the car battery in order to supply power for charging the battery.

6. Difference in designs and mechanisms.

Starters use high-torque motors that can handle the initial load required to get your engine running smoothly. They engage with a small gear called a pinion gear that meshes with the engine’s flywheel teeth.

Alternators consist of several key parts, including stator windings, rotor assembly, diodes, voltage regulator, and pulley system. As your engine rotates, it drives a belt connected to the alternator pulley.

This rotation generates alternating current (AC) within the stator windings which is then converted into direct current (DC) by diodes.

Causes of problems for starter vs alternator.

There are different things that prevent optimal performance of the starter and the alternator. Be on the look out for the following;

1. Worn out brushes.

Starter problems are commonly experienced when the brushes inside the starter become worn out. The brushes responsibility is conducting electricity and allowing the starter motor to function properly.

When they wear down, it can lead to difficulties in starting the engine. The effect of time causes the brushes to wear out after their prolonged use.

2. Solenoid issues.

Another common cause of starter problems is issues with the solenoid. The solenoid acts as a switch that connects the battery to the starter motor.

If it malfunctions, it can prevent the necessary electrical current flow from reaching the starter motor. Hence resulting in vehicle starting issues.

3. Car battery problems.

On the other hand, battery problems often stem from old age or extended periods without use or charging. Disconnect the battery if you’re going to leave your car battery for a long time without using it.

Over time, batteries naturally degrade and lose their ability to hold a charge effectively. If a vehicle is left unused for an extended period without being charged, it can lead to a drained battery.

4. Faulty diodes.

Faulty diodes are a frequent culprit behind troubles. Diodes within the alternator convert AC current into DC current that charges the battery and powers various electrical components of the vehicle.

If these diodes fail, it can result in insufficient charging of the battery and potential electrical malfunctions.

5. Worn-out belts.

Worn-out belts can also cause alternator problems. The belt connects the alternator pulley to the engine’s crankshaft pulley.

Hence enabling power transfer between them. If this belt becomes damaged or excessively worn over time, it may slip or break altogether.

This will lead to decreased power generation by the alternator. Which means low power supply to the battery and other electrical components.

Diagnosing Starting Problems

Now that you have a better understanding of starters and alternators, it’s time to diagnose any starting problems you may be experiencing.

If your car is having trouble starting or you hear a clicking sound when turning the key, it could be a sign of a bad starter.

Alternatively, if your battery keeps dying or your electrical system is acting up, it might point to an issue with the alternator.

To determine which component is causing the problem, start by checking the battery connections for any corrosion or loose terminals. If everything looks good there, try jump-starting your vehicle.

If it starts successfully with a jump but won’t start on its own, it’s likely a faulty starter. However, if the battery fails to hold a charge even after being jump-started, then the alternator might be at fault.

Remember, diagnosing car issues can sometimes be tricky and may require professional assistance. Consult with a qualified mechanic if you’re unsure about what’s causing your starting problems.

Furthermore, you might in need of help when fixing the starting problems. Don’t hesitate to consult a qualified professional.

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