A Car’s Starting System Explained
— September 26, 2019 | 2 min read
The simple act of turning a key (or pushing a button) to start an engine is second nature to most of us. What you may not be aware of, though, is that there are multiple electrical hardware components that work together to start an engine. It is useful to know about these components and processes, particularly if you have ever had any trouble starting your car or are looking at upgrading any of these components. It helps you to “talk shop” with mechanics, auto electricians and parts retailers, and do some preliminary diagnosis of any starting system issues you may have.
So what are the key components of a car's starting system? Read on to find out!
BATTERY
The battery could be described as the heart to your car’s electrical system. It’s a key component to supplying current to the starter motor, keeping a current to the ignition system whilst cranking, regulating power throughout the car and providing extra electricity when needed (when the alternator cannot generate as much power as the car currently needs).
Batteries are measured in Cold Cranking Amps (CCA) which essentially is how much current a battery can produce for 30 seconds, at 0 degrees Celsius, before the battery voltage drops below 7.2 volts. Each make and model of car requires a different amount of CCA in a battery as well as its physical size, so be sure to get a battery strong enough to properly operate in your car.
Most modern batteries are maintenance free, but even they need periodic inspection and cleaning to ensure they stay working as intended. One of the main maintenance items on a battery is ensuring the battery terminals and cables are kept free of corrosion and are secured to the battery, as vibration over time can sometimes loosen them.
BATTERY CABLES
Battery cables are large multi-stranded wires designed to carry the high current necessary to power the starter motor, which is one of the most electrically draining processes your car will go through. The number of cylinders, fuel capacity and fuel type your car has will decide how much current is required to successfully power the starter motor to start your engine.
It’s worth mentioning that you can increase your diameter size when upgrading your battery cables, but never decrease diameter size.
Quick size conversion reference:
8 Gauge – 8mm2
6 Gauge – 14mm2
4 Gauge – 20mm2
3 Gauge – 25mm2
2 Gauge – 32mm2
0 Gauge – 50mm2
STARTER RELAY
An electrical relay is a simple but clever device that acts as a switch, allowing a large amount of current to pass through it when activated by a smaller current. In the case of a starter relay, the larger current is the power being drawn from the battery, through the thick battery cables in order to start the engine. Running this power through a starter relay allows the ignition wiring that runs through the rest of the vehicle (such as to the ignition switch where you turn the key, or push the start button) to be much smaller in size/diameter, saving space throughout the car.
STARTER MOTOR
Yes, your vehicle has more than one motor in it! The starter motor has the important job of cranking the engine over (in the right direction!) before it is capable of powering itself with the ignition of fuel and air. Once the current from the battery cables reaches the starter motor, it begins to quickly turn the engine’s flywheel, which rotates the crankshaft whilst the fuel and ignition systems work together to produce combustion strokes in each cylinder. Once the engine has enough power from combustion to crank itself, the starter motor disengages from flywheel to protect its mechanism from wearing out.
IGNITION SWITCH
An ignition switch is what your car key is inserted into (which has been superseded by a ‘Start Button’ in newer cars). The switch is what distributes the electrical current throughout the above electrical components to switch on or off a car’s engine and accessories. There are generally 5 positions or settings that an ignition switch or button can be set to:
- Lock
This is the setting that your car sits in when it is not in use and the key is out of the switch. This keeps all circuits open (not supplying any current) and locks the steering wheel in place to prevent theft and movement of the wheel.
- Off
This is when a key is inserted into the switch but not yet turned. All circuits are open (no current is supplied) but the steering wheel is unlocked and can be moved.
- Accessories
The first click of a key (or a single button press for push-button-start). Power is supplied to all electrical components in the car except the ignition and starter circuits. This means that the sound system will work, windows will be able to be operated, heater will run, but the engine will not run.
- Run/On
Once in this position, the fuel pump may prime and multiple dash lights will appear to light up, related to the various sensors used by the engine, its ancillaries, and safety systems such as airbags, ABS and traction control to indicate they are all functioning correctly. In vehicles that use an ignition key, this is also the position the key will remain in once the car has been started. Vehicles that use a push button start may combine the accessories and run/on stage with the first push of the button, or they may enter a separate run/on stage if the start button is pushed without the clutch or brake pedal depressed.
- Start
This is the spring-loaded, fully turned position that you turn your key to (or press and hold the start button for), in order to engage the starter motor and begin turning over the engine. When turned to this position, power is usually supplied only to the fuel and ignition systems, plus the starter motor to ensure maximum cranking capacity of the battery and protection of other electrical systems in the vehicle, which is why radio and climate control will turn off for a moment during this process and resume once the engine has started. This position is only used until the engine is running, at which point releasing the key will return it to the run/on position. Engine is driving the alternator and generating electrical power, which then gets passed through the vehicle’s electrical system and charges the battery for the next time it is needed to start the engine.