Yesterday I warned you about a short circuit. If you missed it, you can read it Here.
We went over simple examples of how a car’s electrical system works, but when it comes to a real diagnosis, it will get just a little more complicated.
That is because in the car, you will most likely have multiple loads in one circuit.
You have to understand what is parallel and series circuits are, and how the voltage, resistance, and current act with multiple loads in these circuits.
Warning: This might be one of the hardest lessons of this course, make sure to read it a couple of times. It is completely OK if you won’t understand it perfectly on your first time.
In a series circuit, components are linked one after another, meaning there’s just one path for the current to follow. The same current flows through all components, but the total voltage is split among them. If one component in the series fails, like a bulb in your dashboard light string, the entire circuit stops working.
In a parallel circuit, each component connects directly to the power source, so all receive the full voltage, but the current is divided among them. If one component fails, like one of the multiple headlights, the others will continue to function normally.
A series circuit is not commonly used in cars since it comes with some limitations. In a series circuit, loads have to kind of share voltage and current, which can mean not enough power for components to work properly.
We have 2x lightbulbs with 2Ω each connected in series.
The total resistance in a circuit is 4Ω and that means we will have 3A of current in the circuit calculated with OHM’s Law.
The voltage will be shared equally between lightbulbs because they have the same resistance.
The circuit starts with 12V, then the first lightbulb consumes 6V, and the remaining 6V is used by the second bulb.
But what about if we have loads with different resistances?
In this case, we have 1x lightbulb with 2Ω resistance and another lightbulb with 4Ω resistance connected in series.
Now the first lightbulb consumes only 4V (needs less voltage because of less resistance) and the remaining 8V is “consumed” by the second bulb with more resistance.
The problem with a series circuit is that with combined resistance, the current in the circuit might not be enough for both components.
One of the lightbulbs is barely turning ON, because it does not have enough current.
That’s why most circuits in the car are parallel.
A parallel circuit is most commonly used for connecting multiple loads on the same power source.
If we have a 2x bulb with 2Ω resistance connected in parallel, there will be 6A of current for each branch of this circuit.
That means we will have 12 Amps of current from a positive terminal which then splits into 6 amps for each branch.
After these branches meet again both 6 Amps of current join together and there will be 12 Amps returning to negative terminal.
Now, imagine we have lightbulbs with different resistances.
One is 3Ω and the other one is 6Ω.
We can calculate the current for each branch separately using OHM’s law.
For a 3Ω bulb, it is 4A.
For a 6Ω bulb, it is 2A.
The total starting current is 6A, then it splits to 4A and 2A, and once these wires meet again current will add up to that 6A again, returning to the battery negative terminal.
On the other hand, the Voltage will not split. It is the same for all branches in a series circuit.
Like I said in the introduction, this is complicated to understand at first. It is completely OK if you need to read it a couple of times.
P.S. In case you want to learn from a video (including parallel vs series circuit submodule) join my smart DIY mechanic program.
