Connecting Car Battery Wrong Way Round, What Will Happen?


The car electrical system uses DC electricity. That means, the electric current is only unidirectional. So that the two poles must be connected precisely and it forbidden to reversed.

So what happens if we connect the battery cable in wrong side? will it damage the engine?

We will discuss it.

Battery Terminal Position

Battery has a box shape with two terminals located above the battery. The battery cable will be designed automatically according to the position of the battery terminals. So the incidence of the wrongly connected battery rarely occurs because the cable will not be connected if the battery is backwards.

However, when the battery died, the car owner had to replace it with the new one. If we replace it with the same type as before, the battery will not reverse.

If we use batteries from other brands, of course the position of the battery terminals can be different.

So that it is possible for wrong battery terminals to occur.

Then what will happen if I connect battery in wrong way round ?

1. Starting system does not work

The engine starting system uses an electric motor to generate rotational energy and a solenoid as a switch to start the electric motor.

The solenoid in the starting system works based on the electromagnetic force. In essence, the coil in the solenoid will turn into a magnet when it gets an electric current. The direction of the magnetic field inside the solenoid is influenced by the direction of the electric current.

So that when the battery is reversed, the magnetism inside the solenoid will reverse too. That keeps the starter motor from connecting.

So that the starter motor is not running.

But there are several types of solenoids that are not affected by the direction of the current. The solenoid will continue to work properly even if the electric current is reversed. This keeps the motor starter connected.

The starter motor uses an electromagnetic force as well. If the direction of the current is reversed, the starter motor rotation will reverse. And this makes the starting system work but the engine does not start.

2. Blown Diode rectifier

The rectifier diode is a component to make the AC current from the alternator change to DC current. So that it can be used to recharge the battery.

What happens if the battery is in the backward position?

First you need to know that the diode works by blocking an electric current on one side. So at AC current, the direction of the electric current moves in two directions. The diode will block one direction of current, so the current out from the diode has only a direction. That's DC current.

This rectifier is located between the alternator output and the battery positive main cable. And the rectifier has one ground wire.

If the battery is in an inverted position, the battery positive cable will be connected to the negative terminal of the battery, and ground will be connected to the positive terminal of the battery.

What will happen ?

The current will flow from the ground to the battery positive cable. And this will not be blocked by the diode, because the current flows from behind the diode.

The good news, it still doesn't spoil anything. Because the circuit of charging system is still cut off.

But when you press the starter button, the current will be directly connected to the battery negative terminal without load.

That is very dangerous, because if the current flowing without load, it has a very large value. The risk, the diode will burn. So you will find a thin puff of smoke from the alternator area.

3. Fuses broke

Still as we discussed in point 2, when the battery is connected in the backward position, there is a possibility that a large amount of current flows in the electrical circuit. So that all electrical systems in vehicles are at risk of damage.

But you don't need too worry, because the vehicle has fuses.

Fuse is a safety component to avoid large amounts of current from flowing across the circuit.

Fuse has a limit, if the amount of the current that passes through the fuse exceeds the limit, the fuses will be cut automatically. So that the circuit is safe.

4. Some electrical components broke

Although the circuit on a vehicle has fuse, it is designed to protect the circuit if the current flows to the fuse first. The fuse is located after the battery positive terminal before the circuit. So that when a large amount of current is detected, the current will stop at fuse.

However, if the battery in backward position, current will flow from the ground. That means the current will pass through the circuit, then enter the fuse.

So that the large amount of current went through the circuit even in a short time.

It could burn some of the electronic components.

So the risk of something as trivial as this is quite large. Because some electronic components may not function when you fix the battery position.

And electronic components that are damaged, can't be repaired. It needs component replacement so that the circuit can work normally.

So, the best way is prevention.

When you are going to install the battery, make sure you check the battery terminals 3 times. Most of people, are confuse on the battery terminal not on the connector. This is because there is no difference between the positive and negative terminals of the battery.

What distinguishes, only the logo is sometimes disguised on the battery.

So don't install the battery if you don't know where the positive terminal and where the negative terminal.