What Happened When You Jump a Car The Reversed Way?


One of the most problem in our vehicle is engine starting failure. This problem can arise from various causes.

The most common cause, is the battery. The vehicle battery does not have full voltage, so it is unable to run the engine starting system.

The solution? many people use the jump start method.

But what happens if we connect the jumper cable with the wrong way?

Jump start method

This is a method to start the engine with a battery from another vehicle. So even if the battery in our car dies, it can still be turned on through the help of another car battery.

To get jump the vehicle, we have to connect two batteries in parallel position. That means, the two positive terminals of the battery will be connected and the negative terminal will be connected to the negative terminal.

This makes the electrical system in our car have a voltage with the same value as the battery in another car (jumper battery).

So, all electrical systems including the starter system will run normally.

When the engine is running, you can disconnect the jumper cables. The vehicle charging system will supply all the needs for electrical energy.

Then what happens if we connect the jumper cables in reverse?

We connect the positive jumper battery terminal to the negative origin battery terminal. And the negative jumper battery terminal is connected to the positive origin terminal of the battery.

This will create a series, where positive meets negative and negative meets positive.

But the problem here is that the two batteries are connected directly without passing the load.

Load is an electrical component that requires an electric current. The resistance value at load will affect how much current flows.

In the above case, the two batteries are connected directly by two cables. So there is no load on the batteries connection.

What happens if it is closed circuit without load?

The resistance value becomes 0, so that nothing blocks the electric current. This makes large amount of the current flowing through the cable.

In fact, all the current stored in the jumper battery will flow at the same time.

What are the consequences?

1. Sparks appear

When you connect one jumper wire to a different battery terminal (positive to negative), it will hold the two batteries together.

So the positive and negative terminals on the two batteries (which have not been connected by a wire) become power and ground.

If we connect the two terminals using a jumper wire directly, large amounts of current will flow immediately.

So that when the jumper wire approaches the battery terminals, it will produce sparks.

2. Jumper wire burned out

The intensity of the electric current shows how much energy is flowing. Cables use copper as a conductor. Copper in the cable has a limit to accommodate the flow of electric current.

The larger the diameter of the copper, the greater the current that can be flowed.

When a large amount of current flows through the copper, and it exceeds the capacity of the cable, it melts the copper.

This is the same as an electric water boiler, where the large amount of current will flow to the iron so the iron becomes hot.

When the copper in the cable is hot, it melts the insulation that covers the cable. So that smoke will appear and you will smell burning rubber.

Sometimes, a fire can also occur and it can spread to other parts.

3. Battery loss of voltage

Just like what I said above, when both of battery terminal connected directly, it will flow a huge amount of current. This is an event to balance the potential different.

Battery is useful because it has potential different. So, when you connected the battery through the load, it will flow an energy to the load. So the load function.

but the longer it is used, the smaller the battery potential difference. When the battery potential difference is gone, it can be said to be a battery loss of voltage. So it needs recharge.

In the above case, a huge amount of current will flow of the battery. So that in a short time the battery potential difference will be gone.

That makes the battery jumper which is initially full charged, becomes a loss of voltage.

Of course the current consequences are not too frightening, because this can be overcome with a battery recharge.

The thing you need to pay attention is point number 2. when the jumper cable burns, it can spread to other parts. And the thing makes it difficult, the jumper cables are hot so it is impossible for us to touch them or remove the jumper cables.

Therefore, when you encounter sparks when you jump a car, don't continue. Do a check, make sure you have connected the battery terminals correctly.