Why does the engine continue to run when the negative terminal is removed from the battery?

After removing the negative electrode of the battery, the vehicle's electrical system should theoretically stop working immediately, because the battery is one of the main power sources of the vehicle's electrical system, and the negative electrode is the part that connects the body (usually as a ground wire). However, in some cases, the engine may continue to operate even if the negative battery connection is removed, often because the electrical system and engine management system design inside the vehicle allow for temporary electrical interruptions. Here are some possible reasons for this:

Action of capacitor

Capacitor storage

The engine management system (ECU) and other critical components such as the ignition system may be equipped with capacitors. These capacitors can store enough power for a short period of time to allow the engine to continue running for a while until the power in the capacitor is exhausted.

Continuous power supply of generator (alternator)

Generator continuous supply

After the negative battery electrode is removed, the vehicle's alternator can continue to supply power to the electrical system. The alternator is usually connected to the engine and produces alternating current when the engine is running, which is then converted into direct current by a rectifier to supply the vehicle.

Even if the battery is disconnected, as long as the alternator can work properly, it can continue to power critical systems to keep the engine running.

Vehicle design features

Vehicle design

Some modern vehicle designs allow for a degree of electrical interruption to ensure that critical systems can continue to operate for some time in the event of battery failure or disconnection, giving the driver enough time to safely park the vehicle.

Precautions in actual operation

It is worth noting that although the engine may continue to run after removing the negative battery electrode, this is a temporary phenomenon and is not recommended because:

• Electrical system instability: Removing the negative battery electrode for a long period of time may cause electrical system instability, causing various problems such as data loss and sensor failure.

• Risk of damage: Prolonged operation without batteries or poorly connected batteries may damage alternators or other electrical components.

• Safety concerns: Before performing any electrical repairs, it is best to ensure that the vehicle is completely powered off to avoid electric shock and other safety hazards.

In conclusion, while the engine may continue to run for some time after removing the negative battery electrode, this does not mean that it is safe or reasonable to do so. Before performing any operation that involves disconnecting the battery, you should consult the repair manual provided by the vehicle manufacturer and follow all relevant safety guidelines.