What Causes an Alternator To Overcharge?


Alternator is a self power plant for the vehicle electrical needs. The alternator generates electrical energy to supply the electric needs of the vehicle and performs battery recharge.

So that the vehicle battery is always in full charge position.

The alternator works by converting the rotational motion into electrical energy. The alternator rotor is connected to the engine pulley, the alternator shaft rotation will produce electricity with varying values.

The value is based on the rotor rotational RPM.

That is a sign, when the engine is in a high RPM position, the value of the electrical energy generated by the alternator can be very large. Then, What if the alternator overcharge the battery?

Voltage Regulator Prevent Overcharging

Every charging system is equipped with a voltage regulator. This is a component to keep the voltage generated by the alternator from getting too high.

As I said above, the alternator is connected to the engine pulley directly via a belt. That means, the alternator shaft rotation is affected by engine RPM.

However, the voltage regulator will activate when the engine RPM increases.

There are several types of voltage regulators. One of them is the contact plate or conventional type. This type works using a contact point to adjust the input voltage leading to the rotor coil.

So the alternator works using the electromagnetic force. An electric current will be created when the magnetic field rotates in the coil. In the alternator, the magnetic field is not obtained from the permanent magnet but it is obtained from the rotor coil.

To make the coil rotor have a magnetic force, we need to apply an electric current to the coil rotor.

the value of the voltage applied to the coil rotor affects the strength of the magnetic field formed in the coil rotor.

The voltage regulator has options, whether the rotor coil will be supplied with full voltage (12 V), partial voltage, or 0 volts.

So simply put, the voltage regulator will deliver full voltage to the rotor coil when the engine RPM is low. The voltage regulator will switch to the partial voltage input when the engine speed is in middle speed.

When the engine is at top speed, no voltage is applied to the rotor coil.

So the contact point will switch automatically based on the engine RPM.

Then what causes the alternator to be overcharged?

Contact Point Gets Damage

If the contact point gets damage, of course it will interfere with the performance of the voltage regulator. The contact points can experience switch failure, which causes the input voltage to the rotor coil to always be at full voltage (12 V).

So that when the engine RPM increases, the charging voltage will increase until it exceeds capacity. (15 Volt or above).

What causes the contact point to get damage?

1. Impact on the voltage regulator

The conventional regulator is located outside the alternator. So, this component is prone to collisions. A collision will make the plate at the contact point stuck, so the contact cannot be switched.

2. The contact point is stuck

The contact point is made of steel plate. If the vehicle is not used for a long time, the plate may become stiff. So it doesn't allow for a switch.

3. Corrosion

Corrosion and rust are things that often appear on components made of metal. This rust will interfere with the contact points to get switch.

What's the solution?

Component replacement is the best solution. This component is easy to replace, because it is located outside the alternator. So you don't have to take anything apart.

But conventional voltage regulators are only used in vehicles produced in the past. Vehicles produced in the era of 2000. most of them use an electronic voltage regulator.

Then what makes the alternator overcharge on the electronic voltage regulator?

Faulty transistor is the reason that makes the alternator overcharged the battery.

Transistors are electronic components that are used to select the input line for the rotor coil. Just like the conventional regulators, electronic regulators also have input with full voltage, medium voltage and low voltage.

However, electronic regulators use transistors as a substitute for contact points.

Of course this can reduce the risk of damage caused by contact points. However, if one of the transistors is damaged then the alternator may undercharge or overcharge.

The bad things, the electronic regulator is located inside the alternator. So, when this failure occurs you have to replace a unit of the alternator.

However, this is a rare thing. Electronic alternators are more durable than conventional regulators.

What happens if I let the alternator overcharged?

This can damage some of the electronic components in the car. The ECU has been set to use 12 Volts, if the voltage on the system exceeds 12 Volts, the ECU and some sensors can malfunction.

So that there is a problem with the engine.

The bulb on your vehicle lighting is easier to break. This is because the filament of the bulb receives electricity with a voltage above the capacity.

Your car battery also dies faster, because the overcharge will make the battery electrolyte evaporation more massive.

So if you detect an overcharge on the charging system, fix it immediately.