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What Would Cause the Alternator To Not Charge the Battery?

This time we explain what causes the alternator to not charge the battery, repair it, inspect components, and maintain it.

The alternator or car dynamo ampere is one of the most essential components in a car engine. Sometimes car owners do not care about the feasibility of the car's alternator. Even though the condition may not be suitable for use. The cause would be a worn component inside. As a result, the alternator works not optimally when supplying electricity to the battery components. You will have difficulty starting the car engine.

car-alternator
The alternator is damaged and cannot charge the battery.

Without the alternator, the electric currents would never be in the engine. The alternator functions to provide intake or produce electricity to the battery and other panels, such as lights. When you start the engine, the current will be supplied to the battery by converting the AC voltage to DC voltage.


Almost all of the engine's electrical components require an alternator, such as engine cooling fans, power steering, lights, wipers, and fuel injection components. Actually, a car without an alternator can still run. But only limited to battery power reserves to turn on the engine's electrical components.

Alternator models also vary for each type of car. Generally, the alternator has a regulator in it (IC built-in). But, the older alternator models had an outside regulator. Whereas in the new type, the built-in IC is more comfortable to repair by opening the top cover.

How to Repair a Damaged Alternator

The following are steps to repair damage to a car alternator.
  1. Check the alternator bearing by turning the alternator pulley using a dynamo tester.
  2. Carefully disassemble the components inside the alternator using proper equipment.
  3. First, clean the alternator components before you take measurements and checks.
  4. Check the bearing housing. If you find damage such as cracks or breaks, you have to replace them with new ones. Pay attention, the bearing house's position and the holder must fit appropriately during installation to not loose.
  5. Also, check the alternator brush and measure its length. If the measurement is below the minimum limit (5 mm), you need to change it.
  6. Measure the alternator rotor slip ring diameter. If the slip ring diameter is less than the minimum limit of 12.5 mm, replace the alternator rotor. However, if there are defects, then flatten the surface of the slip ring by turning it.
  7. Measure slip ring resistance; the value is 1.5 - 4 ohms. If the reading is less than the minimum limit, re-clean the rotor and check for leaks in the rotor winding.
  8. Check the stator windings for defects and leaks. Then measure the alternator stator resistance; the value is 20 ohm. If the measurement is outside the acceptable limits, there may be a leak in the roll.
  9. Replace the bearing carefully and use the correct equipment, according to the bearing size and mount.
  10. When finished assembling, test the alternator using a dynamo tester and install the alternator in your car.

Signs of Alternator Faulty

Often people don't know about the signs if the car's alternator is having a problem.
Therefore, we give you easily recognizable signs to see if the alternator is still fit for use or damaged.
  1. You start the car engine, but the battery indicator light turns on. This is a sign that the car's alternator is having problems because it can't generate electricity.
  2. The car cannot be started even though you have changed the battery. It is due to the lack of output voltage generated when charging the alternator.
  3. The alternator makes a loud noise because the bearing is damaged, or the alternator rectifier diode has broken.
  4. The light of the car's headlights is getting dimmer (when driving at night) is a sign that the power supply from the alternator is starting to weaken. Or the amperage supply is so small, and the light begins to dim.
  5. An overcharge occurred. Suppose the alternator output is higher than 15 volts. In that case, it will cause an overcharge and damage the battery because it becomes hot, and the battery liquid boils. As a result of overcharge, the headlamp lights up too brightly and flickers when the engine rpm increase.

A Guide To Checking The Condition Of Your Car Alternator

Here is how to check your car's alternator components at home. Is it functioning normally or needs replacing? You can find out easily.
  1. Prepare supporting equipment, such as wrenches, screwdrivers, or other metal tools.
  2. Try starting your car. Bring the metal closer to the end of the dynamo ampere rotation or alternator. If the metal sticks, your alternator is still in good shape and can still function properly. On the other hand, if the metal cannot stick, there is damage to the components.
  3. Check the mass cable that leads to the car battery head. Start the car, remove the mass cable bolt on the battery head and rub it on the battery head. If sparks appear on the mass wire, the alternator is still functioning correctly. Conversely, suppose there are no sparks on the cable. In that case, the alternator performance will not be optimal when charging the electricity to the car battery.
  4. Finally, check the fuse leading to charging the alternator. Also, check the engine fuse box, is there a broken fuse or not? If you find it on the alternator, replace it immediately.

How To Maintain Your Car Alternator

The following is how to easily maintain an alternator.
  1. Do not add excessive electrical load to the car as this can shorten the alternator and battery life.
  2. Immediately repair the damaged alternator component so as not to cause damage to other parts. For example, if there is an overcharge, you also need to check the IC, diode, and rectifier. If it has been weak or does not function normally, it must be replaced with a new one.
  3. Check the electric charging cable from the alternator to the car battery because it is very prone to rust by dirt and water. As a result, it becomes brittle due to corrosion. If this happens, make sure you replace the electric charging cable from the alternator to the car battery with a newer one. Ensure the wiring system is useful to prevent short circuits that can damage the car battery or alternator.
That's our explanation about the alternator doesn't charge the battery, signs of damage, how to check the components condition, repair, and maintain the alternator. Hopefully, this information can help when there is a problem with your car's alternator.
Ryan Daniel
Ryan Daniel Ryan Daniel is a car enthusiast. Since owning his first BMW at a young age, he has loved the automotive world even more.