Is the alternator defective? These are the symptoms and costs!

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Alternator tuning Dynamo e1577687551188 Alternator defective? These are the symptoms and costs!

If the alternator of a car is defective, the battery will also go on strike after a short time. We tell you the signs and typical defects. Read how to check the LiMa yourself. In every car, a generator is responsible for generating electricity and that is the alternator or the LiMa for short. This designation was defined at the time when the alternator only produced the light from the vehicle. Today's alternator now supplies all power consumers in a car with the energy they need to function properly. Although the alternator is not a consumable part, defects are not uncommon and the alternator itself is not always the cause. The following is an overview including jump labels for the article:

Function of the LiMa in the vehicle

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The generator converts mechanical energy from the crankshaft into electricity through its internal rotary movements. The excitation field is generated by a rotor the size of a fist which is usually converted into a three-phase alternating voltage. This is fed into the on-board network. The generator mostly drives in fan belt or a V-ribbed belt that is connected to the LiMa via the pulley. The alternator also charges the starter battery while driving. The alternator uses an engine output of around 4-6 hp to produce electricity. To do this, of course, it uses fuel. For this reason, the modern alternators are controlled as required, in this way the energy conversion is much more efficient. In the event of a strong acceleration, the generator output is first reduced, thereby reducing the resistance. In a phase of overrun when the engine is due to the fuel cut does not use any fuel, the LiMa then has to deliver more power, so the resistance is increased. (Back to overview)

Functions of an alternator

Today the alternator is usually a three-phase generator. While driving, this generates electricity that is used by all electrical consumers in the vehicle. For example the ventilation, the heated rear window, the radio, etc. The engine control unit also needs power pulses to function properly. The LiMa also loads the starter battery on while you drive. As we all know, a battery is the car's energy store and, as it were, forms the back-up of the generator, even while driving. If the combustion engine is not running, the battery will be discharged if consumers such as the Sidelights, the radio or the Stationary heating system are activated. The parking heater also needs electricity and that is particularly fatal on short journeys. Because then at some point the current from the battery is no longer sufficient to start the engine. (Back to overview)

Cost of an alternator

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If the alternator is defective, the new one costs around 130 to 450 euros, depending on the vehicle model, the generator power and the alternator manufacturer. But of course there are also installation costs between 80 and 350 euros. The price of the powerful, water-cooled alternators, on the other hand, can be more than 650 euros. A used replacement alternator is recommended for repairing an older car. Refurbished alternators are sometimes available for as little as 30 euros. For this purpose, however, a deposit for the old part will be charged, which will be reimbursed when the defective alternator is sent or returned directly. When purchasing a LiMa, you should make sure that all parts required for it (e.g. the alternator regulator) are included in the package or that these are additionally purchased. Authorized dealers offer good replacement generators that are original quality. For this you only pay 55 to 75 percent of the price of the new parts. (Back to overview)

Alternator power

Today's modern alternator provides sufficient power at idle speeds between 650 and 900 rpm to supply the consumers in the car with electricity. Three-phase generators are more powerful, more reliable, smaller and lighter than before. They weigh about 8-11 kilograms. The output of the alternator is matched to the consumers in the car. A maximum of 10 percent less performance is tolerated if all consumers in the car are activated at the same time. The vehicle battery can then bridge this 10 percent. Due to the steadily increasing number of electrical consumers in our cars, the charging current of alternators has increased more and more. Today's alternators generate 100 to 250 amps, depending on the vehicle type. In addition, the extended comfort functions available in our modern car are also pantographs. And it is also the modern engine technology such as the high pressure pump for fuel supply as well as the solenoid valves on the injection nozzles that draw electricity. (Back to overview)

The charge control lamp provides information on a defect

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One of the important "tools" that helps you to check the operation of your alternator is built into the pilot's field of vision. It's the charge indicator light in your instrument cluster. The battery symbol lights up when you operate the ignition and goes out when everything is OK. However, if it still lights up when the engine is active and the vehicle is stationary, this can indicate that consumers that are switched on are not receiving the required power and that the battery is currently being used to support the system. A quick step on the accelerator pedal should then turn off the control lamp, then everything would be fine. If it continues to glow, it could be a sign that your LiMa is defective. (Back to overview)

When is the LiMa defective?

Three-phase alternators are maintenance-free and usually last the entire life of the car. However, if an alternator is broken, the current from the battery is gradually sucked empty. The engine can then even shut down while driving, because the engine control unit and the fuel pump need electricity to function correctly. Drivers should be skeptical if their car has a hard start in the morning even though they had driven a long distance the day before. If that was the case, the starter battery should be fully charged. (Back to overview)

What usually breaks with the alternator?

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  1. The wear of the carbon brushes in the alternator regulator
    a.) Symptoms: The charge indicator light is on and the battery is not charged.
    b.) Solution: Renew regulator or carbon brushes
  2. Defective alternator regulator
    a.) Symptoms: The battery is overcharged and becomes hot. The battery is too weak. The charge indicator light gets brighter the higher the speed. In the worst case, the lamps burn out.
    b.) Solution: Replace the alternator regulator.
  3. Defective bearings on the belt drive or defective freewheel
    a.) Symptoms: Noises can be heard from the drive of the belt such as whistling, grinding. The battery is not charging. Your charge indicator light is on.
    b.) Solution: Check the belt drive and the freewheel and replace the bearings if necessary
  4. Defective or corroded cable connections
    a.) Symptoms: The charging voltage is too low. Differential voltage between LiMa and battery.
    b.) Solution: Check the lines and connections and replace them if necessary.
  5. The tension of the V-belt is too low
    a.) Symptoms: Flickering charge control lamp, the V-belt slips through and it squeaks.
    b.) Solution: Tension the V-belt or replace it.
  6. Short circuit of the diodes or interruption
    a.) Symptoms: When stationary, the battery discharges with the defective positive diode.
    b.) Solution: Disconnect the battery and replace or repair the alternator.
  7. Defective winding of the LiMa
    a.) Symptoms: The car's charge light is on and the battery is not charging.
    b.) Solution: Replace or repair the alternator.
  8. Defective rectifier in the alternator
    a.) Symptoms: Battery does not charge and the indicator light is on.
    b.) Solution: Replace or repair the alternator.

This is how you check the alternator with the multimeter

The alternator is easy to check. With the multimeter (which is available in stores from around 20 euros) you can check the charging voltage of your alternator. Just do the following:

  1. Set the voltage range on the multimeter to 15 or 20 V.
  2. Connect the black clamp to the ground and the red clamp to the positive pole.
  3. With the engine turned off, the multimeter should read the car battery voltage from 12,2 to 13,6 volts (If the voltage is below 12 volts, it is advisable to charge current with a charger.)
  4. Switch on the engine, then the charging voltage should be around 13,4 to 14,8 volts when idling.
  5. Repeat the measurement at 4000 rpm, the voltage should remain constant.

If the voltage does not reach the values ​​when the engine is switched on (after a few seconds), this indicates a defect in the alternator. To rule out damage to the wiring, you should repeat the measurement on the contacts of the alternator. If the multimeter shows a significant difference, you should have the cabling checked! If the voltage at 4000 rpm rises sharply above the value displayed when idling, one can assume a defect in the alternator regulator. The car battery could then overheat and your on-board electronics could be damaged. In your workshop, the mechanic also checks your alternator with an oscilloscope and interprets the measured value curves correctly. (Back to overview)

Defective alternator regulator

The alternator regulator or the voltage regulator is integrated in the generator. It should always keep the generator voltage constant to ensure that there are no voltage fluctuations that could damage the electronic components inside the vehicle. The regulator keeps the generator voltage at around 14 volts. This means that the voltage is below the gassing voltage of the starter battery. The two carbon brushes in the alternator regulator may be worn out. Then they are visibly shortened. In an older vehicle, the carbon brushes can be replaced, which costs only a few euros. If the alternator regulator has to be replaced entirely, it costs 20 to 80 euros. The installation time is added and, depending on the accessibility, is 10 minutes to an hour. Sometimes additional units have to be removed in order to replace the alternator regulator, so you should contact a workshop. (Back to overview)

Check the V-belt and belt drive

The tension of a V-belt and the freewheeling of the pulley can be checked quickly. If the bearing is damaged, you will hear a grinding-squeaking noise when the motor is switched on, which comes directly from the freewheel on your LiMa. If the V-belt is defective, you can sometimes remove the pulley from a built-in generator and replace the bearing in it. The replacement will cost you between 20 and 60 euros. (Back to overview)

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Here are a few tutorials on changing the LIMA!

Repair alternator, overhaul, change generator, remove + install


Change alternator and freewheel | VW AUDI SEAT SKODA

Change alternator - Instructions for VW Passat / Golf / Audi A3 / A4 / A6 / Octavia

(Back to overview)

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