Why is my generator light fluctuating


Last updated on August 20, 2007

Original at www.batteryfaq.org


5.1 How does a vehicle's charging system work?

Logical circuit diagram of the charging system

Graph: alternator power

Graph: vehicle charging voltage

5.2 What if my "Battery" or "Generator" light is on? (Or does the display show no charge level?)

5.3 What if I cannot keep my battery fully charged and the battery test did not reveal anything?

5.4 How do I check whether my charging system is powerful enough?

5.1 How does a vehicle's charging system work?

According to Dan Masters' diagram, a vehicle's charging system consists of an alternator (or DC generator), voltage regulator, battery, and indicator light or indicator. Another good source of information on basic vehicle charging systems is Perry Babin's Basic Car Audio Electronics website at http://www.bcae1.com/charging.htm. A detailed description of how an alternator works can be found in Nathen Eagle's article Using an Alternator in Renewable Energy Projects or Bob Hewitt's article Alternators - what are they, how do they work and what breaks ??.

If the engine is running, that's it primary The purpose of the charging system is to provide electricity for the car's electrical consumers, e.g. ignition, lighting, sound system, extras, etc., and to recharge the vehicle's battery. The output power of the generator is directly proportional to the speed of the engine and the temperature of the generator. Charging systems are usually selected by the automaker to cover at least 125% (at high speeds) of the maximum load from the original equipment so that the car battery can be recharged. This is the reason why short journeys and traffic lights at night or in bad weather may not fully recharge the battery, especially if the load is increased by additional built-in extras such as a powerful audio system, lighting or an electric winch. Vehicle charging systems are not designed to charge completely discharged batteries, as the stator or diodes could be damaged by overheating.


[Source: Vintage Triumph Register]

The output power curves for 65A and 85A alternators are shown at the bottom of the Balmar Generator Performance Diagram. Note that the 65 A generator in this example has a higher current output at lower speeds, which the larger generator delivers from around 3300 revolutions. Also note the difference that the size of the crankshaft pulley makes. A larger crankshaft pulley results in a higher generator speed, which means that the generator produces more power at a lower engine speed.


[Source: Balmar]

Amperage: current intensity; crank pulley: crankshaft pulley

When the charging system fails, a "battery" or "generator" warning indicator or light will usually come on, or the volt (or ammeter) will not read "good". When you increase the engine speed and the generator light brighter the battery must be fully recharged and checked. When the light weaker the problem is mostly with the charging system. Another simple test of the charging system is illuminating a wall with the headlights at night while the engine is running. If you turn off the engine and the light dims, the charging system will produce a higher voltage. If the light gets brighter, you likely have a problem with the charging system. The control light (also called "idiot light") is a direct comparison between the output voltage of the charging system and the output voltage of the battery. For the next test, you need a fully charged battery that you know is OK. Temporarily replace the old battery with this battery and run the engine at 2500 rpm or more for two minutes. Depending on the load and the ambient temperature, the output voltage should increase to 13.0 to 15.1 volts during this time. Most vehicles with a good charging system will measure between 13.8 and 14.8 volts on warm days, depending on the type of battery the charging system was designed for.

Some automotive charging system designers prefer lower input voltages, such as 13.8 VDC, to reduce water consumption and, for wet, low maintenance (Sb / Ca) starter batteries, the cost. In the long term, this combination results in the battery becoming undercharged and acid stratification occurring, gradually causing the battery to lose capacity due to the build-up of lead sulfate or causing premature failure. One possible solution is to periodically recharge the battery with an external charger to remove sulfation or to increase the input voltage supplied to the battery, as described by Chris Gibson at http://www.smartgauge.co.uk/alt_mod.html. Other solutions include using an adjustable or "smart" voltage regulator, adding resistance to the test lead to the regulator (if present), or balancing the battery. Increasing the end-of-charge voltage or equalizing charge increases the water consumption in wet batteries, so the electrolyte levels must be checked more frequently.

As with the Bosch voltage regulator example below, most voltage regulators are temperature compensated in order to properly charge the battery in different environmental conditions. When the ambient temperature drops below 25 ° C, the charging voltage is increased to overcome the higher resistance of the battery. If the ambient temperature rises above 25 ° C, the charging voltage is reduced. Other things that affect the charging voltage are the generator temperature, the battery condition, the state of charge, sulfation, current load and electrolyte purity.


[Source: Bosch]

If the battery terminal voltage is below 13.0 volts when the engine is running and the battery proves fine after charging, or if you are still having trouble keeping the battery charged, then check the output voltage of the Charging system and doing a stress test. Also check the quiescent current, the load when the engine is switched off. (See Section 10.) A slipping generator belt or an open diode will significantly reduce the output power of the generator. If the output voltage is above 15.1 volts at an ambient temperature above freezing, if the electrolyte levels in the battery are frequently low, the electrolyte is "boiling" or there is a smell of "rotten eggs" in the area around the battery, then the battery is overcharged and the vehicle's charging system should be checked.

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5.2 What if my "Battery" or "Generator" light is on? (Or does the display show no charge level?)

The "battery" or "generator" light is a sign of a significant deviation between the voltage supplied by the charging system and the battery voltage. Some vehicles have a voltmeter or ammeter that is designed to indicate whether the charging system is working. The battery and the charging system have to work together to provide electrical power to the vehicle and keep the battery charged so it can restart the engine. The most common reasons are in this order:

  • Low electrolyte levels

  • Generator belt slipping or broken

  • Corrosion between the end terminals of the battery and the battery terminals

  • Faulty charging system

  • Defective battery

If the electrolyte levels and generator belt are fine and the battery terminals are free of corrosion, take your vehicle to an auto parts or battery store and have the battery and charging system tested (highly recommended) or use the troubleshooting guide above. In the United States and Canada, some stores like Auto Zone, Sears, Wal-Mart, Pep Boys, etc. check it out for free. The first three simple mistakes in the list have already led many to have their good batteries replaced. A new battery can cause a weak generator or starter to fail.

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5.3 What if I cannot keep my battery fully charged and the battery test did not reveal anything?

The vehicle's electricity needs will normally be first covered by the charging system and then the battery is charged with the remaining energy. For example, if the total consumption is 14 amps and the charging system is generating 35 amps at 2500 rpm, there will be up to 11 amps available to recharge the battery, which will take about 6 minutes. If the charging system is running at, say, its maximum output of 90 A at 5000 rpm, then the battery is usually recharged within two minutes. Suppose the engine is idling and the charging system can only generate 10A. Then four amps are required from the battery to make up the difference in order to cover the electrical consumption of 14 A. The battery continues to discharge. This is why there is a greater burden on short journeys, traffic lights or bad weather; the starter battery could not be recharged or even "completely" discharged.

To continue the example from above, let's assume that there is a non-original 400 watt high performance audio system at 69% efficiency, a 20 A electric winch, or a 276 watt light installed, which adds an additional 20 A load. To convert the wattage of the power amplifier into amps, multiply the wattage of the amplifier by 0.5 to 0.85 (depending on the efficiency of the amplifier) ​​and then divide by the operating voltage. To convert the output of the winch or the lighting (in watts) into amperes, divide the wattage by the operating voltage. With a total current load of 34 A and a speed below 2500, the battery will be in a 90 A system never charged. If the engine is running in this case, the battery must provide the fault. The solution is to upgrade the charging system to 125% or more for the new Load at the most. In this example, based on frequent traffic light traffic, a high capacity charging system of 105 amps or more would be required to fully charge the battery. High generator temperatures can further reduce the maximum output of a charging system, so cooling and coordination with the continuous load is important. Heat destroys generators, which is why Bosch offers water-cooled models, for example.

For boat owners, Balmer recommends that the starter (s) for wet batteries have 25% of the total capacity and 35% to 40% for AGM (Ca / Ca) and gel (Ca / Ca) VRLA batteries. The size of the generator belt is also important. A single 1 cm belt drives a generator up to 80 amps, a 1.27 cm belt up to 110 amps, and multiple belts over 110 amps. Ample Power has an excellent guide, Troubleshooting the Alternator System.

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5.4 How do I check whether my charging system is powerful enough?

A simple test to determine if the charging system has enough power is to check the battery's state of charge after the surface charge has been eliminated. If the state of charge is constantly above 95%, the charging system fully charges the car battery depending on your driving habits and the current load. If it is consistently below 80%, consider upgrading the charging system to generate more electricity. There are several ways to increase the performance of your charging system, including changing the pulley diameter, replacing the alternator with a more powerful model, adding a second charging system (for a dual battery arrangement), replacing the voltage regulator, etc. An auto electrics workshop or alternators can help you with this. If the charge level fluctuates, you may want to consider using a temperature compensated "smart" quick disconnect charger to fully charge your battery. If you have a high current load while the engine is running, set up a dual or multi battery system, with the high load on a deep cycle battery bank. If a lead-acid battery is constantly undercharged or overcharged, it will lose power and fail prematurely.

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