bison logo

Causes of damaged voltage regulator (AVR)

If your voltage regulator has been damaged then there may be many causes and reasons behind this. In this post, we’ll look at all those reasons and also how to fix them. Let’s get started.

Table of Contents

An AVR, an automatic voltage regulator, is a device or component that stabilizes or regulates a voltage supply. Therefore, the AVR helps keep the voltage the alternator produces constant.

In this article, BISON will focus on generator AVRs. Let’s look at what can cause AVR damage and how to prevent it.

Engine speed

Excessive engine speed can damage the diesel generator’s automatic voltage regulator (AVR). An AVR is a device that helps maintain a steady output voltage from an alternator and is usually designed by the generator manufacturer to operate within a specific engine speed range. If the engine speed exceeds this range, it may cause the AVR to malfunction or fail, resulting in unstable voltage output and possible damage to the generator or other connected equipment.

There are several causes of an excessive increase in engine speed. One possibility is that the engine is overloaded, which could cause it to rev up to meet the increased power demand. Another option is that the engine governor responsible for regulating engine speed is malfunctioning or has been adjusted.

Suppose damage to the AVR and other generator components must be prevented. In that case, it is imperative to ensure the engine is operating within the recommended speed range and to address any issues causing it to over-accelerate. It may involve adjusting the governor, replacing a faulty component, or addressing any underlying problems causing the engine to run outside its normal range.

overloaded generator


Diesel engine alternator overload can cause AVR damage in some ways. Here are some possible mechanisms:

Overloading can cause the AVR to work harder to maintain the correct output voltage, leading to overheating and failure.

Suppose the load on the generator exceeds the AVR’s rated capacity. In that case, it may not be able to maintain the correct output voltage, causing voltage fluctuations that can damage the AVR and other electrical components.

If the generator is overloaded for extended periods, it can cause wear and possible failure of the AVR and other components.

Overloading can also cause the diesel engine to work harder, leading to higher temperatures and increased wear, which can eventually cause the AVR and other components to fail.

It is worth noting that overloading a diesel generator can also cause damage to other components, such as the engine, alternator, and bearings, and lead to the generator’s failure. If damage must be prevented, it must be ensured that the generator is not overloaded and is operating within its rated capacity.

Power surge

Power surge

Power surges can sometimes damage a diesel engine generator’s automatic voltage regulator (AVR).

One method is electrical overstress, which occurs when an AVR is exposed to a higher voltage than designed. It can cause components of the AVR to fail, resulting in a loss of control of the generator voltage output.

Another way is through an electric arc, which occurs when the current through the AVR suddenly increases. Malfunctions may occur by damaging circuit boards and other parts of the AVR.

Finally, electrical surges can also mechanically stress the AVR, especially if the generator runs at high load levels when the electrical surge occurs. It can cause the AVR’s mechanical parts, such as bearings and gears, to fail.

To prevent power surges from damaging the AVR, you must ensure the generator’s electrical system is properly grounded and protected by a surge-protective device. Regular maintenance and inspection of the AVR are also required to ensure it is in good working order.

Short circuit

A short circuit in a diesel generator can cause damage to the AVR in several ways.

  1. Direct damage: A short circuit will cause a high amount of current to flow through the AVR, causing it to malfunction or even burn out.
  2. Indirect damage: A short circuit can also cause the generator to generate abnormally high voltages, causing the AVR to overload and malfunction.
  3. Heat damage: The increase in current caused by a short circuit will also generate a lot of heat, damaging the AVR and other parts of the generator.

Short circuits must be addressed as soon as possible to prevent damage to the AVR and other components of the generator. If you suspect a short-term problem with your diesel generator, shut it down immediately and seek professional help to diagnose and fix it.


Aging can cause damage to the automatic voltage regulator (AVR) in diesel generators. One possible cause is the buildup of contaminants on the AVR components, which can interfere with its ability to regulate voltage precisely. As generators age, pollutants can build up to levels that cause problems with the AVR.

Another possible cause of AVR aging damage is wear and tear on the components of the AVR itself. Over time, an AVR can wear out or become damaged, affecting its performance and causing voltage regulation issues.

Finally, aging can also damage an AVR by gradually degrading its construction materials. Over time, these materials break down and may become less effective at performing their intended function, causing problems with the AVR’s performance.

In general, it is vital to perform regular maintenance on diesel engine generators, including replacing worn or damaged parts and cleaning AVR components, to help prevent problems due to aging.


How to troubleshoot an AVR for a diesel generator set

To troubleshoot an AVR on a diesel engine generator, you first need to ensure the AVR receives the correct input voltage from the generator. Next, you must check the AVR’s output voltage to ensure it’s in the suitable range. If the output voltage is not correct, you may need to adjust the AVR settings or replace the AVR entirely.

To troubleshoot an automatic voltage regulator (AVR) on a diesel engine generator, you can follow these steps:

  1. Check the AVR for any loose or damaged connections. Make sure all wires are securely connected and show no signs of damage, such as burns or fraying.
  2. Check the output voltage of the AVR. Use a voltmeter to measure the voltage at the output terminals of the AVR. The voltage should be within the range specified by the generator.
  3. Check the control inputs to the AVR. The AVR may not work correctly; if it is not receiving the correct input signal. Make sure the control signal is within the specified range.
  4. Check the reference voltage of the AVR. The reference voltage is used to control the output voltage of the AVR. Use a voltmeter to measure the reference voltage and ensure it is within specification.
  5. Check the excitation current of the AVR. The field current is used to control the output voltage of the AVR. Measure the field current with an ammeter to ensure it is within the specified range.
  6. f the AVR still does not work correctly, you may need to replace it. See your alternator manual for instructions on how to return the AVR.

If you are unable to troubleshoot your AVR, you can contact a BISON service technician.

What is the importance of an automatic voltage regulator in a generator?

An automatic voltage regulator maintains a constant voltage to the generator. The generator’s performance may be affected if the voltage is not supported.

Utilities, equipment, and machinery powered by generators may fail because sparks may occur due to unstable voltage.

The automatic voltage regulator ensures consistent load current, thus ensuring the life of the equipment. This helps to undo the damage caused by the volatility.

A generator without a regulator cannot meet the power requirements. Because due to the upregulation, the voltage cannot be adequately distributed among the appliances. Therefore, the terminal voltage decreases over time as the load requirement increases.

How to replace an AVR for a diesel generator

To replace an automatic voltage regulator (AVR) in a diesel engine generator, you will need to perform the following steps:

  • Please turn off the generator and disconnect it from any power source.
  • Locate the AVR and remove any covers or cases to protect it.
  • Disconnect the AVR’s wires and remove any mounting hardware holding it in place.
  • Mount the new AVR in the same position and orientation as the old AVR and secure it with mounting hardware.
  • Reconnect the wires to the new AVR, connecting them in the correct order and direction.
  • Test the alternator to make sure the new AVR is working correctly.

Suppose you are unfamiliar with how a generator works or unsure how to safely and correctly perform this process. In that case, it is essential to follow these steps carefully to ensure your new AVR is installed correctly and your generator continues to operate safely and efficiently. It is recommended that you seek help from BISON’s technical personnel.

AVR voltage too high or too low

Excessive voltage can cause premature failure of electrical and electronic components, such as circuit boards, due to overheating. Damage from overheating is cumulative and irreversible. Frequent occurrences of minor overheating can cause as much component damage as a few severe overheating. It’s like slicing a loaf of bread – you can get many thin and very thick slices – but when you get to the end, you’re done.

Motors, on the other hand, can often benefit from a slightly higher voltage. The reason is simple. As the voltage level increases, the current decreases, and a lower current usually means less heat is generated within the motor windings. At some point, the voltage level supplied may be so high that it damages the motor, but this level is much higher than the voltage level of the electronics.

Keeping electrical and electronic components cool often ensures their longevity. A slight reduction in voltage levels allows many electronic devices to function flawlessly while minimizing their temperature. Of course, the motor is not.

Just as higher voltages help reduce motor operating temperatures, low voltages cause motor overheating and premature failure. Low voltage forces the motor to draw extra current to deliver the expected power, overheating the windings. A rule of thumb for electric motors is “for every 10 degrees Celsius (50 degrees Fahrenheit) the motor runs above its rated temperature, the life of the motor is reduced by 50 percent”.

When voltage levels are low, not only are motors and circuit boards at risk of damage, but long-term problems with either usually indicate a voltage problem.


BISON concluded that the automatic voltage regulator is a critical generator part. Without it, generators are prone to power shortages and sparks. Without the AVR, the voltage will not be stable. This instability can badly affect the performance of the generator.As a generator AVR manufacturer, BISON specializes in providing high-quality generator AVR for global customers.

So if you’ve always liked a high-quality AVR, this will help. This will ensure the generator runs long, even if the load or operating temperature changes. AVR can protect functions from interference. And will try not to damage the electrical appliances on it.

When used correctly, it can increase the lifespan of your AVR.

a) The more stable the engine voltage, the less frequent the change of AVR; the smoother the transistor switching action in the comparison circuit, the smaller the probability of AVR damage.;

b) If the output load is relatively stable, the AVR changes less frequently, and the smoother the transistor switching action in the comparison circuit, the smaller the probability of AVR damage.

c) The more stable the engine speed is, the smaller the oscillation fluctuation caused by currency changes on AVR.

d) Frequent “idling,” overload operation and significant load differences are the main reasons for AVR damage.

Typically, generator AVRs are located in one of three locations. It can be found in the alternator’s main control box, in the alternator terminal box, or under the rear cover of the alternator (usually only on tiny portable units).

If the AVR on the generator fails, the generator will lose excitation. This loss of excitation will cause a sudden drop in voltage across the generator, and this loss of voltage can cause the generator to shut down due to an Undervoltage fault.

If your generator is not set for Undervoltage protection, then the generator may continue to run, which could cause severe damage to your equipment.

The error voltage is the difference between the actual and reference voltage.

Amplifiers and exciters are provided at the receiving end of the voltage. The error voltage reaches the amplifier. The error voltage is then amplified and supplied to the exciter.
Exciter output control regulates fluctuations in alternator voltage.

contact us

Please complete our contact form and we will soon get back to you with expert advice.


Get in touch to speak with our experts!

enquire today

Speak with our sales manager today for additional information or an obligation-free quote.