Generator Output Voltage Too High: Troubleshooting Guide

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Generators are critical for backup power during power outages, emergencies, and for off-grid power supply. 

However, sometimes they can malfunction and produce a high output voltage, which can damage appliances and electronics. 

Here at Generator Hacks, we found out that, on a yearly basis, 60% of generator users, especially portable generator users, complain of generator voltage being too high for no reason, resulting in havoc.

Hence, to avoid that from happening, we came up with this article to explain why generators produce high voltage, the risks associated with high voltage, and steps to troubleshoot and fix the problem.

Let’s get started.

Why does a generator produce high voltage?

Generators produce electrical power by converting mechanical energy from an engine or turbine into electrical energy. This process is known as electromagnetic induction. 

The generator’s rotor spins inside a stator, which contains copper wire coils that produce an electromagnetic field. 

The motion of the rotor induces an electrical current in the coils, which is then output as AC power.

Based on these, several factors can result in a generator producing high voltage, including:

  • Engine Speed: The engine’s speed determines the frequency of the AC power produced by the generator. In most cases, generators are designed to produce 60 Hz or 50 Hz AC power, depending on the region. If the engine runs at a higher speed than designed, the frequency of the AC power output will also increase, resulting in high voltage.
  • AVR Malfunction: The Automatic Voltage Regulator (AVR) is an electronic device that regulates the generator’s output voltage. The AVR senses the voltage output and adjusts the generator’s excitation current to maintain a steady voltage output. If the AVR fails, it can cause the generator to produce high voltage.
  • Faulty Capacitor: Generators use capacitors to smooth out the AC power output and prevent voltage spikes. So, when the capacitor is faulty, it can cause the generator to produce high voltage.
  • Winding Faults: The generator’s stator and rotor coils can develop faults due to wear and tear, overheating, or other issues. These faults can cause the generator to produce high or erratic voltage output.
  • Load Imbalance: Lastly, if the load connected to the generator is imbalanced, it can cause the generator to produce high voltage. For instance, if one phase of the generator is loaded more than the others, it can cause that phase’s voltage to increase, resulting in high voltage. Or, let’s say, after the load dropped, the generator’s voltage would increase.

Risks Associated With High Voltage

High voltage from a generator can cause several risks, including:

  • Electrical Shock: High voltage can cause electric shocks to anyone who comes into contact with the generator’s output wires or terminals.
  • Fire Hazard: High voltage can cause electrical fires, especially if the generator is connected to appliances or electronics that cannot handle high voltage.
  • Equipment Damage: Lastly, high voltage can damage appliances, electronics, and other equipment connected to the generator, resulting in costly repairs or replacements.

How to Troubleshoot a Generator with High Output Voltage

If your generator is producing a high output voltage, you should troubleshoot the problem immediately to avoid risks and damage. 

Here are the steps to follow:

Step 1: Check the Engine Speed

The first step is to check the engine speed using a tachometer. 

The engine speed should match the rated speed for the generator to produce the correct frequency and voltage output. 

If the engine speed is too high, adjust it accordingly to the manufacturer’s specifications.

Step 2. Check the AVR

If the engine speed is correct, the next step is to check the AVR. The AVR is usually located near the generator’s alternator and is easily accessible. 

Check the AVR’s connections for loose wires or corrosion, and inspect the AVR for any physical damage or burn marks.

If the AVR appears to be in good condition, use a multimeter to test the AVR’s output voltage. 

The output voltage should match the manufacturer’s specifications. If the output voltage is too high or too low, replace the AVR.

Step 3: Check the Capacitor

If the AVR is not the issue, the next step is to check the capacitor. To do this, turn off the generator and disconnect any loads connected to it. 

Locate the capacitor, which is usually located near the alternator or AVR. 

Check the capacitor for any physical damage, such as cracks or bulges, which may indicate that it is faulty. 

Use a multimeter to test the capacitor’s capacitance, which should match the manufacturer’s specifications. 

If the capacitance is lower than the specified value, replace the capacitor.

Step 4: Check for Winding Faults

If the capacitor is not the issue, the next step is to check for winding faults in the generator’s stator and rotor coils. 

This requires advanced knowledge and skills in electrical engineering, so it is recommended that you hire a professional to perform this step. 

A professional will use specialized equipment, such as a megohmmeter, to test the insulation resistance of the coils. 

If the insulation resistance is lower than the specified value, it may indicate a winding fault. The faulty coils will need to be replaced or repaired.

Step 5: Check the Load Balance

If none of the above steps identify the issue, the last step is to check the load balance. 

Check the loads connected to the generator and ensure they are balanced across all three phases. 

If one phase is overloaded, it can cause the generator to produce high voltage on that phase. 

If the loads are unbalanced, redistribute them equally among the phases.

Don’t Leave Your Generator Running With High Voltage

A generator that produces a high output voltage can pose a serious risk to people, property, and equipment.

It is important that you troubleshoot and fix the issue immediately to avoid costly repairs or replacements.


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