How to fix A Generator with Under Voltage Or Not Putting Out Full Power

A generator with under voltage or not putting out the right power can damage your appliances. Having a lower voltage supply in it will cause them not to function at a desired level. This will occur suddenly and without expecting it.

Here are the main causes of this problem and how you can fix it.

Preliminary Checking

  1. Check all the fuses for possible busted and replace it if any.
  2. Clean the terminal if all of them are working.
  3. Check for possible rust in every connector if any clean it. A rust in connector can cause weak or loss connection therefore, the power can no longer pass through it perfectly. A power loss can be expected.
  4. Check for any possible cable breaks or damage, if any just replace it. Same as I mention above it can cause weak or loss connection.

Busted Circuit Breaker

A busted circuit breaker can also cause a low voltage output and sometimes no voltage at all. The circuit breaker function is to protect the system from possible overload and short circuit. It will automatically shut down the system if it occurs.

When a power surge happen it will draw large amount of current which is more than the circuit breaker capacity. Another thing is that, when you connect several high power appliances and started them at the same time it will trip the circuit breaker.

The simple solution to this is to turn the breaker into on and off position in succession. Afterwards, start the generator and test the output voltage using a voltmeter if it has already producing normal value.

If it doesn’t work test the circuit breaker using an ohmmeter. Measure the resistance by connecting the test prong into the two leads of the breaker. If it shows a resistance reading it means that the breaker is good. Otherwise, if it reads an infinity the breaker is busted and you need to replace it.

AVR (Automatic Voltage Regulator) Adjustment

The AVR is probably the main cause of having a low voltage output of your generator. This circuit is the one responsible for regulating the output voltage. This circuitry is located inside the generator’s alternator. You can simply pull it out by unscrewing the back of the alternator. Typically, there are two screw is located in there.

Inside of the circuit board you can notice a small adjustable screw in it. This is called a trimmer. Basically it is a potentiometer same as the volume control of your audio amplifier. When you adjust the volume control of your amplifier clockwise the sound level will become louder while turning it counter clockwise will lower its volume.

This is identical to your generator’s AVR potentiometer. By adjusting it clockwise you will increase its voltage. This will probably solve your problem. Try to connect a voltmeter on the generator’s receptacle when adjusting the appropriate voltage.

Caution: When adjusting the AVR voltage the generator is running therefore; live current is present in there. Be careful not to touch any live wire, you can use gloves for your protection.

What voltage should a generator put out?  

Most appliances are running at a voltage ranges from 110v to 120v. However, I suggest your generator output voltage should be higher than that. The reason behind it is that, when you put a load on your generator the voltage will drop. The heavier the load the more voltage it will drop. I suggest a 125-Volt or you can plug in your typical load and test it with a voltmeter.

Faulty Capacitor

A faulty capacitor will cause an under voltage output. The main purpose of a capacitor is to regulate the voltage. It stores charges to keep the voltage in the upper level as the alternator keeps throwing voltage on the load. If the capacitor is defective the voltage will drastically drops down as it never stores charge in it to maintain the ideal voltage level.

By visually inspection you can easily notice if the capacitor is faulty because it looks busted, bloated or burned. You can remove the capacitor from its terminal and replace it with the same value. You can test it using a multimeter or a capacitor tester.

Be careful in removing the capacitor as it has a residual charge inside of it. Do not touch the two terminal and you need to discharge it first for your safety. This is done by shorting the two leads of the capacitor using a screwdriver. It will create a momentarily spark on its two lead that tells you that the charge on it is gone. You can now safely hold its two lead terminal.

The capacitor value is in microfarad (uF) and the voltage is in V. The uF and voltage value of it is written in the body of the capacitor. Bring it along when you buy on the electronic or electrical store for parts replacement. The voltage value of it should not be less than the specified value. It can be higher but, definitely not lower. If you replace it with a lower voltage value it is unable to handle higher than that and will certainly damage it again.


An overload can also cause dropping the generator’s output voltage. This occurs when you plug too much appliances on the generator which is more than the generator’s rated capacity. This will result in slow down of the generator speed that affects its voltage and frequency as well.

For example, you have a 5,000-watt generator and the appliances total load you apply is 6,000-watt. This will cause the generator to overload. In some instances, the generator’s overload circuitry will activate and eventually stops or shutdown the system.

The simple solution to this is try to lessen your load by unplugging some of your appliances.

The Generator’s Speed Control

A slow rotational speed of the alternator can also cause a low voltage output. When the generator’s speed control setting is set at lower value it will drastically affect its voltage. The simple solution to this is to adjust the generator’s speed control.

Clogged Fuel Passage

A clogged fuel passage can also cause under voltage. This will result in an insufficient fuel supply that goes to the alternator. Due to inadequate fuel supply it will slow down the generator’s rotational speed and drops the voltage.

The two main parts to be check are the fuel filter and the fuel injection. The simple solution to this is to clean their passage for any possibility of being clogged.

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