Why Do My Lights Flicker When Using a Generator? (Here’s Why)

Power outages can cause a range of problems from temporary annoyance to serious damage to appliances and your home. You feel more secure knowing your home has a backup power source to the electric grid. But when you run the generator and the lights start flickering, that sense of security vanishes.

Flickering lights while the generator is operating indicates anything from an easily corrected loose connection to imminent failure of the generator. It’s essential to discover the cause of the problem as soon as possible.

Here are some of the methods you can use to check your generator for issues when your lights start flickering:

• Measure your generator’s RPM
• Test for electrical overloading
• Check all cables and connections
• Examine the fuel line
• Check the AVR settings

You’d be surprised how many factors can go into the smooth operating of a backup electrical generator. Read on if you’d like to know more about how to stop your lights from flickering as you run your generator.

Electric generator plugged in

Why Do Lights Flicker When the Generator is Running?

The major reason for flickering is voltage fluctuations. Think of your lights as a canary in the coal mine. The flickering will be the first and most obvious indicator of problems with unstable voltages in your generator.

This is especially true for LEDs. They are far more sensitive to fluctuations than Edison bulbs are.

Your alternator should be producing a steady 1,800 revolutions per minute (RPM) for a water-cooled generator.

An air-cooled generator’s alternator will spin at 3,600 RPM. If the rate is appreciably higher or lower than that, it could lead to instability and electrical fluctuations. Your flickering lights will be a symptom of the problem.

Why Might Your Lights Flicker When Using a Generator? 

  • Defective dimmer or switch
  • Wiring connections that are detached or out-of-date
  • Service complication with electric utility
  • The light plug is disconnected
  • Loose or unsuitable lightbulb
  • Voltage drop produced by HVAC system or appliances
  • Faulty meter box
  • Main service cable connection error
  • A circuit is experiencing a sensory overload

How Do I Measure My Alternator’s RPM?

Use a tachometer or an ammeter. Turn off the engine and disconnect the generator to make sure there is no load applied to the generator.

Turn on the engine for 30 seconds. Take a reading with the tachometer or ammeter. The number that appears will be your RPM.

How Do I Test My Generator for Overloading?

Your generator’s engine size determines how much power it can supply to your home. If you have a large home with a sump pump, high-end kitchen appliances, central air and heat, a media room, and so on, you will require a lot of power for backup when there’s a power outage.

If your energy use edges towards capacity, your generator may drop frequency and voltage. As your energy usage varies, the generator’s voltage could fluctuate, causing lights to flicker.

Check the owner’s manual and determine the maximum load for your generator. Test the generator to make sure it can handle the indicated load.

Turn almost everything off. Then turn one appliance back on at a time. Note how much energy is being used when the lights begin to flicker again.

If it’s significantly lower than the minimum load listed, then you’ll have to check your electrical and mechanical systems.

How to Stop Your Lights from Flickering on Generator Power

There are many reasons why lights flicker when using a generator, but let’s discuss the most dominant explanations and your next steps to resolve the issue.

Make Sure Your Generator is Connected Properly

Your generator has something called a “neutral.” Oftentimes, if this floating or bonded neutral plug is not fully attached to your generator, it could cause the electrical voltage to fluctuate.

Additionally, generators are overall not as powerful as the utility itself. If the problem persists after checking your connection, the issue could be internal and in need of an expert eye. 

Change the Lightbulb Type 

The most habitual reason for your lights to flicker when using a generator is that you may want to acquire a new bulb, preferably one that is incandescent rather than LED.  

LED light bulbs are notorious for flickering while linked to your generator due to their incompatibility with your dimmer. Nonetheless, people tend to gravitate towards LED bulbs because they are far more cost-effective and energy-saving. 

Contact Your Local Electrician

Not all solutions are achievable on your own. It’s vital to know when a predicament may require some assistance. 

If the fault on your generator does not seem obvious, calling the company that installed your generator or even your local electrician is the safest option. If you let it sit without repair, the consequences could be hazardous. 

Access an Oscilloscope

Find someone who can provide you with an oscilloscope to monitor your alternating current (AC) and direct current (DC) lines. The most dominant type of oscilloscope available today is digital.

Oscilloscopes are quite expensive. Therefore it’s better to contact someone who already possesses one.

What Mechanical and Electrical Problems Should I Test in My Generator?

The Fuel System

Examine the fuel line. A generator’s gasoline or diesel fuel tank is connected by pipes to the engine. Find out if the fuel is dirty or the fuel line is clogged or pinched. Make sure the filter is not clogged. Check your carburetor. It could also be clogged.

The entry of fuel into the generator is set by the fuel controller, MPU, and actuator. Check the settings. Compare them to the ratings in the owner’s manual.

Check the fuel pump to see if it’s damaged. The more advanced systems, such as the fuel injector, may have to be examined by a specialist to see if they are working properly.

Automatic Voltage Regulator (AVR)

The AVR automatically maintains your generator’s voltage at a set value. It begins the process of converting AC current to AC voltage. It works almost like a thermostat.

It will adjust the system as the load and operating temperature change. Once the system achieves capacity, it settles into equilibrium.

Read the AVR settings. If they match the standard settings in the owner’s manual, then you can check the AVR off your list. It’s working properly.

But if the AVR readings are varying more than a few volts, this means its internal controller is going bad. You can’t fix this. It’ll have to be replaced.

Cables and Connections

If all of the above systems are working correctly, then carefully check every cable and connection in your generator. Voltage fluctuations can occur due to worn-out cable leaking or peeling.

Check electrical cable insulation. If its resistance value isn’t adequate, it could be causing shorting.

Examine every cable terminal and connection to make sure nothing has corroded, broken, or gotten loose. Sometimes, plastic covers will get loose and cover the contacts.

Insects often get in there as well. Adjust or remove everything that’s amiss.

What Other Problems Could Be Causing My Generator to Make Lights Flicker?

  • The insulator on one or more of your spark plugs could be cracked. This would cause power fluctuations.
  • Also, check for heavy carbon buildup. Use a spark plug tester to see if there’s a visible spark when the engine is working.
  • Poor maintenance causes more problems than most factors. Increased wear and tear leaves your generator more vulnerable to power surges.
  • Old age could be the culprit. Engine parts can fail. As they do so, they can draw unevenly on your electrical system.
  • Check your records on the generator. How old is it? Has it lasted past its expected service life? If so, it’s time to consider replacing your generator.

What Should I Do Next?

If after all your efforts, you can’t find what’s wrong with your generator and you are still experiencing flickering, this is the time to bring in a professional.

Your generator may be suffering from a faulty part or a failing mechanical system. Most homeowners don’t have the expertise to fix these problems.


  • https://diary-of-electric.blogspot.com/2018/12/causes-of-voltage-unstable-in-generator-and-the-solutions.html
  • https://www.thisoldhouse.com/electrical/21015441/power-on-demand-how-it-works
  • https://www.generatorjoe.net/html/stepxstepgenerator.html
  • https://generatoradvisor.com/what-size-generator-do-i-need/
  • https://www.generatorsource.com/How_Generators_Work.aspx

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