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How Does an Electric Generator Work?

Generators allow businesses and homeowners to continue their daily operations during a power outage. In an emergency, a backup generator may even save lives. Look below at how generators work and learn how to troubleshoot common generator problems.

Energy transformation

In the early 1830s, Michael Faraday discovered the principle of electromagnetic induction. He learned that moving conductive material through a magnetic field generates an electric current. Modern generators use a rotor to create a magnetic field that forces an electric charge from one end of a copper coil to the other. This produces electrical energy in the form of an alternating current.

Parts of a generator

There are eight main components to a generator.

1. Generator engine

The engine supplies the mechanical energy necessary to generate electrical energy. The bigger the generator engine is, the more power the unit produces. Most portable generators or home-sized standby generators run on gasoline. Industrial generators run on a variety of fuels, including diesel, liquid or gaseous propane, and natural gas.

Lubrication is required to help the engine run smoothly for long periods and to prolong the generator’s life. Check oil pump levels every eight hours of generator operation. Change the oil and check for leaks every 500 hours of generator operation, approximately once every three weeks of continual use.

2. Alternator

The alternator contains a stationary stator and moving rotor inside a housing. It converts the engine’s mechanical energy into electrical power. The stator consists of copper wire coiled over an iron core. The rotor produces a moving magnetic field around the stator through induction, permanent magnets or through a small source of direct current called an exciter.

Alternator durability plays a significant role in the life of the generator. Metal housings last longer than plastic ones, and ball bearings are preferred over needle bearings. Brushless designs have a longer life, require less maintenance, and run quieter than other designs but are only available in larger units.

3. Fuel tank

The fuel tank usually holds enough fuel to last for an average of 6 - 8 hours. On small generators, the tank is part of the skid base or is mounted on top of the generator frame. Commercial generators may require installation and use of a permanent external fuel tank.

4. Voltage regulator

The voltage regulator is part of a four-step cycle of voltage regulation that equalizes the generator output:

  1. The voltage regulator converts a small portion of AC voltage and converts it to DC current, which is fed to secondary exciter windings.
  2. The exciter windings use direct current to generate a small AC charge that powers rotating rectifiers.
  3. The rotating rectifiers convert the AC voltage to direct current a final time.
  4. This direct current boosts the rotating electromagnetic field produced by the rotor, increasing the generator output of AC voltage.

The generator cycles through voltage regulation until it reaches full capacity, then produces just enough DC current to keep the unit operating at full capacity. When a new load is added to the generator, voltage dips slightly, triggering a new cycle until equilibrium is reached again.

5. Cooling and exhaust systems

Both the combustion reaction used to fuel the generator and the friction created by moving parts produce heat. Large industrial generators may use a water-filled cooling tower or a combination of hydrogen and water to cool the unit. Smaller residential and commercial units use a radiator and fan as the primary cooling system. At least three feet of space on each side is required for free air flow.

The exhaust system must be vented outdoors. Incomplete combustion reactions produce carbon monoxide, an odorless, invisible gas that slowly suffocates humans and animals. The exhaust pipe should lead away from doors, windows or other openings to the house or building.

6. Battery charger

The generator start function is battery-operated. The battery charger keeps the battery charged by supplying it with a direct current float voltage of 2.33 volts per cell. Since the battery charger voltage is isolated, generator output is not affected.

7. Control panel or operation gauges

Control panels measure generator output current, voltage, and operating frequency. Some units have an auto-start option that automatically engages the generator during a power outage. The automatic function also monitors output during use and shuts the generator off when power is restored.

Engine gauges may display oil pressure, coolant temperature, battery voltage, engine speed, and how long the generator has been running. Many generators have a fail-safe that automatically shut the unit down when it exceeds safe operating parameters.

8. Frame

Every generator has a customized housing for structural support. The frame also provides a way to ground the generator for safety.

Common generator problems

Most people do not think about their generator until there is a power outage. Here are some common problems you may experience.

Low or gummy fuel

If you only use your generator in emergencies, the fuel level may be low. Check it and add more if needed. Fuel that sits for extended periods degrades and becomes gummy. If degraded fuel has clogged your carburetor, the engine may need an overhaul before it will start. Consult a licensed mechanic for assistance.


Standby generators contain an automatic shut-off switch that activates when the unit overheats. Overheating is frequently caused by low oil levels. Turn the generator off and add up to a quart of motor oil to your unit. Check your owner’s manual for specifics.

Tripped circuit

Both power surges and overloading the generator can cause the circuit breaker to trip. Check your home’s access panel for blown fuses or a tripped breaker. Reduce the number of appliances powered by the generator to avoid tripping the circuit again.

Not level

Many generators require a level surface to operate. Move your portable generator to even ground and try again.

Worn out parts

Check the owner’s manual for information on how frequently air filters, fuel filters, and spark plugs should be replaced. It is a good idea to keep spares on hand in case of an emergency.

Drained Battery

If the self-starter fails, the battery may be dead. You may be able to field flash a portable generator with an electric drill. Make sure the drill is set to rotate forward. Plug it into the generator’s 120-volt receptacle and hold the trigger down for several seconds. The small electrical charge generated by the drill should start the generator. If this does not work, try running the drill in the opposite direction in case the reverse switch is in the wrong position.

For additional help troubleshooting or repairing your generator, consider asking a licensed mechanic for assistance. Verified Experts on JustAnswer have years of experience and are available any time, day or night.

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