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How does a generator work?

Standby generator power is crucial for businesses in this day and age, and having a reliable critical power system in place can save the day in the event of an unexpected mains outage.

Diesel generators are a popular choice for businesses who need to be able to ensure no disruption to processes or loss of data due to a power cut. A power outage can happen at any time (usually when you least expect it). Outages can be caused by issues with the national grid, severe weather, electrical current failure and more.

So, you need a backup power supply to minimise downtime and keep your business online. But how do generators work, and why should you consider adding one to your business plan?

At Vital Power we specialise in UPS (Uninterruptible Power Supply) solutions as well as generators, and our team has put together this guide to everything you need to know about generators and how they work. So, read on to find out more about our backup power generators…

What is a generator?

First things first – what is a generator anyway? A generator is a device (standalone or unconnected to the mains) that produces electrical power. They are used to produce electric current power and electricity when the mains power has an outage, blackout or brownout.

Generators are most often used as standby power options, and our range of backup generators is designed to provide emergency critical power solutions for businesses in emergencies and power outages. Generators come in a variety of sizes and types (from a classic standby generator to portable generators), and can function to power homes, small businesses, commercial sites (such as distribution centres), or organisations (such as hospitals and universities).

Electric generators come in a few varieties and can be powered by various fuels. Diesel generators are some of the most popular for industrial use thanks to their affordability and efficiency. Petrol (or gasoline) generators are generally used for smaller loads, and tend to be louder than diesel equivalents. There are also natural gas generators – which are obviously more environmentally friendly than both petrol and diesel generators. Another type is propane generators, which is an eco-friendly option usually preferred when natural gas generators can’t be used.

Step-by-step: How a diesel generator works

Fuel Injection

Within the diesel generator, the combustion process begins with the first injection of diesel fuel into the engine’s combustion chamber. This is usually done with a fuel injector, which sprays a fine mist of diesel into the compressed air within the cylinder.

Air Compression

The diesel engine then compresses the air within the cylinder. This compression raises the temperature of the air inside, creating an environment for combustion. Diesel engines use higher compression ratios than petrol engines, which is why they’re so efficient.


Once the air is sufficiently compressed, the fuel injector sprays diesel into the hot, compressed air. The high temperature causes the diesel fuel to instantly combust. This rapid combustion generates a significant amount of heat and expands the gases within the cylinder, pushing the piston down.

Piston Movement

The force generated by the combustion process causes the piston to move down within the cylinder. This movement is converted into rotational motion through the engine’s crankshaft.

Crankshaft Rotation

As the crankshaft rotates it drives the generator’s rotor, which is connected to the electrical generator. This rotational motion is converted into electrical energy through electromagnetic induction.

Electromagnetic Induction

The rotor, usually a magnetic field, rotates within a set of conductors, or stator. This relative motion starts an electrical current in the stator windings, following the principles of electromagnetic induction as described by Faraday’s Law.

Generation of Electrical Power

The induced current in the stator windings produces electrical power. The generated electricity is produced in the form of alternating current (AC).

Voltage Regulation

To ensure a stable voltage output, diesel generators typically incorporate voltage regulation systems. These systems monitor the generator’s output and adjust the electrical field or excitation to maintain a consistent voltage level.

Generator components

Cooling Systems

Diesel generators produce a substantial amount of heat during operation. Cooling systems, for example radiators or heat exchangers, dissipate this heat to prevent overheating.

Exhaust System

The combustion of diesel fuel produces exhaust gases. Diesel generators are equipped with exhaust systems, including mufflers and sometimes catalytic converters, to manage and minimise emissions.

Control Systems

Advanced diesel generators feature control systems that monitor and manage various factors, including load, temperature, and fuel levels. These systems can automatically start or stop the generator based on demand.

Generator - Vital Power

How do generators make electricity?

Generators don’t actually make or create electricity. An electric generator uses a process and converts mechanical energy (or chemical energy) into electrical power. This process involves forcing electrons through the generator’s electric circuit. Diesel generators use the fuel to generate mechanical power in a diesel engine that is then forced into a circuit to power buildings, devices and more.

Despite what you might naturally assume, when it comes to diesel generators there isn’t actually any real ‘generation’, or ‘creation’ of electricity. The way generators provide a source of power to the devices connected is electromagnetic induction.

The process of electromagnetic induction was discovered by Michael Faraday in the 19th century, and refers to a way of converting mechanical energy into electrical energy.

So, in basic terms, this is how generators work to provide a source of electrical power:

Inside the generator, a copper coil called the armature sits between two poles in a magnetic field. This is then rotated by a shaft powered by an internal combustion engine or some kind of turbine.

When the armature passes through the field, it generates a voltage or electromotive force (EMF) in the coil. This voltage then causes a current of electricity to flow – this current is the electrical energy ‘generated’ by the generator.

The electrical output from the generator is typically alternating current (AC) power. Some generators produce direct current (DC), but AC is much more common.

Do generators automatically turn on?

Generators work using a control system to operate, and need to be switched to in order to power electricity. This can be done manually, though this means that in the interim after the outage and before the generator is switched on, you may have some downtime. This can lead to data loss, loss of profits or disruption to your daily processes.

Many businesses opt to use a control panel with their backup generator in order to automatically switch between mains power and generator power. Using ATS (Automatic Transfer Switch) or AMF (Automatic Mains Failure) panels is one way to ensure a smooth transition and to limit any loss of power. ATS or AMF panels automatically detect the A/C supply and loss of mains power, and will switch to the generator when it needs to.

Wondering which panel is right for your generator? Read more about ATS or AMF panel choices on our blog.

What are the parts of a generator?

Generators are made up of lots of parts, with nine main ones:

  • Engine
  • Fuel system (pipes, fuel tank and more)
  • Control Panel
  • Alternator
  • Exhaust System (also called the Cooling System)
  • Voltage Regulator
  • Battery Charging Point
  • Lubrication System
  • Main Frame or Assembly

Parts of a generator - Vital Power

Generator Engine

Perhaps unsurprisingly, a generator’s engine is one of the most important parts. How much power your generator produces and how many devices or buildings it can power will be decided by the size and overall power of the engine.

Generator Fuel System

Another big hitter, the fuel system is what keeps your generator running. The overall fuel system is made up of a number of parts – including a pump for fuel, a return pipe, fuel tank and a connecting pipe running between the engine and the fuel tank.

Generator Control Panel

As the name suggests, the control panel is what controls the overall running of the generator. ATS or AMF panels can automatically detect loss of A/C power from the mains and switch the generator power on.

Generator Alternator

The alternator (sometimes called the genhead) controls the process by which mechanical energy (or chemical energy) is converted into electrical energy. The alternator system creates the electromagnetic field that generates electricity.

Generator Exhaust System / Cooling System

By their nature, generators get hot. The electrical generation process produces a lot of heat, and it’s important to keep things cool so nothing burns out or overheats. Diesel fumes and other heat will be removed by the exhaust.

Generator Voltage Regulator

It’s important that the generator power is regulated for a steady flow that won’t blow any devices. If required, the voltage regulator can also convert power from A/C to D/C.

Generator Battery Charging Point

The charging point means the generator is always ready when you need it for emergency or standby power. It supplies a consistent flow of low voltage energy to keep the battery ready.

Generator Lubrication System

All the parts – nuts, bolts, levers, pipes – in a generator need to keep moving. Keeping them lubricated with enough oil can stop generator parts from wearing, rusting and breaking down. While the generator is in use, it’s important to keep an eye on the lubrication level.

Generator Main Assembly / Frame

What holds it all together – a sturdy frame structure that holds all the above parts together.

For a full guide to all the parts in a well-equipped critical power system, read more about our generator parts diagram.

What size electric generator do I need?

It’s important to get the right sized generator. If it’s too small, you won’t be able to power everything you need in the event of an outage. Undersized generators can also struggle to power the load you need, which can cause outages and strain on the machinery. However, a generator that’s too big can also lead to a wastage of resources, damaging any connected machines and overspending on the budget.

The size or voltage of the generator you need will depend on how much electrical power output you need. We recommend adding up the wattage of all possible devices, buildings and services you’ll need to power. The Vital Power team can help calculate the total power requirement of your system in kilowatts (kW) and kilovolt ampere (kVa).

Generator Engine - Vital Power

Where to buy a generator

At Vital Power we stock a range of leading brand names, with generators to suit every business or facility. Whether you want to hire a generator or upgrade your site with a generator system of your own, our team can help.

We offer a complete range of major and minor services for generators, so the maintenance of your generator is handled by our team of engineers.

Read more about Vital Power to understand our full range of services, or browse our generator blog posts for more information.

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