Diagram on how a generator produces electricity. (Briggs & Stratton Q6500)
How does a generator work? We all know that generators produce electricity for us to use but most people don’t really understand how generators actually work. To be honest, a lot of people don’t care but some of us do, including you, so welcome to this informative article written to answer your questions.
Intro | How Does A Generator Work?
An electric generator is a machine that converts a form of rotating mechanical energy into electricity. The mechanical energy is obtained from steam turbines, gas turbines, water turbines, internal combustion engines, and even hand cranks.
The British scientist Michael Faraday discovered electromagnetic induction in 1831. He discovered that a moving magnet close to an electrical conductor generates an electromotive force in it. Through his discovery, electricity was transformed from a curiosity into a powerful new technology. It is the principle behind the electric transformer and generator.
The turning disk induced an electric current radially outward. (more)
Michael Faraday built the first electromagnetic generator, called the Faraday disk. It used a copper disc rotating between the poles of a horseshoe magnet. It produced a small DC voltage and current. His invention was too inefficient to be of much practical value.
Experimenters using his principles later realized that multiple turns of wire that are wound in a coil could produce higher, more useful voltages. This discovery that the output voltage is proportional to the number of turns in the coils is the basis of generators and transformers used today. Generators can be designed to produce any desired voltage by varying the number of turns.
This discovery developed into the sophisticated generators we use today. The first generators converted kinetic (mechanical) energy into electrical energy with permanent magnets. At one stage they produced nearly all of the consumed electricity.
Today, the generator uses an electromagnet, and no longer permanent magnets. An electromagnet is a magnet produced in a wire coil by electricity. The construction of the generator differs from the one with permanent magnets. It has a series of insulated coils of wire that form a stationary cylinder (The stator). Mounted within this cylinder is a rotary electromagnet on a shaft (The rotor).
When the electromagnet rotates, it induces a small electric current in each section of the stator. Each section of the stator becomes a small, separate electric conductor. The small currents of the individual sections combine to form one large current. This current is the electricity that moves through the power lines from generators to consumers.
VIDEO | Detailed Explanation on How Generators Work
The current portable generators and home backup generators use the same principles used in industrial installations. A petrol engine drives an alternator that produces the electricity.
Some entry level generators generate 120 volts AC only, while others generate 120 and 240 volts AC. It generates electricity using one of two methods: The regular open frame generator uses a multi-pole alternator based on electromagnetic excitation. A newer variant, the inverter generator, use a brushless alternator with rare earth magnets to generate electricity. The output is converted and delivered to an inverter that cleans up the signal.
In this discussion, I explain in more detail how a portable generator works, and I even compare them to whole house standby generators.
Components of a Generator?
To understand how a generator works we’ll start by dissecting the generator and briefly discuss the different components.
Alternator
The alternator is the component that generates the electricity. We call the machine a generator because it generates power, not because there is a generator inside. The common name for an alternating current generator is an alternator while you should call a direct-current generator a dynamo.
Modern synchronous generators use revolving field alternators. The armature windings are stationary and provide the power without using brushes. The slip rings and brushes deliver the DC excitation power to the revolving field windings so that the electrically generated magnetic field rotates.
Alternator vs Generator — What’s the Difference?
Many people confuse alternators & generators. (Amazon : Westinghouse 120001)
The speed of the revolving field is the same as the speed of the motor; it determines the frequency of the AC voltage. The regulator controls the voltage and amperage by varying the current in the DC field windings. The generator converts the engine power to electrical power. A synchronous generator has precise control over the voltage and amperage it generates. But, with varying loads it cannot always keep the frequency constant. You will hear this as the small drop in engine speed when a load is applied to the generator.
The AC frequency depends on two factors: the number of poles in the alternator and the speed of rotation (rpm). A two-pole generator must maintain a constant speed of 3600 rpm to provide 60 Hz. A four-pole generator rotates at 1800 rpm to produce 60 Hz. Unfortunately, a gas engine is underpowered at 1800 rpm; it can only deliver maximum power at close to 4000 rpm. To keep the engine within its power band generators use two-pole alternators. The regulator controls the frequency at 60 Hz by controlling the engine speed at 3600 rpm with a stepper motor.
Voltage Regulator
The voltage regulator control the current in the DC field windings, it measures the output voltage and compares it with a reference voltage. The circuit then adjusts the excitation current of the magnetic field windings up or down to keep the output voltage at its rated value.
VIDEO | Replacing a Voltage Regulator on your Generator
Cooling & Exhaust Systems
Cooling a synchronous generator is essential because it produces lots of heat. Portable generators use forced air circulation to cool both the engine and the alternator. A fan driven by the engine takes in cooler air from the atmosphere and blows it internally across the two. All heated air disperses back into the atmosphere. The open frame design of the generator dissipates heat better, but the engine, fan, and generator noises are louder. There is no noise blanking and the noise can be annoying to bystanders. Therefore, you need to move the generator a distance away to make it bearable.
Engine
Generator engines stem from small stationary industrial engines. Most engines used in portable generators are four-stroke engines. At the required 3600 rpm, four-stroke engines deliver more torque than two-stroke engines, and they adapt easily to clean air regulations. The power requirements of the generator determine the engine size. They start from 50cc Overhead Valve (OHV) engines up to twin-cylinder 670cc, 4-stroke, OHV engines.
Honda uses their own Engines to Power their Generators
The Honda EU3000iS is powered by their GX200 4-stroke engine.
All the engines use forced air from a fan attached to the one end of the crankshaft for cooling. The same air passes over the alternator in most portable generators although some have a second cooling fan for the alternator.
Big and small engines use transistorized magneto ignition systems to ensure that the engine starts immediately and runs smoothly. The smaller engines start with a recoil starter system that requires you to pull the cord to start the engine. Some bigger generators have an additional 12 Volt electric starter motor for starting the engine. The recoil starter remains for use as a backup.
Lubricating the engine is normally by splashing oil on the critical components of the engine internals. I’m aware of only one portable generator engine that has an oil pump to force oil circulation.
All engines use unleaded gasoline with an octane number 86 or higher to ensure the engine will meet emission control regulations. The compression ratios are relatively high too. The exhaust of the generator engines reduces noise levels as much as possible. They also build a spark arrestor screen into these exhausts to prevent bushfires.
Fuel System
Fuel tanks are normally steel units and mounted on top of the alternator and the engine. Even the smallest of these engines use a float type carburetor, and it is the reason we must use the generator on level ground. It uses a fuel shut to close off the fuel supply from the tank to the carburetor. You use it with a drain valve that’s fitted to some carburetors to drain fuel from the system. For carburetors without a drain valve, you close the fuel shut-off valve while the engine is running and the carburetor run dry. The carburetors on most generators use a manual choke for cold starting. Generators fitted with remote start fobs mostly use an automatic choke. A dry type washable or throw away filter protects the carburetor from inhaling dirty air.
Battery Charger
Some generators provide a battery charger output for charging car batteries. The alternator normally has a separate small winding for this purpose. A rectifier converts the AC from this winding to unregulated 12Volt DC on the control panel that’s protected by a fuse.
More advanced generators with electric starters rely on a small onboard battery to start the engine. The battery charger maintains the battery voltage while you use the generator. It uses a sample of the unregulated 12 Volt DC voltage to charge this battery. A built-in regulated battery charger controls the charge delivered to the battery to prevent overcharging.
Control Panel
The control panel provides a convenient means of mounting all the controls and voltage output receptacles. They usually fix it to one side of the generator, but some models have it mounted to one end. Controls, outputs, and current protection switches are grouped neatly and marked clearly. On some models, rubber covers protect the outputs from dust and moisture. The advantage is that these connectors maintain good contact during extended use.
Westinghouse Control Panels are Easy to Use
Westinghouse WGen9500 control panel shown.
Sizing generators
Manufacturers show the size of a generator either in Watts (W) or Kilowatt (kW). They may also express it as Volt-Amps (VA) or Kilovolt-Amps (kVA). KW is the unit of real power and kVA is a unit of real power plus re-active power. The kVA value will always be higher than the kilowatt value.
We calculate the power requirements of the generator using the Watts figures. When specifying equipment loads, protection circuits, and wiring sizes you use the VA, or the RMS voltage and RMS amperage.
Specifications show generators sizes with two ratings, starting power or start-up power and running power. Running Watts, or rated power, refers to the maximum continuous power a generator can supply. The starting wattage is the most the generator can deliver for a short period before the protection circuits remove power. It is a buffer that provides extra power for appliances and tools that need it when starting up.
Portable generator vs. home backup generator
Portable generators are meant to be portable; you must be able to move and transport the generator without special equipment. Therefore, the weight of the generator finally limits the power and portability.
Home backup generators weigh a lot and are permanent installations done by professionals. They connect the generator to the house wiring with an automatic transfer switch. They install it on a solid base, and the generator has a permanent cover with sound damping material. These units use bulk fuel storage facilities.
In comparison to portable generators, home generators are expensive. Home generator installation costs are high too, from $4,000 to $10,000. Despite the costs involved, they offer some advantages over the portable generator installations.
Portable Generators
Besides powering the home, you may use portable generators on job sites. Take it to camps, and other remote locations, or use it for tailgating and food trucks. In addition to their versatility, they are cheaper too.
However, as a home backup unit they have many disadvantages:
- Portable generators powers pre-selected key appliances but not all of them.
- You must be present to detect the power loss. Then you have to remove the generator from storage, earth it, and top-up the fuel.
- You may need to protect it against stormy weather.
- Next, you manually connect the generator to a transfer switch before you can start the generator and manually switch over the circuits.
- Depending on the electrical loads and the size of the fuel tank, you must refuel it every 4 to 10 hours.
- You must periodically check the fuel level and power loads.
- When utility power returns, you have to stop the generator and prepare it for storage.
Automatic home standby generators
- These units are not portable, but fixed permanent installations dedicated to back up the home power supply.
- They either power the entire home or selected circuits by monitoring the load.
- It detects when utility power falls away and starts up the generator automatically.
- Without your involvement, power switches over to the generator unattended, and it controls the house circuits automatically.
- The generator will need no refueling when connected to your natural gas line.
- Propane and diesel options offer long run times.
- You may monitor some installations remotely from your smartphone, tablet or PC.
Fuel selection
You will prefer natural gas, where available in sufficient quantities because it burns clean, the price is reasonable, and your generator runs indefinitely.
Propane is clean-burning and stored in a pressurized outdoor tank. It is stored on site and must be re-filled. You use Propane when natural gas is unavailable or inadequate.
Diesel has the advantage that it is not flammable and its tank isn’t pressurized. On the negative side, it’s not as clean burning as natural gas or propane, and you must stabilize diesel to keep it fresh.
The smaller portable generators mostly use gasoline. Gasoline has a limited shelf life and you must store it in airtight explosion proof containers. You need to stabilize gasoline to prevent gumming and must drain the fuel lines before you can store the generator.
Examples of Generator Installations
Power just the basics
A simple, economical approach provides automatic backup protection for essential circuits such as the well-pump, refrigerator, furnace, and sump pump. They start at 7,000 Watts and costs start at $1,949 plus installation fees, depending on which company you choose. Prices will vary.
Smart power where needed
Whole-house protection, without paying for the bigger generators that do the whole home. It can protect all your home’s circuits by cycling power on and off as needed for different appliances, and you decide what gets priority. Depending on the installation they deliver between 16,000 Watt to 22,000 Watt, and prices start at $3,459 plus installation. Prices will vary. Choose wisely. Do you research on the reputation of the company.
Power it all, all the time
These units offer complete peace of mind. Whenever there’s an outage, the power switches over and stays on at all times throughout your entire home. They range from 22,000 Watts to 150,000 Watts, and prices range from $4,799 to $30,000.
Difference between inverter generator and a conventional generator
A problem of the regular generator is distortions in the alternator’s AC signal. It’s not a pure sine wave but effectively simulates a sine wave. The following drawing shows the wave from a typical non-inverter generator.
The Westinghouse WGen7500 is an example of typical gas generator.
Design flaws in the alternator cause signal distortions that mostly do not matter. However, sensitive electronics such as WiFi units, cellphones connected to a charger, radios, and computers, can overheat and malfunction.
Frequency shifts
Another problem is that the synchronous operation of an engine driven generator is not entirely controllable. (. Also discussed in our previous article Inverter Vs Generator? What’s The Difference? It must deliver a sine wave with a constant frequency of 60 Hz with less than 1% deviation. However, the speed of the engine determines the AC frequency, which is difficult to control precisely. The engine must maintain a constant 3600 rpm to do so, but when the generator load changes it fails. When the load suddenly changes, the engine speed drops, or it speeds up. The controller reacts but the engine cannot adapt fast enough, and speed changes lag. The variations in engine revolutions cause a frequency shift away from 60 Hz.
The Honda EU2200i is an example of an inverter generator.
The blue sine wave in the drawing shows a pure sine wave with 0% THD. The AC sine wave should preferably be without any distortions or noise in the signal. When you compare the blue line to the black line, you can see how the shape of the wave changes due to the signal distortions. The frequency shift that’s caused by changes in engine speed is also visible as the two frequencies shift apart. The results of the frequency shifts are noticeable in speed changes of induction motors.
What’s Total harmonic distortion?
The black line in the above picture is a complex sine wave which is just a composite of multiple waveforms called harmonics. Total harmonic distortion (THD) is the sum of all harmonic waves of the voltage or current waveform compared to a pure sine wave. The harmonic distortions of the sine wave have been with us since they delivered the first utility power. They were negligible at first because of the lack of non-linear loads before the 1960s. Since then non-linear loads became more prevalent. These loads include electronic ballasts, computer power supplies, Industrial welders, and variable frequency drives.
The current flowing in power systems can increase when unwanted harmonic distortions are present that causes higher operating temperatures. In motors the higher frequency harmonics increases core loss, resulting in excessive heating of the rotor core. These higher order harmonics can also affect communication transmission. If left unchecked it raises the temperature of electronic components. The harmonic interference can shorten the life of electronic equipment and cause damage to power systems.
No national standard dictates total harmonic distortion limits, but IEEE Std. 519 recommends values for acceptable harmonic distortion. From this recommendation, they set voluntary restrictions on voltage harmonics at 5% THD and 3% for any single harmonic.
Parallel Mode
Paralleling conventional generators that provide redundancy in power backup installations are common in industry. They use specialized switch-gear that skilled electricians must install. The manufacturers of inverter generators found a unique way of making it available to unskilled users. Because the inverter module supports sine-wave synchronization, it was possible to offer a simple, cost-effective solution.
Run in Parallel & Double Your Power | Yamaha EF2000iSv2
Double your power output by running 2 in parallel. (AMAZON)
To let two inverter generators run in parallel mode, you join special parallel mode connectors on the generator with a connection cord. The parallel cord has a connection module with outlets that can deliver double the power available from the individual generators. Parallel cord connectors differ amongst generator manufacturers. You may only connect two compatible inverter generators from the same manufacturer.
With the parallel cord connecting two generators there is no risk of damage to the generators when only one generator is running. The inverters can handle it because they have to allow one generator to start or stop at a time. It can also happen that one generator will run out of gas with the other still running. Know that you can only connect or disconnect the parallel cord while the generators are not running.
How does an inverter generator work?
The inverter generator generates a pure sine wave at the correct frequency and amplitude. This is independent of the engine speed. In the drawing, of sine waves the blue wave is the output from an inverter.
An inverter generator uses an engine to drive a multi-pole brushless AC alternator that uses rare earth magnets to produce multiple high voltage AC signals. It has a high-frequency AC signal, with fluctuations in both the frequency and voltage. It rectifies the AC from each pole to DC; which is joined into one DC output. This DC voltage (180-200 VDC) supplies power to the inverter module. The inverter controls power devices like the engine speed with a microcomputer.
VIDEO | What’s an Inverter Generator?
The inverter has a PWM controlled circuit, generating its own 60 Hz sine wave. It amplifies the sine wave and uses the high voltage DC from the rectifiers to produce the 120/240 Volt AC output. The AC generated is independent of the signal values and distortions in the alternator. The micro-controller uses a stepper motor to control engine speed by varying the throttle to minimize fuel consumption and noise.
On the control panel you’ll find an economy, or “Speed control switch,” which locks the engine speed to maximum power. This switch operates in two or three modes to let the inverter module control engine speed for the quietest and most fuel-efficient mode of operation. It works best when powering resistive or constant loads like lighting, TVs, computers, electric heating, video games, etc.
When set to the constant speed mode, the engine speed remains at the most efficient speed. We use it with inductive loads like air conditioners, refrigeration, vacuum cleaner, and hand drills.
Manufacturers recommend using the full-power speed with high startup loads. A startup current created by a utility starting up is immediate and lasts for about one to two seconds. The engine cannot pick up speed immediately when the load suddenly increases. While the engine picks up speed, the current delivered to the inverter is lacking.
The advanced alternator used in inverter generators runs cooler than the synchronous alternator used in conventional generators. Its design exposes the windings, and they use forced air to cool it. Because of the improved cooling developers can cover the generator with noise reducing panels. It makes the generator quieter, and it has an appealing design too.
How much does a generator cost?
A rough guide based on size/type
Regular and Inverter generator price comparison :
To make a fair cost comparison between an inverter generator and a conventional one, I set out to find equally powered models from one manufacturer. I repeated the comparison with a second manufacturer, to make sure that my cost comparison is fair.
I compared the complete range of generators from both manufacturers to see how their model prices compare. Then I selected two models, an inverter generator, and a cycloconverter model — A cycloconverter converts a constant voltage, constant frequency AC wave to another AC wave with a lower frequency. Since both generators deliver the same wattage, I calculated the comparative dollar cost per kW. It turned out to be $776/kW for the Inverter generator and $509/kW for the cycloconverter model. Then I repeated the calculations for the second brand. I found that, for both, the dollar per kW cost is about 50% more than a regular generator.
I noticed that for any manufacturer the $/kW prices vary considerably between models with different wattages. So, I examined all the inverter generators from the two manufacturers to find the most cost-effective models. I found that for manufacturer ‘A’ their most cost-effective inverter delivers 2200 running watts. For manufacturer ‘B,’ it is a 2800 running watts generator. For both, the 1000-watt inverter generator is the most expensive per kW at close to $1000/kW. This means that if you choose wisely, you will be able to select a more cost effective model from the range. Generally, expect the buying price of the inverter generator to be about 50% to 90% more than a regular generator.
✓ To learn more about the cost of buying a generator read our dedicated article : How much does a generator cost?
Cost difference — Are inverter generators worth the extra cost?
In the above comparison, you pay around 50% more for the inverter technology. However, when we compare features, you’ll see that you buy more than just clean power.
- Some models have multiple pole alternator They reduce maintenance requirements and noise.
- Engine wear is lower because the engine is running at lower engine speeds when the economy switch is engaged.
- Models that feature an economy switch can reduce fuel consumption.
- It delivers clean power that is safe for electronic devices.
- Inverter generators are remarkably quieter than conventional generators.
- Some models offer a parallel mode to run two identical inverter generators in parallel, doubling the power output
- It has an appealing design.
Is the cost difference worth the advantages? It depends on your own set of requirements.
Dual Fuel Portable Generators
The distinct and principal advantage of buying a dual fuel generator is that it will be able to either use gas or propane. To determine how the gasoline consumption of dual fuel generators compare to their propane consumption we compared six generators from six manufacturers. The generators ranged from 7,500 to 12,000 Watts running power.
The dual fuel engines run on gas and propane, so the engine is not optimized for propane like engines designed exclusively for propane. The combustion process of propane differs from the combustion of gasoline. An engine is less effective on propane than gas as shown by the consumption figures given in generator specifications. But they pack a lot of energy into the small storage containers used for propane. The advantage is that the generator runs double the time that it runs on a tank of gas.
Gas vs. Propane consumption
To compare the fuel consumption of dual fuel generators, we need to look at their kilowatt-hours per gallon figures. For generators, we can interpret kilowatt-hours in the same way as you would miles per gallon with a car.
I’m using the specifications of a Champion Dual fuel inverter generator to illustrate my point. The chosen generator model for this example is the popular 100307 (3500W) — gives you 3.75 kilowatt-hours per gallon on gasoline. The power output on gas is 3500 starting Watts, and the running Watts is 3200.
On propane, it gives you 2.14 kilowatt-hours per gallon, and it delivers 3150 starting Watts and 2880 running Watts.
Therefore the output on propane is 10% less than running on gas. Propane consumption is 1.75 times more than gas consumption.
The main advantage it offers is that it runs on propane for 14.5 hours on a 25% load. It’s double the time it runs on a tank of gas. The figures from the other manufacturers deliver the same consumption and power ratios.
Versatility
Maybe the best example of the versatility a dual fuel generator offers can be a natural disaster. One that forces you to use the generator for days. Supplies of gasoline and propane may be interrupted periodically. However, it is unlikely that it will happen to both power sources at the same time. It is a lot simpler and more convenient to store bulk quantities of propane than gas. With a reliable dual fuel generator, you can use the type of fuel that is available to you. When one runs out, you switch to the other, and you have power for days.
Effectiveness
The dual fuel generator is less fuel efficient when using propane, and it also delivers less power. Yet, it can an effective backup machine like any other generator. The primary consideration is that you must choose your model carefully. You should use the propane figures when comparing models and choose the one that delivers the wattage you need as backup. The same is true if you need a dual fuel generator for any other task like taking it on camping trips or remote work sites.
Dual-Fuel vs Whole House Generators
Dual fuel portable generators are more versatile in that it runs where needed, it is easy to maintain and a lot cheaper. Maintenance on whole house generators are on the expensive side, and they also require installation. When comparing permanent home installations to dual fuel generators, the dual capabilities of the dual fuel models are even more decisive.
Applications / Uses for Generators
Backup power for your house
Depending on where you live, may determine how critical home backup is to you. For example, having generators can be a lifesaving source of both prime and standby power. Having a generator helps you to get back up and running straight away.
Standby power for businesses
Regardless of the size of your business, we recommend investing in a generator to keep it up and running during a power cut. Electric generators provide backup power to continue doing business during an unpredicted power outage. Generators can provide backup power to protect goods in coolers or keep the environment cool.
Temporary power on a construction site
Contractors work on many building sites where mains power is not available. Generators are often the only available power source. A carefully selected generator is essential for those invaluable power tools that keeps you competitive and ahead of competition.
Temporary power on a farm
Maybe you need power to comfort chickens, milk the cows and pasteurize milk during a power outage that last days. On remote farms, the generator is the only power source and then a permanent installation with bulk storage is a fantastic solution. Even as a backup to solar power.
Caravans/camping in remote locations
Small electric generators are ideal for camping and caravan trips as they provide power for lighting, entertainment, mobile phones and more. It may even be powerful enough to power appliances such as microwaves, hair dryers, showers, and even air conditioning.
Outdoor catering facilities
Wedding venues and other large outdoor catering events from your food truck may require a generator for power. You may use it to power extractor fans, freezers and fridges, lights, music, and point of sale applications.
Emergency life support
A generator that powers a small medical facility may be a life saver. To those who rely on machines to keep them alive it offers the freedom of being out in the open. Independent of utility power.