It is important to have a generator when the power goes out. Whether it’s for just a few hours or long term, most people do not want to be without their electrical appliances. The generator sets can vary in size, features, fuel types, fuel efficiency, run time, safety features, and price.
Before proceeding with generator buying, it is important to know what to look for in a generator to narrow down your options. We will take you through each of the essential features in some level of detail to guide you.
In North America, the power output of any generator is expressed in units of Watts (W) or just Kilowatts (KW). A 4-KW machine will deliver enough power to light up a hundred 40W light bulbs. In many parts of the world, the power output may be expressed in kilovolts – amperes (kVA) units. For any single-phase machines, watts = volts x amperes. The primary difference between the two units is the power factor of the connected load.
The three power ratings usually associated with generators are:
- Maximum Power: Generators deliver maximum wattage for about 30 to 60 minutes at a 10% duty cycle.
- Surge or starting power: Generators can tolerate the surge power for only a few seconds, mainly during the starting of motor loads. These are also known as starting wattages.
- Continuous power output: Also known as the running wattages, this can be delivered 24 hours a day at a hundred percent duty, limited by refueling consideration. It is, however, recommended to load the generator sets below 80% of the continuous rating for a longer lifespan.
Some of the manufacturers call their maximum rating the surge rating to confuse the issue. Others highlight their surge or maximum ratings to sell their product. Out of all the power outputs discussed above, continuous power is the one available to meet all your power needs as long as you want it.
The surge ratings are only applicable during the start-up of loads like electric motors, welding machines, battery chargers, and uninterruptible power supplies.
Consumer class generators can provide 1.2 to 1.5 times extra surge currents over their continuous ratings, while the construction class machines can surge 2 to 2.5 times their continuous output.
The performance of a generator set is judged by its ability to
- deliver the power requirements of the household it is connected to,
- while maintaining the desired power quality,
- serving the expected life with routine maintenance,
- in a safe manner.
The voltage and frequency vary with loads because they form a large fraction of the generator capacity, and these small generator sets do not carry enough rotating mass to keep the RPM steady.
Electric Power Quality
Power quality is defined as the ability of any electrical system to adhere to the established voltage, frequency, and waveform specifications.
While the loads may vary, you would like your generator set to have some form of control to hold the voltage steady. The under-voltage overheats the motor and dims lights, while over-voltage can lead to installation failures and short circuits. If you choose a conventional brushed or brushless type of generator, ensure that they carry some form of automatic voltage regulation.
All inverter-type generators need precise voltage control to operate electronic loads like computers and other digital devices.
Any conventional two-pole generator requires 3600 revolutions per minute (RPM) to generate power at a 60 Hz frequency. You will require a very sensitive governor to keep the revolutions of your Genset close to this speed. Inverter generators can adjust their speed according to load requirements and bypass the frequency/rpm nexus effectively.
Total Harmonic Distortion (THD and Clean Power)
Ideally, an alternating current should have a mirror image sine waves that are often referred to as pure sine waves or clean power. In practice, every wave carries some disturbances to distort its original waveform. Any non-sinusoidal is made up of infinite sinusoidal components called harmonics. Each harmonic has a frequency ‘n’ times the fundamental frequency (n varies from one to infinity). Total harmonic distortion presents the degree to which any voltage or current waveform is distorted.
Harmonics can cause transformer losses, motor losses & vibrations, damage to sensitive electronic equipment, and unbalanced neutral currents.
Brushless generators can cause as much as 40% distortion to these waves. If you are going to run Digital Equipment such as laptops, lab equipment, etc., you should look for a Genset with less than 5% distortion at full load. While some manufacturers provide the distortion data, others are silent about it. It is needless to mention that generators with lower total harmonic distortion are more expensive.
Engine or Prime Movers and their life
Light-duty gasoline fuel-powered generators have an operating life of close to 500 hours. You have to scrap such engines in 5 to 7 years. It is a much better bargain to buy a generator with reputed engine brands like Honda, Briggs, or Kohler.
All these engines have cast-iron cylinder sleeves, forged crankshafts, overhead valves (OHV), and ball-bearing mains. In addition, many of these top-of-the-line engines have features that distinguish them from other competitors, such as the fuel injection system of Kohler and the aluminum pushrods of Honda, to name a few.
Types of Generators
As a homeowner, you have four choices when it comes to the selection of a generator for your home.
- Standby generator installed permanently.
- A portable generator that can be moved around.
- One of the smaller inverter generators.
- A portable power station.
Some of the inverter and portable generators can be transported to a tailgate, while others are used as a backup power source at your house. Portable power stations use large batteries to store power and are used where it is impractical to run an outdoor generator.
We have discussed the different types of generators classified based on operation, quality, fuel burned, and application in our detailed article on the subject.
Gasoline is the default fuel. Most of the engines have been designed for it. However, it has storage and safety problems associated with it. Some owners use a propane generator, which is more expensive and less energy-dense than gasoline. But it has an infinite storage life.
Diesel engines cost 30 to 50% more than their gasoline counterparts but provide generator power for decades without major problems. If you want to go green, you can consider using solar panels in your home or your RV.
Just to recap, standby generators have higher initial costs, should be installed by a certified electrician, start automatically on power outage, have higher ratings among the four options above, provide diagnostic features and provide you with many fuel choices.
On the other hand, portable generators are less expensive, run on gasoline, can be used on and off from your house, should not be used in an enclosed space or very near your house, and requires shielding by a canopy during the rain.
The different choices for fuel for the generator sets include gasoline, propane, natural gas, diesel, biodiesel, and emulsified diesel. Important factors to consider before deciding to go with any particular choice of fuel are
- the cost of the engine,
- availability of fuel during the normal time and power outages,
- fuel consumption and related costs.
- impact on the environment,
- difficulty & costs associated with the fuel system installation, regulations related to storing fuel & fuel tank size, the shelf life of the fuel & the need for a fuel stabilizer. The larger fuel tanks will translate to much higher initial costs,
- safety of the personnel and fire hazards, and
- engine life
Some generator models will allow you to switch between the different types of fuels listed above. A dual-fuel generator aims at solving the fuel availability issue during times of emergency, thereby providing more flexibility and reliability.
The dual-fuel system can use two fuels at a time in a mixture. One type of fuel is used to crank up the system. Then the governor adds the secondary fuel source until an optimal mix is achieved. Dual fuel engines can run on a single fuel without the other fuel. However, it may require a particular fuel out of the two to start the engine. The starting fuel usually has a lower ignition temperature of two.
Carb or EPA Compliance
Carb-compliant generators are made to meet the stricter standards for emissions set by the California Air Resources Board, also known as CARB. If you are in California or other US states that follow the CARB regulations, you must check for the CARB compliance label on the generator set before purchasing it, as it is not permitted to sell or purchase non-compliant machines.
If you are in other states, you must still ensure the Environmental Protection Agency or EPA compliance. EPA is a federal body that can impose fines or sanctions for violations.
Occasional or Consistent Use?
The quality of the generator required depends greatly on its usage pattern. Most consumer generators from any reputable brand will work if you plan to use them only during an emergency or recreational use. However, if you buy a generator for consistent use, like at construction sites or outdoor applications, you should go for commercial generators.
Most stated warranties are for consumer use. The warranties for commercial applications such as using a device at a job site are much shorter.
Bigger fuel tanks allow you to have a longer time between refueling. Most standby generators come with a fuel tank suitable for about eight hours of run time at half the rated load. This duration can increase or decrease depending on the actual load. Larger tanks are more expensive and heavier when in full tank condition.
Some expensive portable generators come with the possibility of being fuelled from an external source, such as a natural gas pipeline.
Generator Placement and Operation
It is quite common to store a portable generator indoors and move them out of the storage area during an emergency and connect them to the home’s electrical system. However, you must exercise certain precautions listed below while placing and operating your portable generator.
Things to consider – Portable Generator Placement
- Never operate a portable generator indoors.
- Locate them at least 20 feet away from the house with their exhaust always facing away from all the doors and windows of your house.
- Place the generator on a level surface away from any source of excessive moisture or dust.
- There must be a clearance of about 6 feet on all the sides of the generator when it is running.
- Never allow children near the operating portable generator at all times.
- A portable generator must always be stored indoors and regularly inspected.
- You must prepare a protective canopy if you intend to run your portable generator during rain or snow.
Unless you are a diehard recoil cord fan for pull-starting an engine, consider buying a generator with an automatic or electric start.
A fixed system such as a standby generator is always connected to the fuel source and your home’s wiring. The automatic mains failure (AMF) mechanism, known as the automatic transfer switch, detects any loss of power, isolates the designated emergency electrical loads from the grid, and automatically starts up the generator. When the grid voltage restores, the AMF system connects your home’s electrical system back to the grid and turns itself off.
You are not required to be at home to operate the system. The typical transfer time of the AMF system is in the range of 10 to 30 seconds.
Many portable generators provide the convenience of electrically starting them through a push-button alternative. The only additional cost to operate this system is in buying the generator batteries, if not already included. It is a necessary feature for all engines displacing more than 300 cc. Some manufacturers include remote starting kits to provide additional convenience.
What To Look For In A Generator – Other Important Features
The noise level of any generator depends on its rating and the load it is handling. The smaller generators have noise outputs of 50 dBA, where dBA denotes the decibel measurement bias towards frequencies more sensitive to the human ear.
Generators with more than a 4 kW rating typically generate 70 dBA noise or more. This is sufficient to have your neighbors complaining about the noise levels. Most manufacturers specify noise levels at a distance of 3 m from the machine running at full load. Diesel generators have higher noise levels than the corresponding gas-powered models.
Electronic fuel injection results in better fuel economy, improved responsiveness, fewer exhaust emissions, and eliminates the need for a carburetor. In EFI systems, electronically operated injectors supply a precise quantity of fuel. This allows the catalytic converters to function properly and improve fuel efficiency and drivability.
An EFI system has an electronic control unit (ECU), a fuel pump, fuel injectors, and sensors on the engine and its exhaust and intake systems. These sensors measure temperatures, crank and camshaft positions, exhaust gas composition, and throttle position and feed the data back to the ECU.
The ECU then determines how long the injectors should remain open and the ignition advance. ECU may increase the injector pulse width during cold weather for an easy start-up.
Portable generators can be moved from one place to another and are connected to the load only when needed. The smaller size generator can be carried and placed by hand. The larger units are provided with wheels and lift hook bars to enhance movability.
Most units with a bigger generator size come with wheel kits to easily shift them around. If they are not a part of the complete generator package, you may have to purchase them separately. The wheel kit may comprise two or four wheels, depending on the unit’s weight. Adding wheels using generator dolly kits with basic tools is fairly simple.
Lift Hook Bar
Generators bought for commercial or industrial applications might have to be lifted to higher floors in the building. Lift hook bars are provided to facilitate the lifting.
Connecting a Generator to Your Home
In our detailed article on the topic, you can learn the details on how to hook up your portable generator to your home. In this section, however, we will talk about the provisions you must look at (in your selected model) before generator buying to facilitate connection to your home.
A smaller portable generator may have a couple of NEMA-5 120 V AC outlets and two or three USB ports. If you want to wire the generator directly to your power inlet box, you will definitely require a 240 V plug. As the generator is placed outside, you must look for GFCI-protected outlets in your portable generators.
If you use your generator to power your RV, you may need an RV-ready (TT-30R) outlet.
If you have selected a portable generator with more than a 4 kW rating and do not want a single power inlet box, you will require 240 V plugs with more numbers of 120 V outlets. Four or more such outlets will allow you to better use the wattage by distributing the load. Multiple outlets are more useful if you are going to use your portable generators at a campsite.
The removable console in a portable generator allows you to connect your power equipment directly without going through your home wiring or running extension cords outdoors. This console can be taken indoors while the generator is still operating in the open.
Do you need a Transfer Switch?
A transfer switch allows you to safely connect your portable or standby generator to your home electrical system while disconnecting you from the power grid at the same time when you lose power. It eliminates any possibility of backfeeding the power to the grid and using extension cords which can easily get overloaded and overheated.
Backfeeding from generator use has resulted in the deaths of dozens of utility workers who were working to restore the faulty lines. To prevent back feeding, your transfer switch must be of ‘break before make‘ type.
A manual transfer switch must be operated by the homeowner, while the operation of an automatic transfer switch does not require any human intervention. Most electrical codes and local regulations require a certified electrician to install the automatic or manual transfer switch. You can install the transfer switch between the meter and the main distribution panel of your electrical system or downstream of this panel.
Safety Related Features
Many new generators come with a variety of potentially life-saving features. Some of these include low CO engine, carbon monoxide detection & automatic CO shutdown, availability of fuel gauges, and low oil shutoff. You must sincerely consider these safety measures before deciding on the best generator for your needs. Let us discuss these features in detail, along with other safety tips.
Carbon Monoxide Detection
Carbon monoxide is an invisible, odorless, and deadly gas that can kill you in minutes. As per CPSC reports, at least 700 people died between 1991 and 2011 from inhaling generator exhaust. Many deaths from these numbers are due to gross ignorance about the dangers of inhaling it. There are records of acute CO poisoning from Gensets that were 30 feet away from the victims, but the prevailing wind was towards them.
Many generator manufacturers include carbon monoxide detectors in their generator sets. These CO detectors measure carbon monoxide levels near the generator.
Though initially considered nuisance components, more and more brands are now offering this technology. Some brands, like Honda, have even announced to include this in their entire lineup.
Automatic CO Shutoff
This feature automatically shuts down a generator if the carbon monoxide sensor detects dangerous levels of carbon.
Look for the following certifications on the packaging to verify that the generator you are considering meets desirable CO safety standards.
- ANSI / UL 2201 – Certified for CO safety.
- ANSI / PGMA G300 – Certified Safety and Performance.
Some Gensets have introduced catalytic converters that can dramatically reduce the carbon monoxide levels in the exhaust. These low CO engines provide additional safety against the risk of CO poisoning.
The fuel gauges allow you to know how much fuel remains in your Genset at a glance. This is particularly useful during long blackouts to plan to refuel.
This safety feature on a generator allows it to shut down if the oil level falls below a certain minimum to prevent engine damage. Though a common feature on any standby generator, it is increasingly getting provided on portables.
Do you have to turn off the generator to refuel?
Gasoline is highly flammable and explosive. Shut down the engine and allow it to cool for at least 10 minutes before refueling. Take care not to overfill the fuel tank leaving sufficient room for fuel expansion. Otherwise, the fuel will overflow onto the engine and can cause an explosion or at least a fire.
You must wipe off any spilled fuel and allow sufficient time for the residue to evaporate before restarting the generator. Move the fuel can away and keep an ABC fire extinguisher within reach. Gasoline has a short shelf life due to oxidation. Either use it within 60 days of purchase or use a suitable fuel stabilizer.
Does the generator need to be grounded?
While CPSC has convinced the public to place their portables outdoors, the outdoor locations pose a significant risk of electric shock as it is difficult to keep the generator and yourself dry during inclement weather conditions and water accumulation.
Most owners’ manual requires the generator set to be grounded by driving the copper rods several feet into the ground. As per OSHA, you must use grounding rods with most generators delivering power to the home, RVs, trailers, and other structures through a transfer switch.
OSHA allows the generator frame to provide ground if the generator system has no permanent connection with the grid.
How much power should your portable generators feed?
Lastly, you will have to figure out how big a generator you need. The answer, of course, depends on how much power you want to feed to your electrical loads at any given time, the running wattage, and the starting wattage your generator set requires to feed. As stated earlier, the difference between the two wattages is due to the large starting current drawn by certain loads like a motor, fluorescent lamps, fans, pumps, air compressors, etc.
The right generator for your power requirements should be able to provide 15 to 20% more power than your total running wattage requirement. In case most of your loads require higher wattage at the start, the surge rating of your generator sets comes into play.
In any case, the recommended wattage for your generator set should be the sum of the highest starting wattage out of all the equipment and the total running wattage of all the balance loads.
Hence, please consider your actual loads, their running and starting wattages, load distribution on different lines, load imbalances, starting sequence, etc., while sizing your generator, as detailed in our article, “What Size Generator Do I Need?“
If the generator cannot keep pace with the connected load and gets overloaded, the voltage of the backup power will drop, resulting in dimming or flickering of lights, motors running slowly, the engine labors, and may stall. This can overheat the generator windings and burn out any motor or transformer.
We have dedicated a complete article on the subject for your better understanding.
We hope that our detailed portable generator buying guide will help you make an informed decision about buying a generator. Did we miss anything? or do you want us to provide details about any other topic related to a portable generator? Do let us know by providing a comment in the below comment section.