What is an Inverter Generator?

All About Inverter Generators

What Makes Inverter Generators Different from a Conventional Generators?

Alternating Current (AC) doesn’t send electricity in one direction. Instead, it’s constantly switching polarity. While DC wiring has positive and negative wires, AC wiring has neutral and hot wires to move electricity as it changes direction. Grid power uses large generators that deliver electricity that smoothly alternates between positive and negative current. If you hooked an oscilloscope to one of your home outlets, you’d see a smooth sine wave on the screen, moving at a rate of 120 times per second, or 120 Hz.

A portable generator has an engine attached to an alternator. This alternator makes alternating current with a frequency around 120 or 240 Hz. Due to engine speed fluctuations and interference, the actual speed and waveform can vary. This is called “dirty” power. If you hooked an oscilloscope to one of the outlets on these generators, you’d see a jagged wave with spikes. Most appliances work fine with this type of power, but electronics can’t handle these fluctuations. Run a TV or a computer off of this unregulated power, and they may exhibit some glitches. Run these devices for too long, and they will fail.

An inverter generator has an inverter that smooths out the flow of power between the alternator and the sockets, so it’s just like the electricity you get at home. This smooth waveform power, or “clean” power makes it safe to use these inverter generators with your electronics.

What is Total Harmonic Distortion?

Total harmonic distortion (THD) is the amount the electric current deviates from a pure sine wave. A generator without an inverter will usually have a THD of 9-15%. These generators also have trouble maintaining steady output when they’re near their maximum supported load. For example, instead of producing 60 Hz power, it may be closer to 50 Hz during peak loads. This usually isn’t much of a problem for electric motors and heaters, but it’s hard on electronic circuits. LCD screens and computers are the most sensitive to these frequency changes.

Generally speaking, any generator with a THD of 3% or less is perfectly safe to use with any electronic device. Some companies advertise THD as low as 1.5%, but this won’t appreciably improve the life or function or your appliances.

Is an Inverter Generator Better than a Traditional Generator?

It is, if you need to power electronics. The generator’s smooth power delivery will keep your devices functioning normally, and the circuitry won’t overload and burn out from current fluctuations.

If you don’t need to power electronics, you can save money by buying a conventional generator. Sometimes, these models can be as much as 50% cheaper than an equivalent inverter generator. However, part of that price difference is due to how these generators marketed. They’re the budget option, so they don’t come with all the features you normally get with an inverter generator. Hour meters, automatic chokes, and sound deadening are often left off these cheaper models. Be sure to read over the specifications before you make your purchase. You may find it makes sense to spend extra on an inverter model to get the features you want.

What’s the Difference Between a Power Inverter and an Inverter Generator?

A power inverter uses the inverter to convert DC power into AC power. For example, a 12 volt car inverter plugs into a 12 volt port, then passes electricity through switching circuitry to turn steady current into alternating current.

An inverter generator uses an inverter to alter the current coming out of the generator, so it more closely matches the output from a household outlet. There’s no switching going on, since it’s already using alternating current.

Can You Use an Inverter with a Traditional Generator?

Technically, yes. However, you can’t buy an aftermarket inverter, attach it to a generator, and get the same results as a purpose-built inverter generator.

You can buy a pure sine wave inverter that convert 12 volt DC power into 120 volt AC power. If your generator has a 12 volt automotive port or terminal connectors, you can connect your inverter and have enough power for a couple small electronic devices. Keep in mind that using an automotive socket limits output to around 150 watts, no matter the maximum current supported by the inverter. Even with terminal connections, the power your generator supports will usually fall short of the 500 watt maximum of the largest 12 volt inverters.

In other words, you can use this method in a pinch, but you shouldn’t rely on it. You also can’t transform all the electricity from your generator into clean power, no matter how small it may be.

Do All Sockets on an Inverter Generator have Pure Sine Wave Electricity?

All AC sockets get power from the inverter. That means you get the same clean power, whether you’re using a household outlet, an RV shore power outlet, or a home backup outlet.

12 volt DC and 5 volt DC USB outlets use a rectifier to convert AC power into DC. Since these sources are direct current, they supply a steady stream of power, instead of a sine wave.

Can Inverter Generators be Used Indoors?

No! Using any generator indoors could kill you!

One of the byproducts of combustion is carbon monoxide. This odorless gas attaches to red blood cells in place of oxygen. If you inhale enough CO, you can saturate these cells, preventing them from delivering oxygen to your body. This causes suffocation and death. In 2015 alone, 393 people in America died from accidental carbon monoxide inhalation. Most of these deaths were caused by people buying generators during power outages and using them inside their homes.

Generators must be several feet away from buildings and awnings to prevent carbon monoxide buildup. That includes basements, garages and open windows.

There has been some confusion over the new ANSI/UL 2201 certification. Introduced in 2018, this safety standard is slowly making its way into consumer generators. This standard requires reduced carbon monoxide emissions, as well as a carbon monoxide detector that can shut off the engine. This standard is voluntary. It does not eliminate CO emissions, so there’s still a risk of poisoning, if you use one of these generators indoors.

When you buy a generator, you need to plan ahead. Buy extension cords that can handle the power you will use, so you can keep your generator and your appliances separate. Keep in mind that most 120 volt sockets are rated at 20 amps, instead 15 amps, like your home outlets. That means you can transfer more power using one of these sockets. You can also use a breakout cable with RV outlets, so you can use these sockets to power multiple appliances.

What’s the Difference Between Open Frame, Hybrid and Enclosed Inverter Generators?

The most popular type of inverter generator is an enclosed generator. This design has a case that completely surrounds the engine and alternator, which greatly reduces noise. However, all that extra material makes these generators heavy. Most enclosed generators have a maximum output of 2,200-4,000 watts, but there are a handful of models that make as much as 8,000 watts.

Open frame generators have a metal frame that the engine, gas tank and alternator attach to. There’s nothing to absorb the sound, so these generators can be very noisy. This design is mostly used for commercial generators, where noise isn’t much of a concern. Open frame designs are also used for the largest portable generators to keep weight manageable. A 10,000 watt generator typically weighs over 200 lbs. without any sound deadening.

Hybrid generators use a design that’s somewhere between an enclosed and an open frame generator. They still have an exposed metal frame, but there are insulated sections around the engine. This reduces noise without making the generator too heavy. Hybrid frames are common for RV and home backup generators.

Are Inverter Generators Less Efficient than Conventional Generators?

No. An inverter doesn’t affect the amount of output in any way. However, high power inverter generators are rare, because most high draw applications won’t benefit from pure sine wave power. That means it’s not worth the extra cost of adding an inverter.

What is the Best Inverter Generator?

There is no “best” generator, or even a “best” generator brand. The best generator is the one that best fits your needs. Here are a few things you should look for, depending on your application.

Emissions and Fire Prevention Regulations

Inverter generators aren’t cheap, so manufacturers don’t skimp on features. Almost any inverter model will be CARB compliant. “CARB” stands for California Air Resource Board. This organization creates emissions standards that go beyond what is required by the EPA. Several states and the Canadian province of Quebec follow CARB requirements, not just California. 

In these areas, you can only legally use your generator if it’s CARB-compliant. Likewise, spark arresters can be found on almost any inverter generator. These devices catch sparks coming out of the exhaust pipe before they can start fires. They’re required in most outdoor areas, especially if there’s a high fire risk.

Tailgating and Camping

If you don’t want to annoy your neighbors, look for a quiet generator. If you don’t want to annoy yourself, look for a generator that’s light and easy to carry.

USB ports are becoming increasingly common, as buyers want to charge drones, smartphones and other electronic devices. When you’re shopping around, be sure to check the amperage. 2.1 amp USB Type A ports support fast charging, but 1 amp ports don’t. USB Type C is the best choice for new, high power draw devices, but it may take years before they’re readily available on generators.

RV Shore Power

If you want to stay on good terms with your neighbors, look for a quiet generator. Want low noise and low weight? Consider getting a pair of enclosed generators that support a parallel connection. Most parallel cables have built-in outlets for RV power.

Like spending time outdoors? Consider what you want to power when you’re relaxing in front of your RV. Some models have extra 120 volt ports, along with 12 volt and USB sockets for outdoor appliances and portable electronics.

You should also consider parts and repair support. The size of dealer networks and the availability of phone and online support varies widely from brand to brand. Good support makes it easier to deal with problems on the road.

Double check measurements, so you can be sure you have space for your new generator in your RV. Dimensions quoted for generators that include a wheel kit should be accurate. However, you’ll need to add a couple inches of height, if you’re adding an accessory wheel kit.

Home Backup

If you want a generator for home backup, look for a model that works with a transfer switch. This device cuts the connection between your home and the grid, and sends power from your generator through your home’s wiring. This switch must be installed by an electrician. If it’s wired in wrong, the generator’s power could go into the grid, potentially electrocuting a line worker.

Propane doesn’t go stale like gasoline. This makes a dual fuel generator a great choice, if you’ll go months between uses.

Work Power

Commercial warranties can vary widely from brand to brand. While you’d expect guarantees to be shorter for work use than residential use, some companies only offer a few days of protection, or none at all.

You may need to attach an external grounding rod to meet OSHA and municipal safety regulations. This rod attaches to a grounding terminal on the generator. If you use this connection, you normally have to change a couple wiring connections on the generator to redirect the ground to this rod.

Who Makes the Quietest Inverter Generator?

As of this writing, the quietest generator you can buy is the Honda EU1000i. It makes a maximum of 50 dB as measured from 30 feet away, and just 42 dB at 25% load. However, it only makes 1,000 watts of peak power and 900 watts of running power. Also, humans can’t distinguish loudness differences of 3 dB or less. That means there are several similarly sized generators that are effectively just as quiet in real world conditions, even if the numbers are higher on paper.

If you want to buy the quietest generator that fits your power requirements, look for a fully enclosed generator. Can’t find a model that makes enough power? Using a parallel cable, you can join two enclosed generators, so they act like one large power source.

Does an Inverter Generator Run on Gas?

Most do. The confusion comes from dual fuel generators, and the way the label “inverter generator” is sometimes misused on portable power stations.

A standard generator uses gasoline to power the engine. Dual fuel generators can run on either gasoline or propane. The engines in these generators have carburetors with jets for both gasoline and LPG, and they have both a gas tank and a connection for a propane hose and regulator.

Portable power stations are sometimes sold as inverter generators. These devices aren’t generators. Instead, they have a battery that stores energy from solar panels and circuitry that converts battery power into standard AC and DC power. Technically, all stations with AC sockets have an inverter, because they need to convert the battery’s DC power.

Some stations use a simple design that switches polarity back and forth, creating a square wave instead of a sine wave. Electric motors won’t work with this type of power. If a power station has a pure sine wave inverter, then the electricity coming from the AC sockets is identical to what you get from grid power.

How Much Power Does a Generator Make? Why Do They Have Two Power Ratings?

Electric motors need extra power to start spinning. Generators have extra “starting” or “surge” power to help get motors get moving. This peak power is only sustainable for 30-60 seconds. The “running” or “sustained” power rating is the amount of power the generator can make 100% of the time.

Dual fuel engines make less power on propane than gasoline, so they have four power ratings. One set of ratings is for gas, and the other is for LPG.

Keep in mind that you don’t want to run a generator at full power all of the time. To save on wear and tear, manufacturers recommend running generators at no more than 85% of their maximum power over long periods. Increasing load also increases engine noise, so using less power will be easier on your ears.

How Many Watts Do I Need?

Most appliances have information on the power they draw printed on the serial number label, or in the owner’s manual. Peak power should be equal to your maximum sustained load, plus the highest starting load for your appliances. Keep in mind that you aren’t going to run everything at the same time.

If you want to make the most accurate measurements, use an electricity usage monitor. This device plugs in between your appliance and the outlet. It has a display that shows exactly how much power the appliance is using.

Can an Inverter Generator Power a House?

A portable generator can power some or most of your house, depending on its output.

Since an inverter generator is safe for electronics, you can use one to power your TV, media devices and computers. It’s also a good idea to use an inverter generator with any appliances with electronic components.

As for other appliances, it mostly depends on the output of your generator. Here’s a breakdown of common appliances, and their power-friendly alternatives.

Will an Inverter Generator Run a Sump Pump?

Yes, as long as your generator makes enough power. A 1/3 HP pump typically use 1,300 starting watts and 800 running watts, while ½ HP pumps typically use 2,200 starting watts and 1,100 running watts.

Will an Inverter Generator Run a Furnace?

It depends on the type of furnace you have.

If you have a gas furnace, you still need to run the furnace fan. A 1/3 HP fan needs 1,400 starting watts and 700 running watts, while a ½ HP fan needs  2,400 starting watts and 800 running watts.

If you have an electric furnace, no. The power draw will be too high for any portable generator. If you’re looking for a home backup solution, consider running space heaters. These devices typically use around 1,500-1,800 watts each.

Will an Inverter Generator Run a Refrigerator?

Yes, most generators make enough power to run your refrigerator. Expect a regular home refrigerator to need 1,500 watts to start the compressor, and 750 watts to run.

Will an Inverter Generator Run My Washer and Dryer?

A typical clothes washer uses around 2,200 watts to start and 1,100 watts to run. However, if you have an electric water heater, you’ll need to set your washer to use tap water. Water heaters typically need at least 4,000 watts of continual power.

An electric clothes dryer needs a lot of energy for the heater. Most models use around 4,500 to 5,500 watts during each drying cycle.
Want to iron your clothes? Expect your iron to use at least 1,200 watts.

Will an Inverter Generator Run My Dishwasher?

Yes. Despite using a heating element, most models only need between 1,200 and 2,400 watts, with an average dishwasher using 1,800 watts.

Will an Inverter Generator Run My Air Conditioner?

Central air conditioners are the most power hungry devices in homes, so no, they won’t run off of generator power. This can be confusing, since generator manufacturers will advertise their models will run A/C. However, they’re referring to RV air conditioners, which use a lot less power.

A generator can run a window air conditioner. Most models need 2,000-3,000 watts to start, and about half as much power to run.

Do I Need an Inverter Generator for My Tools?

Inverter generators are increasingly being pitched toward work use, thanks to the rise of cordless tools. Tool battery chargers are electronic, so they will burn out if you use them with a regular generator. If you use cordless tools, you need an inverter generator to power your charging station.

Basic tools will run just fine without an inverter. However, since power delivery can get uneven at high loads with a regular generator, it may cause fluctuations in motor speeds. This can be a pain, if you’re doing fine detail work.

If your tools have electronics, they should be powered with an inverter. This includes anything with built-in digital controls or gauges.

Will an Inverter Generator Run a Welder?

It depends on the voltage the welder uses.

A 120 volt welder will work just fine with an inverter generator, provided that you have enough electricity to power it. Better still, generators usually have a 5-20R outlet, which supports up to 20 amps of current flow. Most 120 volt welders need a full 20 amps to reach their highest current output. If you only have 15 amp sockets in your home or workshop, you may find your welder runs better on generator power.

You can’t power a 240 volt welder off of a generator, even if it supports 240 volt output. That’s because it needs multi-phase electricity.

When electric power enters your home or shop, it’s 240 volts. However, it isn’t just one stream of electricity. It’s split between two 120 volt sources that run out of sync, resulting in multi-phase electricity. As one source drops down to 0 volts, the other source goes up to 120 volts. This smooths out fluctuations in current, so voltage never drops below 50%. High voltage welders need this type of electricity to work, but a generator is only capable of making single phase electricity.

This is also a problem with 240 volt industrial motors, since they’re also designed for multi-phase power. However, the compressor motors used in large RV air conditioners are designed for single phase power, so they will run on generator power.