power inverters vs generators

What I know (and I'm sure most know more):

A regular portable generator is made to run at 3600 RPM to provide a steady AC power flow. That flow may increase or decrease with RPM fluctuations causing power surges that may harm certain electronics and appliances. They are louder and use more fuel.

An inverter generator converts AC power to DC power and then back to AC power to provide a more stable power flow that won't cause power surge issues you see with regular portable generators, which can damage electronics and sensitive appliances. They also use less fuel and are more quiet.

Generators have to run at a multiple of 60 rpm to provide 60 Hz power because they are spinning a generator that the load is directly connected to. Generally, this means they run at 3600 rpm, no matter how much load is connected to them. Even when using no power, the engine will be running at 3600 rpm. Also, when load is connected to or disconnected from the generator, the engine feels it because it is mechanically coupled to the generator. Since the whole thing has inertia to overcome, the response to a changing load can't be instantaneous. When a load connects, the whole system slows down slightly until the engine can mechanically respond. The opposite happens when load is shed. Since the engine is mechanically coupled to the generator, and the rotational speed of the generator is linked to the frequency of the electricity it produces, the quality of the electricity is not steady and varies as the machine operates.

Compare this to an inverter generator. These devices don't have just an engine and a generator. The output of the generator goes through a rectifer which turns the AC output into DC. The DC then goes through smoothing capacitors that condition the DC power. The conditioned power then goes through an inverter, which takes the smooth DC power and turns it back into smooth, steady AC power.

Why bother, though? In the inverter setup, the generator is not directly connected to the load. The conversion from AC to DC back to AC means that the rotational speed of the generator has nothing to do with the frequency of the output electricity. The frequency and waveform of the AC are all maintained by the power electronics in the inverter. Since that output section is fed by DC power from the rectifier, no matter what the engine is doing, the output power is unwavering provided the generator is producing enough power to match the load. So that's the first benefit: clean power. The second benefit is related. Since the quality of the output is not coupled to the rotational speed of the generator, there is no need for the engine to run at 3600 rpm regardless of the load. Therefore, the whole system can be designed and controlled to run at the most efficient speed under all conditions, making them MUCH more fuel efficient and quieter.

So why do we still have regular generators? Cost and weight. Those power electronics that do the AC to DC to AC trick aren't cheap and their cost rises quickly as their power handling capability is increased. So, a 4000W inverter generator's output section would cost more than twice the a 2000W, and 8000W power electronics would be more than twice a 4000W, and so on. The weight of the system has a similar behavior. The sheer mass of the electronics required to handle increasing wattage quickly starts shooting up.

Since the cost and weight of inverter generators starts spiking quickly with increasing power, you tend to see them in the lower wattage ranges and fill more of a portable role that might power a few devices that might be finicky about how clean their power is. There are some that go up to several thousand watts, though, and many of them now let you run multiple units in parallel to provide higher total outputs and have some flexibility to avoid having a single giant and horribly expensive inverter generator. That cost and size, though, are why you start seeing mostly traditional generators when you start getting up into the higher wattages. They can power more powerful machines that might not care as much if their electricity's frequency fluctuates a couple of Hertz and they can do it at a much more reasonable cost, weight, and footprint than an equally powerful inverter generator.

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say i wanted something equal to 6500 watt generator, what size inverter should i buy?

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A 6500 watt inverter.

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i heard inverters are more efficient so it doesnt need to be as much watts to supply the same amps as generators do

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Stop listening to whoever you heard that from. They're more fuel efficient.

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TigerstuckinMS

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Great answer.

I’m watching prices for a duel fuel (gas/propane) inverter generator to supplement my 8500/6500 gas/NG generator. The pricing curve does increase significantly once you start hitting the 2k watt range. I wanted a unit to be able to handle a window AC but I’m rethinking that since there is no guarantee a 2000 (or 2300) watt inverter generator can handle it anyway, depending on the brand. A Honda is not in my budget unfortunately.

My 3500 predatorinverter will run two fridge/freezer side by sides, tvs, lights, and two windows units. 5000 and 8000 but.

7 gallons of gas used in 24 hours.

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i have a 5500 now that i have to turn off the window unit if i want to run the micro or use a can opener or anything else

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Microwaves and can openers take up a lot of juice. They have high running watts, not just starting watts. The same goes for anything with a heating element like coffee makers, heaters, etc.

If you’re looking for a cheaper inverter, a lot of people here have been buying up Wen Inverters and so far have nothing but good things to say about them.

Harbor Freight’s Predator line of generators is also pretty good.

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Harbor Freight’s Predator line of generators is also pretty good.

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Yep, you just gotta run them and put a load on it. Run it on the 1st of every month and test the load. It really is a good deal if you treat them right and don't ignore them.

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My 3500 predatorinverter will run two fridge/freezer side by sides, tvs, lights, and two windows units. 5000 and 8000 but. 7 gallons of gas used in 24 hours.

I'll take that all day.

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I replaced a 5000 watt Briggs type generator right after Katrina with a Honda Eu3000 inverter. I ran about the same load with each, the money saved on fuel with the Honda during outages since than more than made up for the higher purchase price, and the lack of noise is also worth a lot to me.

I got the 3500 Predator inverter and really like it. It's really quiet and sips fuel. Just follow the break in instructions and first few oil changes. I run it every couple of weeks for 10-15 minutes and it starts up with no problems.

Does anyone know where I can get a 10KW diesel generator that can be exposed? This would be mounted on a gooseneck trailer that is used as a mobile kitchen.