What's the story on generators- inverter vs. regular?

Factual Questions
1

After a few extended power outages and a near-miss in February, I’m considering getting a generator for keeping our refrigerators on, charging our phones, making coffee, and possibly powering the TV/DVR.

Basically I’m torn between getting a small/mid-sized inverter (like a Generac GP3000L), or a considerably larger tri-fuel “regular” generator, like one of the Costco Firman tri-fuel 7500 watt models that can run on gasoline, propane or natural gas.

I’ve got a natural gas hookup for a grill (1/2" line, flexible hose just like the generators use). I’m not terribly interested in keeping 5-10 gallons of gasoline on-hand, nor am I interested in buying a new inverter generator and converting it for natural gas.

Is there a compelling reason to get an inverter generator vs. one of the tri-fuel regular models? THD (total harmonic distortion) is one thing that’s regularly commented about, but I haven’t found anything conclusive- some sites say it’s the devil, while others say that modern-day electronics are smart enough to cope with it without issue, because their power circuity is designed for worldwide use in developing countries with cruddy power.

Anyone know anything about this stuff?

2

Inverter generators are more efficient, quieter and should all provide clean power, as in a constant 120v as 60hz. Non-inverter generators are louder, less efficient and often do not provide clean power, especially as fuel is running low. (Not really an issue for natural gas)

I do think it is important to look for a generator that provides clean power.
The fuel efficiency issue is more a matter of pay now or pay later decision.
The low noise is a really nice feature.

3

During our last (summer) power outage one of my neighbors kept her freezer going with an inverter that connected to her pickup truck’s battery. She had to keep the truck idling, but said it was surprisingly economical.

4

Note the word “should” in that sentence.

In both cases, a generator has an engine (powered by gas, propane, diesel fuel, whatever) that spins an electrical generator of some sort.

In a traditional generator, the electrical generator is just an AC alternator which is directly connected to the generator output. There may be some voltage regulation, which typically adjusts the field current in the alternator to regulate the voltage output. But otherwise, there is usually little to no filtering.

Since there is little to no filtering, instead of a nice clean sine wave, you can have a lot of noise on the AC output, so that it looks more like this than a pure sine wave:

The AC output depends on how fast the alternator is spinning. There’s a governor on the engine which tries to keep it at the right speed, adding fuel when it slows down and cutting fuel off when it tries to go too fast. The response of this type of control is a bit slow, so the AC output can drop in frequency if the engine gets bogged down due to a sudden load (like your freezer kicking on). Depending on how cheap they were with the voltage regulation, the voltage output might also drop under load.

With an inverter type of generator, the electricity is generated either by a DC generator or an AC alternator which is then rectified into DC (I think most are AC alternators these days). The DC is then fed through an inverter which converts it into AC for the generator’s output. An inverter is more complicated, so it costs more, and there are some inefficiencies in the rectification and inverter stages, but usually the output is much cleaner.

But…

There are inverters and there are inverters. A true sine wave inverter is costly and depending how it’s made it can be a bit inefficient. So most inverters are steppers - they output in discrete steps instead of a true sine wave.

Maybe like this:

Or maybe more like one of these:

Natural inductance and capacitance in your wires will smooth out the steps a bit and make the output look more like a sine wave, but the discrete steps can be more noisy than a traditional generator’s noise.

Most devices won’t care much. There’s enough inertial mass in your refrigerator’s compressor motor that the stepped output won’t matter. Phone chargers and such just convert the AC down into a lower voltage DC so the noise just gets filtered off. There might be issues with your coffee maker. Some coffee makers are pretty simple. They are basically just a clever use of heating elements and won’t be affected by AC noise. Other coffee makers (those with timers) have a fancy shmancy tiny little microcontroller inside of it doing all of the control, and that microcontoller can malfunction if the AC power coming into the coffee maker isn’t clean enough. Your TV/DVR might have noisy lines on the screen, but they will probably work, though again, most TVs these days are controlled by a microcontroller which can go a little wonky if there is too much AC noise. While issues like these are possible, in most cases you usually won’t have a problem, even with those types of devices.

Noise aside, in an inverter type of generator, the inverter itself provides the sine wave and the voltage regulation. This makes the output much more stable than that of a traditional generator, especially during rapidly changing loads.

If you go with an inverter type, just make sure it has a decent inverter on it. Don’t go too cheap.

5

I went for a large size traditional gas generator (mobile) and converted it to burn propane, which is very easy to do, and gives you a lot more generator options. I have a 1,000 gallon propane tank so that decision was easy.

I purchased two refurbished standard APC-Smart Power UPS and installed them on two of my house circuits to filter and regulate the power from the generator.

I then built a fiberglass-lined enclosure to house the generator outside of the house.

The system runs all the house circuits that I need. It’s not automatic, but I don’t care.

The whole shebang is pretty quiet, the power is pretty clean (I run my entire AV and communications/computer system during blackouts) and I saved about 1/2 over a standard stationary standby generator.

YMMV

6

So it’s sounding like maybe my best bet is one of the tri-fuel generators and run it off my grill gas line, since it doesn’t sound like an inverter is a necessary thing for most of what I’m looking to do.

7

I’m surprised that an inverter on a pick up could run a freezer.
During a week long loss of power during an ice storm, I used a gasoline generator to run the electric part of a gas furnace, and satellite tv. We didn’t try anything that used as much power as the refrigerator. I’ve thought about running a generator off of bottled propane with some changes to the carburetor, but that could become expensive, and a pain to exchange bottles with icy roads. If it could be run from natural gas from the house, that would be outstanding. I don’t know anything about the code and plumbing requirements to do that.

8

I’ve already got a real, plumber-installed, up to code gas line in my backyard on my deck for my grill. It’s even got the same sort of flexible gas hose and quick releases that the tri-fuel generators use.

So for me, it seems like the tri-fuel ones are the way to go. Here’s an example:

Champion 8000 watt tri-fuel generator.

9

That sounds good.

10

I have a 6500 watt Onan running on natural gas and am quite happy with it. TV, computer, everything runs as normal. The Onan rpm control is very sophisticated and responses instantly. The natural gas burns clean and does not go bad like gasoline. Others have mentioned propane from a bottle and that may not work in cold weather. You need a certain minimum surface area and tank volume to sustain flow in the cold. It does produce more power then the natural gas.

11

A traditional problem of traditional generators is that the lights got brighter when the generator ran fast, and dimmer when the generator ran slow. In the worst case, this could destroy your refrigerator.

This was particularly a problem with small generators, that sped up and slowed down when you added or removed load.

A big generator has enough power that adding or removing load has a small effect, and a big generator powers enough stuff so that turning on one light, or one washing machine, isn’t an enormous % change.

The electronics used for an inverter used to be expensive, and not able to handle much current.

So when ‘inverter’ generators became possible, they started at the small end. It’s still more or less the case: for large generators, an inverter stage is more expensive and less important.

12

FWIW I have only used the regular generators, both that I have is about 6000 watts. Overall I am impressed with it and see little reason to go inverter, though I know there are benefits.

One of them I use it for everything at one home without restriction, it does everything including a large window a/c (largest 110V model), water pump, along with computers and TV. We have a gas dryer there, however we had an electric one before that it could not handle. This generator got us through many power failures including 3 or 4 separate weak long (plus) ones.

The second one we have in our other home, and has gotten us through a week long outage and some other minor ones. This home does not have gas, so the dryer and stove/oven are electric and are not run with this generator, also we have central a/c here which it can not handle. Everything else it runs no problem. We have an extra window a/c unit for power outages and a small plug in stove and a toaster oven we use when needed for those functions.

So the benefit of the regular types for us is, within reason, we can just live our lives and use practically everything during power outages. We have not seen any effects due to dirty power. The down sides is the noise, though we can position them in a way that really reduces that, higher fuel usage, however overall it’s still not much all things considered including we could run more unless we went with a really expensive inverter.

One thing I have noticed with inverter generators is most are 110V only (no 220V) which might in some cases be limiting depending on how things you wish to run are wired to your circuit box.

13

Another advantage of inverter generators is that the engine can easily be made to run at whatever speed is best for the engine. Gasoline engines of several horsepower tend to like to run around 2500 RPM. If the alternator is mounted to the same shaft, though, 2500 RPM can’t give 60 Hz power. You could run the engine at 3600 RPM with a two pole alternator to get 60 Hz power, but that’s pretty fast and doesn’t favor long engine life. Or you could run at 1800 RPM with a four pole alternator, but for a small engine it’s hard to deliver much power at such a low speed. A six pole alternator making the engine run at 1200 RPM is even worse. Another option is to add a speed changing device such as a gearbox or belt drive, but those add considerable cost and maintenance problems.

An inverter system does all the frequency sensitive stuff electronically. Moreover, an inverter system could incorporate storage batteries, and deliver full power within milliseconds of a sudden failure, potentially so quickly you can’t even see the power flicker, and could rely on the batteries for several seconds or even a minute to see if the power failure is long enough to make starting the engine worthwhile, and then start the engine and let it warm up slightly and distribute oil internally before fully loading it. I don’t know how many of these useful advantages get implemented in commonly available systems, but they’re a possibility at least.