Whole Home Gas Generator Q's

GW

Hi all, my friendly electrician told me of the virtues of doing a generator. I know next to nothing (other than running gas lines). I handed him the dough, and the 22KW was delivered. Truly a 'whole home' unit. Now, I'm finally getting around to setting it up, cement pad, gas piped, ready for wiring. It's a Generac.

Now I am posed with a question—what's the minimum capacity on these units? If I am just running lights and a fridge, and the puny boiler kicks on, that's obviously not much KW. The spec sheet says huge amounts of gas (even at 'low' capacity, lots of gas/BTU), I hope I'm misunderstanding something.

Sure, I would run the AC if it's super hot. Chase some humidity.

I'm sure I could pawn it off at a loss if need be. It's still new (never been started)

Thanks

Larry Weingarten

Hi, Did your friend do a load calculation to size the unit? 22kw sounds a bit big. I use a 3 kw generator to power my house if needed, but also have battery backup. Next, I'd read the specs on the unit and see how low it can go. Perhaps it just idles until it sees a load. It depends on how often you'll need it, but you would get cleaner power for electronics from an inverter hooked up to batteries. Also you could skip the generator all together if you got a unit like this: https://us.ecoflow.com/ Regardless, I'd do a load calc for what you really must have on first and go from there.

Yours, Larry

mattmia2

You need to supply the full btu requirement of the engine because of all the reasons you can't let the pressure drop too far to everything else when a big motor or something similar starts. It likely uses somewhere around 3x to 4x the btu as the wattage output. The larger generator will be less efficient at small loads because there are some fixed losses in keeping all those parts moving and magnetizing the rotor and running the engine accessories. It has to run at 3600 or 1800 rpm to maintain the frequency of the output regardless of the load so that decreases the efficiency under light load dramatically. I don't know of whole house inverter generators but inverter generators are much more efficient at less then full load.

The easiest way to get gas to the generator is frequently to just bury a separate polyethylene line from the meter to the generator.

BTW Gererac residential is not so great for durability, it is owned by Briggs and Stratton and uses versions of their engines which aren't really designed for running thousands of hours or continuously for several days.

mattmia2

https://forum.heatinghelp.com/discussion/comment/1809925#Comment_1809925

Modern electronics are going to be the thing that cares least about the quality of the power. There will be a power supply that usually rectifies the line then uses a chopper to make a high frequency pulse to use a transformer or coil to produce the needed voltage that is regulated to get the needed output voltage. Some electronics in to about the 80's(maybe even the 90's for CRT displays) relied on the voltage and frequency of the power line but modern electronics have switching supplies that care very little about what you give them.

GW

Larry, I'm sure he winged it, there wasn't a list of questions. The house is 2800 sq ft of main living but it's expandable to at least 5000 (unfinished areas of the 2nd fl, and 1500 ft of finished basement). I'll talk to him some more. Gas everything, except oven. 3 ton hvac. Thanks

GW

https://forum.heatinghelp.com/discussion/comment/1809926#Comment_1809926

yes it's a gas hog for sure. I did run a 1 1/4" main through my basement.

EBEBRATT-Ed

@22,000 is a big generator. The 22000 is the wattage it will handle so 22000/240volts give you 91 amps at 240 volts and 183 amps at 120 volt.

I have a cousin with a 7000 watt portable generator (Honda) which is a good gen protected by a 30 amp breaker 7000/240=29 amps and she runs her 3 ton AC and everything else on it with no issue (although not recommended). He heat and HW are oil.

Since your other large appliances are gas I am sure you have way more in gen capacity than you will ever need. A 10 or 15 kw would have been fine.

What you have may be a gas hog but how much will it get used?. Probably not very much.

I helped a buddy hook up a gen a few years back and I don't think he has needed it yet.

My cousin with the little 7000 watt Honda is out in the boonies in Somers, CT and may loose power 1-2-3 times a year.

Jamie Hall

In answer to your actual question, it will take some gas to operate whether there is a load on it or not. How much? Depends a lot on the unit, and can vary all over the place, but I'd plan on it taking around 20 cubic feet of gas per hour at idle. That may be specified in the documentation. As to electrical output, the minimum output is, obviously, zero.

Is it more generator than you need? I couldn't say. That depends so much on what you actually have connected in the house — and what you plan to connect. Yes, folks can get by with a much smaller generator, particularly if they don't use electricity for cooking or heating (which are the two big users).

Power quality — is the output a true sine wave — is an interesting question. Most whole house generators such as yours produce very good quality output power (less than 2 to 5 % distortion) at very constant frequency. It is true that many modern widgets don't care that much, however some most assuredly do.

GW

Yes I 'assumed', and didn't have the energy to research it on my own. I had zero idea the 'turn down ratio' wasn't good. Live and learn!

mattmia2

22 kw is probably close to what it would take to start that 3 ton ac compressor with other loads at least by the book. It will probably start on less but in theory its starting current will be either specified directly or specified as a code and will be between 5 x and 10 x the running current.

hot_rod

Did you get a good deal on it? Keep it, how many hours will it actually be used? I doubt the fuel bill will kill you.

If you ever have an extended power outage, days or weeks, you may in fact want that much power. You neighbors may be happy to take some output also :)

We had an ice storm take our power out for several; week. I had a Lincoln welder generator, 7KW. I sure wish I had twice that to live comfortably. Deep well pump, Trane HP, electric stove dryer, diesel engine heater on the truck and tractor, etc

ratio

I read this a while back:

https://substack.com/@kilovar1959/p-146973446

GW

HotRod, I don't think it was a deal, not based on what I see on the 'net. Maybe I'll stick the amp claw on the 3 ton and see what kind of juice it needs. It's a geothermal—probably not super high amperage. I clawed it many years ago when I was puttering with costs per BTU. Besides the oven, everything else is gas.

I wonder if i would be the first dude on the planet to have two gennys—I'm half tempted to put a small one on the other side of the home, and run the boiler, lighting on that side of the home, etc.

The 22kw is all tied in! Just need to wire the thing.

mattmia2

By far the most practical and overall economical solution if you already have the generator and have it mostly installed is to run the small loads off of it as well.

If you want to experiment with the theoretical battery banks and inverters are an option, maybe charge them from the generator and only run the generator intermittently.

ChrisJ

My dad has a 16kw that he's had for quite a few years now. He's never had any issues with it and nothing done other than normal service.

Yes, a 22kw generator is going to suck down fuel even with zero load. That's one of the reasons I went with a 10kw and not one of the 19-20kw ones I was looking at.

Unless your power goes out constantly for weeks at a time you're not going to have any issues.

On a side note I was told by a generator expert that so called "dirty power" or non-sinewave issues aren't a thing with conventional alternators and that's a cheap inverter issue. I've personally never had an issue even with a dirt cheap Coleman 4kw from 1992. I put a scope on it and it certainly looked like a nice sine wave to me.

Jamie Hall

Correct, @ChrisJ , on the "dirty" power. And the cheaper the inverter generator, the worse the problem is. The older alternator generators — which run at 3600 or 1800 rpm — usually have very good to excellent wave forms. How much of a hassle it will be with various equipment — all over the map. Anything powered by a "brick" or a wall wart will probably never notice the difference. However, electric motors may tend to overheat on messy power, particularly bigger ones. Older electronic equipment — notably older high fidelity sound systems — will be very unhappy. Depending entirely on the design of the power supply, they will hum like crazy, and there is a very real risk of burning out the power supply transformer.

ChrisJ

https://forum.heatinghelp.com/discussion/comment/1810009#Comment_1810009

Why would a classic linear power supply care?

Jamie Hall

It's a matter of what frequencies are present. A classic power supply — let's say for a big Dynaco tube amp — is designed quite specifically, using the impedance of the power supply transformer (which increases with frequency) and large capacitors (whose resistance decreases with frequency), combined with some resistance to effectively short out any frequencies in the power supply higher than 60 hz, and at the same time to smooth out the humps (if you will) from the remaining 60 hz. Generally the first stage of the power supply is the one affected by higher frequencies. Smaller inverter generators approximate a normal 60 hz sine wave with stepped voltage increments (the really cheap ones are very close to a 60 hz square wave) — and those stepped increments are, electronically, made up of much higher frequency power. That first filter stage looks to the higher frequency harmonics very much like a dead short across the power supply output leads — resulting in excess heating in the transformer (remember, its effective resistance increases with frequency). This excess current also appears across the rectifiers. Neither one will be happy. Worse, the following filter stages are optimized to effectively short out the remaining 60 hz ripple — and are quite ineffective at filtering higher harmonics, leaking to hum at some higher frequency.

None of this is a problem with modern switching power supplies, as they rectify the incoming current, then chop that DC into relatively high freqency square waves, feed that through any necessary voltage changes rectify it back and charge a capacitor with it (that's somewhat simplified). Further, many modern devices are either fully digital or at worst class D amplifiers, which are much more tolerant of odd power at very high frequency (well beyond sonic range)(some tweeters do sense the very high frequency ripple resulting, with more or less catastrophic results, but if you can afford one of those you can afford an amplifier with a power supply which doesn't do that).

One other thing I didn't mention: a number of turntables and CD drives use synchronous motors. They don't care that much about the stepped power, although they will heat up more than they should, but they do care. Very much. About rock solid frequency stability. This, oddly, is one area where inverter generators are usually superior to most smaller alternators, which tend to sag on heavy loads.

Of course if you are more or less in the golden ear fraternity, all this is moot — your system is being powered through a regulated, filtered, and stabilized power supply anyway!

Sylvain

This guy makes a lot of experiments.

(some?) inverters don't like motors:

https://www.youtube.com/watch?v=hhonq0WSq_c

Now for old school technology

About frequency, have an alternator driven by whatever motor but with a big flywheel to absorb more easily any load variation.

I also remember from my studies about 45 years ago that alternators to be used with a recpocating engine must have extra damping windings which are not needed when driven by a turbine.