Sizing big generator

I have been looking for a standby generator that will run my whole house including 2 heat pumps. After closely examining specifications, it appears that all of the 20KW + generators are rated on 3 phase even if you are bying single phase.The catch is that a 30Kw generator will only put out out about 20Kw on single phase and giving consideration to power factor of less than 1 and I am not sure anything operates at 1:1 power factor but more like .8:1 in reality you can depend on about 17 or 18 KW out of a 30KW generator. Am I wrong?

Had one locally that I could probably have got you. It was an IH v-8 truck engine set up to run on propane with an 80 kw single phase generator. Maybe a bit much for your needs . I'm no help on your actual question though.

I have a 30 kw Cummins Onan generator that runs on propane or natural gas. It is single phase 220 volts. My house is 3,000 sq. Ft. It will run everything all at once, incl. 2 AC umits, electric water heaters, and electric oven. It can run full capacity 24/7/365. It has a 4 cyl. GM fork lift type engine rated for 10,000 hours running 1,800 rpm. Your Home Depot type generators have lawn mower type engines in them running at 3,600 rpm. Most of them have load management electronics that will start and stop up to 2 AC units to manage the load. Nothing at all wrong with those units, I just wanted the commercial quality. Diesel units are fine if you want to change the fuel out periodically. If you buy your generator from a reputable company it should put out more than rated output.

On power factor correction one would have to do some research as to the generator's ability to compensate for loads that were leaning inductive (ELI) or Capacitive (....the ICE man), starting surges and all that. Going to assume the problem would be handling big inductive loads. One would think the heat pumps are capacitively compensated to run in the 0.85 PF arena which is the limit for my COOP. I don't know where inrush surges fit in, aka are they limited to 0.85 too or is there an exception and if so what it is.

On single phase are you talking about a 240V swinging Wye where the 3rd phase is magically produced from the single phase power line? We had a community water well installed and no 3 phase was available. The pumps required 3 phase and the power company put in such a contraption since at the time we couldn't afford to pay the $50k required to bring in the 3rd line. Not familiar with any of the specifics, just know the overview. On our high HP well pumps, it was a nightmare. I am not aware of the design of the pumps as to how they looked to the power co.....L-R-C. But after about 6 months of putting up with it, we magically found the money (side note at a bank) and got it installed. End of problem.

On what you get for what they specify, one would surely have to look at the equipment specs to see the conditions for the rating. 17-18kVA out of a 30 kVA unit sounds kinda low to me.

Best I can do as my pedigree was not industrial power and it's application.

I bought one with a 4 cylinder GM engine in it with an Italian (MeccAlti) Gen end. I hope that it is as good as the GM engine in a Daewoo fork lift that I bought back in the 90 something.

I run the whole farm on a diesel Onan 19 kw generator. I only have one heat pump unit, but I have never found that it can't run anything/everything at once. Realistically, there are only a few things running at one time. If it meant the jump from 20 to 30 kw (and the associated price) I would be shutting off one of the heat pumps when on gen power.

As a side note: I put in a new heat pump unit about five years ago with a D.C. fan motor. The company said they would void the warranty if they were able to prove that I ran the heat pump on power supplied by my power plant. I heat with wood in the winter and summer outages are rare so it has never been an issue - I haven't needed to run the heat pump during an outage since I got the new one. A newer unit may not want to run on generated power or the company might want to back out of a claim due to that shiny new power plant in the yard.

(quoted from post at 20:00:41 03/17/17) I run the whole farm on a diesel Onan 19 kw generator. I only have one heat pump unit, but I have never found that it can't run anything/everything at once. Realistically, there are only a few things running at one time. If it meant the jump from 20 to 30 kw (and the associated price) I would be shutting off one of the heat pumps when on gen power.

As a side note: I put in a new heat pump unit about five years ago with a D.C. fan motor. The company said they would void the warranty if they were able to prove that I ran the heat pump on power supplied by my power plant. I heat with wood in the winter and summer outages are rare so it has never been an issue - I haven't needed to run the heat pump during an outage since I got the new one. A newer unit may not want to run on generated power or the company might want to back out of a claim due to that shiny new power plant in the yard.

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am sure that's what you were told so do not misunderstand and think I do not believe you. Having said that Carrier sells both heat pumps and whole house generators. So this does not go for all heat pump company's and all generator's. Having said that the electronics in todays units need clean steady power for lack of a better way to describe. I think your dealer may be thinking about the older smaller or at least less sophisticated generators of the past. If your generator is old then maybe he is right. I used a generator on my last unit to run in heat, it was a gas unit so capacity was not an issue and all control's were relays and contacts, read no chip's or circuit boards. The new unit does have all this so I will not at this point try our 25 year old portable on it. I have a newer portable and am unsure of it as well. Check with the Mfr. of both the heat pump as well as the generator. It wouldn't be the first time a dealer had an opinion that was not backed by the Mfr.

(quoted from post at 20:40:40 03/17/17) I have been looking for a standby generator that will run my whole house including 2 heat pumps. After closely examining specifications, it appears that all of the 20KW + generators are rated on 3 phase even if you are bying single phase.The catch is that a 30Kw generator will only put out out about 20Kw on single phase and giving consideration to power factor of less than 1 and I am not sure anything operates at 1:1 power factor but more like .8:1 in reality you can depend on about 17 or 18 KW out of a 30KW generator. Am I wrong?

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All kinds of single phase generators up to 40Kw and some up to 50kw.
Looking for auto start, pto driven or portable ?
What kind of transfer switch ?

I think a 30kw generator is overkill for a wholehouse application. If you want to go that big forget about DIY-ing ... you'll need a professional installation. That's a lot of juice.

You can easily get 36kW single phase units.

I have 20kW for house, put soft start on AC compressor to ease load.

(quoted from post at 06:21:45 03/18/17) I think a 30kw generator is overkill for a wholehouse application. If you want to go that big forget about DIY-ing ... you'll need a professional installation. That's a lot of juice.

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lot depends on the size of the heat pumps and the strip heaters as emergency or backup. Two two and half ton unit's with 7.5 to 10 kw heat strips each will eat up a lot of power. With a 15 to 20 kw load with out fans or compressor's running or any other house loads I would be questioning if 30 kw is enough with out more info. Add in a water with two from memory 4500 watt elements along with refrigerator's, freezers, hair dryers, electric ranges, toasters, microwaves and so on. Once you decide to go whole house it will take a big unit. Certainly with switch gear you can select what your emergency needs will be and only supply to certain breakers as in not whole house. This works until it doesn't and she wants to know why she has to put up with all the noise and expense and still not be able to use everything.

I know what you mean AngleIron ... women don't care how you do it -- when everyone else in the neighborhood is dark they want to be able to crank the heat, cook a turkey, throw a party, etc.!

I've got 2 heat pumps, both have soft start -- but if you wake up without power they will hit the heat strips immediately. To save on overall cost I have a 13kw unit and run just the main heatpump first to warm up the house then everything else.

When I worked at a hospital back in the 70's, they had 4 generators powered by 12-71 Detroits that ran on natural gas.

To get to the basics. You need to take a amp load reading. Of everything you plan to run. Be sure to take Locked Rotor Amps.Most of the generators today have regulators that will produce clean power. Some of the older ones do not and I would not trust the small portables.18 KW out of a 30KW something is wrong. Most generators can be wired for the voltage and phase you need. I have worked on 2.7 to 2000 KW single phase. I would stay with a name brand. Stay from Generac.

I'm not sure but I think carrier
stopped selling generators.

Pat,You are doing an Apples to Oranges thing single vs 3 phase gens.,A single Phase Generator puts out what it is rated at,a 3Phase only puts out 2/3s to 3/4s on single phase what it is rated for on 3 phase.a good single phase generator 20KW=83Ampes,25KW=104A &60KW on startup,35KW=146A & 90KW startup,45Kw=188 Ampes &110KW startup loads. In a PTO unit,you can go to 100KW load carrying.To answer your question,I'am running a full farm plus 3HPs(5 ton+ 2 2Ton units )with a25KW unit.I'am looking to go to a 35 or 45 so we can run the grain dryers if needed. 20 or 25KW will fill your bill totally.

(quoted from post at 17:16:32 03/18/17) Pat,You are doing an Apples to Oranges thing single vs 3 phase gens.,A single Phase Generator puts out what it is rated at,a 3Phase only puts out 2/3s to 3/4s on single phase what it is rated for on 3 phase.a good single phase generator 20KW=83Ampes,25KW=104A &60KW on startup,35KW=146A & 90KW startup,45Kw=188 Ampes &110KW startup loads. In a PTO unit,you can go to 100KW load carrying.To answer your question,I'am running a full farm plus 3HPs(5 ton+ 2 2Ton units )with a25KW unit.I'am looking to go to a 35 or 45 so we can run the grain dryers if needed. 20 or 25KW will fill your bill totally.

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Single phase loading of a three phase generator is 57.7% of the nameplate Kw capacity.