Help sizing a generator for home backup?

[Industrial Toys]

I never had any issue at all running my entire property on a 3.7kw air cooled 3600rpm Yanmar single cylinder diesel generator. Excercising load management of course. No issue at all running my jet pump. I still have it as my last ditch back-up.

I can't use my electric heat, even though I reconfigured my electric hot water heater to use less current, I can't use my welders or compressors or clothes dryer. But every light on the place works, fridge and freezer and in varous outages, I never thought, I wish I had more power. My 7.5 KW sets are nicer to have, but in truth, if I had a slow running 3.7KW Diesel, I would rather use that.

 

[PILOON]

I run a 8 kw 'portable' thru a proper panel that is OK for most times. Also it is electric start and always on a battery 'keeper'.

BUT
I was offered a "new, in box" generator head that is 20KW 120/240 V @ 60Hz at the crazy price of $300. (and could be dickered down)

While very tempting I turned it down as I realized that matching it to a proper diesel motor would be a tricky and costly effort.
First idea was my CUT pto but not enough HP as well as RPM issues.
It is designed to run at 1800 RPM so that is limited to a diesel or fancy gearing on a gasser.

May be wrong but I determined that to be properly rigged I'd need an engine in the 30-40 hp range and that with some sort of governor to maintain proper cycles.
Just to major a project for the gains.

It is a JinLong ST20 and web search indicates a very reputable firm.

 

[Carl_NH]

I run a 8 kw 'portable' thru a proper panel that is OK for most times. Also it is electric start and always on a battery 'keeper'.

BUT
I was offered a "new, in box" generator head that is 20KW 120/240 V @ 60Hz at the crazy price of $300. (and could be dickered down)

While very tempting I turned it down as I realized that matching it to a proper diesel motor would be a tricky and costly effort.
First idea was my CUT pto but not enough HP as well as RPM issues.
It is designed to run at 1800 RPM so that is limited to a diesel or fancy gearing on a gasser.

May be wrong but I determined that to be properly rigged I'd need an engine in the 30-40 hp range and that with some sort of governor to maintain proper cycles.
Just to major a project for the gains.

It is a JinLong ST20 and web search indicates a very reputable firm.

Same here - our 7.5KW does "enough" would be great to have more!

You are correct the 20KW will need 35-40HP for direct drive. We had a 15KW PTO generator on the farm in the late 60's with a disconnect and 200 amp service / transfer setup (not usual in that time) and ran this off a JD420 with 28HP.

The skid mounted genset had gearing to run the generator at 3600 RPM with a 540 PTO input and the 15KW unit powered the whole farm.

 

[John_Mc]

If I were buying again I would get an inverter style. I would also get one that could run on propane as well as gasoline.

There are aftermarket kits to allow your existing generator to run on either gasoline or propane. I installed one on my old Generac 4000EXL and ran it for years switching between gasoline and my 500 gallon in-ground propane tank. It ran fine, and it was great not to have to worry about running into town during a multi-day power outage for more gas. It was especially great when the power was out in the surrounding towns, and none of the gas stations were pumping gas. (That generator died from lightning damage.)

I have a kit to convert my Honda EM6500 generator to dual fuel as well, I just haven't installed it yet.

 

[RalphVa]

I have the Isuzu on a battery tender, an old outdoor Battery Tender. Tried a solar panel. Wasn't enough.

If you have NG, it would be a no brainer to use it. Did not want propane on the site. House is all electric. Worked with propane filled process plants for 31 years. Don't want it on my property.

Ralph

 

[John_Mc]

If you have NG, it would be a no brainer to use it. Did not want propane on the site. House is all electric. Worked with propane filled process plants for 31 years. Don't want it on my property.

NG would be a no brainer if you have it available. For those of us out in the boondocks, it's not an option.

 

[defranks]

With a well, I壇 go with a minimum of 6500-7500 running. Besides, I doubt a 4000 watt unit will have a 4 wire 240 outlet to power the house. Ive never have Seen a diesel generator that uses only 1 gal of fuel a day, and I致e been around generators for 20 years. I could sell a million of those. Heck I壇 cut the utility feed and power my house 24/7 at a cost of $2.50 a day

Yeah, I'll take two of those myself.

 

[BrokenTrack]

I run a 8 kw 'portable' thru a proper panel that is OK for most times. Also it is electric start and always on a battery 'keeper'.

BUT
I was offered a "new, in box" generator head that is 20KW 120/240 V @ 60Hz at the crazy price of $300. (and could be dickered down)

While very tempting I turned it down as I realized that matching it to a proper diesel motor would be a tricky and costly effort.
First idea was my CUT pto but not enough HP as well as RPM issues.
It is designed to run at 1800 RPM so that is limited to a diesel or fancy gearing on a gasser.

May be wrong but I determined that to be properly rigged I'd need an engine in the 30-40 hp range and that with some sort of governor to maintain proper cycles.
Just to major a project for the gains.

It is a JinLong ST20 and web search indicates a very reputable firm.

You would only need a 27 hp tractor.

You have to remember that a tractor is rated at its pto shaft, so the stated pto horsepower of the tractor, is the power available to turn the generator. At 750 watts per hp, 27 hp will do the job. (20,000 watts divided by 750 watts per horsepower equals 26.6 horsepower). (If people want to split hairs with some other losses 27 pto hp might only produce 19 KW, but an average house uses about 10 KW at any given time, so it is more than enough).

To match the generator input shaft speed of 3600 rpm to get the proper 60 cycles, you could easily get a pto induction gearbox. Surplus Center, who advertises on here has them for around $400. Add in a pto shaft for $180, and you could have had a 20 KW generator for $750 or so. That is a pretty decent price for the KW it is producing. Homemade PTO generators abound on youtube for that reason.

(I am sure you had other reasons not get that generating head, and so I am not saying you should have gotten it or not, but there really is not much to a pto generator either)

 

[Sawyer Rob]

Anyone who has spent any amount of time running pto powered tools, should have learned it takes two pto hp per 1,000 watts of generator. I don't care about the "paper" 750 watt rule, there are loss' and no generator OR diesel runs at 100% efficiency, so to run a 20kw generator at full power you would need 40 pto hp...

Yes direct drive is more efficient, but I STILL would not want to have my diesel/generator running maxed out, so I'd AT LEAST want to use the 80% rule.

I do agree, it would have made a nice package, that would have easily ran most homes and lasted for many many years.

SR

 

[Travelover]

The OP states that power rarely goes out and rarely for long and that he is willing to sequence bigger loads. Based on that and no AC, a 5000 to 7500 watt generator should be adequate. If propane or natural gas is available it is a big convenience as opposed to storing gasoline. Costco sells some dual fuel generators and has a generous return policy.

I was in a similar position at my last house in Michigan and a 5000 watt surge / 4000 watt continuous generator worked fine for the 27 years I lived there. It would have been convenient to have a smaller inverter generator just to keep the lights on during longer outages and just fire up the big generator for the furnace or well pump as needed.