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.

 

[BrokenTrack]

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...

Efficiency is already factored into the equation: pto horsepower ratings are measured at the pto, so 27 hp is available to do work, that is why on tractors it is measured at that point. It is also measured at pto rpm speed so the tractor is not operating at peak rpm.

They rate tractors this way so it is a real-world application.

You can power a 20 kw generator with a 40 HP tractor of course, but you can power it with a 400 hp tractor too, it is just over-kill in either situation.

Look at commercial gensets: 21 KW units only have 32 HP engines on them.

Isuzu 21 kW Diesel Generator

 

[LittleBill21]

i actually have 2(3) generators. i have my 7k for when i need my well, dryer, stove, electric water heater, etc.... but those uses are low. i then wire in an inverter generator(2 if needed) and primarily run off that. my 7k can use close to 1g per hour at close to full load, the inverters run for several hours on a gallon, and are a crapload quieter.

if you don't need everything all the time, the inverters cut it for me when i don't need 240v or high amperage.

 

[Sawyer Rob]

Efficiency is already factored into the equation: pto horsepower ratings are measured at the pto, so 27 hp is available to do work, that is why on tractors it is measured at that point. It is also measured at pto rpm speed so the tractor is not operating at peak rpm.

They rate tractors this way so it is a real-world application.

You can power a 20 kw generator with a 40 HP tractor of course, but you can power it with a 400 hp tractor too, it is just over-kill in either situation.

Look at commercial gensets: 21 KW units only have 32 HP engines on them.

Isuzu 21 kW Diesel Generator

Like I said, direct drive is more efficient, over pto hp, and no matter, the 80% rule still applies, at least on tractors for tools on the pto...

So, your example, pretty much fits into that equation for direct drive...

SR

 

[newbury]

Hi, folks. Does anyone have any insights regarding sizing a portable generator for home backup?
<snip>
That being said, any recommendations regarding what'd be an adequately sized portable generator to provide backup power for my home? In terms of usage/load, my goal would be to maintain power to the pumps/computer associated with my propane boiler (home heat + hot water), well pump, freezers (one chest, one upright), refrigerator, air exchange system, and then I guess some lights and probably a laptop/phone charger. I don't own air conditioners nor would I plan on running power tools during a power outage. <snip>

I should also mention (perhaps very important) that my power doesn't go out very regularly. Furthermore, if and when it does go out it rarely lasts more than a few hours. And again, this is perhaps twice a year. I just happen to live in a very cold part of the country (Northern Minnesota) and a modestly priced generator seems like reasonable "insurance" against frozen pipes!

Thanks for your time..

Well I have not seen any recent posts by the OP.
Now I've lived in Northern Vermont, and I'm cheap.
I've lived in houses that you could almost fly a kite inside if there was a strong breeze outside.
If his power only goes out twice a year for a few hours and he is worried about frozen pipes he should let them drip. For all else he should be able to just hunker down, heck he has a woodstove for heat. If he's worried about his freezers they won't warm up if it's cold.
Try not to open the fridge too often.
Then like Eddie wrote just get a decent small inverter generator and some extension cords.

 

[BrokenTrack]

That is so true, but a lot of that depends on the family structure.

I used to do that when the power went out, but now that I have four daughters, three of whom are teenagers, life is a little bit different. Lighting a single lightbulb and the refrigerator is no longer going tocut it. For me...for my wife, yeah it is fine, but not teenagers in 2020! (LOL)

I really like PTO generators just because you get so much more clean power for the same amount of money, and most people on here (hence the forum name) have tractors. A few weeks ago the power went out, and my kids did not even know we were operating on back-up power.

I have always loved Tiny Houses, and lived in a few, so we are planning to retire to one when the littlest daughter leaves the nest. If we do that, we will go to cogeneration for heat and power. We got a nice spot, but its a LONGGGGGGG ways from grid-power!

It is not that I am antisocial, but...

 

[MAD777]

We are all being anti-social these days!