OT: Size required of portable generator?

What size in watts of an electrical power generator will be adequate to power my barn during brown or black out of electricity? My highest usage per month in the last yr was 1477 KWH. My barn dominion is all electric. Anyone have a brand/model to recommend. I'm considering a Westinghouse dual fuel(gasoline/LPG).
Thanks for any replies, Jim

Hey there Jim. FIRST of all you have to consider:

Instantaneous POWER in Watts (Volt x Amps) and ENERGY (Volts x Amps x Time) IE Killowatt Hours KWH like
the utility charges you to compute the size of the genset.

It needs to be POWER RATED large enough to supply YOUR MAXIMUM load in Watts, plus I add an extra 20 to
25 percent. Be cautious of Max Power or Surge Capacity or Continuous Power Ratings in your selection
!!!!!!! Don't operate too small or just on the edge is my advice, IE Max PLUS 20% minimum Id use.

SECOND the voltage needs to match, is the barn supplied (and do you require) with true 120/240 Volt
Single Phase Three Wire ??? or is it 120 VAC Only ???

THIRD what sort of Transfer Switch/Method are you going to use, manual or automatic, does it switch Hots
and Neutral or Hots only ??? Plug/Receptacle and Cord connected or how??? SAFETY !!!! so no way to back
feed and energize the Grid when on genset Power !!!!!!

FOURTH Grounding and Bonding, and switching/transfer methods, that determines if the Genset should be
configured with a BONDED or a FLOATING Neutral and the requirements for a Grounding Electrode....

THAT ALL BEING SAID only you can compute the size as based on YOUR load NOT OUR GUESSES OR THE SIZE WE
USE

AFTER YOU determine the max load and size you need, Billy Shafer is the EXPERT and Go To Guy regarding
gensets, and then I can help you with all the other issues noted above

Best wishes Jim, I will be in your fine State over Thanksgiving Lord willing

John T

Does it have a smart meter?
A smart meter will show the demand.

I was going to buy a Westinghouse until I found this outfit.
Price was right, made in USA and free shipping.
Untitled URL Link

Take your largest load you need to run and calculate the load. We needed 20Kw to milk but had to shut off a lot of things for it to work. We went to a 25 and then found out the buried wire to the post was too
small.

I think starting electric motors will be an issue you can't
accurately calculate.

example:
I have a electric chainsaw that uses less than 15 amps 120v when
running. 15x120 = 1800w.

So you would think a 3500w/4000w surge generator will work..

NO. The starting amps for chainsaw is over 70a.
Generator will shake, rattle and grunt.
Not good for the generator.

The generator won't even think of starting a 1.5 hp 120 volt air
compressor... It too uses about 1800ws

So all your calculating doesn't take into account lock rotor
amps..

My point, motors are totally different animals..

Best to go too big than do the math if you have big electric
motors in your barn.

After you determine the size you need check out Electric Generators Direct. I bought a 11K standby unit from
them about 8 years ago. Great price and very good people to work with.
Generators

Dual fuel is a good way to go. I have a propane genny waiting a fuel line to make the installation complete.
Propane usage is nice with a 30 year shelf life, but burns roughly twice as much in comparison to gas.

TxJim, I have a 25kw Winpower pto generator for such emergencies. Put your JD to work and it is one less engine to maintain/exercise. I know it is overkill, but I got it for $450 after the Y2K scare was over.

My $.02

Mike

Jim I am sure the Generac haters will chime in but when we built this retirement home I installed
a propane fueled 20KW Generac . Hard wired to a transfer switch that goes to a panel we call
essential. Well, refrigerator/freezers ,hot water heater and most lights. We do have a gas log for
emergency heat. Unit has around 400 hrs after 7 years and has been god sent. Just never without
power. What ever you get have it installed with automatic transfer switch. New Generac has 7 year
warranty, and around these parts sell about 80% of all new installs.

jm
How big of an air compressor will your 20kw generator start?

How big is your Air Conditioner? Water heater?
Electric or gas range?

My son, cousin, and me all have the dual fuel Westinghouse. Did all the shopping and
considered it to be the best bang for the buck. They switch fuels back and forth smooth.

Electric water heater, 220 8 hp well, are the big loads, as stated the house has two breaker panels the compressor part of the air-conditoner heat pump is NOT on the generator but we can run the fan and use the gas logs,never a problem. So far I have never really ever heard it sound like it was loading up. Had one outage 3 years ago where it ran solid over two days. Most outages are 3/4 hrs at the most. Have a thousand gallon propane tank and go two years without filling then it will never be more than 1/2 down. I consider it one of the smartest thing I have ever done. You can be setting here watching TV and power go off and within 20 seconds it will be back on.

As John said, you need to provide more information about your loads before anyone can give you any useful recommendations. You can calculate your AVERAGE power from your utility bill, but that's not going to help you properly size the generator. The generator has to be sized for the MAXIMUM INSTANTANEOUS load it must handle. Look at the biggest appliances or machines you need to operate when the grid goes down: Pumps, air conditioners, elevators and electric heaters all draw a lot of current. Worst case scenario would be for all your loads to turn on at once; if your generator can handle that surge, it will have no problems with typical loads.

We got by here for many years with an 8Kw Dayton/Winco unit powered by an Onan NH 24 Hp gasoline poweredengine, with load management we could have lights, well pump, furnace blower on the natural gas furnace,TV and cook with a micro wave and the wife's sewing machine or computer . I did cut the water heater off during the day and let it regenerate during the night. Worst thing was having to keep it filled with gasoline. I replaced it with a 20 Kw Onan fueld by natural gas that is hard wired to the house through a manual transfer switch, It is nice to have an uninterruted fuel source.

The older 1800 rpm generators of most makes are more durable and the copper windings in them allow them to carry their full ratecload continious as opposed to some of the modern 3600 screamers and the water cooled versions are almost always quiter.

Thanks for all replies. Yes I intended to hard wire with an automatic switch. I stated my highest electrical usage for a month was """1477 KWh""". Isn't that sufficient? It's been many yrs since I studied alternating current electricity.

jm
I'm lucky, my power outages don't last very long.
Last time power went out at supper time.
Good excuse to go to town to eat.
Power was back on before we got home..

Like I said, trying to use a generator to power motors
may not be a good thing..

Propane is the only way to go...no fuel contamination issues and usually best price per BTU. Buy it in late August for the best price.
I have an 11kw Generac backup for my house that never let me down. I have gas appliances including water heater and clothes
dryer.

Hi again Jim, hot down there huh DRATS !!! My daughter says I cant visit her in the summer because Im
too high maintenance lol Once there I had her go out start the car let the AC run a while then pick me up
at the door lol. To top that off I just heard someone on the news state the average power required to
charge an average EV is FOUR TIMES that required to power the AC for an average home GRRRRRRRRRRRRR Of
course as an engineer and despite the word average, I know it depends on ambient temp, how much the EV
needs charged, insulation, size of home on and on and on SOOOOOOOO many variables and unknowns. REGARDLESS
its gonna take a bigger electrical grid provided by gas or coal, nuclear, wind or solar to charge a bunch
of EV's PLUS run the AC, and MY DAUGHTER HAS AN EV (she loves) PLUS SHE HAS AC !!!!!!!


You now ask I stated my highest electrical usage for a month was 1477 KWh. Isn't that sufficient?

UNFORTUNATELY NO As I stated below:

KWH is a measure of ENERGY which is Volts x Amp x Time. What the utility charged you (Volts x Amps x
Time) and what was the maximum POWER (Volts x Amps) you used ARE TWO DIFFERENT THINGS

Watts (Volts x Amps) is a measure of instantaneous POWER (Whats the max current you need when all
necessary is running)

Your generator needs to be big enough to supply the max current draw at your operating voltage PLUS
adequate surge capacity to start devices such as compressors or cooling units etc. which may draw 3 to 5
times as much current (as normal running current) to start up

If you had an ammeter (like a clamp on) or a more exotic watt hour meter that tells you how much current
you are drawing when all your necessary tools/appliances/devices are operating NOW THAT CAN PROVIDE THE
INFORMATION NEEDED

A simple clamp on ammeter when alllllllll the necessary tools/appliances/devices are operating isnt hard
to use provided you are safe.........Then the minimum POWER (Volts x Amps) can be easily calculated and
then increase that size as necessary to allow any compressors or coolers etc to start up.

Id love to help and sorry I cant give you the short sweet answer you seek, BUT YOU NEED TO KNOW THE MAX
CURRENT the shop requires to size the generator. Again what someone else uses or any guesses are no help
YOU HAVE TO KNOW YOURRRRRRRRRRRRRR REQUIREMENTS. Get an ammeter or hire a sparky this isnt rocket science
and is a really easy number to obtain. Whats the electric service to that building ?? 100 Amp or 200 Amp
etc ??? Thats NOT definite but can help some.

Best wishes Jim, I'm on your side and am trying to help here

John T

(quoted from post at 04:22:26 07/21/22)
Thanks for all replies. Yes I intended to hard wire with an automatic switch. I stated my highest electrical usage for a month was """1477 KWh""". Isn't that sufficient? It's been many yrs since I studied alternating current electricity.

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No, it's not sufficient. This is like saying, "I like chocolate. How much wood do I need to build a birdhouse?"

1477KWh is how much power you use. That does not give you any indication of the variable load you place on your electrical system. That can vary from a couple of cell phone chargers to having the water heater, oven, well pump, and central air running all at once.

OK thank you all. I get a clamp on amp meter. As I stated it's been since mid-1960's since I've given much thought to alternating current.

(quoted from post at 07:54:16 07/21/22) jm
I'm lucky, my power outages don't last very long.
Last time power went out at supper time.
.

Click to expand...

Geo
I never stated my electricity was habitually off. It was off/on back in February last year during the unusual cold spell. Texas news has been discussing brown/black outs due to usage exceeding the Texas electrical generating capacity SO I WAS ATTEMPTING to be prepared if that became a reality. There will be many more 100+f days before the Texas weather cools off.

Usually the ideal generator size is twice as large as what the purchaser believes is required .

John T. I know generatots are rated in watts and service entance boxes are rated in amps So if you knew how many watts to make an amp would that give a decent estimate of size fenerator needed. I did have a 5,500 what portable generator and was only for 120 volt and just used a heavy extension cord in threw a window of house. Was not big enough to power the well pump but we got by for over a week in ice storm in 2005

Id look at the size of the service entrance in amps and find something close to that, or at least large enough to run the
essential loads.
We got along OK with a 25KVA for a lot of years milking cows. If you have a lot of large motors to run, a 40 or 50 KVA might be in
order.

Rod

> I stated my highest electrical usage for a month was 1477 KWh. Isn't that sufficient?

There are 720 hours in a month, so your average power consumption is about 2000 watts. (1477 kw-hr ÷ 720 hr = 2 kw) That might lead you to believe you can get by with a 2000 watt generator.

On the other hand, let's suppose you had some monstrous load plugged in for one day that used up all that 1477 kw-hr in 24 hours. 1477 kw-hr ÷ 24 = 62 kw, so you would need a 60,000 watt generator.

Obviously the answer is somewhere between 2000 watts and 60,000 watts. You need to sit down with a pencil and paper and add up all the major loads that you'll need to run at the same time. Some appliances will be labeled with their power or current requirements. Others you'll have to guess based on the sizes of their circuit breakers. If you know the horsepower rating of a motor, multiply the horsepower by 746 to get the power requirements. Then double that number to allow for starting current and power factor. Decide which of the largest loads need to run at the same time and add them up. The result will be your MINIMUM generator size.

Mark
If I'm understanding you correctly on my all electric barn(home) then I probably would have more than enough portable electrical generation with a 8000-10,000 watt generator. I seriously doubt my wife will be washing/drying clothes during a short electrical brown/black out. Electric water heater & electric kitchen range are the largest loads unless emergency heating elements HVAC unit come on which is very rare. Can a 8000 watt generator start/operate a 2 ton AC compressor & 30 gallon water heater with other electrical loads at a minimum?

Mike
Thank you & Yes I have several tractors that I could power a portable generator with. But being disabled & with my advancing age I was thinking of an automatic generating system that I could operate with no help required.
Thank you again for your idea.
Jim

Things add up quickly.

Water heater 3500 watts (or more)
AC unit 3500 watts (or more)
Refrigerator 500 watts (general info)
Freezer 500 watts (general info)

Those things could be 8kw running load. Anything using a motor will have a short term, higher draw during starting. Nothing here allowed for a lights, stove burner, or microwave. Do you have a well pump you will need for water?

We can cover the refrigerator, freezer, oil boiler, and a few lights with a 4kw portable. That won't start our deep well pump, so anything more than a few hours of outage where we can run a few cords from the portable, we go to a 15kw PTO unit. I am starting to look at 20kw installed units as it can be a pain to move things around and set up the PTO unit and fuel for a 60+ HP tractor to set and run a generator isn't cheap. For an installed standby unit, I would say you should be looking in the 15 to 20kw size range to allow for running loads and starting loads that may come on while those loads are running. For the difference in cost between a small unit or a larger one, it is worth the difference not to have to run around and turn things off, so you don't overload the generator if something does start that you didn't plan on. JMHO

I have Coop water no deep well just 2 people no children at home. Water heater could be turned off during an electrical brown/black out/ I utilized my wood burning stove in Feb. 2021 when I experienced electrical rolling black outs

(quoted from post at 08:15:36 07/22/22)
I have Coop water no deep well just 2 people no children at home. Water heater could be turned off during an electrical brown/black out/ I utilized my wood burning stove in Feb. 2021 when I experienced electrical rolling black outs

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Would likely be ok without the water heater and electric stove and 8000W .
A CDRU3 hard start kit on the AC will reduce the starting load applied to the generator .
Transfer switch ?