You will probably need a 22kw just to start your A/C. I'm guessing by house size you probably have a five ton A/C unit which will be about 150a to start just that alone.

You made no mention of which appliances are gas and which ones are electric, so listing appliances is of no use.

As far as the hot tub you can use load shedding or NO contactors to drop that load as I assume it will not be needed during a power outage.

quote:

Originally posted by Pyker:
The gen will run from a 1000 gal LP tanks.

You're probably already aware, but in case you aren't, when you're estimating how long the tank can fuel the generator be advised the propane companies only fill to a percentage of max capacity - the ones here fill to 80%.

quote:

Originally posted by Skins2881:
You will probably need a 22kw just to start your A/C. I'm guessing by house size you probably have a five ton A/C unit which will be about 150a to start just that alone.

My house has a 5 ton AC unit with a LRA of 118. My 14.5kw diesel genset cannot start it, even if it’s the only appliance. I may install a Microair soft start kit on my AC, which will bring the max startup draw to 30-35 amps, well within my generator’s ability to start it. The only problem is a soft start is expensive at around $350.

I realize this may not be for everyone depending on where you live but here is what we have done. We have two houses to power. Here in hurricane central we have been without power in 90-100 degree September for as long as 3 weeks. We had a portable 9.5 kw that was a miserable failure-it couldn't even keep the freezer going. I said never again.

15 years ago I chose a 40 KW SDMO generator from a Miami company, powered by a John Deere diesel engine. (I have a John Deere dealer nearby and parts and service are readily available). It services just like my John Deere tractor. It has a sound enclosure so it is quiet and is weather proof, but I built a shelter over it just the same. It powers the whole house and does not strain to do so. My house is wired with an automatic switch, so when line power drops for a period the generator kicks in. When line power drops the lights flicker and the generator takes over so that we hardly notice. The second house (my office and guest quarters) is on a manual switch. The generator is programmed to start and run for a half hour once per week to exercise itself. We are on a ranch so have diesel tanks and a diesel fuel nurse trailer which I park next to the generator in hurricane season. At the time we were choosing a generator, a wise electrician advised me against propane due to the cost of running a generator for long periods. You also have to consider needing delivery of refills of propane during an emergency. My generator has a 25 gallon tank. I keep the tank topped off when it is running but it will run under load for at least a couple days on one tank.

Our most recent hurricane was Sally last September and we lost line power for several days. We hardly noticed. Other family came to our house to get cool while the lines were down. Power has gone down periodically a number of times over the past 15 years but Sally was the longest period since Ivan and Dennis in 2004 and 2005. All in all I am pleased with the way this generator has performed over the years.

quote:

Originally posted by sigcrazy7:

quote:

Originally posted by Skins2881:
You will probably need a 22kw just to start your A/C. I'm guessing by house size you probably have a five ton A/C unit which will be about 150a to start just that alone.

My house has a 5 ton AC unit with a LRA of 118. My 14.5kw diesel genset cannot start it, even if it’s the only appliance. I may install a Microair soft start kit on my AC, which will bring the max startup draw to 30-35 amps, well within my generator’s ability to start it. The only problem is a soft start is expensive at around $350.

You can get hard start kits a lot cheaper than that, like $10-15. It's just a capacitor. I'm not sure what the Microair product is, but I imagine it's just a capacitor too. Worth a shot at trying for the price.

Not close to the expertise of others here but I would suspect you don't want to be maxing out the Amps on any generator... it is probably best for the unit to be running in the midrange most of the time....and just able to kick it up if something requiring more kicks in....

quote:

Originally posted by Skins2881:

quote:

Originally posted by sigcrazy7:

quote:

Originally posted by Skins2881:
You will probably need a 22kw just to start your A/C. I'm guessing by house size you probably have a five ton A/C unit which will be about 150a to start just that alone.

My house has a 5 ton AC unit with a LRA of 118. My 14.5kw diesel genset cannot start it, even if it’s the only appliance. I may install a Microair soft start kit on my AC, which will bring the max startup draw to 30-35 amps, well within my generator’s ability to start it. The only problem is a soft start is expensive at around $350.

You can get hard start kits a lot cheaper than that, like $10-15. It's just a capacitor. I'm not sure what the Microair product is, but I imagine it's just a capacitor too. Worth a shot at trying for the price.

I looked at the hard start kits, but I’m not sure if it would do what I want to lower the startup draw. The soft start kits slowly ramp up the voltage over about .8 of a second. They’re mainly used to prevent initial load shock in industrial applications, like water pumps or inertia loads, but they have the added benefit of greatly reducing the startup requirements. They also limit the number of cycles per hour to prevent thermal loading, and add to the life of the equipment. They are popular with the RV crowd because it allows them to run a roof air unit from a 2000 watt generator.

They are not capacitor based, I think. They seem to work by ramping the voltage and amperage up on a curve instead of the all-at-once way that a DOL (direct on line) hookup does.

Like a mini VFD or something?

Add on soft starts are hard on motors, advise against it.

Yes, I think soft starters are basically a VFD without the variable speed controls. This is new to me, so everything I know is basically from a little reading, some youTube videos, and product reviews.


Here's an article on the difference between VFDs and soft starters that I found helpful.

This is the product I was considering. There is another brand (Hyper Engineering), but I haven't seen as much about them.

Microair ASY-368-X72

After my post earlier, I went to Microair's website and read through their specs. It looks like the EasyStart does have a capacitor, but you bypass the built-in one. If I try one of these, I'll post on this site all about how it is working.

offgrid, everything I'm reading says it is easier on motors. Where are you finding it said that they are harder on motors?

Repaired, maintened industrial woodworking equipment. Installed soft starts on a handful of heavy use single phase motors early on, premature motor failures.

Machine with 3ph motors, variable frequency drives. VFD's common failure.

Do you remember what soft starts you installed, and how long ago was this? Were they Siemens VFDs?

quote:

Originally posted by sigcrazy7:
Do you remember what soft starts you installed, and how long ago was this? Were they Siemens VFDs?

10yrs. Sprecher Schuh and Allen Bradley 1PH, don't recall the brands/re-badged 3ph VFD's. The 3ph VFD's were a fair amount more reliable then a 1PH soft starts. Change how a motor starts/stops from its stock form.....

Size the generator to start what you have. Better off in the long run.

A person could write a book on the subject of house generators. We are all different. I yield to no man in my cheapness. When our power goes out we want to survive. We have a basement. It is just my lovely wife and I. No need for AC, we can go downstairs. We need enough heat to stay alive, water from a well, toilets that flush and basic lighting. Propane runs all our "flame appliances". Our 12,000 watt generator uses about 1.8 gallons of propane per hour at full load and about 1.2 gallons at half load. We are home most of the time. I leave our control on "off". If we go to town for 3 hours and the power goes off, no need for the generator to run. We can turn it on when we get home if we want. During extended power outings I run the generator about 9 hours a day total which keeps everything pretty happy. This works for us. If someone else requires life to go on exactly as normal, God Bless Them as long as they are willing to pay for it. By the way a 22kw generator uses about 4 gallons of propane an hour at full load and about 2.9 gallons at half load. Assuming a 1000 gallon tank full (800 gallons) the tank will be dry after 8 days of continuous running at full load. At $2 a gallon that will cost $1600. Half load would be about 11 days. Using my system of running it 9 hours a day the 800 gallons would last almost three weeks with our 12kw generator. Everyone has to choose what works for them and their willingness to spend their money.

Fuel consumption is a thing. I am of the opinion that you should spec the smallest generator possible that lets you get by. Enough power to keep you comfortable, but you don't NEED all the comfort of full power, unless you are rich and really don't mind paying for it!! Also, if your tank runs dry ten days into a long outage, can you get more propane? Has the propane company run out? Can they even deliver more? I know for a fact that in Florida the entire state runs out of propane during ANY hurricane and you cant get any propane delivered for probably 3 weeks until things stabilize...

Up north you NEED heat. Of course you need water, so well pump is important for some. And then sump pumps are important for others.

Down here in Florida, I don't have to worry about dying of cold. I have city water, don't have to worry about well water. We don't have sump pumps. I can run my entire house (minus 220V) with a 3500 watt inverter and be comfortable. You'll have to decide what you NEED and what you WANT. And what you are willing to pay for.

I have a $2000 Honda 3800 watt generator (that I bought used for $400) and some small inverter generators and I'll have as much power as I need in the next hurricane outage....

quote:

Originally posted by offgrid:
10yrs. Sprecher Schuh and Allen Bradley 1PH, don't recall the brands/re-badged 3ph VFD's. The 3ph VFD's were a fair amount more reliable then a 1PH soft starts. Change how a motor starts/stops from its stock form.....

Size the generator to start what you have. Better off in the long run.

Thanks for your insights. As for sizing for your maximum startup requirement, that is usually good advice, but less so when it comes to diesel powered generators. When I do not require AC, cooking, or clothes drying, my house will usually run along drawing only 1.5Kw or less. Buying a large 35Kw diesel unit to satisfy only the AC startup would leave the generator grossly overpowered for most of the time. Not only is this fuel wasteful, it can subject the diesel to wet stacking after prolonged periods of low-load operation. Therefore, it is way more efficient and safer for the generator to run a smaller unit. Gasoline/NG/LG generators don't suffer this problem, although they will be less efficient if up-sized way above the normal load requirements.

What I need is some kind of transfer switch for the soft start, so I could run my AC compressor DOL on line power, and from a soft start on gen power. Best of both worlds.

Rheem has certified the soft start kit that I mentioned, and it will not void any warranty. Perhaps they have improved over the years if a manufacturer is now okaying their use.

I can't add much except that I have a 20kw generator that runs my entire 2500 sq/ft house when the power goes out no problem. I am running propane for heat/hot water, stove, grill. I just put in a hot tub so we will see how it goes but I've not had any problems. I'd definitely go bigger and not worry about being underpowered.

quote:

Originally posted by frayedends:
I can't add much except that I have a 20kw generator that runs my entire 2500 sq/ft house when the power goes out no problem. I am running propane for heat/hot water, stove, grill. I just put in a hot tub so we will see how it goes but I've not had any problems. I'd definitely go bigger and not worry about being underpowered.

You can either add load shedding to drop hot tub if you are approaching limits of generator, or utilize a Normally Open (NO) contactor to cut off the hot tub when you lose power. It's unlikely.that you would ever have a problem in the winter since you use propane for heat, unless the propane is combined with a heat pump instead of A/C. The summer when running A/C is when you might possibly run into an issue if the hot tub heater and A/C kicks on.

The good news if you are home during an outage you could simply turn off the power to the hot tub and it won't freeze during the summer. If you are traveling though it's possible there might be a chance of overloading the genset. You should be able to find out the KW of the hot tub heater in your owners documents and ask your generator installer to give you suggestions.

quote:

Originally posted by Skins2881:
Like a mini VFD or something?

The soft starts we use in the marine industry change the cycles and start up cycles are much lower (as well as amps) we use them on yachts with chillers and they help considerably with startup amps not tripping shore power breakers. Ours are around $750 a piece, but they do a lot of things household ones wouldn't need and are more compact and waterproof and ramp up percentage/time is user adjustable. We now have variable speed air conditioning chillers where the chiller and compressor runs non stop and adjusts the speed it's running at to meet demand. They also help with generator loading as when you lose power and then turn power on, you don't get a giant load from everything coming on at once.

If I had a 14 kw, whole house generator I sure as SH** would spend $350 or $750 so that my A/C would work with the generator IF I wanted to run it. 3 days in summer weather here in South Florida without A/C and you'd wish you had died in the hurricane, it's absolutely miserable. With a VFD startup will be no issue. I have several yachts running 5 ton chillers (and a 1HP sea water pump, and a 1 HP chilled water pump) cycle on at the same time with a single 240v/50 amp cord feeding it and many other items on the yacht. A 14kw puts out around 60 amps @ 240 volts if memory serves me right.

Just some info for the others. Generators (non inverter) run at a constant RPM usually 1800 rpms, some 3600 rpms, all of them (Gas/Diesel/LP). The governor just puts more fuel into the engine to maintain the same rpm's with more load. The newer diesel generators run pretty clean and can run them for extended lengths of time at even as low as 30% load. closer to 80% load is a little better, but generators for a house or yacht never run the same load, at night usually much less A/C demand. Also you burn fuel based on KW draw. A 20 kw with a 10 KW demand is going to burn about the same fuel as a 14KW generator with a 10 KW demand. You don't want to be grossly over-sized, but a little over-sized won't hurt anything.

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