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Anybody own a Whole House NG Generator?

meaux on Sun February 05, 2006 11:24 AM User is offlineView users profile

I'm lookin to buy one of these things but I don't know what KW rating to get, or expect...How's the maintance? Happy? So far, I'm expecting to shell out about $10K...

I have all the modern day electricial appliances, microwave, fridge, etc. and a pool pump. The A/C unit is a 5ton...3000sq. ft. home...I may add another Freezer and Refridgerator later...

I know after hurricaines Ivan, Dennis, and Rita etc., I ain't leavin...

-------------------------
Lazy bum who lives off his wife.

01 BMW 530i Sport, 92 Porsche 968, 85 F150, 72 911, 08 GM SUV, 01' Ford Lightnin'

Hal on Sun February 05, 2006 7:18 PM User is offlineView users profile

Many years ago, we used to visit a summer home in the mountains that had no electric. The owner bought a surplus army generator that was pulled by a trailer. Olive drab of course. But it ran of a straight six Chevy engine, and put out 115 and 220 volts. Enough to power his house and garage. Got good gas milage (sitting still) but perhaps checking out army surplus stores may give you a lead if they are still available. Worth a shot. It also was very quiet as it had a regular car muffler.
Hal

-------------------------
"Live each day like it's your last, for some day it will be"

bohica2xo on Mon February 06, 2006 2:35 PM User is offline

Meaux:

Wait for JJM to show up, he has recently been through the permanent backup genset install.

Or do a search of the off-topic threads, we talked a lot about it.


B.

-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

JJM on Mon February 06, 2006 2:49 PM User is offline

My house is small (1,100 SF, NYC) and I don't have central air yet, but my Onan RS12000 powers everything I can throw at it. I ran a 240V 18,000 BTU air conditioner, as well three smaller 120V air conditioners, 5,000 BTU, 6,000 BTU, and 8,000 BTU, not to mention the refrigerator, oil furnace, dehumidifier, attic exhaust fan, three computers, two televisions, toaster, microwave, and just about every single light in the house, you name it (I really wanted to push it for the purposes of testing). At one point, I was reading a total of 50.6 amps on one leg, and 46.9 on the other leg.

Keep in mind I have oil heat and hot water, and natural gas for the stoves and dryer, so my electrical requirements aren't really that steep. If I had electric heat and hot water, electric stove and dryer, all bets would be off for this unit.

Generator itself:



Note the shrubs on the left... they're in shrub heaven now after only one exercise cycle. Dopey gardeners!



Note: The LB and galvanized pipe on the left side coming out of the house is the grounding conductor, though the genset should never have a separate ground (important). NYC requires grounding conductors to be protected in metal piping (galvanized) and bonded at both ends. This was the same for the cold water pipe ground inside too! Nazi's.

Pipe work:



Left to right:

- 1" aluminum conduit for current carrying conductors (#6) and ground (#10)
- ½" conduit for control wires (#12)
- ¾" galvanized gas line

Here's the whole electrical setup:



I know, those walls need a fresh coat of paint! In any event, left to right: 200A 40 breaker panel, 200A
GE ZTX20RM4 Automatic Transfer Switch, 60A service disconnect, 200A main service disconnect, 200A meter pan. Below the main panel is a junction box for the X-10 amplifier, and next to it is a Leviton whole house surge suppressor. (Structured media center is on the other end of the house.)

By the way, that big J-box next to the water meter (circa 1952) that the electric meter is connected to, that feeds four of my neighbors! I get the power first from the street!

Closeup of the automatic transfer switch guts:



Red in black are reversed (came into the meter pan that way) but does it really make a difference on single phase. That little black box mounted on the inside lower left, that's the trickle charger for the genset starting battery.

Another closeup of the automatic transfer switch (low voltage side):



Note the neutral is switched -- a "separately derived" system.

Closeup of the 60A disconnect:



Since this is a separately derived system, notice the neutral bonding there. Usually the disconnect is placed outside, but I didn't like that idea since anyone can just come along and pull the disconnect, and bye bye power.

Starting that 5-ton central A/C is going to be the biggest challenge. Technically speaking, your generator needs to be able to produce AT LEAST the LRA (Locked Rotor Amps) spec of the condenser unit (compressor and fan) as well as the air handler, otherwise you'll stall the genset. However, I believe you can fudge a little bit with generator capacity by putting a "soft start kit" on the compressor to give it a little more starting "oomph" and a delay on the air handler, to cut back on the initial surge. I'm convinced I can start the proposed 3-ton unit for my house using this setup - provided of course I don't have everything else running.

The key with a whole house setup and a relatively small genset is load management. But if you want to be safe, always go with bigger than your needs, which is what dealers always advise (and always oversize). Face it, they don't want to have to rip it out when it doesn't power all that was promised. Let's put it this way, most dealers told me my setup would never work, I needed a least a 20KW to 25KW genset (without central air), though that size might be what you need with that large of a central A/C unit.

I've got only about 9 hours on my unit. Has only been run for break in, monthly exercise (under load), and whenever someone comes over and wants to see how it works.

Maintenance is a breeze, as simple as with any small gasoline engine. I've only changed the oil on mine thus far, and cleaned the battery. Most of the "generator" related components themselves don't require any maintenance, unless your genny uses brushes like mine (most don't).

The biggest issue you might face is your NG (Natural Gas) supply, which almost always comes into the house at too low pressure for the genny to operate. Typical NG pressures are around 5-6" WC and most genny's like nearly double that at 11" WC nominal. Many units Onan can run from 7-15" WC and newer Generac units now run at 5-7" WC. If the generator you consider needs the elevated gas pressure, you need a two regulator setup, one "low" regulator for all the other gas appliances, and the other "elevated" regulator exclusively for the genset. The gas line for the generator needs to be pretty large to, because of their VERY HIGH fuel consumption. At full load, my genset uses 239,000 BTU's, more than most peoples furnaces, dryer, and range combined. Accordingly, you may need upgraded gas service.

Your first step should be adding up your total running electrical load and startup electrical load, then we can take it from there.

Joe

Gary Harrison on Mon February 06, 2006 8:29 PM User is offline

JJ, What is your motive for the BU generator? Is it more cost effective than local power, or simply to provide electricity when local service is out? Is your local electric service out frequently?

Here in Houston, I would have to have probably 50Kw to run my dual AC compressors and cool a 3500 sq ft house. Electric bill usually peaks in Aug or Sept w/ $450-500 monthly bill. Still, w/ the hurricane threat it would be nice to have 10-20 kw available for basics, even w/o AC. W/ kids in college, we've got way too much house, but I guess we'll stay put for a while.

regards

-------------------------
See you down the ROW.

NickD on Tue February 07, 2006 5:37 AM User is offline

Turn everything on you want to use, sit down by your electric meter and see how many KWH you use for exactly one hour so you know what your KW rate is. Multiply that by 1.3 to compensate for PF and that is the size of the generator you want in KVAs.

With public utilities, makes a guy know how dependent he his and we do have idiots living here. Two months ago the electric people were burying a line and while anyone else would do an underground check first, they broke a water main, no water for a day and having electricity without water is no fun either, couldn't even make a cup of coffee. Same with natural gas, phone company, with electricity, or the cable company, over the years, we have lost at least one or the other because some private contractor or the city dug in the wrong place. Your NG generator would be useless unless you have NG. With a major disaster, you would loose everything. Course, if you don't pay your bill on time, these are shut off by other means.

Living out in the country had more independence as long as my 1,000 gallon LP tank was full, just needed electricity that could be gotten with a tractor run generator, had my own well and sewer system so just needed 120 VAC to make things work. But during the energy crisis, LP gas was not regulated, was paying $1.60 per therm while guys in town were getting NG for about 20 cents a therm, that was a ripoff. But now, nothing is regulated, so we all are getting screwed, so much for competition and the so-called American way.



We have a lot of Amish folks living here that are not plugged into anything, maybe they have a better form of life than we do. But riding in a horse drawn carriage without a heater or AC doesn't seem too comfortable, but they get by, even with young children.

JJM on Tue February 07, 2006 2:53 PM User is offline

Gary,

The generator is strictly used as backup for convenience and security. It is NO WAY cost effective (especially now with natural gas prices going to the moon) to use it as a substitute for utility power, and it was not designed for such. We rarely get outages, but keep in mind NYC is THE prime terrorist target, and after the 2003 blackout, it's a good idea to be prepared.

Though a 50KW generator would probably be more than enough to handle those two central air units for that big house, you might be able to get by with less. If you've got two panels, you could have the generator just for one panel. Or you might consider having the ATS lockout (on the low voltage side) one of the units, say the one that covers the living area, and leave the one for the sleeping area run. You could also set-up some kind of control that only allows one unit to start at a time (Bohica would probably know about this), because the starting wattage is what the problem is. I bet your central A/C units don't use more than 3,500 watts each while running, but having them both kick on at the same time would most likely kill anything less than 25KW.

I must be doing something wrong, in the summer my electric bills run $600-$700 month and I'm only cooling 1,100 SF (2,200 SF if you count the basement. My oil bills in the winter are even worse (though this year luckily it hasn't been too cold). Granted, I like it 65F in the summer, and 75-78F in the winter, and we burn a lot of lights (especially outside) but still...

Briggs and Stratton recently came out with an optional module for their units that "manages" the central air (or other large load); if the genset has enough spare capacity, it will allow the central air to kick on. Great idea; if you want central air, simply turn off something else.

Nick,

I planned for the loss of natural gas contingency too. I have two #30 propane tanks, regulator, hose, and conversion kit ready just for the generator, plus another two #20 tanks for the BBQ. At full load, this thing burns 10 pounds an hour, so I've got at least 10 hours of fuel. At half load, I should be able to get better than 15 hours with that supply. Let's put it this way, if there was such a major disaster that we'd lose natural gas too, this thing would be used intermittently as needed.


Those PT generators trailers that are powered by a tractor are pretty cool, my question is how is the 540 RPM that they require maintained. Does the PT unit compensate for varying RPM's of the tractor, or does the tractor RPM have to be perfectly adjusted to 540 RPM?

Joe

Edited: Tue February 07, 2006 at 2:57 PM by JJM

bohica2xo on Tue February 07, 2006 3:38 PM User is offline

Load shedding is a huge part of the backup generator picture - unless you by something that is capable of matching your utility input.

It is common to add a second panel, and move the essential circuits to that panel. Some folks shed load manually, by opening breakers.


Staggered starting A/C motors is in your best interests anyway. Some of the newer units do this. Starting the smaller motors first, and allowing them to come up to speed before starting the compressor motor really does help.

The best answer is 3 phase motors, and an inverter drive. You can soft start a 3 phase motor, and keep the inrush current down. Spreading the starting load over a longer time interval clips the peak off of the load. An inverter can lower the operating cost of big motors too. Replacing my 2hp pool pump motor with a 3 phase unit & inverter was a big cost savings. Now the motor ramps to speed over a 7 second span, and with volts/hertz control & feedback it runs at minumum current to hold rpm.


B.

-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

JJM on Wed February 08, 2006 1:35 PM User is offline

Bohica,

Only one problem with the 3-phase idea: Almost no residential A/C systems are 3-phase. I inquired about getting a 3-ton Carrier Infinity system in 3-phase, but they only come in single phase.

By the way, what make 3-phase converter would you recommend? I did some research on the web, but it doesn't seem like any of the "major" manufactures, like GE, CH, Eaton... don't make them. They all seem to be "odd" named manufactures.

I wish 3-phase would become commonplace in residential. One guy a few blocks away from me has it but had to pay a fortune for it. A lot of homes in Scarsdale, NY, about 1/2 hour from me, have 3-phase standard.

Joe

meaux on Thu February 09, 2006 12:28 PM User is offlineView users profile

Thanks for the pictures Joe, nice install.

I talked to a neighbor yesterday that had a 20Kw Guardian put in by a hardware store for $10K. He said the first think the sales guy asked was, "Whats your LRA on the A/C unit say"? His is a 91 LRA, and he has a 2100 sq. ft. home. Mine says 165 LRA, on a 3000sq. ft. house.
I used a "calculator" on the net and it came up with a recommended 25Kw unit. I don't think that would be right, and I'm just guessing, but with all the junk I have, I'll need a 35Kw. I'd rather have too much than not enough...

I'll start calling in the "free estimates" and see how confused they try to get me... :-) I think I'm gonna have an added charge from the utility company because the Natural Gas is on one side of the house, and the Main Electric is on the other...unless they run the electric wires thru the attic...

Oh well, we'll see...This could be a sure fire way to ward off any Hurricianes around here for the next 10 years... :-)

-------------------------
Lazy bum who lives off his wife.

01 BMW 530i Sport, 92 Porsche 968, 85 F150, 72 911, 08 GM SUV, 01' Ford Lightnin'

bohica2xo on Thu February 09, 2006 10:06 PM User is offline

JJM:

Commercial 3 phase A/C units are common here. I hear some units come with inverter drives, but have not seen one in person.

The nice thing about the inverter is getting the reliability of a 3 phase motor, with single phase service. As well as variable speed operation, feedback.... For constant run applications over 1 hp, the payback on equipment is usually 6 months or so.

As for equipment brands, the "big names" have some inverters - but many are re-branded from asia anyway. I consider Hitachi to be as big as GE, and have had good luck with Hitachi inverters in machine tool applications. A 7.5 hp spindle motor starting and stopping all day long, with dynamic braking. Running half speed with full torque one minute, and 125% of rated speed the next. Or,worse yet - rigid tapping! Instant reverse, based on a shaft encoder input.

Currently, I have a GS-2 drive on the pool pump. Available from These folks , and I have had good service for a couple of seasons now. It runs about 7 hours per day, every day. No more start windings, or corroded centrifugal switches either.


B.

-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

JJM on Fri February 10, 2006 2:33 PM User is offline

Meaux,

With 165 LRA on that central A/C unit, you need 40KW just to start that bad boy -- and that's without any other loads. A 40KW system would likely go well about your $10,000 budget. Heck, my 12KW unit which I did myself ran about $6,000 when all was said and done.

Aside from the central A/C do you have any other big electric loads, like an electric dryer, range, hot water heater, instant-on hot water heaters, steam generators, etc? If so, 50KW might actually be a little whimpy.

You should get a hold of a clamp meter that measures inrush current, and take several of startup current measurements under a variety of conditions to get an idea of what the "real" start-up current is. It might be much less than the nameplate spec.

If you have a friend with a large portable generator (say 18KW surge or larger), who would be willing to let you borrow it for testing, you might want to try adding a soft start kit and time delay to your central A/C (a good idea anyway) to see if the portable generator will start it. And try several start/stop cycles to be sure. You've got nothing to lose. If the portable generator does start the central A/C unit consistently, it would give you greater confidence that you don't need that large of a generator. But of course, the only sure guarantee you won't have problems is to get a big enough generator to power everything at its LRA.

Remember, many vendors told me my proposed set-up would never work (even without central A/C) and I would need a 20-25KW unit minimum and a dedicated generator panel. My "little" 12KW powers the entire house panel with just about everything running.

You could, of course, have the central A/C lockout on generator power, and keep some inexpensive window shakers as back-up.

Bohica,

Since I really want to go with a 2-stage central air unit to allow for oversizing without short cycling and humidity problems. I'm considering a 3-ton to cool an 1,100 SF ranch, plus the basement, which will have a seperate evap. My design temp would be 65F on a 100F day is kind of demanding, so "oversizing" would occur on the usual cooler days.

One issue I know of with 3-phase generators and 3-phase motors is when the power goes out and the generator kicks in too quickly, the motors will trip due to the "out of phase" alignment. The "trick" in this situation seems to be decreasing the transfer time to allow for the motors to come to full rest before restarting. I'm wondering if the same issue would occur with an inverter.

Joe

JJM on Fri February 10, 2006 2:42 PM User is offline

Meaux,

Too add, don't worry too much about the utilities being on opposite sides of the house. You could always run the gas line (using larger diameter galvanized pipe as appropriate) underground over to where the electric meter is (if this is where you're planning to install it).

Keep in mind, it will be very EXPENSIVE to run that generator for an extended outage, because these things REALLY suck up fuel. I never heard my gas meter howl the way it does when the generator in on, and never saw those little wheels spin so fast!

And forget about what they saw about periodic exercising without load, always exercise UNDER LOAD to ensure your generator will operate when you need it to.

Joe

NickD on Sat February 11, 2006 7:39 AM User is offline

My wife an I just purchased this vehicle, with the high price of gas, got it for only $4K with six brand new tires and three brand new marine batteries. In the process of stripping it down now and attempting to get it more like new condition.

It does have a total of 90 gallons worth of fuel tanks, a 30 gallon LP tank, 40 gallon fresh water tank, can warm it up to 72 degrees even in 4 degree weather, has a generator, refrigerator, getting a new microwave, full size refrigerator with a separate freezer door, both cab and roof A/C, a range, place to sleep and go to the bathroom, even take a two gallon shower. In other words, if we lose something here, have a place to go to make a pot of coffee. Water would run out first, but can drive someplace to fill that tank so it can be our second home if nothing else.

Could be questionable as to how much value would be added to your home by making it energy independent, may want to consider buying a motorhome or even a camping trailer that is much cheaper, really don't have to invest that much.












Ha, something I didn't expect, but when driving it, large SUV's that like to run over my Cavalier give me plenty of clearance and really surprised how tiny these SUV's look like, kind of fun having a much larger vehicle.

Bigchris on Sat February 11, 2006 10:12 AM User is offline

Sounds good but what about fuel? You have to buy it too, right?

NickD on Sun February 12, 2006 8:17 AM User is offline

Airlines and car rentals are also having a fuel adjustment charge, wife's cousin is having a family reunion end of June and my wife definitely wants to go as do I. We both live off the beaten path and five of us are going. Takes 16 hours by air and car rental to get there with most of the time spent getting searched by minimum wage guards. With car rental, airline tickets, motels, that week trip could easily cost us $4,000.00 and driving at 55 mph would only take six hours longer by motorhome. Gas should run about $600.00 unless something drastic happens so seemed like the most logical way to go.

For now it's parked at the rear side of my home blocking my nosey neighbors view of my backyard, so serving a great purpose for Dok and me when we go out with being starred at. Wish it would warm up a bit, can't resist working on it, finger tips have hundreds of frost cracks that tend to be a bit painful. Today, I will be sewing new drapes for it.

Like Hamilton, some idiot got his hands in it, finished correcting the !20 VAC and 12V auxillary circuits so the three batteries are staying charge, but under the dash is next, what a mess that guy made. Previous owner said no cruise, found the servo under the hood, and found a broken directional signal controller under the couch with the wires cut off. Repaired the controller with copper pipe and Bondo and painted it black, looks nice and hoping it will work.

Bigchris on Sun February 12, 2006 10:44 AM User is offline

Quote
Originally posted by: JJM

Since I really want to go with a 2-stage central air unit to allow for oversizing without short cycling and humidity problems. I'm considering a 3-ton to cool an 1,100 SF ranch, plus the basement, which will have a seperate evap. My design temp would be 65F on a 100F day is kind of demanding, so "oversizing" would occur on the usual cooler days.

Joe,
I upped my 2.5 ton to a 3 ton unit for a 1400 SF ranch last year and find that the system now feels drafty for the first time. Seems to be a combination of the increased airflow and colder vent temps. I'd advise proceeding cautiously.

parollback on Sun February 12, 2006 4:13 PM User is offline

I run a Generac 15kW. 125 amps @220, 62.5 @220. Runs everything. Got it at Home Depot for $2000. I just have to manually plug it in and throw the transfer switch to use it.

CorvairGeek on Sun February 12, 2006 9:52 PM User is offline

I suspect Joe may be getting to use his generator, I'm sure I speak for everyone when I wish him well. Let us know how it does.

-------------------------
Jerry

NickD on Thu February 16, 2006 7:22 AM User is offline

Here is an interest problem to solve, giving you a very well insulated box with LP gas feeding it and putting out 240 VAC 60 Hertz electricity, no moving parts permitted in that box. So what would you put in there? In theory, 95% conversion efficiency can be obtained and with such a box, we can dump all electrical power lines, we would need just LP or natural gas. Losses in long transmission of electrical lines is huge, won't have that loss. Very low losses in pumping gas.

Just takes a bit of thought to solve major problems, but no one is thinking anymore.

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