How much current through generator connection

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Old 01-16-06, 04:10 PM
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How much current through generator connection

I have recently moved to the country and have decided that having a back up generator is necessary. I have calculated the load I will need for my necessary circuits and have come up with about 8,000 watts continuous or about 65 - 70 amps.

The generators that I have seen have two 120vac 20amp circuits and one 120/240vac 30amp circuit in which you plug into on the generator. How do I get the entire 65 Ė 70 amps going through one connection that will feed through my transfer switch and sub-panel? Does that come through the 120/240 connection?

Many thanks for any guidance,

Mark
 
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Old 01-16-06, 04:44 PM
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that depends on the generator. portables may have a duplex rated at xx each (each half of the receptacle) a full amperage 120 three prong twist lock, and a 120/240 four prong twist lock. are you planning on a portabe or a standby unit ?
i purchased a portable 6k for use in a car trailer and home, wired a gentran 10 curcuit manual transfer switch fed by #10 four conductor. this setup allows multiple use of the generator. standby is permanant, may run on lp or natural gas. (no stale fuel problems) put a good deal of thought into your desires first. then look for the system that fills those requirements. remember, nobody needs everything in the home to function during a blackout, and, that big generator that covers everything has a hefty appetite for fuel even when not running to capacity. post back with any questions or concerns
 
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Old 01-16-06, 04:47 PM
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Originally Posted by mchild
How do I get the entire 65 Ė 70 amps going through one connection that will feed through my transfer switch and sub-panel? Does that come through the 120/240 connection?
You have to buy a big, expensive generator that is capable of generating that much power or you have to re-evaluate how much power you "need" in an emergency situation. Also consider that a generator will not be able to power much in the way of large motor loads like pumps or especially central air conditioners.
 
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Old 01-16-06, 05:38 PM
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I have a diesel setup that works well for me. Yanmar diesel engine is air cooled with Yanmar generator also,( be careful of non Yanmar generator with Yanmar Engine) 10hp engine, 26 amps on 220, 52 amps on 110, 5000 watts continuous, 5500 surge. Uses about 3 1/2 gal per 8 hrs at 70%. I use it to run my camper and my freezer, refrig and one window unit in the house during our hurricane power outages. I have a 120 gal tank onsite with hand pump that I fill with diesel each year. I also have 55 gal aux. tank in my truck with electric pump. Generator stays in back of my truck behind fuel tank. At the end of the year, I pump unused fuel into my truck and refill again for the next year. I treat all fuel with PRI-D. I can run about 12 days if necessary, using the camper air only at night and turning off the house window air. If I have to leave for a storm, I button up the house, hook up the fifth wheel and head for the mountains. I can travel about 800 miles on my truck tank and aux. tank. It is nice not having to depend on getting fuel before or after a storm. Our power has been back on in 7 days in most cases so far. Live south of Daytona Beach. Total cost of set up is approx. $3500. Works great for me and portability gives me some options.
 
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Old 01-16-06, 05:43 PM
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Don't forget to consider engine-driven welding machines. Many of these are also designed to power high-amperage loads through a NEMA 14-50R 50-ampere receptacle. Many of us who own them have subpanels that plug right in for back-up or jobsite power. Downside is they are typically a little more expensive than just generators. Upside is that you also have a good welding machine, which is always handy in the country, and they are designed for long lives. For just the basics, with 9,500 watts of continuous power available, look at the Miller Bobcat 225 NT. They are less than $3000 with free shipping and no taxes.

http://www.millerwelds.com/products/...en/bobcat_225/

http://cgi.ebay.com/Miller-Bobcat-22...QQcmdZViewItem
 
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Old 01-16-06, 05:49 PM
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Originally Posted by ibpooks
consider that a generator will not be able to power much in the way of large motor loads like pumps or especially central air conditioners.
There are generators that are designed to do just that. But I think you are telling him to make sure he gets one with a high enough peak rating to start large motors. Again, I'm mostly familiar with engine-driven welders, but there is a Miller Bobcat that delivers 3-phase 480V for farm pumps and other big loads.

http://www.millerwelds.com/products/...obcat_3_phase/
 
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Old 01-16-06, 06:05 PM
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The 8000 watts you "need" is the wattage. The amperage is only 33 at 240. Most gensets in the 8.5k-10k watts range would be fine carrying this much.

I agree with ipbooks. Do you really need this much, or do you really want to run so much. I can see any fridges and freezers, furnace, well, sump pumps, a few lights, a kitchen circuit, a TV. Beyond that is frivolous in my opinion.
I know MANY folks, myself included, who get by fine with a 4k-6k genset through the longest outages.

I also live in the "country". I move away from the big city a long time ago. I find it real funny when folks move up here, or get weekend homes, from NYC, LI or Jersey and they think this is the wilderness. They think they need to light up the night and have a huge genset just to survive.
Sorry, this is just a minor rant. Don't mind me.
 
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Old 01-16-06, 06:10 PM
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If you have a tractor, they also make a generator that connects to your PTO shaft. I like this because 1.) you're not having to buy two prime movers (the source turning the generator) and 2.) you run the tractor all the time so it's usually ready to go.

......unlike that once-in-a-bluemoon generator engine that's been sitting for 12 months and you don't know if it will start or not.
 
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Old 01-16-06, 06:24 PM
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Originally Posted by Speedy Petey
They think they need to light up the night and have a huge genset just to survive.
I know EXACTLY what you mean! I see city-slickers burning their flashlights walking down paths when the moon is so bright it casts shadows.
 
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Old 01-16-06, 08:08 PM
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Based on your description of the outlets on your generator, it sounds like a unit rated at about 5000 or 5500 PEAK, and about 3500 to 4000 continuous. It may be quite small for your needs.
 
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Old 01-17-06, 05:09 AM
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Thanks for all the responses.

I will be running a well pump, sump pump, two refrigerators, one freezer, kitchen lights, furnace blower (oil heat), and my computer/printer for my home office. Just the basics to keep us functioning. I donít expect losing power to be a regular thing, but since we are one of the last areas to get restored power, it can take several days. I need to work and we must be able to function in the home.

Based on the wattage charts I have seen on various web sites site it works out to about 7,500 continuous watts. I have seen two portable generators that fit my budget and are rated 8,000 continuous and 13,500 start up. I have a 500 gallon propane tank so I will convert it to propane use so that I donít have to worry about refills and I can also use the generator for other needs as they might arise. I looked at the welder/generator setups but I donít want my welder to have to always be out side when in use. Most of my welding will take place in my shop. Plus, my father in law is going to give a welder soon so I donít really need to buy one.

The 70 amps is based on 120vac. Speedy Petey made a good point that the 30 amp rating on the one receptacle is 60 amps on 120. But the 13,500 start up watts is equivalent to 56 amps. Can that also go through the 240/30 receptacle?

Thanks again,

Mark
 
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Old 01-17-06, 05:32 AM
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You mention a well pump. Make sure that the generator you buy can handle your pump. Most portable generators cannot handle these devices because of the very high startup needs.

Depending on the pump you have, you may need a larger generator than you are planning on.
 
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Old 01-17-06, 05:47 AM
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Thanks Bob.

Without pulling the pump out of the well to see exactly what make and model it is I'm not sure how I would determine that. It is on a 220/20 circuit. Even if the pump drew twice that amount on start up it seems like I should have enough power in the generator. What am I missing here?

Thanks again,

Mark
 
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Old 01-17-06, 06:29 AM
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be carefull on that lp conversion. a dual fuel conversion could cost you a 20% decrease in generator output. dedicated lp only will retain output. add up the cost of the portable, lp conversion, and hook-up. then consider an lp standby package and a smaller portable for other uses. just trying to help you avoid the "wooda - cooda - shooda " syndrome
 
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Old 01-17-06, 07:05 AM
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Originally Posted by flopshot
be carefull on that lp conversion. a dual fuel conversion could cost you a 20% decrease in generator output. dedicated lp only will retain output. add up the cost of the portable, lp conversion, and hook-up. then consider an lp standby package and a smaller portable for other uses. just trying to help you avoid the "wooda - cooda - shooda " syndrome
Thanks flopshot. Don't want no w - c - sh!

Losing generator output with the duel fuel setup was not something I had heard of before. From what I had read I thought I might get a bit more power from the engine - not less. But, if I am understanding you correctly, it is the conversion of an engine originally designed to run on gasoline that I would lose the 20%. Right? But, if I bought a generator designed to run on LP then the engine size would be compensated (upped) to still get the output requirement.

Thanks again,

Mark
 
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Old 01-17-06, 07:17 AM
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My suggestion is, if you have the money, buy a whole house standy generator that designed for what you want to do.

A 15k propane unit can be bought for $3000 and would run everything in your home. Has all the wiring and interfaces, self testing/running, auto-start and shut down, etc.. This unit makes 13k on NG and 15k on LP

My 6500/13000 (a 'contractor grade' porter-cable with 13hp honda) will run everything except my heat pump (too high start up load). I do have to be selective with some uses, for example, if I want to run the dryer, I pretty much have to turn everything else off, as the dryer takes about 5000 watts right by itself (the motor only takes 500). If you have a gas dryer, so much the better.

I also have to watch the loading if I need the hot water heater (also electric), as it takes about 2500 watts.

I use a small window A/C to keep things cool.

After Ivan, the generator used roughly 1/2 gallon of gasoline / hour.
I feed everything through a GenConnect and just flip the breakers for the things I DON'T want to run.
 
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Old 01-17-06, 08:19 AM
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Originally Posted by mchild
It is on a 220/20 circuit. Even if the pump drew twice that amount on start up it seems like I should have enough power in the generator. What am I missing here?
It's not uncommon for a pump to draw six to eight times its running current during startup; if your generator doesn't have a high enough peak rating it will stall out when you start the pump.

Also, make sure you have a quality UPS with automatic voltage regulation if you want to run a computer from the generator. Gensets produce very dirty power with poor voltage regulation that will wreak havoc on your computer's internal power supply.
 
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Old 01-17-06, 09:25 AM
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Originally Posted by ibpooks
It's not uncommon for a pump to draw six to eight times its running current during startup; if your generator doesn't have a high enough peak rating it will stall out when you start the pump.

Also, make sure you have a quality UPS with automatic voltage regulation if you want to run a computer from the generator. Gensets produce very dirty power with poor voltage regulation that will wreak havoc on your computer's internal power supply.


So how do I find out what kind of load my well pump is going to draw on satrt up?

Mark
 
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Old 01-17-06, 09:26 AM
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yes, the conversion from gasoline to lp can be done a few ways. dual fuel allows the use of gasoline or lp. dedicated is one or the other. dual fuel requires the carb be vented to atmosphere for proper fuel flow on gasoline which causes the 20 % drop in output due to an incorporated "vacum leak" . perhaps someone has overcome this but not to my knowledge. as far as "dirty power" this is true of low end portables but not so much with units like a high end honda or dedicated home standby. i couldn't sell you one anyway so i'm not advertising, but the generac's i do sell have a very good frequency control system, auto start, auto transfer, auto exercise, low oil shutdown, overcrank protection, low frequency protection, etc. come with a prewired transfer switch and are user friendly . the important thing is the fuel. lp lasts forever, stores in large quantity, and can't flood the crankcase. if you can't safely store over 20 gallons of gasoline you really don't have much of a backup power supply. you can get the specs at www.generac.com
look at the guardian series. 7k, 12k,15k, and up. the transfer switch is for indoor use only but can be installed in an nema 3 enclosure if outdoor installation is required. other than industrial class motors you shouldn't encounter any start loads in the 6-8 times running load catagory. most likely 2 - 3 times running load estimate will cover you. bottom line is be reasonable with your emergency requirements.
 
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Old 01-17-06, 01:09 PM
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Keep in mind Generac's service and in-home warantee work sucks!
Briggs/Cutler and Winco are MUCH better.
 
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Old 01-17-06, 01:28 PM
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Originally Posted by Speedy Petey
Keep in mind Generac's service and in-home warantee work sucks!
Briggs/Cutler and Winco are MUCH better.

The one I have been looking at the most is the B&S model 030210. It is shown on the main B&S web page as a 7,500 watt unit but when you click on the details it shows 8,000 and my local store has it as an 8,000 watt unit. I can get it locally for about $1,100.

So does any one know about this particular model? How "dirty" is the power output? how is the voltage regulator?

Mark
 
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Old 01-17-06, 01:58 PM
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To be clear, I was referring to the larger permanent standby units.
I do know if you have a local service dealer the portables are fine. Very good actually.
 
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Old 01-17-06, 02:02 PM
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Originally Posted by Speedy Petey
Keep in mind Generac's service and in-home warantee work sucks!
Briggs/Cutler and Winco are MUCH better.
wouldn't know. i've only sold 17 with one request for repair. but i will take your technical opinion under advisement.
 
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Old 01-17-06, 02:20 PM
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Originally Posted by mchild
How "dirty" is the power output? how is the voltage regulator?
All portable/small units have poor voltage and frequency regulation simply because of their size. This is okay for motors and lights, but can damage PCs and electronics like cable boxes and flat panel TVs. For only about $100, a UPS is great to have even when you're on line power.
 
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Old 01-17-06, 02:56 PM
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Originally Posted by flopshot
wouldn't know. i've only sold 17 with one request for repair. but i will take your technical opinion under advisement.
I didn't say the units sucked, I said their service sucked.
I don't do service, I just install them. I am not the authorized dealer so I have no say in the warantees. My authorized dealer say it is a nightmare getting serivce from them. It seems they are more intent on feeding big box stores than smaller dealers. This alone makes me shy away from them.
Buy a Guardian from home depot and see what recourse you have after the 30 day store warantee is up.
 
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Old 01-17-06, 03:29 PM
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i hate when a thread goes off topic , but you are correct in one sense. hd ain't gonna do jack. that's why you buy one from a dealer. everytime there has been a problem with generac and the warranty it was the "authorized service dealer " that made the initial denial of claim. no reflection on you as an installer , but if you have not been instructed in the procedure for initial start up , therein lies the problem. frequency, rpm, full load amps, testing of all sensors, etc must be performed by a qualified tech. i tend to believe all mfg's will require these tests to honor a warranty claim. generac, to it's credit, took the standby generator out of the 15,000.00 range of the big boys who were the only choice up to about 1999. they clearly state that the unit is not to be used for primary power and is priced accordingly. it's a niche product and not for everyone. yes, you can get a better quality product, and you'll pay for it . i don't own one. i don't need one. at this point i can store gas ,start my mitsubishi 6k, and make the manual transfer. but when the scanner squeels because the power is out, and i grab my call list to contact my customers, they are very happy to tell me their neighbors are ticked off because they see the lights on at my customer's house. when will i install a standby ? when honda makes one front to back. and i'll have to pay for it. heck. i've talked more prospects out of a generator of any kind because of their capabilities, lack of need, or budget/requirements than i've sold. with that, i'll end my contrubutiions to this thread to keep the moderators happy.
 
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Old 01-18-06, 05:24 AM
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Yes, I think this has gotten a bit off topic. I do appreciate all the info (and yes, I have a UPS for my computer) this thread has provided. But, I'm not sure I really have an answer yet.

My original question was can I get all the watts (continuous of 8,000 and start up of 13,500) out of the generator with the single 240/30 amp connection or is there something else that I will need to do? I can see how the 30 amp connection is sufficient for the continuous state (8,000 watts = 33 amps) but the startup is 56 amps. Can that much apperage safely be drawn through a 30 amp connection? Would that not trip the generator's circuit breaker on that one outlet?

Thanks again for the good discussion.

Mark
 
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Old 01-18-06, 05:39 AM
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Mark,

I have a 500 watt portable generator (6500 watt surge). It has a 240 volt 20 amp receptacle, along with a 120 volt 20 amp duplex receptacle and a 120 volt 30 amp receptacle.

In my case, 5000 watts at 240 volts would be 20.83 volts. Can my generator do this? Not really. The 20 amp breaker should trip.

In your case, the 30 amp breaker should trip when you exceed the 30 amps for any length of time. Will it trip? Eventually.
 
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Old 01-18-06, 06:39 AM
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Originally Posted by racraft
Mark,

I have a 500 watt portable generator (6500 watt surge). It has a 240 volt 20 amp receptacle, along with a 120 volt 20 amp duplex receptacle and a 120 volt 30 amp receptacle.

In my case, 5000 watts at 240 volts would be 20.83 volts. Can my generator do this? Not really. The 20 amp breaker should trip.

In your case, the 30 amp breaker should trip when you exceed the 30 amps for any length of time. Will it trip? Eventually.
Bob,

Exactly!! So how do we get the stated output of these generators out of the generator if the circuits aren't sufficient to flow that much current?

mark
 
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Old 01-18-06, 06:49 AM
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Originally Posted by mchild
My original question was can I get all the watts (continuous of 8,000 and start up of 13,500) out of the generator with the single 240/30 amp connection or is there something else that I will need to do? I can see how
Mark
Yes and no.

While rated for 8000 watts, the life of your generator (and the fuel consumption) would be greatly cut short if you ran it at full load all the time.
How long would your car last if you drove it around with the pedal to the floor all the time?

Seriously, if you want a full 8000 watts 100%, you should be looking at a 12k unit (which would likely have a 50 amp plug vs the 30 amp), and would be much more capable of handling the startup loads you have.

I would also stay away from any B&S powered unit that's over 3500 watts and find one with a Honda or Kohler engine.

The 13k surge is just that, anything more than a few seconds and it would trip the breaker. If you are already running near capacity, you could expect the breaker to trip before the surge falls back down.

As for UPS's, get some. I have one on each computer, as well as each TV. When the power glitches during a storm, I don't lose my TV, weather info and the cable box doesn't spend 2 minutes trying to 'reset' itself. It also keeps things alive until I've got the generator started and warmed up if it looks like the power is going to be out for a while. It also smooths out the power from the generator, which must be pretty clean, because during the 2 weeks or so we were on gen-power, the UPS's never switched to battery due to bad gen-set power.
 
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Old 01-18-06, 08:06 AM
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Originally Posted by Pendragon
Yes and no.

While rated for 8000 watts, the life of your generator (and the fuel consumption) would be greatly cut short if you ran it at full load all the time.
How long would your car last if you drove it around with the pedal to the floor all the time?

Seriously, if you want a full 8000 watts 100%, you should be looking at a 12k unit (which would likely have a 50 amp plug vs the 30 amp), and would be much more capable of handling the startup loads you have.

I would also stay away from any B&S powered unit that's over 3500 watts and find one with a Honda or Kohler engine.

The 13k surge is just that, anything more than a few seconds and it would trip the breaker. If you are already running near capacity, you could expect the breaker to trip before the surge falls back down.

As for UPS's, get some. I have one on each computer, as well as each TV. When the power glitches during a storm, I don't lose my TV, weather info and the cable box doesn't spend 2 minutes trying to 'reset' itself. It also keeps things alive until I've got the generator started and warmed up if it looks like the power is going to be out for a while. It also smooths out the power from the generator, which must be pretty clean, because during the 2 weeks or so we were on gen-power, the UPS's never switched to battery due to bad gen-set power.

Pendragon,

I guess what I need to do is figure out the average hourly draw. Here is what I will have on my back up:

Well pump
Sump pump
Furnace blower (oil heat)
Kitchen lights
Kitchen outlets
Two refrigerators
One freezer
Computer/printer (with UPS)

My calculation on these items is about 7,300 during run time and start up as high as 14,000 - and maybe a bit more. But, just about everything on my back up has run cycles but will not be drawing current continuously. Even the kitchen lights will only be used for a few hours in the evening. The office computer will only be used for an hour or two per day during a power outage - I wonít work more than that. So, I have a lot of motors that will have run cycles, but I donít think it will be often that they will all need to cycle on at the same time.

Thus, if the continuous run load is 7,300, but not everything is going to be running continuously, how do you determine the load you need to provide for? It seems sufficient to me using the 8,000/13,500 unit, but I am here to learn from the experience of others.

Many, many thanks.

Mark
 
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Old 01-18-06, 08:11 AM
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Mark,

I don't know how to properly size a gnerator for a well pump. However, I don't think this generator is large enough for one, especially with those other loads involved.
 
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Old 01-18-06, 08:25 AM
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Originally Posted by racraft
Mark,

I don't know how to properly size a gnerator for a well pump. However, I don't think this generator is large enough for one, especially with those other loads involved.

Bob,

On one web site that I have seen they listed well pumps from 1/3 to 10 HP and they listed the typical running and surge requirements. The surge was double the running in each case.

In my calculations I have assumed a 1/2 HP well pump using 1,000 continuous watts during run time. I am going to see if I can find out what size pump I have.

Mark
 
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Old 01-18-06, 08:50 AM
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You really need to find out how much power these items require, particularlly the well and sump pumps.

Furnace blower (oil heat), figure about 500 watts.
Kitchen lights - easy enough, just add up the wattage of the lights
Kitchen outlets - what's plugged in to these?
Two refrigerators - about 200 each, if they are newer models
One freezer - probably about the same.
Computer/printer (with UPS) - 250 watts for LCD, 300 for CRT monitor

So, we're back to the pumps.

I can tell you that my 5hp air compressor takes WELL over 3500 watts (it bounces the watt meter off the top of the scale) starting and about 1700 running.
 
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Old 01-18-06, 09:40 AM
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Originally Posted by Pendragon
You really need to find out how much power these items require, particularlly the well and sump pumps.

Furnace blower (oil heat), figure about 500 watts.
Kitchen lights - easy enough, just add up the wattage of the lights
Kitchen outlets - what's plugged in to these?
Two refrigerators - about 200 each, if they are newer models
One freezer - probably about the same.
Computer/printer (with UPS) - 250 watts for LCD, 300 for CRT monitor

So, we're back to the pumps.

I can tell you that my 5hp air compressor takes WELL over 3500 watts (it bounces the watt meter off the top of the scale) starting and about 1700 running.

Pendragon et al,

This is what I have used for my calculations:

Well pump 1,000
Sump pump 600
Furnace blower (oil heat) 700
Kitchen lights 400
Kitchen outlets 700
Two refrigerators 1,400
One freezer 700
Computer/printer (with UPS) 1800

As you can see I am using higher numbers throughout and come up with 7,300 watts. I know the sump pump is a ľ hp. Kitchen outlets include microwave and dishwasher but they would not be used at the same time. The two refrigerators and the freezer are not new (probably 10+ years old) so I am using higher numbers there. The only unknown item is the well pump and I just donít have an easy way to determine what that is.

It seems to me the issue is how do you conservatively calculate how many of these pumps will be starting at the same time. I think I have sufficient continuous power (assuming Iím close on the well pump draw) because it looks like I could run everything at the same time if needed. But, in the real world I donít think there would be many times - if ever, that would be the case. So is it reasonable to assume 50% of the items are drawing at the same time? That would be about 3,700 watts or 46% of the rated continuous output.

And then there is the start up demand. How many of these pumps do I need to assume would be all starting at the same time?

Mark
 
  #36  
Old 01-18-06, 10:33 AM
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>Sump pump 600

That's probably pretty close, my 1/2 hp door operator takes 600 watts.

> Two refrigerators 1,400

That's probably high, a watt meter would be a big help to you.
http://www.ahernstore.com/p4400.html (just the first hit yahoo came up with). I think last time I check my fridge, it was around 200 watts running.

>Computer/printer (with UPS) 1800

You have this WAY over estimated, 1800 watts wouldn't even run on a standard household circuit.
My current system is using 277 watts, that's a fully optioned P4, 19" LCD, large all-in-one printer, two smaller printers, a cordless phone, and about half a dozen other devices.

The microwave probably takes it's full 1500 watts. The dishwasher probably takes close to that or more when heated dry or boost water heat is used, but very little when just washing.

Except for your unknown well pump, you are probably fine given these loads and the run times.
 
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Old 01-18-06, 11:48 AM
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I found the control box for my well pump and it is for a Ĺ HP pump. In my assumptions I have been using 1,000 watts for the well pump and I think that is reasonable for a Ĺ HP motor. But even if it uses 1,500, I think I should be okay with the generator size in that I have over estimated all the other uses Ė some by a lot.

Now, are we in agreement that the single 240vac/30 amp connection is sufficient?

Again thanks everyone,

Mark
 
  #38  
Old 01-18-06, 12:10 PM
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Originally Posted by mchild
Now, are we in agreement that the single 240vac/30 amp connection is sufficient?
I think so. Even if you did have some overload problems, you could manually cycle the loads to accomodate. For example unplug the fridges and freezer when you run the microwave or unscrew some of the bulbs in multi-bulb light fixtures or turn off the sump pump when you're showering or otherwise using the well pump.
 
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Old 01-18-06, 12:29 PM
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I am not convinced that an 8000 watt generator can run your pump. I know that a 5000 watt generator cannot. The power to start your pump can be up to three times the amount needed to keep it running.
 
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