Portable generator sizing question (sorry)

[sicklyscott]

Hi Guys -

I've read a number of threads here about portable generators. Although ti was great info I'm not really sure my question was answered (probably more of a preference question anyway). I have been looking at generators in the 5500 watt range but after hearing some local stories about people with standby generators I feel like a 5500 watt unit would be overkill and a waste.

I have gas forced air heat and a gas water heater. My stove only uses electric for ignition. Bare essentials for me would be a couple lights, my fridge, and a furnace. Furnace claims 6.8 amps at 120v (~850 watts), fridge claims a 15 amp line which seems outrageous (~1800 watts). That would be a total of 2600 watts, add in a TV and lights for cushion and the 3500 watt generators would be sufficient. However I've been reading about the fuel consumption and it says "50% load". If I over size the generator, will I gain fuel economy?

I'm beginning to think a 3500/4000 watt unit is enough for what I'd like to use it for, especially if I can manually cycle each appliance on/off (i.e. unplug the fridge or shut off the furnace to power something else for the time being).

Also I've read some good things about Champion generators but always gravitated towards the Generac. Any opinions on these brands?

Thoughts? Suggestions? Stories?

 

[ATTappman]

I can run a refrigerator, an 8,000 BTU/hr window air conditioner, TV, lights, and a couple of box fans on a 3,000 watt generator, comfortably. The amperage on the generator panel reads about 8 amps on average, with a range of 6 to 14.

You could go to Home Depot and pick up a Kill-a-watt meter for $28. Plug each one of your loads into it and see what the wattage reads. Remember that anything with a motor will draw a high inrush current for a second or so when starting. If you can see the motor name plate it will display the locked rotor amperage (LRA). Make sure the generator can supply enough surge amperage to cover that without tripping its breaker.

It seems to me that oversizing the generator will waste fuel, not save it. Oversizing also means more weight, more room taken up in storage, bigger gas tank to siphon before storage, etc. On the other hand the larger capacities sometimes have more features.

Generacs usually get positive reviews, except for their little inverter generators that compete with Honda and Yamaha. Generac has GP and XP series, with the XP being more expensive but getting better reviews. If you want the best, get a 3000-watt Honda or Yamaha, for which you'll have to pay over $2,000.

 

[sicklyscott]

Thanks AT! Exactly the feedback i was looking for. After your response and a bit more reading I'm certain a 35004000 watt unit will be enough for us.

My wife is set on buying a NG powered generator but I can't justify the price. I've looked at conversion kits but read elsewhere that burning NG takes a toll on the motor if it wasn't designed for it. Is that true?

 

[SalA]

I have also been looking at the Generacts, but if you go on Amazon.com...reviews are mixed about their reliability.

Generator Power is something to always go a bit more rather than less. Reactive Loads for any motor or compressor, etc needs at least double the running load during that 2 or 3 second start. So your your refrig while rated at 1,800 watts running probably needs about 3,600 to start up.

The Resistive loads for lights and toasters etc..are constant from beginning to end. Also, you should consider looking at the Propane units. Seems easier, safer to fill and eventually to store a propane tank over gasoline!!!!

 

[brianh]

I have a 3500 it is fine for the fridge and running a few items I run our water pump with it but switch the load so it is dedicated for the pump only.

We routinely have the power go out for 5-7 days once or twice a year here, I do not run the generator full time I usually fill the water tank then run the fridge for an hour then shut down I repeat this every 4 to 5 hours.

It is just a waste and wear to run it all the time, with hurricane sandy we were without power for 3 days I went through 3.5 gallons of gas.

Could have used less but by the third day I had all the trees cut and started using the computer.

 

[SalA]

That' s good. I have two forced air gas burner units as well as 2 Central A/C units that I could run 1 at a time in an emergency or power loss situation, but do need alot of power to fire the AC up in the summer. Each AC unit is 2 phase and protected by two 30 amp fuses. The air handler fan on the heat I believe is single phase and 20 amps. Add a refrig, some lights and and TV / cable box..I am looking at lease a 10K unit. I would only consider a NG..just don't want to deal with the line-up of people with Gas containers especially in the cold weather.

 

[sicklyscott]

Sal - thanks for the opinion. I think we have similar minds.

In the end however I'd probably operate like brianh, and with being in NJ it's not a monthly event that we lose power. I think I'm pretty set on a Generac XG series, probably the 4500 watt peak unit.

Sal - you mentioned the bad amazon reviews for Generac, check out their XG series, supposedly much better than the lower end GP line.

 

[Burtonrider10022]

I can run a refrigerator, an 8,000 BTU/hr window air conditioner, TV, lights, and a couple of box fans on a 3,000 watt generator, comfortably. The amperage on the generator panel reads about 8 amps on average, with a range of 6 to 14.

You could go to Home Depot and pick up a Kill-a-watt meter for $28. Plug each one of your loads into it and see what the wattage reads. Remember that anything with a motor will draw a high inrush current for a second or so when starting. If you can see the motor name plate it will display the locked rotor amperage (LRA). Make sure the generator can supply enough surge amperage to cover that without tripping its breaker.

It seems to me that oversizing the generator will waste fuel, not save it. Oversizing also means more weight, more room taken up in storage, bigger gas tank to siphon before storage, etc. On the other hand the larger capacities sometimes have more features.

Generacs usually get positive reviews, except for their little inverter generators that compete with Honda and Yamaha. Generac has GP and XP series, with the XP being more expensive but getting better reviews. If you want the best, get a 3000-watt Honda or Yamaha, for which you'll have to pay over $2,000.

$18 on Amazon and free 2 day shipping with prime

 

[SalA]

Sal - thanks for the opinion. I think we have similar minds.

In the end however I'd probably operate like brianh, and with being in NJ it's not a monthly event that we lose power. I think I'm pretty set on a Generac XG series, probably the 4500 watt peak unit.

Sal - you mentioned the bad amazon reviews for Generac, check out their XG series, supposedly much better than the lower end GP line.

A couple of my neighbors have the XG units outside their garage. The problem I have is with these portables is you can't use them in wet weather..I think. The whole house units have enclosures. Also, since I am relatively close to my neighbors, I would like something that has some sound attenuation. I will continue my research as there is very little that can be done right now here in NJ.

Good luck with your install!

 

[steve-l]

When sizing a generator, your intended use should be the decider. Are you intending to carry it around or is it rather permanent? How long do you intend to run the generator at any given time? Those two questions are very inportant because they drive a myriad of other questions. For instance, if the use is tool use in remote locations a light generator like you have identified is appropriate. If your use is a home as a replacement of normal power during outages then your requirement is for a completly different class of generator. For instance, light use generators are 2 pole and run at 3600 rpm, they are noisy, have poor fuel consumption and should run for no more than a few hours without oil change and have a really low life expectancy. It sounds to me that you need a 4 pole generator that will run at 1800 rpm. You have natural gas plumbed into the house. It makes some sense to use that if you feel the gas supply will always be there when you need it. If so, the generator must have austinetic valves and stellite valve seats, as NG has no seat lubrication value. (same for today's lead-free gasoline) Otherwise your talking about a diesel unit, with an external fuel tank of at least 200 gallons, external air supply for both cooling and intake, sound box, silenced exhaust and even those units, in your capacity range, must be serviced at 100 to 150 hrs. Financially, a permanent installation normally costs the same as the generator, if you don't do everything yourself. I highly recommend you do correct planing or dissapointment is a certainty. Here are some numbers you will need for fuel consumption.

Generator efficiency (Horsepower in verses KW out) = 85-90%
Fuel consumption
Diesel = .4lb per HP hour (around 6lb per gallon at 20 degrees C)
Gasoline = .5 lb per HP hour (around 5 lb per gallon at 20 C)
Natural Gas = same as gasoline

For planing purposes, 70% of power rating for your max anticipated load.
For fuel consumption planning, use 50% of KW rating and convert watts to horsepower at 736 watts per HP (640 + 15% efficiency loss)

Good Luck,
Steve

 

[Mickey O]

Can't tell you what size to get, it's all according to your needs and if outages are a problem. Just make sure you have plenty of fuel, best generator in the world won't run without it.

I'd like to see a portable natural gas generator with a quick connect, that would be nice.

Anyhow, the reason I'm posting is that I remember reading several reviews on portable generators and one of the big complaints I saw, specifically with Generac, was that they don't have a 220 ~ 240 volt outlet on certain models, may or may not be a concern for you. If you want 220 ~ 240 make sure the generator has it.

 

[Burtonrider10022]

Can't tell you what size to get, it's all according to your needs and if outages are a problem. Just make sure you have plenty of fuel, best generator in the world won't run without it.

I'd like to see a portable natural gas generator with a quick connect, that would be nice.

Anyhow, the reason I'm posting is that I remember reading several reviews on portable generators and one of the big complaints I saw, specifically with Generac, was that they don't have a 220 ~ 240 volt outlet on certain models, may or may not be a concern for you. If you want 220 ~ 240 make sure the generator has it.

You can do this easily aftermarket not sure about factory direct.

 

[sicklyscott]

You can do this easily aftermarket not sure about factory direct.

He has a point actually. I can't seem to find a "portable" unit that is meant to run on NG. As stated above the motors take some abuse if you convert them from gasoline to NG.

With that said, if a motor was built to run on propane (which also doesn't have any lubricating characteristics) is the converion to NG as internally destructive?

 

[Heavy Metal Doctor]

I will also add that 4kw works well for me - a fridge, a separate freezer, oil burner / forced hot air heats the whole house and that still leaves power for a couple lights and entertainment stuff (lap-top / tv / dvd player).
My only drawback is the electric water heater is too much, so I have to heat water on the gas burner (grill or camp stoves) when needed for extended power outages.

 

[Bob-B]

I run a 12+ year old 5Kw Generac for my house. It runs 2 fridges, an oil hot water boiler with 3 zones for heat, CFL lamps, tv, and cable modem all at the same time with no problems. Ran it for 5 days last year after Irene blew thru Long Island, and again last week for another 5 days after Sandy.

 

[RCStocker]

I have stand by generators on both of my homes and one hooked up to my 2 shops.
I have a 1500 watt Honda generator that is 36 years old and still works grest. I can run a refer, freezer, TV, Lights in two rooms without a problem. It is a great little generator.

I have used it at the cabin and for construciton for years. I have larger portable generators and they will run more. It just depends on what you want to run.

Costco had a fantastic generator on sale right now for $1000. It 7000 watts and has a honda motor on it. I Don't know who makes the generator but I think it will work great and you can't beat the price. It will run anything you have in a home. Remember larger generators don't work as hard and they have larger gas tanks.

 

[SalA]

I spoke with a tech support person over at Generact and they stated that if you convert from say gasoline to Propane, you would void the warranty and the unit may not operate to spec. The portable units generally are not built to run NG, at least I can't find one.

Some of the bigger whole house built units are sold with a 3-way conversion option.
Gasoline---->Propane----->NG

 

[Chadwilliam1]

I need to read up on this, I will soon be in the market for a generator.

 

[SalA]

I need to read up on this, I will soon be in the market for a generator.

Everyone I see in the NY-NJ-PA area is performing the same research right now.

My advice on this subject is to go a bit higher then lower on the power load rating. Also note that items that have a startup cycle general will need double the amount of rated loaded. A Refrig manuafacturer may say it can run at about 1,800 watts...but when the compressor starts up, you draw will probably be around 3,600 watts for about 2 seconds. A 100 watt bulb will always draw 100...

Many more details to consider as well!!

Good Luck with purchase

 

[Chadwilliam1]

go big or go home. my buddy just bought one and i think it runs on, gas and propane. that is something I will be interested in.

 

[steve-l]

He has a point actually. I can't seem to find a "portable" unit that is meant to run on NG. As stated above the motors take some abuse if you convert them from gasoline to NG.

With that said, if a motor was built to run on propane (which also doesn't have any lubricating characteristics) is the converion to NG as internally destructive?

Neither NG or Propane is internally destructive. In point of fact these fuels are cleaner and easier on the engine, with caveats. They must use compatible valves and valve seats and the fuel must be introduced equally to all cylinders. This is usually not a problem with centrally located carburator manifolds, but beware if the throttle plate is end manifold mounted, you will melt pistons. Also if the engine is rated for unleaded gasoline, no modifications need to be performed. Be aware though the latent heat of the fuels are not the same between NG and LP, where NG setups require a richer mix of gas to burn correctly. Dealers that sell conversion kits are aware of this.

 

[steve-l]

For back-up power, I wouldn't consider anything but a 4 pole alternator driven by a diesel. Most all light fuel engines are limited duty by design. Most diesels are industrial, continuous rated. Diesel generators run on heating oil. Storing heating oil is very safe, Gasoline is not. LP gas is heavier than air and when leaking, settles in pockets and can easily become explosive, just like Gosoline vapors. NG is lighter that air and if venting is correct, explosive vapors concentrating in pockets is remote, but because the supply is not yours,fuel availability during an emergency is a risk you don't have to assume.

 

[IndyGarage]

In a power outage, bigger is not always better. It 100% depends on fuel availability.

If fuel is not available, as in the hurricane this past week, then a bigger generator just eats more fuel that you don't have.

If the power outage is due to a localized storm, and fuel is available, then the bigger one is going to make you more comfortable.

I have a 5,500 watt that paid for itself on its first use - when our power was out for 7 days straight. It's noisy, although I put an auto muffler on and quieted it a lot, it's heavy and it doesn't get used much. Prior to that one, I had a 3500 watt, which was OK, but you had to watch what loads you put on it more closely, and the gas tank was tiny, so it only ran a few hours on a tank.

My Father in Law had one of those honda 2000 watt camping generators, which I think are only 1600 continuous, and it was lightweight, quiet and got used all the time.

I will never be without some kind of generator again. When you need one, it's usually when everyone else needs one too, so you're not likely to find one easily after the need arises.

I've wondered whether a pair, or ideally just one of those 2000 watt Hondas would be able to tide me over. Then again, on the other end, I've thought about dumping my generator and getting a generator/welder and then it would get some more use....

 

[Jagmandave]

I've had my Generac for 12 years now with no issues, the longest I run it is about 4 hours at a time, enough to get the house cool or warm depending on the season and the fridge and freezer good and cold. My unit is 12,500 surge and burns about 1 gallon per hour at heavy load, much less under light load.

I've had no issues with it save the battery for the electric start dying and the pneumatic tires always going flat. I keep in a weather proof shed and roll it out when I need it, so I replaced those damn tires with solid ones from Harbor Freight for about $10. Since I don't have to roll it far, that worked out perfectly.

I don't agree that it needs an oil change after only 4 hours of use, in fact regular use is better for it than sitting around or being run for only a few minutes. When the battery died it started on three pulls of the cord on a very cold day, but I let it run for about 5 minutes to warm up before I pulled a load on it.

It IS loud, and I plan to see if I can put a car muffler on it to quiet it down, but when you need it you need it. I made a pigtail to connect it to my service disconnect for my A/C, both are rated at 50 amps 220V but it would be far better to set up an either/or transfer switch. The A/C only pulls about 20 amps so that leaves me with some headroom if we lose power on a really hot summer day.

When the winter season comes I keep one 5 gallon can of gas in the shed with it, and every month I pour that into one of the cars and replace it so I'll have at least a good backup. Unless the whole city is out of power I figure I can get to where some gas is, or I can drain the tank on one of my cars if needed. I run it dry after each use before I put it away and I run some Stabil in the gas just in case.

Since I bought it (right after a terrible ice storm that left most of the city without power for a week, but strangely - right in the middle of the outage area, my house and 5 others were still lit up!) I've only needed it twice, once in the summer and once in the winter but it performed admirably and I'm glad I bought it. I do use it around the property at other times, and have run my 220v welder off it a number of times.

 

[Jim_No_Garage]

I've been running a 5000W Master generator for the last 12 years. We recently replaced the gas furnace with a 96% efficiency unit and the slightly increased electrical demand is pushing the limits of the generator. We also added another fridge/freezer to the mix which isn't helping.

I can run that generator 12 hours on a 4.5 gallon tank of gas. We only run 18 hours a day so the gas consumption is manageable.

My plan is to re-evaluate my electrical loads and see if they need to be better balanced across the 2 legs of the 240V. If all my loads are on the same leg it could cause the overloading issue.

Power came back on at 5PM yesterday, so this makes 4 events where we ran the house for several days on generator power - the longest being 7 1/2 days this event. The generator was bought for Y2K but it's run for 1 T-3 microburst, 2 Hurricane/Tropical Storm/Cyclones and 1 Snow Storm / Tree killing event.

I can get a slight deal on Generac models but I'm considering NorthStar from Northern Tool. I am more concerned with power cleanliness as the house is becoming more high tech.

Any input on suggestions would be appreciated. I'd love a Honda Inverter but something of the size I want would be tough to $$$$$$$$.

Cheers

Jim

 

[theoldwizard1]

I ran 2 refrigerators and a full size freezer plus some lights and fans on a 3,250 watt Coleman during the big east coast/midwest blackout.

If you can afford it, look at inverter generator, either Honda EU3000is or Yamaha EF2800i.

I know that the Yamaha can be converted to tri-fuel (gasoline/LPG/NG).

 

[LSU]

One thing about running on NG:

I have a NG generator. Love it but . . .

Last hurricane that blew through upended some large oak trees whose roots were entwined with the NG lines that ran through the neighborhoods.

My generator and gas supply lines were not affected but other folks I know were.

Just something to think about.

I still have my NG and love it.

 

[Burtonrider10022]

One thing about running on NG:

I have a NG generator. Love it but . . .

Last hurricane that blew through upended some large oak trees whose roots were entwined with the NG lines that ran through the neighborhoods.

My generator and gas supply lines were not affected but other folks I know were.

Just something to think about.

I still have my NG and love it.

Which is exactly why a couple large propane tanks are a wise choice. He suggested tri-fuel, so LP will of course be OK. Propane doesn't expire, can be stored much more safely than petrol, and 100lb tanks can be found very cheap on craigslist. BBQ tanks can be found on CL for about 5 bucks a pop, and 1 propane 20lb propane tank is 4.7 gallons.

 

[RKA]

My Father in Law had one of those honda 2000 watt camping generators, which I think are only 1600 continuous, and it was lightweight, quiet and got used all the time.

That's what I used for the latest round of bad news. It's not for everybody, but for a minimalist it works so nicely. Ran the furnace and fridge in alternating cycles, along with a light, radio, and eventually the wireless router/modem when boredom sunk in. 1 tank of fuel (about a gallon) would go about 6-7 hours, whereas my neighbor had his entire house lite up, but needed a gallon an hour to feed the generator. I suspect at some point I'll get another one to connect to this one, and add a 30A twistlock plug outside for a little more comfort and a little less fuss, but for now, this works.

So as others have said, think about the actual load and what would need to be run when. Get what you actually need, because getting more will require fuel you may not have access to. Remember, in most cases something like this is for emergency use not everyday use, so don't be tempted to oversize much if any (and this is coming from someone that almost always oversizes).

As for measuring actual usage, I'm not sure those kil-a-watt devices have the capacity to show start up use on devices like the refrigerator (I've never used them so I don't know). If not, get an amp meter, get a short piece of 12 ga wire, and cut the outer insulation so you have access to the indivual wires and put a male and female plug on either end so you can place it between your device and the wall plug. Measure it that way. For multiple devices like this (fridge, furnace and sump pump), I will usually take the peak readings from 2 our of 3, and add them up and make sure I stay under the peak wattage delivery of your generator. Odds are all 3 won't start up in the same moment, but 2 out of 3 could happen. This is what I've done.