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Features to look for in stand alone generator
I'm looking for a stand alone generator in the 4 or 5000 watt (continuous) range, gas powered. It will be used to run small power tools and for emergency power backup (basically get my furnace going, and keep refridgerator cold).
There is a huge range of prices for these units. What features or construction should I be looking for (i.e. bearing type, brushless, "cleanliness" of the power, etc.)
I've been told that some electronic furnace controllers "choke" on the dirty power from some portable generators.
Thanks for any advice you can give.
John Mc
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Features to look for in stand alone generator
I think the biggest thing you need to know is how much power does the furnace need to start???
How long will the generator operate at any given time....
As I am sure you are aware there are generators and generators..
If you are using one for short burst duration one purchased at one of the large hardware operations will work fine....Many of the construction people purchase them and run the you know what out of them day after day.
But most of those unites have little more than a inexpensive gasoline engine and over a long period of time they will fail when you need them the most....
Again depending on how you will use the unit the engine is a very important part of longevity but it also is a great cost differential. I highly recommend electric start pulling the high horsepower engines can give you a heart attack. 220 output 30amp receptical make sure you get a ground bar to bury next to the unit....you can put a standard surge protector between your hot lead and the furnce if you are afaid of a surge...but not knowing the furnace your bigestproblem is the initial power needed for the start-up...once running the furnace should not pull that much power
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Features to look for in stand alone generator
Yikes, I'm out of time today, but I will participate in this one. I've got a Honda 6500 that's 5000 or 5500W continuous. It does the job described, although it's not too happy about the furnace and water pump starting while the fridge is on. High electric motor starting loads are hard on generators and should be minimized. Using the generator for emergency backup, I juggle loads around and try to keep only one motor load active at a time.
The 6500 even does a decent job with the stove as long as only a bit of lighting is also on. My only complaint is that the cold weather starting isn't great and I usually use a whiff of ether during the winter.
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Features to look for in stand alone generator
I don't have the furnace yet, since the house is under construction. I'm not so much worried about the power rating (including surge) of the furnace generator combo. I can figur that out. It's more the "dirty" power concern. I've heard some of the "Home Depot" store models put out more of a triangualr waveform (not sawtooth, but triangular) which causes some furnace controls and other electronic equipment to choke.
My heat will be a boiler (probably oil or propane fired) Most of the house is radiant floor heating, with a few small pumps to circulate it. These don't draw anything like a well pump (though I will need to run that... separately if necessary). The controller will switch on and off various zones as needed. I might occasionally need to run other electronics as well.
I see specs on harmonic distortion quoted on some units (i.e. "less than 6% harmonic distortion" but I don't know what's considered a good number.
I don't anticipate running this a lot of hours, so I'm hoping I don't need one of the $1500 - $2000 units. On the other hand, I'd be willling to spend more than the $400 or $500 for the low end units, if I knew I was avoiding some of these problems, or otherwisse getting something for my money.
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Features to look for in stand alone generator
In pro audio equipment I’ve found that it almost takes an engineer to sort out the specs. It depends where on the power curve noise and distortion specs are taken, and specs tend not to be comparable.
I'd be more concerned by the possibility of voltage surges, sags, spikes and transients than wave shapes and harmonics. Running a signal through a transformer and power supply tends to shape and clean up many signals. However, if high AC quality is required, there is a variety of specialty power conditioning equipment used by sound companies that have to work with bad AC.
I think that a sine wave is the natural form of a signal produced by an inductor rotated in a magnetic field (basically a generator). If a generator produces a different waveform, then I'd suspect an engineering trick designed to justify a big power spec. High-end equipment don’t usually rely on tricks, because there are always costs to these things. Specs may be pretty illusionary. However, I'd guess that a generator's duty cycle is a pretty good proxy measure for quality. I'd look at the difference between peak and continuous rating and also how long peak levels can be maintained. Something close to a 100% duty cycle and able to sustain peak loads for longer periods probably produces high quality AC too.
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Features to look for in stand alone generator
TomG-
From what I read, a lot of the distortion is caused by harmonics of the main sine wave. I know that triangular waveforms basically are a sine wave with a strong third harmonic (so if you are generating 60 Hz, you'd have a strong 180 Hz component superimposed over it). Spikes and surges tend to get filtered out pretty well by an inductor (transformer), but I don't think harmonics do (I may be wrong on this, however).
I've heard from a couple of people who had problems where the controller on their furnace would not start up on some generators. They put it on a scope and saw a triangular waveform. Borrowed their neighbor's generator, and it ran fine... that one scoped more like a true sine wave.
I'm concerned about that factor, but also about getting a decent basic unit. Unfortunately, I don't know much a bout the mechanical aspects (why is OHV touted as superior on a small gas engine? Is it worth paying extra for? Who makes good engines: Briggs, Tecumseh, Northstar?) What features should I be looking for on the generator half?
John
John
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Features to look for in stand alone generator
I suspect that most generators and inverters put out more of a square waveform. So does the power company. It's just that it runs thru so many transformers before it gets to you that smooth it out into a sine wave. I use a 4400 watt unit to run most of my house. Just had it running for quite a while lately with our ice storm (Buffalo, NY area). Works fine, but I have a lower tech furnace. I ran it all day at my parent's house too. 2 sump pumps, a freezer, a refrigerator, oil furnace and oil hot water heater. You could hear it load pretty good when the freezer came on but the voltage never went below 110 on that leg.
Just saw 5 Hydro Quebec trucks at a local restaurant. Looks like they called in reinforcements from all over! Some areas have been off for 3 days (20 deg and wet cellars!).
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Features to look for in stand alone generator
Oh yeah - the original question. I have a homelite and a generac. I have run the pants off the homelite and it is holding up great! The generac is for the camper when we go to races. Runs great too!
Anything with a honda engine will run forever. OHV engines are supposed to be more fuel efficient and more power per displacement. Hondas are quieter too.
Pressure lubrication (has an oil filter like a car) is supposed to be better, but my homelite doesn't have it and has high hours and still burns no oil (changed regularly).
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Features to look for in stand alone generator
Steve-
Unless you spend big bucks for a "true sine wave" inverter, most inverters put out a square wave or a "modified sine wave" (which is basically a square wave with slightly sloping sides). I would not have thought most AC generators used an inverter. Inverters are used to transform DC to AC. Since there are losses in the conversion, I would figure they'd just generate AC directly, rather than generate DC and convert to AC.
(They only reason I know anything about inverters is because I've been reading up for possible addition of solar &/or wind power to our new home... requires inverting the DC power to AC for running traditional appliances.)
John Mc
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Features to look for in stand alone generator
Yes, true about harmonics and waveforms. The combination of transformers and filter networks in some power supplies do a decent job of rejecting harmonics. Some pro audio power supplies are designed to clean up AC. Never the less, I always used moderately expensive surge protectors that also contained noise filters on all my pro sound equipment. However, I had more sound problems due to poor AC grounding than to dirty AC.
I've heard discussions about armature construction in high-end generators. I believe these engines tend run at half the RPM of standard generators. I've also heard that these high-end features including true sine wave may not be too important for an emergency power backup application. Even equipment with low expected service life ratings may last indefinitely unless utilities become even more unreliable. I don't know how comparable service lift ratings are but they may be good to check.
Similarly, fuel efficiency may not be all that important, but noise was a very important consideration to my wife. That's probably why we ended up with Honda, or at least that's how they're advertised. We may not need the long life but it is quieter. Wife still grosses about the noise even though the generator sits in a shed over 50' from the house. I can comment about generator hook ups to utility equipment if interested.
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