Generator

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These generators tend to be slightly upscale (as in commercial grade) rather than the cheapos you see at HD. Usually not _big_ ones, because they're usually used in circumstances where you're always drawing power. The big ones often operate full time at 1800 RPM.
I recall reading about 3600->1800 or 1200 RPM idle step-downs on mid-range commercial Onans, Generacs and Hondas. It's advertised as a feature to make the generator last longer.
The idea being that the generator itself is much cheaper to make if it's operated at 3600 RPM (eg: most engines produce peak power near to 3600), but the wear level is considerably increased over 1200 or 1800 - hence the compromise of idling lower.
There's an analogous situation with electric motors. It's cheaper to make a 3600 RPM motor than an 1800 RPM one. But most applications need 1800 RPM rather than 3600 RPM, and the cost of gear/belt reduction of 3600RPM is more than the cost savings of 3600 over 1800. Hence, most motors are 1800 except with certain applications.
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Chris Lewis, Una confibula non set est
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Hmm, no big points to make, but a few comments inline:
: > ... ... : : > No, not so rare. MANY generators idle during periods of no-load. : > Most generators around here do, including mine. If there is ANY : > load though, it jumps up to speed incredibly fast. : : These generators tend to be slightly upscale (as in commercial grade) : rather than the cheapos you see at HD. Usually not _big_ ones, because : they're usually used in circumstances where you're always drawing power. : The big ones often operate full time at 1800 RPM. ===> lol, I have an upscale generator? First I've heard of it. It's a Coleman 5000W, one of their "Industrial" lines (not "Commercial"; industrial), a term they seemed to use for anything over 5kW & with all the receptacles, at the time I bought it, on sale, at Lowes. It cost almost a hundred less than the no-name 5.5kW sitting next to it, but it was the only one left. They seem to use the "industrial" on anyh of them that have the duplex receptacle plus a 3-wire and a 4-wire receptacle on the panels. To me, that would make it a "jobber's" generator, more than industrial. ;-) : : I recall reading about 3600->1800 or 1200 RPM idle step-downs on mid-range : commercial Onans, Generacs and Hondas. It's advertised as a feature : to make the generator last longer. : : The idea being that the generator itself is much cheaper to make if : it's operated at 3600 RPM (eg: most engines produce peak power near to : 3600), but the wear level is considerably increased over 1200 or 1800 - : hence the compromise of idling lower. : : There's an analogous situation with electric motors. It's cheaper : to make a 3600 RPM motor than an 1800 RPM one. But most applications : need 1800 RPM rather than 3600 RPM, and the cost of gear/belt reduction : of 3600RPM is more than the cost savings of 3600 over 1800. Hence, most : motors are 1800 except with certain applications. ===> Uhhh, I don't know about that. Besides, it's 1725 and 3450, not 1800 and 3600, right? With an electric motor, the application much more than the speed determines its life. Stresses on the bearings laterally and longitudinally, and % power output are much more the determining factors of the life of an electric motor. So it really only equates to load, not speed, with an electric motor. You have many more varaibles with a generator and I don't feel qualified to speak to any more than "intuition" and educated guesses about most things generator wise.
Are you implying that my idle speed is 1800? I really doubt that from the sound of the motor, but then again I do feel it's well over 600 rpm, but - that sounds pretty high.
You're really getting me curious now; guess I'll have to find a way to measure rpm's after all. I can't stand not knowing some things! ;-(. Up to now, I've figured 60Hz was the only number I'd bother with checking, but, well, curiousity and all that ... knowledge is power (who said that?).
Pop
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It may be a new line, or someone is trying to cash in on touting the "feature".
I don't know whether it's really idling at 1800, it's just the specs I've read for other generators spec it. The speed is effectively irrelevant, because it doesn't have to retain regulation. Just needs to be fast enough so that it doesn't hesitate and gets up to 3600 FAST. Yet another design compromise.

The 1725/3450 speeds are under rated load - sync slip. With no load it's 1800/3600.

If it's the motor alone, true, but it's the whole thing to consider with wear. And it's not that big a factor with electric.
Speed matters far more with internal combustion engine wear.
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You might want to get a real good generator....
Your furnace has a electronic control board in it. Fry it and you screwed with or without power!
Cheap generators provide dirty electricity, this will have a problem with electronic equipment. Should be fine though with refrigerators etc.
If you filter the power through a UPS, that will do ok. Otherwise honda makes a fine line of generators that can do it. Expensive though.
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Standard UPSs produce square waves. I wouldn't want to send that to my furnace.
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Sounds like I need to engage an electrician for this. Since I am in Boston, it's going to add a few hundred dollars to the cost, even if he just drops by for fifteen minutes! I was hoping to avoid that, but it sounds like I am way out of my depth here.
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Do you know how much electricty your furnace needs?
That would be a good place to start.
I have an interesting story - which unfortunately probably doesn't apply to your situation - but it illustrates that you want to KNOW what is really happening before making assumptions.
In January 1978, a blizzard hit our area of the mid-west and left us without power for 3 days.
Being a good neighbor, I fired up my coleman stove and made some soup and took to the octegenarian next door. She thanked me for the soup and asked me to sit for a bit. I noticed her home was toasty warm.
She explained to me that our homes had had coal furnaces with gravity air feed that had been converted to natural gas. She was sure that mine was the same as hers. She said that she just switched the furnace to "manual" and let it run. If the house got too warm, she turned the furnace off. I did the same. We were warm and cozy. Many folks had frozen pipes.
My wife and I read "The Long Winter" by Laura Ingalls Wilder aloud to each other and enjoyed the time off. -----
Find out what you have, before trying to figure out what you need.
------- Good luck! P.S. Consider getting a Propane or Natural Gas powered Generator. Gasoline stinks and is flamable to store and pour. Phil
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wrote:

I guess that is your reward for being nice to her.

Folks with the same furnace arrangement you had?

Remove NOPSAM to email me. Please let me know if you have posted also.
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Only inverter style gens have voltage dependant rpm. Your standard unit runs at 3600 a small unit may use 1/4 to 1/3 gallon on a light load of 400 watts for a furnace. Honda EU or a Yamaha inverter may only need 1200-1600 rpm to make 400 watts and get much better run time and much more engine life. Idle control on my unit only cuts no load run from 3600 to apx 3300 not much of a reduction.
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Soudns like you have what I call an "octopus". Which some folks call a millipile generator gas valve furnace. Glad you had heat. Incidentally, get th at old energy hog replaced some time, you'll save enough on the gas bill to afford a generator.
Tongiht we are doing freezing rain in NYS. I'm wondering if we have a power cut in the near future. The octo across the street has a gas range, and has heated her kitchen with the range. While worrying silly about carbon monoxide.
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Errrr... Your having flashbacks to the old days...
Most modern UPS's either use a stepped wave (cheap ones) or the more expensive units do make a sine wave. These sine waves can be cleaner than what you get out of the power grid.
Think about it... The square wave would be a problem with transformers... In modern computers they ALL use transformers to convert the power down to 5v and 12v. They dont make UPS's to blow up computers, but to save them from power spikes and voltage dropouts. One side you can look at though is that square sine waves do their damage over the long periods of time. Almost any UPS can work well for a little while.
This makes me want to look at my APC ups now.... Geeez
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Errrr..... Virtually ALL modern computers use switching power supplies. Which is direct rectification of the AC to DC (at 160V), filtering, and then AC modulation at some high frequency (20Khz-60Khz or even higher) through a toroidal step down transformer, then rectification back to DC, filtering and regulation.
[The advantage to this is that the toroidal transformer can be very small at this frequency. At 60hz, a "normal" step down transformer at these power levels would weigh 20 pounds or more. In contrast, at 60Khz the toroid weighs well under a pound. The economics are such that these switching power supplies are vastly cheaper to build and smaller than "classical transformer" supplies]
These power supplies are fairly insensitive to line quality, and really don't mind square wave at all - in fact the high voltage filtering is much more effective.
What these power supplies (and ordinary transformers) intensely dislike is fast transients, or things that can cause them (eg: _very_ sharply square square waves lead to inductive spiking especially through ordinary transformers). These spikes tend to blow holes through transformer insulation or blow rectifiers and high-side capacitors.
"square sinewave" is an oxymoron ;-) The correct term is "modified squarewave".
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Idle control on my 7500w generac is only from 3600 to 3250. You dont get much increase in life with that reduction. Idle is 6-800 rpm. Idle control must spool up to 3600 immediatly on demand of a draw so they cant allow them to really " idle" at 600. For long life a honda or Yamaha inverter style does better as it can run at 900 rpm generating, if minimal current is needed.
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Huh? Are you addressing me? I suspect not because I have NO idea what you're talking about! ;-). Unless I got really mixed up, I haven't even seen a UPS mentioned in this thread.
Pop
: Errrr... Your having flashbacks to the old days... : : Most modern UPS's either use a stepped wave (cheap ones) : or the more expensive units do make a sine wave. These : sine waves can be cleaner than what you get out of the : power grid. : : Think about it... The square wave would be a problem with : transformers... In modern computers they ALL use transformers : to convert the power down to 5v and 12v. They dont make UPS's to : blow up computers, but to save them from power spikes and : voltage dropouts. One side you can look at though is that : square sine waves do their damage over the long periods of time. : Almost any UPS can work well for a little while. : : This makes me want to look at my APC ups now.... Geeez :
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"I know that 3750kw will be plenty of power for what I need"
That ought to run not only your house, but a few thousands of your neighbors too!
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Of course I meant 3750 watts!
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Of course I meant 3750 watts!
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Hmm. Since a 10 HP Tecumseh supplies about 5 KW, what would you need to run 3750 KW?
Typically generators will run with no load. And the thermostat is either battery, or powered from the furnace.
Are you having your 3750 KW generator delivered by semi trailer, and off loaded by crane?
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