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Old 09-03-2005, 09:12 PM
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Portable generators: how long can they run nonstop

I'm talking about the small, portable, roughly $600 gas-powered, air-cooled generators sold at Home Depot, Lowe's, Sears, etc.

These are light-duty generators, making me wonder whether, if needed, one could keep them refueled and running nonstop for, say, 2-3 weeks.

Also, how long should one wait before refueling a hot generator? I am concerned about spilled gasoline.
Old 09-03-2005, 11:20 PM
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I have a 3500 watt Honda generator, according to the instruction manual, it depends on the load you are placing on the generator. For a heavy load, the manual says run the generator at no more two hours per 4 hour period. Lighter loads can run at 3 hours and no load continuous for 4 hours. It also says to never run the generator more than 8 straight hours which in my case, is about one tank of fuel. I have run mine for 20 hours in a 24 hour period without problem.
Old 09-03-2005, 11:35 PM
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I believe we ran one for a week during an ice storm and resultant power outage.
We could run the fan and thermostat controls for the gas furnace.
It is in front of the pump house (ran that too, of course) and required adding oil every four hours. I learned to wake up when I heard the engine begin to miss. I'd briefly shut it off to add oil by flashlight. My family slept on. It's nice to be usefull.
Old 09-04-2005, 01:56 AM
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I have a 10 hp Coleman generator and as far as I know, there's no time limit that it can be operated before "resting".

It will run 6 to 8 hours on a tank of gas, depending on load. We were out of electric power for 24 days after hurricane Opal, and that generator ran almost continuously without being harmed.

If you have a serious and maybe heavy load need for a generator, you might want to spend a little more money for a slightly bigger model. $600 doesn't sound like enough.

When adding gas to a hot small motor implement, be careful, don't spill any and you'll be OK. Or else wait ten minutes or so. Avoid open flames or smoking cigarettes when playing with gasoline.
Old 09-04-2005, 03:52 AM
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We can hear them running in spots in the *rich*subdivision to the south of us, since Katrina. As long as you are careful filling up, I don't see a problem. It's been - what - six days since power went out? I'd put my money on one with a Honda or Briggs & Stratton engine. A pox on Tecumsah.
Old 09-04-2005, 08:59 AM
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I would wag that running it nonstop over 2 hrs the engine will be basically at thermal equlibrium, and steady stress cycles. Or in other words, if it ran 2 hrs there is really nothing additional it has to do to run past that point. As long as you are not overloading the electrical system, I don't see a problem. I personally cycle mine as I have most critical and entertainment systems on battery backup, so I can go quite a while w/o starting the generator. Once started it will also recharge the batteries, which will allow me to shut down the generator. This greatly increases the lenght of time I can go w/ limited fuel.
Old 09-04-2005, 10:47 AM
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As an aside-if you're going to run an engine under that sort of duty cycle, ideally you'd want to perform an oil change immediately before, and immediately after the storm event. Think of how many miles you'd put on the Chevy if it ran at 55 MPH 24/7. In the situation described by John Carter of Mars that's almost 32,000 miles! Well beyond the recommended oil change interval, and many small generators don't have oil filters, either.
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Old 09-04-2005, 11:01 AM
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Quote:
Originally Posted by danceswithcats
As an aside-if you're going to run an engine under that sort of duty cycle, ideally you'd want to perform an oil change immediately before, and immediately after the storm event. Think of how many miles you'd put on the Chevy if it ran at 55 MPH 24/7. In the situation described by John Carter of Mars that's almost 32,000 miles! Well beyond the recommended oil change interval, and many small generators don't have oil filters, either.
Good point. Under continuous use, two oil changes per week is not too frequent, and at least once per week is pretty much essential if you expect to get years of use out of the generator.
Also, when no event causes you to need the generator, it should still be started once every month and allowed to run for 15 to 20 minutes. This keeps it ready for use in emergencies.
Old 09-04-2005, 05:53 PM
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>I would wag that running it nonstop over 2 hrs the engine will be basically at thermal equlibrium, and steady stress cycles. Or in other words, if it ran 2 hrs there is really nothing additional it has to do to run past that point.

Yes, I'd think so too. I wonder why a manufacturer would recommend stopping it at 8 hours - seems like that recommendation makes the product less useful and gains it no protection. In fact, the thermal cycling itself is harmful, so I think it'd be much better to run for 20 hours sraight than to run for 4 stretches of 5 hours with rests in between. By any chance is 8 hours the recommended time for oil changes? Seems short, but not necessarily ridiculous.

Similarly, it's generally better for PCs to leave them running than to turn them on and off, if they work enough hours per day to begin with.
Old 09-04-2005, 10:36 PM
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You should also have an electrician connect a transfer switch, just to be safe. Cite.
Old 09-06-2005, 11:13 AM
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The main concern is oil - my 10 HP gen holds only 1 quart of oil, and these engines consume oil faster than a car engine does - after about 40 hours of use, mine will burn off enough oil that the dipstick gets to the "ADD" mark.

The manufacturer calls for an oil change at 100 hours, and there is an oil level switch that will kill the ignition if the engine gets too low on oil.

While we're on the subject of generators, once you're done with it, run it dry. If you leave it with gas in the carburetor, you'll find it full of gum and varnish a few months later.
Old 09-06-2005, 12:37 PM
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Quote:
Originally Posted by gotpasswords
The main concern is oil - my 10 HP gen holds only 1 quart of oil, and these engines consume oil faster than a car engine does -
Anyone know why? Lawnmowers and four cycle motorcycles don't use oil that quickly.

Quote:
Originally Posted by gotpasswords
While we're on the subject of generators, once you're done with it, run it dry.
I should, but didn't. It starts easily. I've probably been very lucky.
Old 09-06-2005, 01:22 PM
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The main issue is oil. Simple generator engines operate with no oil filter. Dirt, and wear products (metal filings) accumulate in the oil until it is changed.

Like cars, etc. oil consumption varies with the engine, how it has been maintained, broken in, and how old it is. I've seen some lawnmowers that use NO oil, and some that use quite a bit.

In general though, an air cooled engine is going to use more oil compared with a liquid cooled one. An air cooled engine operates over a much wider temperature range, and must therefore have greater operating clearances. Pistons and cylinders go slightly out of round as they heat, and this is worse with air cooling.
Old 09-06-2005, 01:51 PM
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Quote:
Originally Posted by carnivorousplant
Anyone know why? Lawnmowers and four cycle motorcycles don't use oil that quickly.
During Faire, my generator's running for about 20-25 hours per weekend. My lawnmower probably doesn't run for that long in one summer. Multiply that by the six weeks for run of Faire, plus another six weeks for setup and teardown, and I really should be changing the oil twice per season.

With that many more running hours, I'm not surprised it consumes that much oil.
Old 09-06-2005, 02:15 PM
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I know you asked about portable generators, but I thought my experience with standby sets might be nice for comparison:

I've run a 120Kw and a 30Kw set almost continuously before. Obviously, both are diesel engines, and some would argue that running non-stop is better that starting/shutting down daily.

The only time they need to shut down is for regular service, which I did every 300 hours.
Old 09-06-2005, 02:46 PM
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We have a Sears 5500 watt generator and we ran it 10 - 12 hours at a time. This was enough to keep the fridge and garage freezer in good shape and fans on at night and such. I have a hook up to run 240v directly into the breaker box and it runs most of the house (lights, ceiling fans, outlets). I also put a small fan (8") on one of the outlets blowing across the engine itself to help keep the temp down. I check the fuel and oil regularly and add "Fuel Preservative/Additive" during non-use periods to prevent the fuel from going bad (stale). I try to keep my tank near full because air in the tank will expand and contract during the days/nights and cause a condensation (water) build up in the fuel tank. In the humid parts of the country this can be a signifigant problem. At the end of this season, if we get thru without using it, I will drain the tank and refill it with gas & the additive.
A full tank also means 10-12 hrs. of run time in an unforeseen situation.
YMMV, of course.
Old 09-06-2005, 03:41 PM
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Quote:
Originally Posted by Nic2004
At the end of this season, if we get thru without using it, I will drain the tank and refill it with gas & the additive. A full tank also means 10-12 hrs. of run time in an unforeseen situation.
YMMV, of course.
Why don't you just take the occassion to test the generator for 10-12 hours and burn the fuel you'd otherwise waste?
Old 09-07-2005, 10:58 PM
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Quote:
Originally Posted by gotpasswords
My lawnmower probably doesn't run for that long in one summer.
Good point, but I'm mowing two acres, say two hours a week, eight hours a month compared to eight hours running the furnace blower and instrumentation with the generator. No oil for the mower, a quart for the generator. You'd think I'd see and smell that much oil being used in the generator.
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