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Old 10-09-2011, 06:15 AM   #1
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Hours on Generator...

I've been looking at some used rigs, and often one of the selling points is "hours on the generator".

Since I have no frame of reference for this, what exactly am I looking for here or need to watch out for? Do generators have a shelf life, or need anything expensive (other than routine maintenance) after so many hours?


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Old 10-09-2011, 06:36 AM   #2
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I went to the onan school in 1993. We were taught The design life of the onan generator is ten thousand hours.

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Old 10-09-2011, 06:46 AM   #3
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The RV Doctor: Gen Hours

Here is an article that addresses the subject--you can decide the merits of the authors.

When you say a selling point is hours on the generator I assume you mean few hours?

Low hours is not always a good thing and more hours is not necessarily a bad thing.

Basically a well maintained generator will last a long long time---the article says indefinately. But a generator is an engine and other moving parts so it will wear.

A generator with low hours may not be a bargain if it has not had proper care---you need to see if it pulls the load it was designed for. Start it up and then put a load on it--you will get an answer in a few minutes. Run everything in the rig that should be able to be powered simutaneously and see if the generator can handle the load.

If fuel sits untreated in an unused generator for too long it can varnish and clog the fuel lines effecting the preformance dramatically. So depending on the age of the rig it should have a fair amount of generator hours devoted to running it to care for it properly. That requires a repair that can be expensive. Like any other engine sitting for long spells w/o use is not a good thing.

An original generator ( a few hours may mean a new one) that has many hours can be a clue as to how the rig was used. Having 500 -700 hours may mean that it was boondocked more than used in a park; or perhaps in some commercial way requireing it run under it's own power. Not that that is good or bad but it would just be something to know. It may account for hours on a generator but it may mean the generator still has many hours of use left in it.

Lots of generators actually get used very little---my generator has only been used twice in nine years because it was needed. Both times were because of power outages. That is typical of many RV's. The other times I have operated my generator were mearly to make sure it was getting enough workout and fresh fuel to extend it's life; to charge my batteries and to preform maintenence and cleaning of my rig. Fairly typical---I run my generator at least twice per month for about an hour--even if I have fuel stabilizer while it is in storage.

There are some variables which I cannot help with; diesel, LPG, gasoline. for instance.

Someone whos knows a lot about generators will come along and be more specific about how many hours is too many.
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Old 10-09-2011, 06:48 AM   #4
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The less you use it the shorter the shelf life.

Low hours on an older genset is not necessarily good thing. According to the operating manual for my diesel generator, the generator should be exercised (run) at least 2 hours each month under 50% load for optimum service life. It also states, "three one hours is not as beneficial as one two hour run". My point, a salesman will brag about a 5 year old generator that only has 50 hours use...not necessarily good. It should have that many hours in two years if only used for exercising.

I ran mine yesterday for two hours with both a/c's and the electric water heater on and that put about 30 amps load when the water heater was heating.

A gasser may be different.
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Old 10-09-2011, 07:09 AM   #5
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Generators need exercise to remain in good operating condition. There are two reasons for this:
(1) The whole generator needs to run under load long enough to heat up internally and boil off accumulated moisture in the windings and the electronic control modules. Dampness is a major killer of the electrical and electronic components.
(2) The engine itself needs to run a bit to circulate lubricating fluids and move fuel through the filters and injector pump (diesel) or carburetor (gas) to avoid gumming up the fuel system.

A good quality generator has a very long service life - at least several thousands of hours. Probably not so long for the cheap contractor grade units sold in discount warehouses, but that is not what is generally found in motorhomes. So, low generator hours is not a big plus, and VERY low hours (less than 12/year) may well be a negative. Goodness is a happy medium, say maybe 50 hours per year.

I have 1900 hours on my 7 year old Onan diesel generator and it is going strong. It has had one repair in that time - a wire broke off an electronic module. The module was still good, but it couldn't tie into the circuit to do its job. It gets an annual oil change when I do the coach engine, and new air & fuel filters every other year.
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Old 10-09-2011, 11:16 AM   #6
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When we bought the first moho, the big selling point was the diesel generator. "You will never wear it out" was the claim of the salesman.

When we went to trade in on a new moho the generator had about 300 hours. Now it was: "Oh, that is a lot of hours on a generator, they don't last much longer".

Yeh, right.

There was an article a few years back about a Onan that had 25,000+ hours on it and still running.
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Old 10-09-2011, 11:37 AM   #7
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My Onan manual calls for it to be run once per month for 1hour under load. This on gas unit.
My prior MH had an Onan as well and was not run according, very low hours for the years and miles and I never had a problem with it, ran like a champ.....
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Old 10-09-2011, 12:12 PM   #8
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I have my serviced by the book. It has 358 hours on it. That is 14,160 miles. The way it is figured is 358 hrs x 40 miles per hr. So with that said I think it is just now broke in good.
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Old 10-09-2011, 12:25 PM   #9
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An older unit with low hours is not a good thing. I would rather see one with higher hours...at least 50 to 100 hours per year of age.

My 2 cents worth.

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Old 10-11-2011, 12:02 PM   #10
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One has to wonder how all those "Standby" generators function when called upon in an emergency if an emergency never occurs?

I suspect they are not run for two hours every month like some recommend our motorhome generators need to be run.

Gas generators may experience some fuel varnishing and hence not start when needed. Diesel generators do not have that exposure.

Yet they seem to be reliable when needed.

I believe the primary reason to run the generator is to keep the electrical generation portion in tune.

If one never used the generator except for the recommended 2 hours per month under load, a 10 year old rig would only have 240 hours on it.
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Old 10-11-2011, 01:24 PM   #11
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My digital hour meter(Onan 8.0 diesel) quit at 1753 hours quite a long time ago. I'd guess it has at least twice that number and it runs perfectly. All maintenance is performed on a schedule and it has had exactly one "repair" in its lifetime. It quit charging its own battery and needed a new voltage regulator. Maybe one day I'll slap a new lcd in there and it will display the actual hours ....or, maybe the actual metering system is dead and I'll never know. I can't bring myself to really care, though. I'd bet a silver dime that the Cummins in the back and the Onan up front will be in fine working order long after the coach in between gives up the ghost.

As far as exercise; I give it at least two hours a month under load if the rig is not being used. If we are in it; the genny gets plenty of exercize running the AC down here in the heat belt.

At my office; I have a huge unit with a DD 8V92. Its onboard computer cranks that screamin' beast up every two weeks and runs the snot out of itself(I love the sound of a 2stroke diesel). I once asked a tech why the schedule was so narrow. He stated the primary reason was to "waste" fuel. You don't want 250 gallons of diesel in the tank just patiently waiting for a power outage. Use and replace with fresh on a regular schedule. Second reason was to excercise the generator head...no mention of the engine at all though there are some benefits for it, I'm sure. This is a critical use generator unlike the luxury units in our coaches. Probably some pretty good reasoning behind it.

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Old 10-11-2011, 02:06 PM   #12
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One has to wonder how all those "Standby" generators function when called upon in an emergency if an emergency never occurs?
Standby generators are wired of course through a buildings electrical system through an Automatic Transfer Switch, when the power goes off the generators start and they pick up the power load until city power is back.
Some generators have a timing unit system built into them to start and run them for a preset time per week.
My building generators are run one 1/2 hour every week with no load, they have to be started and stopped manually. This is done to assure that the genset will start, run the unit up on temp and to prevent what is known as wet stacking, cleans the moisture out.
In an emergency situation my generators have never failed, we do keep a yearly maintenace agreement on them and they are checked out quarterly.
The generators are run once a quarter at full load.

Hope this helps your understanding

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Old 10-11-2011, 02:36 PM   #13
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The owner's manual recommends running the generator monthly for two hours at 50% load, (24 hours a year).
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Old 10-11-2011, 05:36 PM   #14
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For what it's worth, the 15kw onan gen on my last rig had 8,480 hours on the clock when I traded it in last month and it still ran like a top. The gen head was rebuilt around 5k hours and I had to replace the starter twice. Otherwise just changed the oil and filters every 100 hours. That was powered by a 3 cylinder Cummins, a lot different from the 5-10kw units most of us have, but shows that generators can have a very long service life if properly maintained and is in line with what ga traveler said about the design life.

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