Can I run my Onan while plugged into shore power?

[mrad]

My new to me 5th wheel has an Onan 5500 generator. Can I exercise the Onan while being plugged into shore power at home?

[Grit_dog]

Good explanation wa8xym!
Regarding generator excercise, here’s a funny story. Just bought a 2017 camper with a built in Gen set. Orig owner used the camper once only. Generator has 8 hours on it, 2 of which he recalls and believes the dealer ran it during some warranty work in 2018? presumably.
He swore the generator was a LP generator. I could see the pics and knew it wasn’t. But somehow that thing is sucking 4 year old or older gasoline and actually runs! Lol I don’t condone it, more amazed than anything.
For normal situations, if you’re not running non ethanol or better fuel than that, just stabilize what left if it will be sitting for months. Personally I’d pump out all I could, and leave a couple gallons of quality or stabilized at a minimum in it during the off season.
No need to run it weekly or even monthly, depending on your fuel quality.
In the off season, I’d winterize it like any other small engine and fire it up again the next year.

[wolfe10]

Every time this discussion comes up, there are a range of answers from:

"Best Practices" to "What I get away with".

You have to decide on your basic philosophy concerning mechanical systems and follow it.

[edatlanta]

I always shut my shore power breaker off before a generator run as well as turn off all big load items such as electric water heater or a/c's.

I also run my generator the first of every month for 1 hour with a load. Works for me 11 years full timer.

[mr_andyj]

yep, Onan, not cummins onan, but same thing. Onan generator. Yes, do as they suggest, or dont do anything, I have not had issues...
Cummins does not make generators, they just bought Onan, and Cummins does not make the generator engines either unless something changed.

[phil-t]

mr_andyj wrote:
The main reason to run the gen is to move the awful ethanol gas through. For this you do not need a load to be placed on the generator head or the engine.
The other reason is to exercise the generator head, which you DO NOT need to do weekly or even monthly. It is good to do once a month or every two months, but depending on the gen it is not really that necessary.
On my old Onan I would let it sit all winter, and even a few years for one sitting, and all was fine. I could not tell any difference in either the gen or the engine.
If you will not use it for a while it is best to run the carb dry or at least use Stabil gas additive to keep the gas from turning to varnish in the carb. There are other methods of course...
As for transfer switches or circuit breakers or however your particular RV switches I, nor anyone, can say, that is particular to your setup.

Are these recommendations comming from Cummins Onan? I can't find those recommendations anywhere. Cummins suggests 30 days for a load exercise and it is to warm up the generator head and expell any moisture causing corrosion. Time would likely depend a lot on environment of storage. Gascondition is, again, greatly affected by storage conditions, mostly moisture.

[mr_andyj]

The main reason to run the gen is to move the awful ethanol gas through. For this you do not need a load to be placed on the generator head or the engine.
The other reason is to exercise the generator head, which you DO NOT need to do weekly or even monthly. It is good to do once a month or every two months, but depending on the gen it is not really that necessary.
On my old Onan I would let it sit all winter, and even a few years for one sitting, and all was fine. I could not tell any difference in either the gen or the engine.
If you will not use it for a while it is best to run the carb dry or at least use Stabil gas additive to keep the gas from turning to varnish in the carb. There are other methods of course...
As for transfer switches or circuit breakers or however your particular RV switches I, nor anyone, can say, that is particular to your setup.
My fav setup is to put a Y in the fuel supply so I can draw from the motorhome tank or draw from an aux tank which I have 100% gas so the gen is stored wtih 100% gas (not toxic ethanol). The gas will last longer than the alcohol and will last even longer with Stabil. Better yet to physically drain the carb for long storage.

[CA_Traveler]

Per above 2 active AC sources have the potential for failure problems.

I always power down all high draw appliances before switching power sources which ATS switch arcing and contact pitting to a minimum.

[way2roll]

Seems like this topic comes up monthly. Several schools of thought. I wouldn't do it. Sure the ATS should protect everything but for the 15 seconds it takes to unplug and start the genset, why wouldn't you unplug to mitigate the risk - even if it's a low risk? IF the ATS should fail it's a VERY expensive mistake. There is also differing opinions on having to exercise your genset at all. I do. Most do, but some don't and never have issues. It's also not cut and dry which gets priority, gen or shore power. This can depend on the rig, year, a bunch of factors.

In Short, yes you can. The questions; should you and will it have any benefit? The easiest solution is to unplug before starting the gen and all those questions/concerns become moot.

[wa8yxm]

Actually the generator has priority. But
Before you start the ONAN. in fact 3 minutes before you start the Onan, turn off shore power OR turn off main breaker inside RV

If you use option 2 (Good if it's raining) then start the generator and wait for the transfer switch to CLUNK before you turn breaker back on (or one minute from Varoom)

Again turn off main breaker befoer shutting down Generator and leave off for 3 full minutes or wait 3 minutes after shutdon to restore shore power .

WHY

Some hardware in the RV takes 3 minutes to fully shut down so it can do a normal restart instead of a much harder. damaging resteart.. primarlly air conditioners.

Reason 2: Hot switching (Starting/stopping Genny with shore power on and loads present) Can destroy the transfer switch.

[valhalla360]

Reisender wrote:
Yes. It will default to generator power if the generator is running. That is the job of the transfer switch.

This assumes everything is wired up and working properly.

It takes 5 seconds to unplug and there is no doubt you won't be back feeding.

Unplug before exercising the generator.

[rlw999]

mrad wrote:
Thanks. If I am starting it weekly to keep gas running through it, is it best to unplug it? Can I start it while plugged in then unplug it?

Unless you have a particular concern about burning the gas in it, doing it every week is probably overkill. Exercising less frequently may make it less onerous to unplug or turn off the shore power each time.

Onan themselves recommend a 4 week schedule:

To prevent such problems, it is recommended to run gasoline generators at a minimum of 50 percent capacity (2000-watts, or one air conditioner for a 4000-watt set) for two hours once every four weeks. This is necessary to help keep moving parts lubricated, expel moisture and control fuel varnishing in the carburetor. A long two-hour exercise period is preferable to several short periods

[Lantley]

One of the first things the dealer told me was to unplug before starting genset. Technically the transfer switch should allow you to remain plugged in however, the transfer switch is a mechanical device that can an does fail.
There is simply no reason to remain plugged in, no reason to take a chance.
Unplugging is easy enough to do. Unplugging makes it 100% foolproof vs. hoping everything works as designed.

[Reisender]

Yes. It will default to generator power if the generator is running. That is the job of the transfer switch.

[phil-t]

I have run my 5500 Onan while plugged in. It switches to generator power - I did it simply to exercise the genny while I was campground hosting for 3 months. I think I did have an issue with the genny hour meter though. I think it continued to run after shutting down the generator - somehow being energized from the shore power. My hour meter went from 4XX hours to over 2000 this winter and I never used it except to exercise it monthly while plugged in.