Running the generator while on shore power?

Magumba · 01-07-2010, 02:46 PM

We have a 2003 Itasca Suncruiser 38G with an Onan 5500 watt generator. We live in the camper full time and it's cold outside. I had a habit in our 95 Itasca to run the generator weekly when dumping the black tank to keep the generator happy and ready to start if needed. I ran the generator under no load since I didn't unhook the shore line and plug into the generator outlet. Also we took short trips often and I ran the generator under load every change I got. We also lost power more times that I can count.

Our 2003 has an automatic transfer switch. We were told on the walk through not to run the generator with the shore line plugged in since that can mess the Intelapower system up.

Does running the generator while plugged into shore power create a problem for the electical system?

If so I've been thinking of turning off the generator output circuit breakers and then running the generator. Is that a good solution to the problem?

Thanks, stay warm.

Always-RVing · 01-07-2010, 02:58 PM

There are electronic switch over circuits to go from generator to shore power and back. I don't like running both at the same time, but I'm not sure if it really hurts anything. I shut off all high power consummers b4 going on generator or back. The generator's breaker will trip easily if coming online with a heavy load so I switch-over and come up gracefully.

Onan's operator book said something about running the generator once/month for 4 hrs under a 50 % load. The generator needs the load for the monthly run.

JMonroe · 01-07-2010, 03:32 PM

I started up the gen set, same one you have, one time forgetting it was plugged into shore power (where I store it). The system didn't like it. No real damage, it tripped a couple breakers, including one on the gen set.

namwob · 01-07-2010, 04:19 PM

Okay to keep shore power while running gen set but all loads should be turned off during switch over.

KIX · 01-07-2010, 07:18 PM

I think most auto transfer switches default to genset. So if you're connected to shore power and start the genset the transfer switch will transfer to genset supply until genset is shut down.

dengraham · 01-07-2010, 08:16 PM

I understand, in theory, there is no problem to start your generator and put loads on it to exercise it; even when plugged up to shore power. The transfer switch will transfer the power source from shore power to the generator and therefore the shore power is no longer coming into the coach. All generators should not be started and just run at an idle; that is bad for any engine. When you turn off the generator the transfer switch drops the generator source and picks up the shore power. (This sudden jump back can be hard on some circuits depending on what is and can confuse the energy management system but normally it will recover. To avoid the confusion, I personaly just disconnect the shore power before starting the generator; give it a load and when I am done, shut off the generator and plug the shore power back in. I'm like a manual transfer switch but therfore don't confuse the EMS. Make sense? This help?

MrTransistor · 01-08-2010, 02:31 AM

Hi Magunba,

If you have a 30 Amp. power cord, I can’t help with suggestions.

If you have a 50 Amp. power cord, then I suggest you check these threads:

http://www.irv2.com/forums/f101/ques...fney-8631.html

http://www.irv2.com/forums/f101/tran...ked-47042.html

http://www.irv2.com/forums/f101/gene...ure-45009.html

Magumba · 01-08-2010, 08:15 PM

Thanks for the help I'll keep the 1/2 load reminder in my bag of tricks.

mrschwarz · 01-09-2010, 09:55 AM

I have 50 amps and rewired my 01 Suncruiser from 30 to 50 amps. It's never a good idea to switch from shore to gen (or vice versa) with a heavy electrical load. You will get a lot of arcing of the transfer switch contacts which can lead to failure. The transfer switch is a big relay. When the coils are not energized (in all three of my motorhomes), the electrical system is connected to shore power.

When the generator is started, the transfer switch coils are energized and the electrical system is connected to the generator. At that time, the shore power cord is isolated from the electrical system. I don't think it matters if it's plugged in or not. The key is to shut off everything with an on-off switch (like TVs, AC, etc.).

When I get ready to leave home in the summer, I shut down electrical devices, start the generator while still connected to shore power, restart the AC, and then disconnect the shore power, in that order. I have never had a problem caused by that.

Roadking · 01-14-2010, 09:03 PM

I concur totally with Mr Schwarz. There is no need to disconnect the shore power, however, don't start the generate if you are pulling a heavy load on the shore power, or if you have any devices operating that are sensitive to power surges. I turn off the AC, the Xantrex charger, the digitial TVs, and I unplug the lap top computers. The transfer switch is a mechanical switch (more correctly a relay) and it will switch from shore to gen when generator power is detected. In my rig this causes the Xantrex to shut down all circuits on the 30 amp sub panel which supplies power to the duplex outlets in the coach...including the TV and Microwave. The Xantrex then goes thru its cycle and about 30 seconds later power is re-established to the duplex outlets. Not exactly an instatanious power surge, but still a surge. The circuits that are not on the sub panel, like the washer/dryer, AC compressors, and water heater loose power and get power reapplied instantly after the mechanical switch and thus, these circuits get a more significant surge.