Shore power vs generator power

Topic: Shore power vs generator power (Read 772 times) previous topic - next topic

Shore power vs generator power

March 07, 2022, 11:35:32 am

I am currently plugged into shore power. I have the intention to exercise the generator but am curious which has priority? When I start the generator does the power auto switch to the gen and how do I tell? Is there an indicator when viewing the power watch?

Re: Shore power vs generator power

Reply #1 – March 07, 2022, 11:40:18 am

On our 2003 U320, generator takes priority. Start the gen and listen by the transfer switch. You should hear it "clunk".

Re: Shore power vs generator power

Reply #2 – March 07, 2022, 11:48:11 am

While your question DOES have an answer (depends on which source was set up as priority in the ATS), following "best practices", not sure it matters.

To prolong the life of the ATS, you do not want to change sources under load as that arcs the points in the ATS. And if going from a load on shore power to load on generator, the effect on the generator would be like starting you car and immediately going to 70 MPH on a cold engine. Can it be done-- sure. Is it "best practices"-- no.

So, turn of loads (particularly high loads like roof airs, water heater, etc). Turn off shore power breaker and unplug. Start generator and let it warm up for a few minutes. Add loads back in. Run at 1/2+ load to exercise generator.

Then turn off loads, let generator cool down under no/minimal load for a few minutes, shut down generator. Plug back in and turn on shore power breaker. Turn loads back on.

Actually takes longer to write than to do it.

Re: Shore power vs generator power

Reply #3 – March 07, 2022, 11:52:10 am

My coach shore power has priority.

Re: Shore power vs generator power

Reply #4 – March 07, 2022, 11:58:06 am

Quote from: dicksop – March 07, 2022, 11:35:32 am

I am currently plugged into shore power. I have the intention to exercise the generator but am curious which has priority?

Why do you want to exercise the generator?

Re: Shore power vs generator power

Reply #5 – March 07, 2022, 12:11:25 pm

So this was my learning curve. I accidentally started generator while connected to external power and as soon as it engaged it popped one of the breakers. It was in the middle of summer and took a while to sort out. . I follow the technique Brett recommends to this day with without problems. I thought it was caused by phase being out of sync, but no longer a issue.
Scott

Re: Shore power vs generator power

Reply #6 – March 07, 2022, 12:25:59 pm

I like having shore power as the priority as if the generator is running I would never plug
into shore power but being plugged in I have started the generator without thinking and
and as Brett said I unload the system before shutting off the generator or unplugging the
coach.

Re: Shore power vs generator power

Reply #7 – March 07, 2022, 12:45:03 pm

Quote from: dicksop – March 07, 2022, 11:35:32 am

I am currently plugged into shore power. I have the intention to exercise the generator but am curious which has priority? When I start the generator does the power auto switch to the gen and how do I tell? Is there an indicator when viewing the power watch?

The idea behind the automatic transfer switch is to prevent you from trying to power the grid with your generator and surprising some lineman who knew, that one moment before, the power line was cold.

Re: Shore power vs generator power

Reply #8 – March 07, 2022, 01:18:44 pm

Wolfe10
The only loads I have on the shore power at the moment are 4 small Lasko heaters and of course the magnum2812

Re: Shore power vs generator power

Reply #9 – March 07, 2022, 01:25:01 pm

DJ
I exercise the gen every month on recommendation from this forum,and to keep the fuel from maybe gelling as the temp here in Canada are consistently in the minus temps Fahrenheit. I think it probably is good for the seals as well. I start my AH as well to keep the nozzle from clogging so it makes sense to do the both of them monthly at the same time

Re: Shore power vs generator power

Reply #10 – March 07, 2022, 03:38:08 pm

Quote from: D.J. Osborn – March 07, 2022, 11:58:06 am

Why do you want to exercise the generator?

Best practice to keep it fully functional. I think most of us run once a month. We also run AquaHot at least once a month.

Re: Shore power vs generator power

Reply #11 – March 07, 2022, 04:01:23 pm

Just curious about your intentions and plans. While I agree that regular exercise is good I also recognize that it can do more harm than good if done incorrectly. I think it's better not to exercise a system unless it can reach full temperature and then be operated for perhaps an hour. For a generator I believe that means at least one-half load and for a motorhome I believe that means actually being driven.

Re: Shore power vs generator power

Reply #12 – March 07, 2022, 04:23:38 pm

Quote from: D.J. Osborn – March 07, 2022, 04:01:23 pm

Just curious about your intentions and plans. While I agree that regular exercise is good I also recognize that it can do more harm than good if done incorrectly. I think it's better not to exercise a system unless it can reach full temperature and then be operated for perhaps an hour. For a generator I believe that means at least one-half load and for a motorhome I believe that means actually being driven.

Correct on all counts.

The good news is that irrespective of ambient temperature, you CAN load a generator to 50+% of capacity. May take block heater, several space heaters, battery charger, water heater electric element if equipped, etc. In warmer climes, have run one roof A/C on cool and one on heat. Whatever it takes.

Easy to plan out amp load before even going to the coach.

Re: Shore power vs generator power

Reply #13 – March 07, 2022, 04:29:02 pm

In my 2014 IH45 and maybe the other newer coaches.

I shut my invertors off when I am parked on shore power. Had 2 events where shore power went out and since was not using AC we did not know the power pedestal breaker had tripped and we were running on invertor. Found out when buzzer started going off to inform us the battery was getting low.

In my coach if the inverter is not turned on, and or still connected to shore power before starting the generator the transfer switch will not switch over to generator. Don't know why but learned I have to make sure inverter is turned on and shore power is unplugged before starting generator.

Re: Shore power vs generator power

Reply #14 – March 07, 2022, 05:45:32 pm

As Brett stated, always turn off all major loads whenever switching from Shore Power to Generator or the other way around. I learned this the hard way on one of our first trips a few years ago. We had the generator running while driving with both AC's running full blast as it was over 100 degrees outside.
We arrived at the campground, and all they had was 30 amp service. I wasn't thinking and just shut off the generator under full load, Mistake #1, Then with everything still on, plugged into the 30 amp service, Mistake #2. Both AC's started (or tried), and it fried the circuit board on the front AC, and rendered the rear AC useless. Having both AC's on 30 amp service, Mistake #3.
Made for a miserably hot night in the Coach.
Couldn't get the circuit board for 3 days. It was so hot, went to WalMart and got a portable freestanding AC, vented it out the window and "survived".
Morale of the story......Follow Brett's guidelines to the letter. It will save you a lot of grief!

Re: Shore power vs generator power

Reply #15 – March 07, 2022, 10:43:57 pm

Peter,

Back to your original question about which has priority, as Brett said, it depends. Some of our coaches are set up with generator as priority and some shore power priority. On my coach the shore power has priority over the generator, other peoples' coaches are set up the other way. If I am plugged into shore power and start the generator, the generator engine runs with no load on it.

I had never thought about which way my coach was set up or what the ramifications were. I learned an uncomfortable lesson one Montana weekend at a Cummins repair shop. I was having some work done which spanned a weekend. Since we live full time in the coach we could not stay in it locked up inside the shop so we moved it just outside the door. They graciously allowed me to plug in to keep the batteries charged but my power cord would only reach a 15 amp outlet. No big deal I thought. Well, Saturday and Sunday turned out to be real scorchers. My beautiful 10 KW generator would not over power the 15 amp shore service so no air conditioning. I will not make that mistake again (I hope).

Richard

Re: Shore power vs generator power

Reply #16 – March 08, 2022, 07:07:00 am

Quote from: Jan & Richard – March 07, 2022, 10:43:57 pm

They graciously allowed me to plug in to keep the batteries charged but my power cord would only reach a 15 amp outlet. No big deal I thought. Well, Saturday and Sunday turned out to be real scorchers. My beautiful 10 KW generator would not over power the 15 amp shore service so no air conditioning. I will not make that mistake again (I hope).

Why didn't you just disconnect the shore-power cord and operate on the generator?

Re: Shore power vs generator power

Reply #17 – March 08, 2022, 08:27:28 am

Quote from: Jan & Richard – March 07, 2022, 10:43:57 pm

My beautiful 10 KW generator would not over power the 15 amp shore service so no air conditioning. I will not make that mistake again (I hope).
Richard

If all is as it should be, the automatic transfer switch, is at it's heart, a double pole double throw relay with the shore power connected to the normally closed contacts and the generator to the normally open. This is assuming that the majority use will be shore power. When you start your generator, the electricity from the generator powers the coil in the relay, switching the state of the contacts and connecting your coach to the generators while making certain that the shore power is disconnected.

Maybe you needed to re-set the circuit breakers on your generator?

Re: Shore power vs generator power

Reply #18 – March 08, 2022, 10:38:24 am

Quote from: D.J. Osborn – March 08, 2022, 07:07:00 am

Why didn't you just disconnect the shore-power cord and operate on the generator?

The cord was plugged into an outlet inside the shop and the garage door was closed and locked over the cord. I did not figure that my inconvenience was enough of a reason to call the emergency contact number on the front door. So I just lived with it. But I did learn something about my coach that I had not known before.

Richard

Re: Shore power vs generator power

Reply #19 – March 08, 2022, 10:41:34 am

Quote from: Jan & Richard – March 08, 2022, 10:38:24 am

The cord was plugged into an outlet inside the shop and the garage door was closed and locked over the cord. I did not figure that my inconvenience was enough of a reason to call the emergency contact number on the front door. So I just lived with it. But I did learn something about my coach that I had not known before.

Wasn't there some way to disconnect the cord at your coach—or is it permanently hard-wired?

Re: Shore power vs generator power

Reply #20 – March 08, 2022, 10:52:20 am

99's are permanently attached to a cord reel.

Re: Shore power vs generator power

Reply #21 – March 08, 2022, 11:09:49 am

Same with my 98 U320. Attached

Re: Shore power vs generator power

Reply #22 – March 08, 2022, 11:11:30 am

Quote from: craneman – March 08, 2022, 10:52:20 am

99's are permanently attached to a cord reel.

If that's the case then I think a disconnect/circuit breaker between the cord reel and the transfer switch would be an excellent addition!

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