generator priority?

[Wiley1]

Today I started my generator while I was connected to shore power. After a few seconds, I heard beeps from my inverter/charger. This tells me that my ATS (automatic transfer switch) is wired for generator priority. Why?

I would like the generator to be ignored when shore power is available.

Is there any reason that I shouldn't re-wire the ATS so it gives priority to shore power? What am I not considering?

 

[psdtime]

My theory, say you are plugged into shore power and the power supply is insufficient for the devises you plan to run, you could start your generator and it would power it. For example, you are plugged into a 30amp plug at a campsite, but you have a 50amp RV and you are concerned about not having enough juice to power her hairdryer, the coffee maker and microwave when you are making breakfast.

 

[Lt Keefer]

My theory, say you are plugged into shore power and the power supply is insufficient for the devises you plan to run, you could start your generator and it would power it. For example, you are plugged into a 30amp plug at a campsite, but you have a 50amp RV and you are concerned about not having enough juice to power her hairdryer, the coffee maker and microwave when you are making breakfast.

Bingo.

 

[Wiley1]

My theory, say you are plugged into shore power and the power supply is insufficient for the devises you plan to run, you could start your generator and it would power it. For example, you are plugged into a 30amp plug at a campsite, but you have a 50amp RV and you are concerned about not having enough juice to power her hairdryer, the coffee maker and microwave when you are making breakfast.

Sure, but you could also unplug the shore power.
My rig is 30A. If the shore power is really dirty, that's exactly what I would do.

 

[dkoldman]

Today I started my generator while I was connected to shore power. After a few seconds, I heard beeps from my inverter/charger. This tells me that my ATS (automatic transfer switch) is wired for generator priority. Why?

I would like the generator to be ignored when shore power is available.

Is there any reason that I shouldn't re-wire the ATS so it gives priority to shore power? What am I not considering?

I agree with all of the above about the why, but I will answer your question in red.

Yes, you can wire your coach so the generator will be ignored if Shorepower is On. But you require a AGS system that is capable to do so.

I had my coach wired this way when it was brand new. It was actually my 1st mod.

It works like this...

I have Onan EC-30 AGS system
I had a 24vdc transformer put on the inbound SP line IN FRONT of ATS. The transformer send signal direct to the EC-30 so the EC-30 always knows if SP is on or off. It does bot care if it 50amp, 30amps or 20amps.
If your have your AGS configured properly an in the Auto or Quiet mode, it will not allow you to start the generator if SP exist. If you want to run the genny, you must unplug or simple take the AGS out of AUTO or Quiet Time mode.

The other thing that is neat and I admit I do for play, but say you pull up to park RV, set levelers etc. My engine continues to run as well as the ACs. When I plug up SP it will automatically shut the genny off

 

[16ACE27]

Today I started my generator while I was connected to shore power. After a few seconds, I heard beeps from my inverter/charger. This tells me that my ATS (automatic transfer switch) is wired for generator priority. Why?

I would like the generator to be ignored when shore power is available.

Is there any reason that I shouldn't re-wire the ATS so it gives priority to shore power? What am I not considering?

The real question is:

Why are you running the generator if you don't want it to power the RV?

 

[Wiley1]

Yes, you can wire your coach so the generator will be ignored if Shorepower is On. But you require a AGS system that is capable to do so.

I'm sure your AGS is wonderful, but I don't see how it has anything to do with my situation or the question that I asked.

An 30A RV ATS is a dumb switch, capable of only one decision. When power is available on port A, it is passed through to the output. When no power is available on port A, whatever power is (or isn't) available on port B is passed through to the output. Simple Whatever is connected to port A becomes the priority.

The output of the ATS (120vac, either from the genny or the shore cable) connects to the input of my 3000kW inverter/charger. That device really doesn't know or care where the power came from as long as it is clean.

I am proposing that I swap cable A with cable B so that shore-power is selected by default. I am having difficulty imagining any situation where generator power would be preferred over shore-power.

I came here only to ask if anyone sees any flaw in my plan.

 

[16ACE27]

I'm sure your AGS is wonderful, but I don't see how it has anything to do with my situation or the question that I asked.

An 30A RV ATS is a dumb switch, capable of only one decision. When power is available on port A, it is passed through to the output. When no power is available on port A, whatever power is (or isn't) available on port B is passed through to the output. Simple Whatever is connected to port A becomes the priority.

The output of the ATS (120vac, either from the genny or the shore cable) connects to the input of my 3000kW inverter/charger. That device really doesn't know or care where the power came from as long as it is clean.

I am proposing that I swap cable A with cable B so that shore-power is selected by default. I am having difficulty imagining any situation where generator power would be preferred over shore-power.

I came here only to ask if anyone sees any flaw in my plan.

Turn off the generator - mission accomplished.

Again - why run the generator if you don't want power from it?

What am I missing??

 

[Wiley1]

The real question is:
Why are you running the generator if you don't want it to power the RV?

How is that "the real question"?
There's always somebody who wants to change the question to something else. But, I'm happy to answer.

Today I just wanted to test and exercise the generator. That would be reason enough.

For the first five minutes, the generator oscillated fast/slow/fast/slow. That drove my inverter/charger nuts, and it switched over to battery power and back several times. In that situation, I would like the wonky generator power to be ignored.

The real real question is:
Is there any reason that shore-power should not be the priority?

 

[16ACE27]

How is that "the real question"?
There's always somebody who wants to change the question to something else. But, I'm happy to answer.

Today I just wanted to test and exercise the generator. That would be reason enough.

For the first five minutes, the generator oscillated fast/slow/fast/slow. That drove my inverter/charger nuts, and it switched over to battery power and back several times. In that situation, I would like the wonky generator power to be ignored.

The real real question is:
Is there any reason that shore-power should not be the priority?

The same reason your wonky generator power shouldn't be sent to the load buss. If you have generator running problems to iron out and don't want the generator loaded, open the generator output breaker.

To exercise the generator it needs to be loaded at 1/2 capacity for at least an hour.

 

[EA37TS]

If I recall correctly a few years ago at the FMCA Convention in Wyoming, during an Onan generator seminar, an Inan Engineer mentioned why an RV ATS is wired to give priority to the generator and why shore power should be disconnected before starting the generator.

Contact Onan and ask them if your idea will have any impact on the generator.

 

[dkoldman]

I'm sure your AGS is wonderful, but I don't see how it has anything to do with my situation or the question that I asked.

An 30A RV ATS is a dumb switch, capable of only one decision. When power is available on port A, it is passed through to the output. When no power is available on port A, whatever power is (or isn't) available on port B is passed through to the output. Simple Whatever is connected to port A becomes the priority.

The output of the ATS (120vac, either from the genny or the shore cable) connects to the input of my 3000kW inverter/charger. That device really doesn't know or care where the power came from as long as it is clean.

I am proposing that I swap cable A with cable B so that shore-power is selected by default. I am having difficulty imagining any situation where generator power would be preferred over shore-power.

I came here only to ask if anyone sees any flaw in my plan.

The answer to your question in post above is below, and is direct to your 1st post question.

YOU STATED: I would like the generator to be ignored when shore power is available.

Is there any reason that I shouldn't re-wire the ATS so it gives priority to shore power? What am I not considering?​

My post agreed by saying I too like having my generator IGNORED when shore power is available.

I then went a step further and show you exactly how I do it.

You also asked if you shouldn't rewire, my method did involve a rewire.

Then you also asked what you were not considering, I told you of an option to use an AGS as it will do that for you automatically.


But with that said, it obvious that is not want you wanted to hear/read. Of course I would have no way of knowing that, I was just answering your questions.

 

[Lt Keefer]

There are a number of threads on this issue on IRV2. Maybe the answer is there as I didn't read them all. I like my genny to be dominant but then I have a 50 amp coach that sometimes gets 30 amp shore power.

 

[Wiley1]

The same reason your wonky generator power shouldn't be sent to the load buss. If you have generator running problems to iron out and don't want the generator loaded, open the generator output breaker.

To exercise the generator it needs to be loaded at 1/2 capacity for at least an hour.

That is useful information but, again, not relevant to my question.

1. My generator doesn't perform well for the first five minutes. Until it warms up, I don't want my inverter/charger to be exposed to that unstable waveform.
2. I do not have a "generator output breaker".
3. Once the generator has warmed up and the output is stable, if I want to load it, all I have to do is unplug the shore power cable.

So far, nobody has mentioned a good reason not to make shore power the priority.

 

[Wiley1]

There are a number of threads on this issue on IRV2. Maybe the answer is there as I didn't read them all.

Thank you for that. I will definitely go over there and read that thread. Perhaps those guys are better at staying on topic.

 

[MCP-THOR]

Thank you for that. I will definitely go over there and read that thread. Perhaps those guys are better at staying on topic.

I don’t want to risk pissing anyone off by not giving a precise answer, but have you contacted Southwiire or whoever your ATS mfr is? They can answer your first question of why is their product and wiring instructions set up that way. Perhaps it is not a technical issue and it’s only an industry standard because most are used in that manner.

If it is not a technical requirement then give it a try and let us know how it goes. That’s my nonprecise answer to your second question.

 

[Beau388]

The ATS primary function is to prevent the unplugged shore line from becoming hot when the generator is started. In the old days (I had a 1968 class A coach) shore lines were connected directly to the coach and we had to manually transfer the coach's input from the shore line receptacle to the generator receptacle. The receptacles were in the closet beside the 120 volt CB box.


I don't know about all coaches but my ATS (PPS) has a generator delay that is user settable from 20 seconds to 120 seconds and the EMS had an additional delay of 15 seconds and 136 seconds.

 

[Lt Keefer]

The ATS primary function is to prevent the unplugged shore line from becoming hot when the generator is started. In the old days (I had a 1968 class A coach) shore lines were connected directly to the coach and we had to manually transfer the coach's input from the shore line receptacle to the generator receptacle. The receptacles were in the closet beside the 120 volt CB box.


I don't know about all coaches but my ATS (PPS) has a generator delay that is user settable from 20 seconds to 120 seconds and the EMS had an additional delay of 15 seconds and 136 seconds.

That makes sense. It may be possible, however unlikely, that a running generator could put power to the shore power cable. In my last coach, the generator only powered a plug in the shore power cable storage compartment.

 

[RACarvalho1]

Is there any reason that I shouldn't re-wire the ATS so it gives priority to shore power? What am I not considering?

Besides the reason given so far, I really like Generator priority:
I want to have the generator on when I move the slides before departing and that also means the generator will be powering the ACs....
So after I put the slides in and retract the jacks, all while the ACs are on, I don't need to turn off the ACs before I disconnect the power cord, I just go outside, disconnect the power cord (the last step before departing), store it and go... all while the AC is running...

 

[16ACE27]

That is useful information but, again, not relevant to my question.

1. My generator doesn't perform well for the first five minutes. Until it warms up, I don't want my inverter/charger to be exposed to that unstable waveform.
2. I do not have a "generator output breaker".
3. Once the generator has warmed up and the output is stable, if I want to load it, all I have to do is unplug the shore power cable.

So far, nobody has mentioned a good reason not to make shore power the priority.

Just because you are ignorant of the generator output breaker does not mean it does not exist - it does.

Why would your Onan generator be different than every other one made and installed in an RV?