Rear AC

[Miramar Owner]

I fire up the generator and run it for about 45 minutes, under load, every 2 weeks while in storage for the winter. I usually run a couple space heaters to add the load but last week it was over 70 degrees so I turned the AC instead. The front AC worked as normal but the back AC wouldn't do anything. It acted like it didn't receive power from the generator at all...wouldn't even run the fan with the air off. I even turned off the front AC and tried to run the rear only...still nothing. I know I have ran the rear AC off the generator at least for 5 days when I dry camped last summer. Any thoughts as to where I should look. It's probably another month before I can try it on electric, but I don't think it is a problem with the AC itself. It is a 2016 Miramar 34.4.

[Chance]

Have you checked breaker for rear A/C?

If you haven't already, I'd start there. With two A/Cs it's normal for them to be on different breakers.

I'm assuming your rear A/C is from factory, and that you have larger 5,500-Watt generator that can run both simultaneously.

[Miramar Owner]

Yes it is a 5500 watt generator. I did look at the breaker box and didn't see any tripped. Maybe I should have tried resetting the breaker? I am curious if there is any where else, from the generator, the power could be tripped....like the transfer switch.

[Chance]

Originally Posted by Miramar Owner

Yes it is a 5500 watt generator. I did look at the breaker box and didn't see any tripped. Maybe I should have tried resetting the breaker? I am curious if there is any where else, from the generator, the power could be tripped....like the transfer switch.

If breaker isn't tripped, the above would be my next suggestion. I'd check to see if other electrical loads on rear-A/C side of panel are getting power.

With 50-Amp service, approximately half of the electrical loads and breakers are on one leg, and the other half on the opposite leg. Each of these legs are +/- 115-Volts to ground, but opposite in phase, so that there is 230-Volts from one leg to the other.

As I understand it, the generator is different from shore power because it only produces 115-Volts and with only one leg. This means that in order for all coach electrical to get power from generator, both legs in electrical panel have to be connected together.

How this is done on your RV I'm not sure, but would troubleshoot by first determining if it's only the rear A/C that may not be getting power, or if roughly half of the motorhome is also not getting power. I normally use process of elimination to narrow possible problem areas.

[Miramar Owner]

Chance, thanks for your responses to my rear AC problem. I have solved the problem, but first let me tell you of my "help" from Thor. I called customer service for support and talked to a young lady there. Upon further investigating I found 2 plugins that also didn't work. She told me it was battery issue and I needed to run the generator for at least an hour. I tried that and of course it didn't work...so I called back. I talked to a guy that told me the battery had nothing to do with it. He said most likely a wire had rubbed of it's insulation and shorted out. I said, "does it make sense to you that it has worked fine all winter until now and while parked it rubbed off the insulation." He then yelled, "YES! Look I am sitting behind a computer screen trying to solve YOUR problem and THAT is what I think it is."
At that point I hung up and got out the manual again. I finally discovered there are 2 breaker switches on the generator itself. One of them was thrown. I had purchased an additional space heater to heat it up while running the generator during the winter and they were both on the same circuit. I later moved one to the back. Anyway, other than the frustrating call to Thor, the problem is solved.

[Metalman]

Chance-As I understand it, the generator is different from shore power because it only produces 115-Volts and with only one leg. This means that in order for all coach electrical to get power from generator, both legs in electrical panel have to be connected together.

Is it possible that the generator has two 120 V outputs (two circuit breakers)? Could they each be referenced to the same ground, so there is 0 volts between the two outputs and 120 volts between the neutral and each output (hot). But that would mean that the neutral would be carrying double the amperage when both AC units are running.

[Chance]

Originally Posted by Metalman

Chance-As I understand it, the generator is different from shore power because it only produces 115-Volts and with only one leg. This means that in order for all coach electrical to get power from generator, both legs in electrical panel have to be connected together.

Is it possible that the generator has two 120 V outputs (two circuit breakers)? Could they each be referenced to the same ground, so there is 0 volts between the two outputs and 120 volts between the neutral and each output (hot). But that would mean that the neutral would be carrying double the amperage when both AC units are running.

It'd be great if we had a wiring schematic to see exactly why there are two breakers at generator, and how/why the front A/C was working while the rear one wouldn't. I suppose each breaker could protect a separate leg of the 50-Amp service, but without more information we are just guessing.

As to excessive amperage when both A/Cs are running, I don't think that would necessarily be a problem because the motorhomes wiring is sized for 50 Amps, and a 5,500-Watt generator is rated just below that. Therefore, it seems on the surface that even if all generator power went through one leg, and the neutral, it should still be within the wiring's current capacity. Again, without a drawing this is just a lot of educated guessing.

[Hooligan2]

The Onan 5500 generator has 2 30 amp circuit breakers. Each supplies power for one leg of the 50 amp service. (50 amp service provides 50 amps to each leg.)

[Metalman]

Hooligan2, Thanks for the schematic. When both generators are running, all current is passing through the neutral wire on the shore power cable, so I suspect the same happens when the generator is supplying power.

[wredman]

Originally Posted by Hooligan2

The Onan 5500 generator has 2 30 amp circuit breakers. Each supplies power for one leg of the 50 amp service. (50 amp service provides 50 amps to each leg.)

good info, is the generator capable of supplying 29.9amp on both circuits at the same time? Or will there be some degradation at the usage end?

When connected to a 30amp service (via simple wire converter) both of the 50a legs are supplied buy the single 30amp leg, so inside the coach, 16 on one and 16 on the other would trip the outside supply breaker. Is this correct interpretation?

[gmc]

Originally Posted by wredman

good info, is the generator capable of supplying 29.9amp on both circuits at the same time? Or will there be some degradation at the usage end?

When connected to a 30amp service (via simple wire converter) both of the 50a legs are supplied buy the single 30amp leg, so inside the coach, 16 on one and 16 on the other would trip the outside supply breaker. Is this correct interpretation?

A 5500 Watt generator is capable of sustaining a 50amp load (w/v=a so 5500/110=50). There is typically a short term surge capability. It likely has two 30amp breakers - so each leg is limited to 30amps - with total of 50.
A sustained 60amp (or 58.8) will trip out something - and would be an unlikely scenario as well.

When connected to 30amp service via 50-30 adapter - you have 30 amps to share across both legs in any proportion (limited by downstream breakers of course). It can be 29 and 0... 15 and 14... but crossing 30 total will trip the pedestal main (and more likely melt the adapter before that... they aren't that good). You need to use care with what you draw through this setup. Typically no more than one A/C unit - water heater should be on propane.
Remember you are limited to less than 1/3 the normal available power in this mode... '50amp' service on properly wired pedestal provides a full 50 amps to EACH leg - for 100amp total.

[Metalman]

Greg - Remember you are limited to less than 1/3 the normal available power in this mode... '50amp' service on properly wired pedestal provides a full 50 amps to EACH leg - for 100amp total.

So in that case wouldn't the neutral be carrying 100 amps?

[Hooligan2]

The neutral leg would only carry the difference in current in each leg.. If one leg is 50 amp and the other is 20, the neutral carries the 30 amp difference. Good explanation here. RV Wiring
Probably should have used this diagram instead of just the 50 amp. The 30 amp dogbone has a jumper between the 2 hot legs. That link in the photo is still good.

And of course the current actually provided depends on the actual load. 50 amps available on each leg but only 10 amps current flow if just the nightstand light is on.

Thanx wredman-- I was getting wrapped around the axle at one point.

[wredman]

the two circuits are out of phase with each other.

[Metalman]

Wedman,
Since we are dealing with a single phase power source, please explain how they can be out of phase from one another.

[Hooligan2]

RV Tech Library - Shore Power Connections

If you plug an RV into a 50 amp service you have an X and a Y phase. Each phase is capable of 50 amps therefore you have a total power capacity of 12,000 watts from these two poles (50 amps x 2 poles x 120 volts = 6,000 watts each). A 50 amp shore power receptacle contains 4 wires - the X phase, Y phase, neutral, and a ground lug. The X phase feeds one side of your breaker panel while the Y phase feeds the other half. Remember between the Red and the black wire is 240 volts 2 phase. But we split it and either wire only carries 120volts to ground single phase.


The long version is here: http://www.myrv.us/electric/Pg/50amp_Service.htm

[JamieGeek]

Note that the 5500 generator is only 1 phase, though. So when running on the genny both of the 50a lines are running the same phase. (See the genny specs here).

Thus the only time the 50a circuits will be out of phase will be when plugged into a 50a plug at a campground.

Using the genny, or a 30a dogbone they will be in phase.

[gmc]

And for an RV WITHOUT true 220/250 appliances - we don't care whether they are in phase or not...

Some RV's have true 220/250V appliances and MUST have the 2 phase power to run them... The 30A dogbone - or 1 phase genny won't work for those.

[Chance]

Originally Posted by Metalman

Greg - Remember you are limited to less than 1/3 the normal available power in this mode... '50amp' service on properly wired pedestal provides a full 50 amps to EACH leg - for 100amp total.

So in that case wouldn't the neutral be carrying 100 amps?

Originally Posted by Metalman

Wedman,
Since we are dealing with a single phase power source, please explain how they can be out of phase from one another.

When connected at campground with 50-Amp shore line, Line1 can flow up to 50 Amps, and Line2 can also flow up to 50 Amps. But the Neutral does not add, it actually subtracts.

Remember that in alternating current, voltage and current goes from positive to negative, then back to positive and so on. In this case when L1 is at peak positive then L2 is at peak negative. So when L1 is near peak voltage and current, then L2 is flowing in opposite direction. The neutral would actually be close to "0" Amps, not 100 Amps.

I oversimplified above for clarity because it can get more complicated. For the most part, this is the way it typically works. That's why 50-Amp power cord only has one neutral -- it should never see more than 50 Amps on neutral conductor. And that happens when one leg is at 50 Amps and the other at 0 Amps.

[Hooligan2]

Originally Posted by JamieGeek

Note that the 5500 generator is only 1 phase, though. So when running on the genny both of the 50a lines are running the same phase. (See the genny specs here).

Thus the only time the 50a circuits will be out of phase will be when plugged into a 50a plug at a campground.

Using the genny, or a 30a dogbone they will be in phase.

Brings us back to the two 30 amp circuit breakers on the genny.