Does my idea make sense, would it be functional?

[Sean Steele]

I am in the planning stages of adding solar to my Fifth Wheel for boondocking. My target is 400-800 watts of solar on the roof, 100 to 400Ah of LIFEPO4 and a 2000 to 3000 watt inverter. All of that is pretty basic. My question comes in when I start thinking about running the AC. I know running one off of solar is possible but very impractical. My rig is currently 30 Amp but I already bought all of the stuff i need to convert it to 50 Amp. For those that don't already know, a 50 Amp RV actually has two 50 Amp legs in its service panel. I already have a 50 Amp ATS and a Generator. So, I was thinking that I would add a generator port on the outside of the rig, next to where the shore power connects. I would run 50 AMp shore power to one side of the ATS and on the other side, run the inverter output to one leg and run the generator output to the other leg. When changing the panel over to 50 Amp, I would have all of the circuits, except for the AIr Conditioner and the converter/charger on one leg and put the AC and Converter/charger on the other leg. When connecting the ATS to the panel, I would run the leg powered by the Inverter to the leg powering the main circuits and the leg powered by the generator to the other side. In effect having everything powered while on shore power, having only one leg powered by the inverter and when needing AC or to charge the batteries thru the converter/charger I would run the generator.

So, does my plan hold water? I can try to clarify anything if not already clear. Has anyone already done this sort of setup?

Thanks in advance,
Sean

 

[snoobler]

Nope. You'll have two out-of-phase AC sources sharing the same neutral, thus your neutral won't be neutral.

 

[Sean Steele]

Ah, I was worried about that. I'll have to give that a think.

 

[Sean Steele]

Nope. You'll have two out-of-phase AC sources sharing the same neutral, thus your neutral won't be neutral.

Ok, so you may have been using these particular words to make the statement simpler. So, this question is not argumentative. The normal 50a power coming into an RV is actually two legs of 50 amps that are out of phase and sharing a neutral and common. L1=120V, 50A to ground... L2= 120v, 50A to ground... L1 to L2= 240V, 50A.

Is this different? Also, in an RV, neutral and ground at tied together. Does this make a difference?

 

[snoobler]

No. The only difference between a household split phase 240V and an RV 50A plug is that the RV never uses 240V, but the AC panel is basically the same (minus the 240V connections, oven, dryer, water heater). Neutral and ground are also bonded.

If you could sync the inverter and generator, then it could be done. This is how parallel inverters work,

In a regular split phase situation, the legs are 180° out of phase, thus their sum is always 0 at neutral. If they are not 180° out of phase, their sum will be non-zero meaning your neutral and your neutral bonded ground won't be zero, and your 120V legs won't be 120V either. Picture your neutral/ground voltage "wiggling" 60X per second. However much the N wiggles reduces the peak voltage on both legs.

 

[HaldorEE]

230 VAC is single phase. It is coming from a center tapped winding on the power transformer with the center tap connected to ground and labeled neutral. From hot to hot is 230V from neutral to either hot is 120V.

You could get a Victron Multiplus now for a single 120 VAC circuit, then add a second Multiplus for the other power leg (creating a 230 VAC, center tapped power output). The Multiplus inverters talk to each other to keep the waveforms properly synchronized (like a pair of Honda generators with a link cable).

I would want a lot more than 800W of solar if trying to power an Air Conditioner though.

What kind of climate do you live in? Would an evaporative cooler work for you? It would be much easier to power from solar.

I have a small portable evap cooler for my van. It is adequate here in the desert. Wouldn't be much help in the deep south.

 

[HaldorEE]

No. The only difference between a household split phase 240V and an RV 50A plug is that the RV never uses 240V, but the AC panel is basically the same (minus the 240V connections, oven, dryer, water heater). Neutral and ground are also bonded.

If you could sync the inverter and generator, then it could be done. This is how parallel inverters work,

In a regular split phase situation, the legs are 180° out of phase, thus their sum is always 0 at neutral. If they are not 180° out of phase, their sum will be non-zero meaning your neutral and your neutral bonded ground won't be zero, and your 120V legs won't be 120V either. Picture your neutral/ground voltage "wiggling" 60X per second. However much the N wiggles reduces the peak voltage on both legs.

Do RVs not use 230 VAC? I thought AC typically required this.

 

[snoobler]

Nope. 120VAC. If 240V, that would prevent all 30A RVs from having A/C. BIG A/C units are 15,000 BTU/h

About 4500W surge and 1500W run. If there are dual units, they are on differerent legs.

From Dometic installation manual:

 

[Sean Steele]

Thank you both for very detailed responses. Now I understand the issue.

Haldor, the solar/inverter will never be running the AC. That was the idea behind having that circuit on the leg powered by the generator.

Since you mention the Multiplus, could it function as the intermediary to combine the two inputs like it does in hybrid mode to combine mains power and inverter power? I already have the ATS but since the Multiplus is a combination of MPPT, inverter and transfer switch, I could go that direction instead of modular if it simplifies the application

 

[Sean Steele]

Do RVs not use 230 VAC? I thought AC typically required this.

No, the roof units are just 110 and usually less than 20A.

Sorry, Snoobler beat me to it.

 

[HaldorEE]

Nope. 120VAC. If 240V, that would prevent all 30A RVs from having A/C. BIG A/C units are 15,000 BTU/h

About 4500W surge and 1500W run.

Thanks I have never owned an RV that uses shore power. Since I only have Mutiplus 2000, I was planning on using a 30 A connection for shore power in my van.

And even though I live in Phoenix, AZ no AC for my van.

 

[snoobler]

I run A/C via a Victron Quattro 4kW/48 with 3kW of panels and 12kWh of batteries, I can run it about 8-10 hours per day with decent sun with only minor impact to the battery.

The Quattro is 120V output only, so I have L1 and L2 jumpered in a way identical to the way a 30A adapter jumpers L1 and L2 of a 50A RV plug.

Curious why you're upgrading to 50A? Do you need the extra power? It seems overly complicated.

 

[Sean Steele]

The change to 50 was for the extra power while on shore power. While on 30A, I have to turn off my AC in order to use the electric water heater, microwave or my toaster oven for fear of tripping the breaker. I figured going 50A was the easiest way to split up the circuits as well and be able to run multiple devices at the same time. I plan to upgrade my AC from 13,500 to 15,000 BTU and get a more efficient unit at the same time. I've found a couple with startup watts of 1800.

That being said I plan to start chasing 70° in October so I hope to not need AC all too often after that. I figured having the AC and converter/charger on one leg of the panel and everything else on the other would make it easier to feed the panel from the inverter. Powering the other leg with our generator was an after thought.

Given my need and planned solar, how would you go about it?

 

[HaldorEE]

Thank you both for very detailed responses. Now I understand the issue.

Haldor, the solar/inverter will never be running the AC. That was the idea behind having that circuit on the leg powered by the generator.

Since you mention the Multiplus, could it function as the intermediary to combine the two inputs like it does in hybrid mode to combine mains power and inverter power? I already have the ATS but since the Multiplus is a combination of MPPT, inverter and transfer switch, I could go that direction instead of modular if it simplifies the application

The Multiplus is a DC to AC inverter, an AC to DC battety charger and an AC transfer switch. The solar charge controller is a seperate box.

I am not sure what you mean by combine. It only has one AC input. It will automatically switch between AC and DC input to power your AC loads.

As you said it can boost the AC input with power from the battery if your AC input power is limited.

 

[Sean Steele]

Oh, sorry. Must have been remembering incorrectly. Thought it had a charge controller in it too.

Ok, I think I have it. Use the ATS the normal way and use a Multiplus in hybrid mode to combine generator input with it's inverter output to make up the power needed to run everything. Same as you would if you were plugged into 20A shore power. I'd need to have the generator running and set the limit on the AC input to 15 or 20A. Of I don't need the AC, then I just leave the generator off. Damn, I already bought a 100A converter/charger too.

 

[snoobler]

Is this fear or experience based? 30A * 120V = 3600W, and all of those high-drain items use 1300-1600W each, so you should be good with two running. The only gotcha is the surge on the A/C.

A $350 soft starter can be added to any existing A/C, so keep that in mind when pricing units based on surge current.

I would consider a deployable array, i.e., a compatible set of panels you could setup outside the RV that would join in parallel with your roof-mounted panels. There are other inverters that work in 240V split phase and have AC inputs. You could get a 5kW AIMS or Sigineer inverter (big surge capacity). You could feed your ATS with shore power or generator and then the ATS output would go to the inverter, which would then output to the AC distribution panel... inverter is a man-in-the-middle that does everything, but it gets its power from batteries, grid or genny as needed.

This would also work in 120VAC mode without having to rewire the trailer.

 

[Sean Steele]

Experience based. I think my AC may be getting tired and drawing more than specified. It should run on my 2500watt surge generator but it kills it. The ac some times trips it's own 20A breaker on startup but only rarely. I have had the 30A main breaker trip if I forget to turn something off before running something else.

I have a "briefcase" panel but I doubt it would be compatible. It is 120watt/18v but is one of the ones that is intended for "solar generator" charging. It has multiple connectors as well as built in USB ports. I don't plan on running the AC off of the inverter but a deployable expansion panel is in the back of my mind

 

[snoobler]

Clarification:

Is it popping the breaker in the trailer or on the generator? If Genny, it has nothing to do with your trailer. If trailer, it may only be due to the genny not being able to supply adequate voltage, and the current surges.

2500W genny is inadequate for the surge of an A/C unit. Not kidding when they can be as high as 4500W (3X run).

For deployable, you need to be thinking along the lines of your original panels. Let's say you have 2S2P 200W panels mounted for a total of 800W. It would be best to have 2SXP of the same panels.

 

[Sean Steele]

It pops the breaker in the trailer when plugged into shore power. By spec, my AC should never draw more than 1800 watts. That is the listed startup draw for my model. I assume it is drawing more because the compressor motor isn't running as efficiently as it did when new. Shouldn't it trip the breaker if it was drawing more than 2400 watts on a 20A breaker or do they have a serge rating too?

 

[Sean Steele]

I don't know where I would even store two more of the same panel other than on the roof. In which case, they would just be connected to the system all the time. I have a small fifth wheel, 28', with limited storage space.