Safe way to wire 240 volt mini split?

[jmonk]

Situation - '59 ambassador with shell off awaiting frame repair.

Contemplating HVAC, need two zones. Original plan was two separate 110v 9,000 btu systems; one on tongue and one rear mounted on frame extension.

Rear mounted system is heavy and ugly. increased weight (easily 100 pounds between frame extension and condenser) that far back could cause shell/frame separation even with center bath conversion transferring weight forward.

Ugly is just ugly and that's not cool.

The best solution I can think of is to use one multi-zone mini-split mounted on the tongue but multi-zone units require 240 volt power. Is there a safe way to wire for this.

It can't be as simple as adding a 240 breaker into a 50 amp panel... can it?

I kind of understand the 50 amp RV connection in that it's a 240/120 circuit, but simply sticking a 15 amp 220 breaker in the 50 amp panel of my trailer seems way too easy. Something that easy usually results in something bent, broke, or burning.

[rmkrum]

Assuming you have 50 amp service already in the trailer wired to a decent breaker panel, yes. All you need is an appropriate dual circuit breaker on both hot leads. The handles must be tied together properly. And that will power the unit.
Although not everyone understands this, 50 amp 4-wire trailer has two 120 volt circuits. Across both the lines you get 240 volts. Wired like a house.

[azflycaster]

If the two 120 legs are phased the same, you only get 120 volts, not 240.

[rmkrum]

Uh, no. You get zero volts if it’s phrased wrong or you get 240 across the two hot legs if it’s phased properly. That’s flat out the only way it works, period.

The only way you would see 120 volts is to measure from one hot lead to the neutral lead.

Been doing power system design for longer than I want to admit. Designed 2-phase and three phase 60 cycle commercial power distribution and lab grounding systems as well as working on aircraft and shipboard systems for most of my long career...

(And can’t type worth a darn on my phone, either...&#129322

[pdavitt]

Originally Posted by jmonk

The best solution I can think of is to use one multi-zone mini-split mounted on the tongue but multi-zone units require 240 volt power. Is there a safe way to wire for this.

It can't be as simple as adding a 240 breaker into a 50 amp panel... can it?

I kind of understand the 50 amp RV connection in that it's a 240/120 circuit, but simply sticking a 15 amp 220 breaker in the 50 amp panel of my trailer seems way too easy. Something that easy usually results in something bent, broke, or burning.

Listen to rmkrum, he's got it correct. The only thing I would add is that the full terminology for your house power and the standard 50A service available at RV Parks and Marinas is "120/240V Split Phase". The 50A RV service gives you 12,000 watts of available power.

I would recommend you do a little studying on how all this really works, so you can sleep well at night.

Pat

[rmkrum]

Yup. Exactly the right words I had trouble coming up with. CRS disease, I guess. Plenty of power assuming you use a decent shore power cord and pedestal to power it.

[jmonk]

I think I understand how this would be accomplished outside of an RV/trailer, but is it the same up to the separation of 12v DC?

120/240 load center with 50 amp main, dual pole breaker for HVAC, and single pole for 110 requirements including the 12v power supply?

My only RV electrical experience is a dental van I operate for a non-profit. It's wired similarly but with two separate 120v load centers. Apparently each load center is a leg from the 50 amp RV feed.

[rmkrum]

To get power for the split AC you would need the feed to go to one load center

[pdavitt]

Originally Posted by jmonk

I think I understand how this would be accomplished outside of an RV/trailer, but is it the same up to the separation of 12v DC?

120/240 load center with 50 amp main, dual pole breaker for HVAC, and single pole for 110 requirements including the 12v power supply?

My only RV electrical experience is a dental van I operate for a non-profit. It's wired similarly but with two separate 120v load centers. Apparently each load center is a leg from the 50 amp RV feed.

I drew this a while back, it generally demonstrates a way of wiring 120/240V panels. Hope it helps.
Pat

[jmonk]

Yes, one load center; I had that in a previous post but waited to post it and got logged out. When I tried to post it I lost the post.

There are so many things that are so thoroughly documented that it's surprising to me no one has drilled into this particular topic. If a person's intent is to do something different with HVAC it needs to be considered literally from the frame up.

I'm still waiting on the estimate from my welder and I've nixed extending the frame to accommodate a second 120 mini-split. That's a game changer in a few different ways. (Heavy, costly, and most of all ugly)

There are so many threads that document most other topics that I feel like posting more would merely muddy the waters, but this topic isn't like that. I'm grateful for the knowledge people so freely share and hopefully as I move forward I can contribute useful documentation of this particular modification in a way that does the community service.

I'm still a little way out from "turning wrenches" so to speak, but will start a separate thread in an HVAC forum.

Suffice it say that this conversation has been invaluable in knowing how I'll move forward. I would not have imagined it would be possible to run a 240 mini-split on a trailer using and RV hookup. Thanks so much everyone.

[gklott]

Originally Posted by pdavitt

Listen to rmkrum, he's got it correct. The only thing I would add is that the full terminology for your house power and the standard 50A service available at RV Parks and Marinas is "120/240V Split Phase". The 50A RV service gives you 12,000 watts of available power.

Originally Posted by rmkrum

Assuming you have 50 amp service already in the trailer wired to a decent breaker panel, yes. All you need is an appropriate dual circuit breaker on both hot leads.

This is correct - 2-pole breaker and a 4-wire branch circuit (2-hot, 1-neutral, 1-ground) to the mini-split. Have only one panelboard (i.e., loadcenter) in the trailer. Recommend consulting NFPA 70 (National Electric Code) Article 551.45 for the panelboard requirements. You should then only connect to 240/120V 50A shore power or to a generator like the Honda EU7000i that has a 240/120V 30A circuit-breaker-protected output.

HOWEVER, should you do this, you MUST BE VERY CAREFUL when using use any type of 30A-to-50A or 15/20A-to-50A dogbone adapter. You must turn off the mini-split circuit breaker BEFORE connecting, and you will not have air conditioning. Once you have a 240V branch circuit, I recommend never using a dogbone adapter.

Also, be sure and follow the wiring methods in NEC article 551.47 when wiring to your mini-split components.

73/gus

[jmonk]

Yeah, I had considered the lack of AC with the 240 mini-split when no 50 amp service is available. I still haven't figured out a contingency plan for that, but I do have a window unit that I used while removing the interior. It fit out the front access door and worked better than nothing, but not much in the middle of a South Carolina summer. I'm kind of hoping that better insulation and mirrored window tint will help that.

[RobH41]

I'm using a small 10,000 btu mini-split on a little Argosy Minuet rebuild I'm currently working on. It's a 240v single phase powered unit so I'm using a Simran 5000 watt capacity 120 to 220 step up transformer just to run just that AC unit. It will run on regular 30 amp 120v service that most campgrounds have. It only draws about 4 amps when running or about 900 watts, so it should have enough headroom for the start-up load.

[jmonk]

If you're not afraid of off brand stuff I've had really good luck with our pioneer mini split. It's a 9,000 btu unit and it runs on a single 15 amp 120 breaker. My original plan for our ambassador was to run two of them. One on the front and one on the back but I just couldn't shake the idea of that 72 pound rear unit sitting behind the shell on a frame extension, not to mention it would have been hideous.

The 9,000 btu system comes complete for under $700 and right now their offering free shipping. Make sure you seal your connections well and have an HVAC guy pull a vacuum on the system. It should run like a champion and use less power than a household refrigerator. There's no surge load either as the thing ramps up slow. You'll hear it when it starts if you're right by it. I really can't say enough about ours. We've been running it for a couple years now and it's great. They also have a 12,000 btu unit that runs off a single 120 breaker.

[fwjumper]

Why not two low profile roof units with trailer rewired for 50 amp? I don't think I would want a 240 unit that could not be run in 30 amp campgrounds. One roof unit running would be better than nothing. And IMO, roof units would look better. Ultimately, whatever you like is the right answer. Good luck.

[TouringDan]

I plan on installing a 120v 12,000 btu/hr mini split in my 95 34’. I don’t want the complexity and power consumption of a 240v 2 zone 18,000 btu/hr mini split. I plan to insulate some of the windows to improve the performance of the cooling system. If I need some additional cooling, I will install a 5,000 btu/hr window unit in the bedroom. This is how I cool our 66 Tradewind and it is adequate for our needs.

I plan to install the compressor on the front A frame behind the propane tanks. I will probably move the propane tanks forward about 3” to provide adequate room for the compressor. I intend to run the refrigeration lines underneath the Airstream and within the wall cavity up to the air handler next to the wall cabinets.

I included specs on the system in the Mini Split HVAC thread (posts 9 and 10).


Dan

[jmonk]

So many ways to approach this based on demand and application. It illustrates the fact that the best way is really left to interpretation. Then you start to factor in personal preference and things get weird quick.

I spent a lot of time in helicopters and as a result in crew briefs for more flights than I care to count. Part of that crew brief always include Operational Risk Management (ORM). We followed Air Force instructions to the greatest extent possible but especially where helicopter operations were concerned deviation was often unavoidable. The mantra of ORM during those briefs was "within the parameters of safety and good judgment". That meant conferring with all the expertise available and going ahead with what needed to be done. This community provides a vast pool of expertise and I'm glad for it as I go ahead with what I'm doing.

I'm hoping to balance the differences between my application and what may be useful to a broader range of trailer users. Why I'm doing this will, at some point, supersede the usefulness to the overall community, but I believe that the majority will benefit in useful ways.

I love this place.

[55AS]

Originally Posted by jmonk

If you're not afraid of off brand stuff I've had really good luck with our pioneer mini split. It's a 9,000 btu unit and it runs on a single 15 amp 120 breaker. My original plan for our ambassador was to run two of them. One on the front and one on the back but I just couldn't shake the idea of that 72 pound rear unit sitting behind the shell on a frame extension, not to mention it would have been hideous.

The 9,000 btu system comes complete for under $700 and right now their offering free shipping. Make sure you seal your connections well and have an HVAC guy pull a vacuum on the system. It should run like a champion and use less power than a household refrigerator. There's no surge load either as the thing ramps up slow. You'll hear it when it starts if you're right by it. I really can't say enough about ours. We've been running it for a couple years now and it's great. They also have a 12,000 btu unit that runs off a single 120 breaker.

I too have had good luck with the Pioneer mini-split units (highseer.com). I have installed the 12,000 BTU 120 volt unit (also acts as a heat pump) on 2 Airstreams. On my 55 Flying Cloud it was more than adequate. On my 67 Overlander it was marginal in the high summer heat, particularly getting the rear bath cold. I think it would work perfectly on the Globetrotter.

[55AS]

Originally Posted by TouringDan

I plan on installing a 120v 12,000 btu/hr mini split in my 95 34’. I don’t want the complexity and power consumption of a 240v 2 zone 18,000 btu/hr mini split. I plan to insulate some of the windows to improve the performance of the cooling system. If I need some additional cooling, I will install a 5,000 btu/hr window unit in the bedroom. This is how I cool our 66 Tradewind and it is adequate for our needs.

I plan to install the compressor on the front A frame behind the propane tanks. I will probably move the propane tanks forward about 3” to provide adequate room for the compressor. I intend to run the refrigeration lines underneath the Airstream and within the wall cavity up to the air handler next to the wall cabinets.

I included specs on the system in the Mini Split HVAC thread (posts 9 and 10).


Dan

Make sure you understand the clearance/airflow requirements before finalizing your location. I wanted to hide mine behind the shiny LP tanks but ended up with it in front to ensure proper airflow.

[jmonk]

With two zones I don't think I'll have any problems cooling. We're looking to do a center bath so the rear will be bedroom, hence the separate zone. I would like to know what insulation you're using in the overlander though. The ambassador is only 2 feet more trailer, but we are likely to get in to some heat even if we don't travel far. Temps get close to 100 here in SC but the humidity is what kills us.

For what it's worth to compare. I had a 5,000 btu window unit that I used while tearing out the interior. It kept things survivable but barely and that was only if the trailer was cooled in the morning. If it got past about noon there was no cooling the space down. Even if it was cooled starting before it got hot comfortable wasn't even on the same scale. Covering the windows made a pretty significant difference.

I'm leaning towards multiple layers of foam insulation board largely because it's so readily available and it's also something I can get my head around.