Power system design to run AC 24/7 for 2-3 days

[Worg]

Is anyone into the tech side of van or RV power system design?  I want to be able to travel safely with short muzzled dogs in the summer (outdoor temps of 85-100).  If there are no hookups, I need a way for the vehicle to run AC 24/7 for 2-3 days via a generator (I assume) or ?  I am starting from the ground up and am willing to buy whatever van or rv that will allow the modifications to do this, however I don’t know where to start.  Basically, boondocking with heat sensitive dogs that need to be kept in 70-71 degrees when it’s very hot outside.  Let me know where I would start.  Thank you!

[jcussen]

Depends on your generator and its fuel consumption. Some big diesel pushers have fuel tanks big enough to do it. Many smaller class c's or b's not possible. For non generator use, massive solar and battery is necessary. Outdoor temps of 85 to 100, you will need  good ac's and good insulation.

[oldjohnt]

Worg, good question, here's my take if you need to run say for example a 13,500 BTU rooftop AC unit 24/7 for a few days:

NOTE the heat load and temperature and insulation and sun bearing down on the unit  or shade cover and its size and a ton of other variables affect the answer so this can ONLY be a rough approximation NOT intended as accurate, don't take this to the bank lol 

NOTE a small 5000 to 6500 BTU home window unit might work in a small well insulated van especially if parked in some shade cover (subject to all the factors above) which wouldn't require as much fuel or capacity as I figure below !!!!!!!!!!!!!!!!!! Another more efficient option might be a small min split system which might not (subject to size and heat load) require as much as below..................... 

1) If you use a gas generator the VERY MINIMUM size that "can" work, especially PROVIDED you install a Soft Start on the AC which really helps for start up, would be a portable 2200 Watt Inverter Generator (my preferred type). While that can work (subject to load and genset) its  fairly close for comfort with no extra power available for other uses. If you want larger, portable gensets come in sizes such as a 3000 or 3500 Watt and much larger. Costs vary for a loud noisy open construction unit up to a much quieter more expensive unit.

2) HOWEVER to allow for expansion and other loads such as say a battery Converter/Charger I would recommend at least a 2800 Watt

3) An ONBOARD GENSET may be available in say a Cummins Onan 2800 Watt or another common size is a 4000 Watt

4) FUEL:  Typical for an RV onboard genset is they draw fuel out of the regular main gas tank usually set so they cant draw down too deep. Of course for a portable you need to carry gas cans and how long they can run ( 4 to 6 or more hours subject to fuel capacity and actual load and times) prior to refill can be an issue.

5) Subject to actual AC load and how often the compressor cycles for how long (depends on temp) you might be looking at say 2 to 4 quarts per hour of gas to power the generator

There are other options such a a HUGE solar system with one HUGE battery bank at one HUGE expense,  but subject to sunlight and actual AC load for 2 or 3 days THATS NOT REAL PRACTICAL ......even if sure with enough capacity it can work. For a small vehicle a person may run the dash AC and used the van gas and engine if it doesn't overheat.  The van engine with a huge alternator and DC to DC converter charger to charge a battery bank and use a 12 VDC to 120 VAC big enough (3000 watt) Inverter is an option NOT real practical nor my choice lol  

Theres no right or wrong answer, it depends on your use and needs and budget

 

John T 

[Randyretired]

I have seen some pretty innovative setups on you tube using solar to power mini splits.  In one case solar panels were stored in a way that these were extended out beyond the roof to allow for more solar panels.  This solar with a good battery system could be a good start.  However, we know there will be times the sun doesn't shine so a backup generator with auto start could be used.  With a high efficiency mini split the power required is greatly reduced.  For our RV we have installed a mini split and we love it.  It is a 12,000 btu unit that uses about 450 watts and it keeps our 39' Teton comfortable.  Our comfort is 74 degrees and it has maintained that in temps into the lower 90's so far.  It doesn't get any warmer than that here so I don't know how it would perform in temps above that.  I suspect temps near 100 would not be comfortable  without a larger or multiple  units.  In our case we don't have enough battery capacity to cool after the sun goes down but where we are at the temps cool very quickly when the sun goes down.  With a large solar array, a robust battery system and a generator backup system I am sure what you want is possible but pricey.  As far as insulation our Teton is better than average but a long ways from really good.  It also has numerous air leaks.  A better insulated air tight unit would be a lot easier to cool.  A smaller unit with good insulation and air tight with a small generator running a mini split would be the least expensive setup.  I am not familiar with any reasonably priced RV's that have really good insulation and are air tight so you may have to build it or have it built.  With a little innovation it seems like an extended run tank setup should be possible to keep the generator  running.  Since any system is subject to failure you might need to consider that if you are not around to watch it.  A window AC or RV AC could be used instead of a mini split but these units will require a lot more power and the surge at startup will need to be considered. 

[Kirk W]

3 hours ago, oldjohnt said:

Theres no right or wrong answer, it depends on your use and needs and budget

John gives some very good advice, but I'll add just a few more things to think about. The first is that where you plan to go and the weather you will need to deal with plays a major role in what you will need. There are very few RVs that are well enough insulated and air conditioned to be able to keep temperatures in the low 70's when in places that see daily highs over 100° and it requires at least avoiding direct sun when into the mid 90's. If you stay in the mountains or far north that will make things far more possible because the heat gain will be much less problem. Even with 50A power that is reliable and 2 air conditioners, I found that 100°+ days in direct sun most RVs will struggle to keep temperatures below 80°. I have been told that the highest price/quality of larger RV which have 3 large air conditioners can be kept at the chosen temperature even in the hottest weather, but I have never owned one so do not really know. 

[Daveh]

If you are starting from the "ground up" as you say I would, obviously, buy a van with a good air conditioner system. One of the problems is that RV AC are not that great. If you are getting just a small unit, then a single or double AC unit may be fine, but in a larger unit you will need at the very least a double unit and that puts a big draw on the electric.  If we knew some of the specifics like the size you were thinking of and the items Kirk asked about we could give you better advice. Many of us are either adding or changing our our typical RV AC units as they are much more efficient. 

The other thing I would add to John's advice is that if you look at the gas generators I kind of like the option of two 2000 watt inverter generators. I am thinking of the Honda's. You can use them seperately or they can be paired into a 4000. That way they are easier to move around and when you don't need to go all out  you can use just one of them.

Another thing I would consider is that (again depending on the number of ac units), I would add a lithium battery bank and a good hybrid inverter such as made by Magnum or Victron. The benefit of a hybrid unit is that it can  supplement the generator with power from the battery system at peak draws. As John mentioned ACs cause problems when the compressor kicks on and it is at these points the power generally fails. The batteries could also then serve as a backup should a generator fail but that will require a larger bank  and you would only get a few hours. That would be a high risk, to dogs and batteries situation, and you would want to avoid it.

The other possible component is to add solar which could charge the batteries and wit a larger battery bank prevent you from operating the generator 24/7.  Operating ACs off of solar is not a reasonable solution in very every circumstance but it can be a nice supplement. 

Are you going to be with your dogs all the time? If not I would really design my system to have backups and some type of alert. There are products sold that will provide you texts or the like if the temp gets to high.

Soooo, tell us the size unit you are thinking of and we can give better assistance. The first line of response for sure is buy a unit with a built in generator or get one or two gas powered inverter generator. You don't necessarily need to by one of the Honda EU series but I would start by looking up the Honda EU2000 and 3000. That is generally the reference standard for any inverter generator.

If you want to know more about the Rv electrical systems work in general I have always liked Jack Mayers site. It tells you how all the pieces fit together.    http://www.jackdanmayer.com/rv_electrical_and_solar.htm

 

[rls7201]

If you elect to go with a well insulated van conversion, a 8K AC with a 2.4KW ONAN generator will work. Set up the generator to run off the van fuel tank and you'll have enough fuel to go for a week or better. That's how Roadtrek has been doing it for many years.

Richard

Edited July 12, 2020 by rls7201

[Daveh]

10 minutes ago, rls7201 said:

If you elect to go with a well insulated van conversion, a 8K AC with a 2.4KW ONAN generator will work. Set up the generator to run off the van fuel tank and you'll have enough fuel to go for a week or better. That's how Roadtrek has been doing it for many years.

Richard

Right if you go with something like that the problem becomes much more manageable and that would be a great solution. The living space desired really drives the answer.