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Keeping a roof ac going without using the generator or shore power


jan50

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Hello All,

 

I am reaching out for help from anyone who has knowledge of keeping a roof ac going without using the generator or shore power. Any feedback would be appreciated.

 

Question:

Is it possible to add deep cycle batteries, a bigger inverter and solar panels to a class b rv so I can use the roof ac anytime I want? Can the generator recharge the batteries when they get low?

 

Background:

I want to buy a class B rv to run daily errands, to use as a mobile office, to go camping once every couple of months and to travel to Florida twice a year. I have owned class C’s in the past and I want to try a class B so I can use it on a daily basis without standing out wherever I go, and for ease of driving. It would replace my car.

 

I want the inside to be customized to look like a little cabin.
I found some inspiring pictures which I posted here: http://www.discountcatholicstore.com/rv.htm

 

I found a licensed general contractor who is local who can do the interior custom work. (There are no rv dealers who will do it in this area.) He has told me that if I want to use the house ac on an everyday basis to run errands and use as a mobile office, I would need to install deep cycle batteries (enough to handle using the ac for 3 – 5 hours) and a bigger inverter. He can also add solar panels. Of course, the rv will have a generator but I’m not sure I would be willing to use it in the parking lot of a strip mall; especially since rv generators tend to be very noisy. Also, the contractor said something about not wanting to use the generator for hours on end.

 

Maybe it would be easier to just get a quiet generator and just use that – rather than install deep cycle batteries, an inverter and solar panels???

 

Thanks!

Jann

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Maybe it would be easier to just get a quiet generator and just use that – rather than install deep cycle batteries, an inverter and solar panels???

 

Thanks!

Jann

 

With a class B that would be your only practical option for A/C. I would take a look at the Honda/Yamaha inverter generators. They are as quiet as you get and extremely reliable. There is no real issue with running your generator for hours on end. It's perfectly fine to run them 24/7 if you wish.

 

You probably don't want to be running one in a mall parking lot, but the amount of batteries and the size of inverter you would have to carry to run a roof top A/C is just not practical in a class B. Not even taking into account that you would never be able to mount enough panels to keep a battery bank of that size charged on solar alone.

 

There are other options though.. like the mightykool 12v swamp cooler and the like. I don't have any personal experience with them though.

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Here's a mini-split that will do what you ask. You will need about 8 golf cart batteries to run it all night and about 1,200-1,500 watts of solar on your roof to recharge them, but with only a 560 watt draw to produce 12,000 BTUs it is doable. The key is efficiency. This model has an EER of 21.43, plus will produce efficient off-grid electric heat in milder weather too, sparing your propane for the real cold spurts.

 

http://www.geinnovations.net/solar-electricity-cost.html

 

http://www.geinnovations.net/Specifications.html

 

Here's Kingtec's 16k BTU roof mounted ac. It is not quite as efficient drawing 18 amps (at 48v DC to make 16k BTUs. The model I first listed only draws 11.5 amps to make 12,000 BTUs of cooling. Both units have variable speed rotary compressors which will scale back drawing less current when less cooling is needed, conserving power and avoiding hard, power robing starts of a conventional piston compressor AC.

 

http://kingtecsolar.com/products/solarpoweredairconditioningunits-k25tf-4-k50tf-4/

 

Here's another model with a little better efficiency than the King unit, but not as much as the first unit I linked to: http://www.hotspotenergy.com/DC-air-conditioner/Specs-DC48VRF.pdf

 

Of course a quiet generator will be your cheapest option and I doubt you will have enough room on the roof of your class B (even with side mounted or slide out double stacked solar panels) to support more than 600 watts or so of solar panels.

 

Chip

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As Yarome said, your only practical option is a generator. A class B has very limited roof to space for solar panels and no place to install to install the number of batteries you would need to run an air conditioner, including those suggested by previous posters. Perhaps a lithium battery setup might have the power, but they are incredibly expensive and cutting edge technology. Still, without some way of charging them it is a non-starter. I know very few folks with large Class A's or big 5th wheels who have enough room and capacity for the solar and battery needed. It's just not gonna happen in a Class B.

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As Yarome said, your only practical option is a generator. A class B has very limited roof to space for solar panels and no place to install to install the number of batteries you would need to run an air conditioner, including those suggested by previous posters. Perhaps a lithium battery setup might have the power, but they are incredibly expensive and cutting edge technology. Still, without some way of charging them it is a non-starter. I know very few folks with large Class A's or big 5th wheels who have enough room and capacity for the solar and battery needed. It's just not gonna happen in a Class B.

Adding just a little bit to this is the fact that you would need most of your storage space to carry batteries and portable solar panels to set up when you stop. Is it possible? Certainly it could be done but practical? Not at all.

 

When you look to generators, keep in mind that you need one with enough power to supply the starting load as well as run current for the air conditioner. Class B roof air should be pretty small in capacity and thus need fewer amps to get going, but it is important to remember that it takes more to get it started.

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I recommend checking with those who are doing similar living. If the guy at this link doesn't know, he'll surely know of someone who has something set up: Cheaper RV Living

 

Personally, I don't believe you'll be able to generate enough from solar exclusively to run the van office. Its not the battery storage, its the real estate needed for solar panels. You will probably have to resort to some sort of external source to recharge.

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It is possible to do. If you have enough money to throw at it, and are willing to compromise enough in other areas - such as living space.

 

You would have to use Lithium batteries because of weight factors (in my mind at least). You would compromise your living space to put enough of them in - but not greatly. Then you have to use a super efficient AC unit as discussed above. They are out there. And you have to limit your usage off of battery - if you are talking about 3-5 hours then that is more doable than overnight. But it will depend greatly on your insulation values and the cubic feet of conditioned space.

 

All in all it is going to cost a good bit, and you will STILL need a genset for when you need more capacity. So I would stick to just the genset. They are pretty quiet if you install the right one the right way - I would not hesitate to run one in a mall parking lot.

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Our camper has room for about 3 kW of solar (but we are starting with 1.1kW). I have considered running our small 6k BTU side mount AC off of solar and LiFePO4 but will probably just stick to climates that do not require much AC. We put in great insulation and the 6k unit does cool our living space down to 68 when the outside temp is 85, but it takes about thirty minutes to an hour. It draws 4.8 amps at 115V so uses roughly 600 watt-hr to achieve that drop. We only have around 2400 watt-hr of battery capacity so the best we could do right now is cool off the camper before going to bed and hope the night temps keep it cool.

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Wow, so much help! Y'all are awesome! After reading everything and doing a little research, I am going to go with just using the built in generator. I will try to find the quietest one there is - that is installed inside the unit. I'll look into the gen set. If there are any other suggestions in this regard, please let me know.

THANK YOU ALL!

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Generators in Class B RVs are usually installed under the rig. You don't want that burning fuel inside. My Sportsmobile conversion had 380 watts of solar on the roof which is the maximum we could fit on my long body van. I never ran the a/c unless I was on shore power since I did not have a generator but a good fan does wonders for feeling cooler.

 

Linda Sand

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The roof AC is powered by 120 volts ac power. The engine alternator only puts out about 13 volts dc. You would need a very large alternator running that 13 volts to very large inverter....simply not practical.

 

As to whether a gen can be run while driving....yes...lots of people do it to both power their domestic fridges and to run their roof ACs while driving.

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Wow, so much help! Y'all are awesome! After reading everything and doing a little research, I am going to go with just using the built in generator. I will try to find the quietest one there is - that is installed inside the unit. I'll look into the gen set. If there are any other suggestions in this regard, please let me know.

THANK YOU ALL!

Jann, Please do not run your generator inside your Class B !! it has to be installed outside away from you as it will kill you from the fumes , it will also need outside air to cool it, if you must have it in the rv, it will need a new cut out compartment on the outside completely insulated from the inside and with a fan or someway to keep it from overheating, I hope you come back and read this. Ed

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I am always curious about whether roof/house AC can run by the engine power while the engine is running in motorhomes. Or is it always necessary to run the generator to use it on the go?

The simple answer is that it can only be operated from shore power or an on-board generator. Even if you had an inverter that was large enough to supply it power, which I've never seen in an RV, you would need a far bigger alternator added to the main engine to supply it the needed power. While it is actually possible to make that work, it is completely impractical.

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Jann, Please do not run your generator inside your Class B !! it has to be installed outside away from you as it will kill you from the fumes , it will also need outside air to cool it, if you must have it in the rv, it will need a new cut out compartment on the outside completely insulated from the inside and with a fan or someway to keep it from overheating, I hope you come back and read this. Ed

I was referring to a generator that is already built into the class b rv from the factory. I was not referring to a portable generator. Thank you for pointing this out though... I appreciate it...

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