12v A/C system

[mojoman]

Planning for a class b build and looking at options for A/C while boon docking. There are 12v DC A/C units out there, 35-45 amps. If I had 200 AH lipo batteries plus 500 watts of solar on the roof I think I could run them most of the day when the sun is out and a few hours at night without a generator. I plan on carrying a 2000 watt honda generator. Seems the most efficient way since you loose efficiency using a inverter to 120v AC. I don't want to install a roof AC so there are split 12v DC AC units available for trucks. I am not too educated in this stuff so anyone have any comments or recommendations on taking this route?

[wincrasher]

I'm sure others with more knowledge than me will soon chime in. From what I've read, you can do it, but you'll spend a ton of money to get 6 to 8 hours of AC running. So if money is no object, and you can rig up around 1000 watts of solar, and 800-1000 amp hours of battery and proper inverter and charger for all this, it can be done. Then, when you've rigged up such a system, then you go down the path of all electric appliances, etc.

But it's far, far cheaper, and probably more simple and dependable, to just find an efficient rooftop AC unit and use a generator. A split system may be doable in this scenario. They are certainly attractive being much quieter.

Good luck!

[mojoman]

With a 12v dc A/C, no inverter, less batteries, less solar to make up for the inverter efficiency loss. I figure during sunlight, the ac will be running mostly on the solar, 200 ah of lipo batteries are $2k, 12v ac about $1.5K. I want to go lipo batteries because they are lighter, install anywhere, more AH available and will charge much faster.

[Davydd]

I doubt you could put 1000 W of solar on a B. I think on a 24 foot Sprinter Advanced RV is topping out at around 600 W covering all available space on the roof.

[booster]

At 500 watts, that is going to be a pretty low output air conditioner. How many BTU is it? If you did decide to do the 110 volt AC and wanted to not have a roof unit, you might want to consider the CoolCat like they use in Roadtrek Chevies and some other vans. Some of the travel trailer folks like Safari Condo, Jayco, etc have started to floor mount them with sidewall, flush venting, similar to what Roadtrek does up high. The floor mount lowers the height of the weight, and makes supporting the air conditioner very easy. It is also very stealthy compared to a roof mount. The CoolCat is made to vent straight out without hanging out of the wall.

[wincrasher]

I just remembered something that might help you - go look at the Tiger Siberian at Tiger Adventure Vehicles.

They fit a window style AC unit thru the rear wall and run it on the inverter. I think it draws something low like 7-8 amps. Maybe you can get some ideas thru what they are doing.

I seriously doubt though, that 200 ah is going to get you very far. That would be a recommended minimum for a B to cover lighting, TV, etc., not air conditioning.

Give us a link to this 12v DC air conditioner you are talking about and we'll have a look.

If it's this one - http://www.dcairco.com/index.php/products/trucks the consumption is 600 watts and the output is only 8500 btu. Probably too small to cool a B. Add to that, the size of the interior and exterior units are huge! where is that going to go?

[mojoman]

Autoclima Fresco 3000, 3250 btu, small but only 16-30 amps 12v dc max. They have larger units but that means more batteries and solar. I figure with better insulation, less window area I can get by with 3250. no problem getting lots of solar on the top because there will be no ac siting up there. I figure I'll only need 500-600 watts of solar to run during the day. Lipo batteries provide more usable AH than acid batteries, you can run them down allot further than a lead acid battery. Lipo charge allot faster too.

[booster]

You will be looking at 50ish amps from the solar in very good conditions, but that will only be part of the day, so you could easily be drawing down batteries for part of the day, and always at night. Having batteries that will charge at 150 amps will do no good if you can only supply 50, and if you are running the AC you would only have 20 amps left for charging and everything else. Even the rigs with big battery banks can get into trouble, because, as has been mentioned repeatedly, you always have to replace what you use sooner or later. Without another method of filling your batteries other than solar, I think you are going to be in trouble on capacity. I think I would do a daily chart of where the power would be going and how much you would be getting from the solar to see how it all works out. Propane frig or 12v compressor?

[mojoman]

I'll have the 220 amp van alternator, my 1000watt honda, or shore power. I just want to be able to run the ac sometimes without a generator or shore power at rest stops or when I want quiet. I would pull over and take a nap or break and run the ac without the generator, it was nice. I don't plan to boon dock that often.

[booster]

If that is the case, you will need to have a pretty big battery charger so you can run the AC when plugged in, or on generator, especially if you have to recover your batteries at the same time. For occasional use like you anticipate, you might well be better to use a 110v air conditioner and inverter, and use the money you save for an extra battery to cover the inefficiencies in the inverter (which can be pretty small in a good inverter).

[mojoman]

I'm going minimal,simple and light, Catalytic Heater,12v /120 fridge,portable oven cooktop, led, no shower,portapotty, laptop instead of a tv which can be charged and run on usb power so I won't really need a inverter.

[wincrasher]

Here's an idea for you then - why not one of those portable room air conditioners people get for cooling a room? All you need is 700-800 watts - you could mount it to the floor and make a 3" capped or vented opening in the side of the van. That could easily be run off a Yamaha 1000 portable generator - which is around 50 db. There are a lot of these units - the smallest footprint I've seen is 13" x 15" by 30" high - there are fatter ones that are only 24" high. Could easily be built into a cabinet. You could size an inverter and battery pack to run this thing if you desired. A 12k btu unit is what you'd need I think.

[mojoman]

I looked into those and almost bought (pretty inexpensive) one until I started finding 12v DC units online under $1K. Cruisencomfort in Az is developing a new 12v DC A/C for cars and RVs, a little higher BTU but its going to cost >$3k. Seems most of this stuff is made in china now, I noticed Espar units advertised on chinese wholesale sites.

[markopolo]

Post links to any 12v air conditioners that you find. I was really interested in going that route but all the units I found were very expensive. A window type 120v air conditioner costs so much less.

The shade provided from covering the roof with solar panels should reduce the cooling requirement as long as there is a sufficient air gap between the the panels and the roof.

Here's some info on running a small A/C on an inverter http://www.classbforum.com/phpBB2/vi...hp?f=12&t=2286 and window type A/C installation http://www.classbforum.com/phpBB2/vi...hp?f=12&t=2156. Might give you ideas if the 12v A/C is too expensive.

[mojoman]

Searching for 12v dc ac's ended up looking at chinese and asian mfg ads then using the description to find a vender.The Autoclimia italian AC distributer is chinese made along with most other ac's. I found heaters and most anything else you find on your RV on these asian wholesale mfg sites. Changing times, my German VW is made in Mexico along with the all american GMC Silverado.

[booster]

You mention lithium polymer batteries for your application. I don't ever recall anyone using them in an RV. Lots of RC cars use them because of the high capacity, charging etc, but they also have a lot of special chargers and fire warnings with the batteries. What do you plan to do for battery charging? You would need the very specific lipo charger on the 110 volt from shore and generator power, and then another special lipo, 12v to 12v, charger on the van alternator circuit.

[mojoman]

Lithium Ion Batteries are quite expensive and are an upgrade for RV batteries. They are a fraction of the weight, last multiple times longer and can be drawn down much lower than a lead acid without damage thus providing more power. They take a different type of charge as they can take more amps faster and at a higher voltage. I used to make my own lipo motorcycle batteries from Dewalt battery packs when I had several motorcycles and got fed up with replacing them almost every year. A 4 cell lipo battery weighs about a 1 lb, size of soup can and can start a car. They are on the market everywhere now. Rather than buying a nice inverter and a new generator, I'm going to spend the extra coin in the batteries and use one of my old portable generators. There are venders who will build your battery pack to your specifications much cheaper than buying one of the pre made ones on the market. Or you can assemble the cells yourself.

[wincrasher]

If you poke around on the google, you'll find some usage of lithium batteries trickling out for use in Marine and RV applications. Definately on the early side of the curve. The weight and size benefits are attractive, but they are still very expensive compared to AGM. You can buy some packaged just like 12v batteries you are used to, with some circuitry included to protect the battery from overcharging, etc. You pay for that too, of course.

Eventually, they'll be on par with regular batteries. Maybe when the Tesla "mega factory" and competitors come online, we'll see the prices come down.

So if you are the early adopter type of guy, go ahead and buy them, as they seem to be ready for prime time if you get the right charging gear. I'll be waiting a few more years, I think.

[booster]

I think the point of my question got lost a bit

You are talking about lithium POLYMER, or lithium ION? The lipo was mentioned earlier, now I see some lithium ion being mentioned. Lithium ion is what I have seen being offered in RVs, and that is why the question about if you were really going to use lithium polymer.

[mojoman]

LiPoFe