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Random Quote: I see said the blind man... as he picked up a hammer and saw.
I have a small cabin on my W/A and do not have room for a generator. Occasionally we want to sleep out on the boat, but the summer can be a little hot. The thought was if I am close to shore power, I will be in a hotel, so I wanted something that I could run off 12v. Bayaire's unit works very well but is around $1000. I basically took their concept and came up with this. It is a cooler that holds block ice, I put a couple of inches of water in it, there is a small bilge pump that runs the ice water up to a automotive heater core that has a built in fan assembly. The fan blows over the cooled core and out comes cool air. The water then returns to the cooler and the cycle is continued. There is very little humidity added to the cabin because the water stays in the cooler. There is a 3 speed switch that came with the heater core/fan that I wired together to the bilge pump. I plug that into a cigarette lighter plug in the cabin and away it runs. Block ice will last for several hours and the cabin is cooled quite comfortably. It is a compramise, like everything on a boat but it was only a couple of hundred bucks and can be run off 12v. The Bayaire system is definitely colder, but it is alot more $ as well. I am open to suggestions on improving it.
Doug
what's the metal pan on top for?????? Consider enclosing everything on top in a tupperware container so you can hide wiring and have someplace to mount the switches. You could silicone the container to the top of the cooler or screw it onto the top lid.....
since you are using a heat exchanger approach to cooling the air rather than just blowing the hot air over the ice to cool it, I would be tempted to place a block or two of dry ice in the cooler with some antifreeze. The dry ice will definitely stay cold all night.
what's the metal pan on top for?????? Consider enclosing everything on top in a tupperware container so you can hide wiring and have someplace to mount the switches. You could silicone the container to the top of the cooler or screw it onto the top lid.....
the exchanger will sweat from humidity in the air if it's appreciably colder than the air.
The pan catches a little condensation, Sea-dad, I thought about dry ice but was concerned with CO2 in the small cabin. The cooler stays in the cabin. The wiring is not finished and can obviously be improved.
Since you made holes in the cooler rather than run everything thru the top, you can do it.
Most places sell it in a heavy brown wrapper, and all you need to do is put it in a plastic garbage bag, twist tie it shut and duct tape the lid shut. good to go. the garbage bag will lock it inside as well as keep if from getting wet. never get dry ice wet it gets very angry.
oh almost forgot the most important part. by using the heat exchanger, all you need to do is lengthen the lines so it's in the cabin and the cooler is oout on the deck. I would be very tempted to find a place in the bilge to put the cooler and run the lines under the dect to the cabin if it works well for you.
Someone mentioned it already, but dry ice sublimes (evaporating solid) into CO2. CO2 will be heavier than air and can flow and collect in any low spot or enclosed area. Potentially very dangerous as it will remove (displace) oxygen from the area...
FYI: Adding "salt" to your ice/water mix will result in a temperature drop; slows the melting rate/increases the freezing rate of the mix. The net result is that the ice melts more and more slowly after the initial addition of salt.
For you techies:
Why does salt melt ice? In pure water, at 0°C, ice melts just as fast as water freezes. You won't see any of the ice melt as long as the freezing rate and melting rates are exactly equal. Adding salt (or any foreign substance) to the water upsets the delicate balance between freezing and melting. Fewer water molecules reach the surface of the ice in a given time, so water freezes more slowly. The melting rate isn't changed by the salt, so melting "wins".
Does adding salt to ice and water cause a temperature drop? Yes. This is how old-fashioned ice cream makers lowered the temperature of the ice cream below water's ordinary freezing point. A mixture of rock salt, ice, and water packed in the bucket around the ice cream mix can bring the temperature down as low as -21°C.
Why does the temperature drop? Energy is required to snap the hydrogen bonds that hold the ice together. The melting ice draws that energy from the surrounding solution as heat.
__________________ [red]MISS TEAK[/red], 25' Parker mod-V Sport Cabin "Life's too short to own an ugly boat ..." www.classicparker.com
Nice job Doug! I have the Kooler Aire version, not sure how well it works yet. Like you I have a cuddy cabin that I am trying to cool. please let me know how well it works out for you.
itwonder, I got the heater core/fan from a company called Flex-a-lite, a Mojave Heater. 800-851-1510. I think it was around $140, the plenum with 2 round air ducts was another 20ish. I liked it because the fan was attatched to the core, an all in one product. You could do something for less money rigging a fan to blow across a seperate core but this was the smallest, neatest way I found.
Wouldn't the dry ice in a plastic bag, sealed up, build pressure as it sublimates?
Yep ! Chip some dry ice into an empty 2 liter pop bottle, add a couple of tablespoons of water, screw the cap back on tight, place outside in the sunshine, stand back and wait.
First, I hope your lighter circuit runs off of your aux battery which is isolated from your starting battery. If not, it maybe a long swim home !
Second, the lighter circuit should have a fues/circuit breaker so your in line fuse is not really required, but extra fusing is always a good idea ! Fuses should always be as close as possible the the "source" and not the "load". Or in your case, the fuse should be as close to the lighter plug as possible.
I think you could possibly "improve" your 'air conditioner' by converting your cooler container to a 12V 'refrigerator' and as others have suggested find a "better refrigerant" such as salt water or radiator antifreeze.
Theres no reason NOT to start the cooler off with block ice as you suggest - but the ice itself will LAST a lot longer if it's stored in a 12V refrigerator!
This is how to convert that cooler to a refrigerator.
Quote:
Convert your esky to a fridge
To some people a car fridge is a luxury item that they can afford to do without, more and more people are finding that there is a distinct advantage in having some type of cooler for those times when they are away from home and need to keep food fresh.
Commercial car fridges differ in their performance and design but they almost all have one thing in common: they cost a lot of money to buy new. The exceptions to this rule are the small imported fridges from Taiwan and China which can retail for as little as $100 in places like K-mart.
This project will show you how to make a fridge similar to those imported units, but at less cost, by converting an existing cooler into a car fridge. Before we go any further, I should point out that if you are thinking of buying all of the parts brand new, don't bother, as it would cost more to do this than to buy a car fridge from K-mart. On the other hand, if you have most of the bits already, or can get them for low cost, then it is worth the time and effort and you will end up with a fridge of higher quality than the cheap imports.
How it works
The type of fridge we are about to build here is basically the same as the imported models and consists of an insulated container that has inside it an aluminium liner instead of the plastic found in a cooler. A special semi-conductor device known as a Peltier effect device is connected to this liner.
Peltier effect devices are as brilliant as they are simple to use. They consist of many small semi-conductor blocks all linked together and sandwiched between two pieces of high heat conductivity ceramic material. They have two wires coming out from between this sandwich, and nothing else.
So how do they work? Without going into a great amount of theory, you simply connect a 12 volt supply (the common ones available are 12 volt) across the input leads, and one side of the device will get hot while the other side gets cold. Simple, but they work.
I should mention here that these devices are in no way as efficient as a conventional compressor type heat pump, but considering that most car fridges are used in the vehicle while it is running (although some manufacturers state that you should not do this!), the current they draw is provided `free' from the car's alternator (while the alternator will draw more power from the engine to provide the power for the fridge, it is undetectable in all but the tiniest of engines).
Materials
So what do you need? Well first you will need a cooler of some kind. This should be no bigger than the 26 litre type, and preferably around the 12 to 14 litre size. If you are going to buy a cooler new, choose one that has as much insulation as possible.
The key to the success or failure of your fridge depends almost entirely on the insulating ability of the cooler. The unit I used - a Willow brand 26 litre - had only about 13mm thick insulation in the walls, almost none in the bottom, and none at all in the lid, the latter being just a hollow moulding. Considering that these things cost around $40 new, that is by no means good enough. Some of the other brands had thicker walls, with the Esky brand being the best I could find. If your unit has thin walls, you will need to add some insulation to the inside, and then a new plastic liner (more on this later).
Now you must get the Peltier effect device. There are a couple of possible sources for these things, some cheap, and some definitely not so. If you have an old `el-cheapo' car fridge that has given up the ghost, you can bet it will have a good Peltier effect device in it, as these things - being solid-state - virtually never wear out. You may have one with a damaged case, and this is a good opportunity to recycle a few bits from it.
Some of the electronics components suppliers also have Peltier effect devices but at ridiculous prices (more than the cost of a cheap car fridge itself). I bought my device from Oatley Electronics in NSW, who sell a 40mm square Peltier device for $25. Now that's more like it!
You will also need a heatsink for the Peltier device on the outside of the fridge. This can either be salvaged from old electronic equipment, made up if you have the skill and the spare aluminium sheet, or bought at almost any electronics hobby store such as Jaycar or Dick Smiths.
To make your fridge as efficient as possible, the heatsink should be as large as is practical for your fridge. As a minimum size, look for something about 120mm x 120mm x 35mm with around ten fins. The larger the heatsink, the lower the temperature difference from one side of the Peltier device to the other, so the more efficient your fridge will be at getting rid of heat. The inside of the fridge will need a heatsink also, to transfer the heat inside the fridge to the Peltier device. This will need a large surface area, and is best made by using a good size piece of 1mm thick or more aluminium sheet. The only other things needed are a fan to cool the outer heatsink, a heat triggered switch, rated about 100°C, as a safety in case the fan should fail (you will get both of these if you buy the parts from Oatley), and a small block of aluminium, about 50 x 50mm and a bit thicker than the cooler wall (including any insulation that you add). You can get this from your local aluminium stockist, or from a piece of scrap.
Converting the unit
If your cooler has very poor insulation (like the one I bought), you will end up with a useless fridge if you do not add some more.
As mine was a 26 litre unit, there was plenty of room for more insulation inside it. I used a secondhand sheet of 30mm thick styrofoam, and added the layers in the following way. Firstly, I cut a piece to fit the bottom of the cooler, curved the bottom edges to fit the inside of the cooler, and glued it into place with neutral cure silicone sealant. Next, I did the same for each end of the cooler, making sure there were no gaps between the end pieces and the piece you have just laid in the bottom.
A word of caution here. The lids of most coolers have a ridge around them to fit it into place on top of the cooler. You must allow for this when cutting the foam for the sides of the cooler. Glue the end pieces into place and cut two more pieces, one for each side, and glue these into place also. You will also need to add some more insulation inside the lid. I cut away the inner side of the lid and shaped two layers of foam to fit it. These were then fixed in place with silicone. By now your cooler will be fairly well insulated, and should make a good fridge. But first, it will need a liner of some sort. I used a ten litre rectangular bucket, which was the same colour as my cooler and cost around $4.
Because it was a bit small, I had to add another layer of foam at each end of the cooler as well as a slightly thinner extra layer on the bottom. This resulted in some 75mm of insulation at each end, 45mm on the sides, 55mm on the bottom, and 60mm in the lid. A far cry from the makers' original dismal effort.
After cutting a groove in the top of the insulation to allow for the flange on the bucket, the liner is fitted into the cooler, and held in place with a few dobs of silicone if necessary. Although the size of my cooler had shrunk from 26 litres down to around 10, I was satisfied as there was not much point having a big fridge if it just didn't work.
Cut a hole in the side of the cooler, right through both the outer and inner walls, just large enough for the block of aluminium. Next you will either need to drill two 1/8" holes right through the aluminium block to take the bolts as shown in the diagram or, if you are using a block thicker than about 25mm, holes from each end to take small, self-tapping screws. Now drill two holes in the outer heatsink, and remove any burrs from both the heatsink and the block.
Now you must make the inner heatsink. I used a piece of aluminium sheet about 200 x 600mm that was folded to fit neatly inside the cooler, in a `U' shape. You must now drill two holes in this sheet, at the base of the U, to match the block of aluminium. Also drill four more holes out further, and de-burr all of them.
Insert the aluminium block into the hole in the cooler, position the inner heatsink and screw them together. Now screw the heatsink into place with four short self-tapping screws or similar. Remove the screws holding the block, remove the block, and smear a coating of silicone heatsink compound (electronics shops) on the face that contacts the heatsink.
Replace the block into the hole in the cooler, and screw it back onto the inner heatsink. Put heatsink compound on one side of the Peltier device, position this onto the aluminium block, with the leads pointing down, the red lead to the left, and press firmly so that the excess compound oozes out. Without moving the device, wipe away the excess compound and then smear some onto the other side of the device.
Now you must position the outer heatsink and, using spring or tooth washers to stop it coming loose at a later date, pull the whole assembly tight. When doing this make sure that you tighten the bolts evenly, as tightening one first and then the other may cause uneven and excessive pressure on the Peltier device and may even cause it to fracture. The whole assembly procedure can be seen in the diagram.
To reduce the load placed on the Peltier device by the heatsink, you may want to do as I did, and screw the heatsink to the outside of the cooler for support. So that moisture does not accumulate between the inside of the cooler and the inner heatsink, you will need to run a bead of neutral cure silicone sealant completely around the inner heatsink.
Putting it all together
Now that you have done this, you almost have a working fridge. The only thing left to do is to wire up the device to the heat switch and attach the fan and cover. The wiring is so simple that a wiring diagram is not necessary.
You must first attach the heat switch to the outer heatsink. I did this with a screw and small metal clip made from a piece of springy steel. Remember to use heatsink compound on the switch as well. Now connect the red wire from the Peltier device to one side of the heat switch and then run a wire from the other side of the switch to a two-way terminal block mounted just under the heatsink. Now run the black wire to the spare part of the terminal block. Cut the fan leads to the correct length, strip the ends, and insert them into the corresponding positions in the terminal block with the wires from the Peltier device, and tighten the connections.
Now all you need is a lead and lighter plug so that you can plug the unit into the car. I used two 1 metre lengths of 10A cable, twisted together, with a cheap lighter plug. The electronics stores sell these things for about $1.20.
To make the fridge safe, and because I was testing the unit straight from a battery, I included a fuse in the positive line at the fridge end of the lead. You may like to use one as I did or you may want to rely on the car's lighter socket fuse. I personally recommend including a fuse in the lead somewhere, possibly in the lighter plug.
The final step is to attach the fan to its cover, and then to attach the cover to the fridge, over the heatsink, with four self-tapping screws. The fan cover can be made from any flanged box that will do the job, from a homemade aluminium or sheet steel job, through to a plastic lunchbox or similar container. The cover should fit as close to the heatsink as possible, so that the fan draws the air through the heatsink, rather than from around it.
A hole must be cut in the box for the air to flow through, and the fan is attached on the outside of this hole with four 3mm bolts and nuts. Once the fan cover is attached, your homemade car fridge is finished and ready for testing.
Testing your fridge
To test the unit, connect it to a large 12 volt battery or a 12 volt five amp power supply, and check to make sure that both the fan is running and blowing air in the right direction (see the diagram), and that the inner heatsink is getting cold while the outer one is getting warm. If all is well, you can put a couple of containers filled with water in the fridge, close the lid and let the beast run overnight. In the morning you should have some very cold water, and a working car fridge that you built (and can fix) yourself.
Cheers and stay cool, the refrigerator WILL use more 12V power than just the fan itself you are currently running, but with this addition/improvement - you should stay cooler for longer, with the same block ice to start with.
My version of a 12v A/C 
