Cheap refridgerator

[kingfisher]

Had to be in the caravan shop yesterday. They sell 12V cool boxes (Coleman, Electrolux) at around 60£. The whole coooling circuit is inside the lid of the coolbox. They even provide a normal lid, so that the whole thing can be used as a standard picnic-on-the-beach coolbox.

Now my boat doesn't have a fridge, just a coolbox. So here we go:

What is there to prevent me from buying a 12V dead-cheap coolbox, and using the lid, (with minor adaptions for size reasons) on board to convert my coolbox to a fridge.

I'm not going to the caribean, just local BE and NL waters, so the output doesn't have to be gargantuan. It will probably corrode to death after two years, but for the price of a (too large in size anyway) compressor, I can have 10 of these things.

Too good to be true?

<hr width=100% size=1>Group of people on the pontoon: skipper is the one with the toolbox.
http://sirocco31.tripod.com

 

[ccscott49]

For this climate, that sounds like a plan to me! Although I think you coud probably buy a peltier unit and incorporate that into your coolbox onboard. Try maplins or equivalent.

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[jeanne]

See the earlier post (scuttlebutt) on the same sort of coolboxes from Tesco. Dirt cheap....these boxes are Peltier effect and draw quite a lot of juice. The secret is to get them cold first by placing a large bottle of ice in them for rapid cooling and freeze anything you won't need for a day or so.

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[jeanne]

Sorry- second post, the previous post was on this forum (not scuttlebutt)entitled Cheap Coolbox..

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[steve_cronin]

Yes the didicated units are much better

On our last boat i installed a Peltier unit. It required a large rectangular hole to be cut into the side of the coolbox.

The one I used had an array of thermoelectric units on one heatsink with a large computer type cooling fan blowing on the hot side. This actually warmed up the space between the coolbox insulation and the galley moulding so i reversed the flow and ducted the warmed air out into the saloon. These unita are not as efficient as a conventional compressor system but with the excellent insulation fitted by (in this case) Hunter Boats, our keeping of a container of "Party Ice" inside the fridge and sensible power usage, that unit worked well for seven years even in a southern Brittany heatwave. We did have a coolbox of the type you mention on an earlier boat (& still have it somewhere) but it wasn't as efficient as the "Coolamatic" ( I think it was called) which is imported from New Zealand as the X3000.

Steve Cronin

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[MainlySteam]

Re: Yes the didicated units are much better

Steve - it may be the same make as the one we have which is, from memory, a Tropicool (maybe that is just the model name) made here in NZ. It has an array with a big heat sink which two 80mm computer fans blow air through on the hot side to take heat away, and another(s?) on the cold side to circulate the compartment air for cooling. It draws 1.5 amp on low and around 4 amp on high and cools an insulated compartment about 300x400x600 deep.

We have a high capacity freezer plant on board and the objective was that we would use the refrigerator mainly for less perishable things such as cheese, freshly thawed meat, etc and for drinks, and if necessary support the refrigerator with frozen bottle of water/beer etc to keep its temperature down. We also did not want to get into the troubles of two compressor plants or balancing the refrigeration between the two.

We have found in the NZ climate (rarely gets over 25C anywhere on the coast of NZ) it is satisfactory for our purposes on the low setting all the time and drops surprisingly quickly from warm start to cool. The hot side is in a locker with the locker vented by a 120mm computer fan running slow to cut down noise by dropping its supply voltage to around 6 v - providing cooling to the hot side by air movement improves the peltier units performance markedly.

I suspect these units are much more efficient than those in the portable coolboxes you can buy. I do not know how much it was, but they obviously cannot be bought for anything like as cheap as portable coolbox.

I think I would do the same thing again.

John

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[johnsomerhausen]

Re: Yes the didicated units are much better

I saw on the web, a year or two ago, a coolbox wher the outer casing was aluminium. it was actually the heat sink for the Peltier unit and that idea made sene if you didn't put it inside an enclosure. Have never been able to find it again. I seem to remember the manufacturer was Australian. Any idea aboaut that ?
Thanks
john

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[MainlySteam]

Re: Yes the didicated units are much better

Hi John. No I am not familiar with the aluminium box ones, but I am currently dealing with some Australian naval architects and a shipbuilder - I will send them an email to see if any of their guys/girls know anything about aluminium "eskis" with peltier units that they keep their "tinnies" in. Be about Tuesday your time before I get a reply.

The aluminium sounds a good idea as the ability to conduct heat away from the hot side of the unit seems to increase the efficiency markedly.

In the meantime the NZ place my unit comes from is here
<A target="_blank" HREF=http://www.tropicool.co.nz>http://www.tropicool.co.nz</A>

John

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[William_H]

Hello Kingfisher the device you speak of is obviously the peltier type solid state the usual give away is that it can be used for heating and cooling. I think the bottom line is that you will be dissapointed.. At least thats my experience. Hired a camper van in NZ some years back had the peltier fridge running all day on car battery and all night on mains power and the fridge was barely cool compared to outside.. The only chance to make them work is to cool the hot side efficiently say with sea water piped to it. Here in oz peltier are a bit of a joke in boats and for camping the big block of ice and good insulation being the common way to go unless you can go to a compressor type
Sorry folks I know many will dissagree but I can't let you all say they are great.

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[MainlySteam]

The only trick is making sure the unit is from a good supplier and the installation is good. We have had success with ours as explained in earlier post, and they are widely used for military and technology based systems for cooling both perishable items (such as blood and vaccines) and electronic heat loads in equipment.

When you see some systems advertised for a price at which one could not even buy a good heatsink or the fans then one is asking for an inefficient unit. Do not write them off on the basis of what seems to have been an inefficient system.

I would also caution against measuring their performance against a 30 - 40C Australian summers day - whatever you use will need to be adequately sized. A peltier unit on a coolbox will likely not cope (but I have seen them do so in more normal environments), both from the point of view of not being a very good installation and because whatever you use will need to be of appropriate capacity and heat exchange capability (condensing wise if gas and air heatsink wise if thermoelectric). Even if you use an appropriately sized system one may have to compromise in efficiency according to the current environment - for example, our reciprocating system's condensor is seawater cooled, and is set up for tropical seawater temperatures, at seawater temperatures in the 15 - 20C range the compressor loses quite a deal of efficiency by running at low pressures.

I am the first to agree that thermoelectric is normallly not as efficient as a compressor unit, but on a small vessel with only a casual need for refrigeration it is an effective solution, and on a small vessel with both refrigerator and freezer it is probably more efficient that trying to run cold leakage arrangements or two compressors.

I am not biased to peltier, we have both a high quality, high capacity reciprocating compressor unit on board, and the fixed peltier system. Neither is inferior to the other, the secret is in the appropriate application of them. I suspect a good peltier portable coolbox in temperate climates will work adequately, and I have seen them do so.

John

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[craigbalsillie]

Even betrter than that..

There's one of these on ebay at the moment.I think it's in the camping part of sporting goods. It was only a tenner the last time I looked,,

Sounds like you're onto a winner with this one..

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[MainlySteam]

Henk

The name brands will usually give you a cooling capacity for the box in their literature. Usually, for the name brands that I have seen around this side of the world, it is either "up to" 20C or 25C below ambient. I would expect the "up to" infers the extreme of ability with good ventilation etc. It is possible to get or build boxes with far greater cooling capacities, even capable of carrying perishable medical products in tropics, etc, but obviously they are dearer. I do not know what the efficiency of the cheaper cool boxes typically is but the thermoelectric array units are typically quoted as being around 60 -70% efficient eg 100 watts in gives around 60 - 70 watts cooling.

If the ambient temperature is 25C, an "up to" 25C box would probably reliably get you down to about 5C and take some time to get there. If you are in 40C ambient then obviously the same box is only going to get you down to 20C or so, maybe, which is hardly cool! This may account for some of the Australian problems quoted in another post - although I do know that the name manufacturers in Australia clearly set out in their product literature what the maximum capabilities of each model of their units are, in which case it is the users fault and not a fault of the unit if they buy one of inadequate capacity.

I would suspect that a thermoelectric unit removed from a name brand coolbox, mounted as you say, would be successful in your climate as long as you are only looking for 15 -20C at most temperature drop against ambient and as long as it is mounted in a box on the boat no bigger than the one it came out of. If you want a larger temperature drop than this then you need more capacity, whether compressor or thermoelectric is a matter to suit the particular circumstances and needs, and is nothing to do with any incompetence of one over the other. Also, be aware that the discrete thermoelectric units you can buy often have a potentiometer or similar adjustment in their controller (as well as the temperature control adjustment itself) to set up the unit for the particular sized and shaped refrigerated box it is serving. The units in coolboxes may (I have no idea if they do) also have such an adjustment inside them which may need tweaking in order to get them to perform to their best if removed and put on another box.

To buy a small commercial thermoelectric unit by itself will cost of the order of USD300-400.

If you do try your suggestion, I would welcome a PM as to how it turns out. I work a lot in the marine industry and the outcome of suggestions such as yours are always worthwhile knowing.

John


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