Building a small fridge advice.

Seagreen

Seagreen

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I'm planning to build a small top-access fridge/freezer in some probably redundant space. (Actually a couple of lockers that have little real function and can be re-fashioned). I'm looking to get about 30-40 litres of usable volume, but wondered what would be the best power source. I don't and won't have gas aboard, but will have some big 12v DC (85-110 ah) batteries, but I'm hoping to run mainly on 240 v shore power with running on engine charging and a bit of solar panel input. The current coolbox is too small and in the wrong place aboard.

Does anyone have advice, suggestions and above all, links to websites which may prove useful? I intend only short term use as a freezer, but what reliable, practical and above all, cheap working compressors or thermo-electric kits have people found useful? I've saved the old workings of a cheap Thermo-electric fridge, but may jettison these. Can the guts of a cheap Thermo-electric fridge be successfully cannibalised into powering another coolbox?

All ideas welcome.
 
The compressor based fridge units are generally the preferred option, as long as you are happy supplying the required power. Should not be a problem if you are marina based, use engine, and also have PV.

Thermo-electric (Peltier) works, but is extremely inefficient, and certainly won't provide a freezer. Maybe OK for a few days if you use it on mains power to cool a very well insulated well filled box down, and then just use it to top up when motoring.

(Personally I use a gas fridge)
 
Thinking aloud, would it be possible to have a two stage system, whereby the "hot" side of the TE system is cooled by a direct in/out flow to seawater? this water jacket would need to be both watertight and probably with its own seacocks? Or am I thinking of the old hull mounted engine water cooling system? Surely as the Sea surface temperature in summer in the channel doesn't really get above 15 degC, a TE system which could cope with cooling to -18 degC below ambient temp may actually produce a working freezer. Loads of pressurised plumbing though.
 
Hi, I have been down the same path and used the peltier sysystem in a pupose built locker in the side of a bunk, was pretty small and virtually use less, ended up becoming just another cupboard, Then I converted the existing ice box to a fridge using the purpose built engel kit, worked really well but due to the poor insulation (which i couldn't improve externally) wouldn't keep ice cream frozen, mind you temps here in an aussie summer will make most on board fridges struggle (on some days) just had 14days+ over 30 deg centigrade, cheers Peter
 
For my opinion forget thermo electric peltier devices. They are power hungry and useless. If you can get a special on CF 25 fridge freezer this can be your best option although not all that efficient in the insulation department.
if you want to use your space and insulate it then you need an isotherm type kit. Here the evaporator (cold bit) is separated by pipes/hoses and gas sealed joints to the remote compressor/ condenser. (hot bit) Not that cheap but really the only option for freezer/fridge. Expect around 40 AH per day current demand. (or less depending on use and ambient temp) I have a friend who has one and despite Oz summers does not use it finding the demand on battery power too much compared with dropping a block of ice in the box. You should build the box insulated and try the ice for cooling. On the other hand other friends have their fridge running 24/7 on marina power and love it.
good luck olewill
 
I did a similar job 2 years ago. Converted one of the lockers under the saloon seating to a fridge by insulating the box and installed a Dometic/Waeco kit compressor in the locker next to it. Very pleased with the result but there are a couple of things I would have done differently - and should have thought of at the time. I did consider a Peltier type system but quickly discounted it due to the poor efficiency.
The Dometic kit can power a space up to 130L but would presumably have to work pretty hard for that. My locker after installing insulation and lining is 65L. It is also low in the boat so partly below the water line. I used closed cell foam sheets for insulation about 8cm thick. Called Celcon or something but available at most builders merchants and recommended by many others here. The lockers I used for the installation are part of a GRP moulding in the boat and sealed all around with the hull as the base. I put the insulation around the inside of the locker which was fine on 3 sides and base but foolish on the side adjacent to the locker where the compressor was to go. I should have put the insulation in the other locker and gained a little more volume in the fridge. This hasn't been a problem but still a waste and something I can change anyway.
The Dometic kits come in a few versions with different shaped cooling plates. I bought the one that was in stock at the time with an oval shaped plate and, with hindsight I should have waited until an L shape was available. I then installed the oval plate with the openings top and bottom, another error! An L shaped plate takes up less space and you can stand a small amount of frozen food on it or use the horizontal part to make ice. My oval shape takes more space and, installed the way I have it, cannot make ice. When I turn it through 90 degrees that should be sorted.

When I'm in the UK I live on the boat with the fridge running permanently. In the summer I have it on setting 2 (out of 6) and it keeps the interior below 3C with the compressor running for about 30 seconds every 5 minutes. This is when the fridge has little in it so about as wasteful as possible. I is connected to 12v but when in my berth is effectively run by shore power through the battery charger. Unless it is very quiet and you concentrate you never hear the compressor cut in and out and it doesn't affect anything else electrical.
 
I have recently finished making my under counter fridge freezer. I had made an 85 litres stainless steel tub made from a plywood plug I mocked up. We have mini um 100mm of king span insulation. This was packed in then and strange corners where insulation was not wast to fit was filled with builders foam. This helped set everything solid as well.
We used a Waeco compressor kit with an oval evaporator plate that we put a bottom into. This now forms a 3 litre freezer within the fridge.
This all works very well and 85 litres is plenty big enough for us the stainless steel tub is nice as it helps dissipate the cold nicely around the fridge. It's also clean. We have a drain on the bottom with a valve and the ability to run the hose into a bucket when cleaning the fridge out
 
Pasarell said:
I should have put the insulation in the other locker and gained a little more volume in the fridge. This hasn't been a problem but still a waste and something I can change anyway.
Click to expand...

I don't think that would necessarily be very good, as the damp from the cool fridge would saturate your wooden bulkhead leading to rot. When insulating anything you need to understand where the dew point is in the insulation.


To the OP
Penguin have a good website
http://www.penguinfrigo.co.uk/

In there somewhere is a volume calculator. It is a great help when working out your space, then whats left after PROPER insulation. The the space is a cube of sorts then this is easy.

Ideally you should have 4 inches of insulation all round, but certainly for the UK, 3 inches would be a satisfactory compromise.

You mentioned a water cooling option; very good but will add to cost which may not be necessary in UK waters, but it does allow the installation of the compressor where you do not need to disperse the heat.

You can get a polypropylene liner made up by Tek Tanks in Alton. http://www.tek-tanks.com/boats/custom-boat-tanks/?gclid=CN-a-8ai4LUCFaHHtAodnSsAVw

It really is worth the effort and loss of space to have decent insulation even in the UK. Properly done it will allow the fridge to run just on solar even in the UK. We acheive this in the Med with 2 x 85 watt panels, and have left the boat on its mooring with fridge on for a week without being on board, and the batteries remaining full.
 
Seagreen said:
. Can the guts of a cheap Thermo-electric fridge be successfully cannibalised into powering another coolbox?.
Click to expand...

It can be done very easily.

I butchered a picnic coolbox which was next to useless, and made a much smaller coolbox which was slighty better but only able to cool a much smaller quantity of food. I use it in the car sometimes if the weather is hot and we are taking stuff down to the boat. But it would just be a waste of a lot of battery power on the boat.


I like the idea of the (Waeco?) device that uses water cooling with the compressor rather than air cooling. Keeps the warm air out of the cabin and is possibly more efficient. In all honesty though, I don't know if they live up to the promises.
 
Seagreen said:
Thinking aloud, would it be possible to have a two stage system, whereby the "hot" side of the TE system is cooled by a direct in/out flow to seawater? this water jacket would need to be both watertight and probably with its own seacocks? Or am I thinking of the old hull mounted engine water cooling system? Surely as the Sea surface temperature in summer in the channel doesn't really get above 15 degC, a TE system which could cope with cooling to -18 degC below ambient temp may actually produce a working freezer. Loads of pressurised plumbing though.
Click to expand...

There is a water cooled version of the Danfoss 35C compressor unit. I have one in a standard Waeco fridge, seawater cooled using a Par Max 1 pump. Despite the fact the fridge insulation is far less than desirable it performs well in Greece, never running for more than about 40% of the time it is switched on, in harbours where the water is very warm, for example, but mostly far less than that.

Fouling of the pump valves is something of a problem, requiring cleaning a few times per season. I find that when we are hauled out the fridge will run indefinitely on a bucket-full of water, catching the discharge from the transom and piping it back to the compressor. A method that I have seen used successfully to overcome the fouling is to pipe the water supply to and from the fresh water tank but this would be a tricky option for my boat.
 
Compressor driven with keel cooler works just great in Greece with mid afternoon temperatures at around 40º C and water temp around 25º C. Consumes quite a bit of power but in those temps the solar panels are not being used for anything but keeping the beer cold!
 
Just show what my thinking was:

I've a "slice" of useless space, currently used by a couple of pointless lockers, just aft of the port berth. This is only about 12" wide, but does go back to the hull, so I'd end up with a thin narrow "cheese slice" coolbox, which would only be about 25L at a guess. I had originally thought that a thermo-electric system would be the most effective (ie., simplest) system to install, as a well insulated box would have had cooling air drawn up from the bilge at about 10 - 12 degC ( Av Channel summer sea temp) over the Heat sink and out over the top of the cabinet. There would also be an advantage as the air would get cooled by the low temp of the box before it got to the heat sink, and what with pre-cooling the box with ice and other frozen stuff, I think I could get it to a near freeze. This being the Channel and Irish Sea, air temp is never that hot. And that it would require minimal input by the battery/engine, from which it would get a good charge.

However, there is room just aft of this space for a small compressor to fit behind a bulkhead next to a battery, so this too is a good option. Worth exploring.

I always feel that coolboxes, especially the ones I've seen, have been let down by poor insulation, and that getting this right is 2/3rds the battle.
I'll certainly check up on those websites. Cheers all.
 
Chris_Robb said:
I don't think that would necessarily be very good, as the damp from the cool fridge would saturate your wooden bulkhead leading to rot. When insulating anything you need to understand where the dew point is in the insulation.

Thanks for the comment but in my case the bulkhead is part of a GRP molding so not an issue
Click to expand...
 
PCUK said:
Just run on economy setting in that case. You'll have to run the engine to charge the batteries anyway.
Click to expand...
May be the case in UK but my 125 watts of solar will run my fridge pretty much indefinitely in Greece. The fridge plus water pump takes about 3.5 to 4 amps at the start of its cycle, reducing to about 3 amps gradually for about 6 minutes. It then shuts down for around 12 minutes before commencing the next cycle. This continues night and day. With 330 Ah of battery the voltage is down to about 12.3 first thing in the morning but soon back up to full charge when the sun gets going. The only time we ever need to run the engine is in poor weather, thankfully rare.
 
I built our fridge with lots of insulation and a s/s box designed to slide into the space inside the insulation as fitted. I also used a water cooled condenser but without an electric driven pump. The condenser sits as a sort of 'plate' on the outside of the hull.

Does it work and am I happy? In a word yes. Its extremely efficient and if I forget and turn it up too much the whole fridge becomes a freezer!
 
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