Fridge / Coolbox Construction

This project started off in one direction, then followed another.  

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We initially used a small camping/picnic cooler box from Lidel. Being impressed with that we went out and bought a CampinGaz version which was far more expensive than our Lidel purchase. With our new coolbox we started to build a cabinet in the van to house it, but after leaving it one day, we came back to find it had been knocked off the bench and the door had been broken. We started to repair it (not easy as its made from PVC, and nothing sticks to PVC very well - hence the grey bit on the one corner), and thought, why not build a complete coolbox! After all, we hated the colour, the door opened the wrong way, and it was slightly the wrong shape inside, plus it was very noisy.

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The coolbox construction is quite basic. A box with a door and a special unit to remove the heat.

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This shot shows what is normally inside the coolbox of the heat transfer unit (heat pump).

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Take more bits off and you find its basically in two halves. Both with fans and a 'heat sink' assembly. Both halves are joined together using a Peltier Effect heat pump. I first came across these Peltier Effect Heat Pump units about twenty years ago when they where introduced in to the RS Components catalogue (trade catalogue of all things nice and useful!). Basically they are a flat object (comes in various sizes), in this unit it is about 2.5 inches square by about 1/8 inch. Depending on which way you apply the direct current voltage polarity, depends on which way it will pump the heat. (cool boxes will cool as well as heat).

The Peltier unit is mounted between two finned heat sinks using heat transfer paste. Then the fans are used to circulate the air past the fins, either to draw heat to the unit for it to transfer the heat to the other side of the Peltier  unit, then the other fan expels the transferred heat away from the unit. I have found them advertised on the internet complete with some controls for over £200! Bought mine for about £100 with a free blue box!. Unlike the cheap cool boxes, the CampinGaz box has a small circuit board which has a small bridge rectifier circuit to ensure the fan runs the same way, regardless of which way its plugged in (for heating or cooling). The other bit of the circuit board had a circuit to measure the voltage, and switch the whole unit off if the battery voltage fell below about 12.5 volts (may have been higher). Although our water boiler and warm air heater both have the same idea, but their cut-out voltage must be set at about 10 volts. The trouble with the cool box was that it would only run if the engine was running! Out came the soldering iron to remove offending voltage detection circuit to enable the coolbox to run all the time (all the accessories including lights run off an independent leisure battery).

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Un-usually.... I consulted the wife on this project. I knew what width I was limited too, as I had already started building the cabinet to house the cool box in. The depth was also about the same. The overall volume couldn't really be any larger, otherwise the heat pump would then be under rated. With consultation with the wife, she decided what she wanted to store. After cutting it down to a reasonable amount (they always want more ;o)  ) and their sizes worked out, we where then able to decide where shelves should be etc. The result of our consultation was the above mold which is profiled for the side of the van and grooves to create ledges for shelves. Due to the grooves etc. the coolbox liner was made in two pieces, then stuck together afterwards.

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After fibreglassing, and the removal of the mold, it looked as above. Above is the completed coolbox liner completed and ready for insulating.

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Of course when you go and buy your new Electrolux or Zanusi fridge, you get a load of 'useful' containers for vegetables etc. Guess what, I too had to make some 'useful' containers for our cool box, hence the molds above. The mold on the right is for a special bin for mounting on the inside a cupboard door, to hold washing liquid type bottles and a plastic carrier bag for waste.

Fridge project v2!

I had progressed quite far with the Peltier Effect Heat Pump unit, but after lots of deliberation, I thought it would be better to fit a proper compressor type heat pump as used in proper domestic fridges. The plus points for this new route is that compressor heat pumps are the most efficient for cooling capabilities and power consumption, and they are more capability of sub zero temperatures. Another plus point is that unlike a 'three-way fridge' they don't need ventilation holes to be cut in the van walls or need flues for the gas burner.

My new fridge would now be using the 'workings' from a 12V compressor fridge to install on to my custom sized case which was made to my wife's specific requirements. 

The fridge I eventually won on eBay stood about four foot tall and was unused, however the outside was heavily 'shop soiled', this didn't matter as I would be discarding the case. (Sorry about the awful colour, but white fridge on white background doesn't work)

First I had to strip the fridge of its casing to recover the 'workings'. Not an easy task as everything had been filled with expanded foam insulation, but with the use of a jigsaw, I was able to split the sides and peel back the outer casing.

Having peeled back the casing, I borrowed a vacuum pump and empty Freon bottle I 'sucked' out all the refrigerant gas (Freon) in to the empty Freon bottle for use later.

The 'S' shaped tube (shown above - though a lot is missing by the time I took the photos) running side to side is the condenser tubing which had been embedded in to the insulation material. The condenser is the part of a fridge which gives off the heat it has gained from the evaporator, which converts the refrigerant gas back into a liquid.

The compressor looks identical to a standard mains powered domestic fridge, however this one is 12 volts DC. Unusually the condenser s not hung on the back as with most fridges, but integrated in to the steel casing. Inside is also unusual as there is no visible evaporator/ice box, again its built in to the lining of the fridge.

Below is the fridge components removed from its normal setting from with in the fridge.

The white panel is the evaporator which sucks the heat out of the fridge cabinet, known as the evaporator as it 'boils off' or 'evaporates' the refrigerant liquid in to gas, hence evaporate. The evaporator will be stuck on to the back of new fridge lining shown below.

The hole in the side of the case/fridge liner was for the earlier idea of using a Peltier heat pump from a coolbox. The hole will now be blanked off with a specially made plug as is serves no purpose with the new 'proper' refrigeration system.

I had hoped to strip all the plumbing etc intact, but after very careful striping of the outer steel cabinet, it was obvious it wouldn't be possible to achieve my original idea of stripping everything out intact. Having to re-plumb the unit brought in a whole new can of worms, the biggest problem being the rejoining of all the tubes, this I have achieved by using a pipe flaring kit and fitting flared screw together fittings as shown on the two photos below (on the bits of copper tube). The ends of the tubes had been rolled over to seal the pipework from the atmosphere to avoid the ingress of moisture (not liked by refrigeration systems) whilst the unit is being rebuilt.

As pointed out above, the condenser wasn't recoverable due to the way it was installed. All the ones I have seen on other fridges have all been the wrong size (I thought I could rob a dead fridge of its condenser) so a new one was required. Like everything else with this van project nothing is standard, so a special was required. 

There's nothing magical about a condenser, its basically a long length of tubing to gives off the heat within it. There was about ten metres of tubing in the original unit, of which I have slightly exceeded in my condenser. With the tubing now being mounted out side the insulation, and a couple extra metres, the condensing efficiency should far more efficient. My new condenser basically consists of a very long length of tubing (standard copper brake tubing) sandwiched between two sheets of aluminum plate with heat transfer compound liberally pasted and 'No nails' glue.

The photo below shows the plate with the tube weaving up and down it, and clamps holding it all in place whilst the glue sets.

Doesn't look much at the moment, but the following photos (when ready) will hopefully make it look a bit better, especially after all the clamps have been removed.

The photo below is the same as above, but with a second plate covering the pipework and crimped around the edge. Finally it was painted mat black to help its efficiency.

The photo below shows the compressor (C) mounted under the fridge case/liner. Within the same cupboard is the fridge compressor motor controller (A) and the thermostat (B). I initially used the original thermostat, but found it very vague and slow to react with a variable differential band. That was dropped in favour of a 240v AC unit which had a row of LED's showing actual fridge temperature. The thermostat was no good in its standard for as it relied on a 240v AC supply, however after some tweaking and ditching of various components I managed to get it to run off the 12v DC van power. Ideally 24volts would have been better, but with further tweaking I managed to get it to settle down with the 12 volts. The white bit in the photo (D) is the rear wheel arch.

The cupboard s now complete, as shown below where it is stood up in my workshop (with the aid of a post gee clamped to its side).

Above the fridge is a small cupboard. All the catches had to be modified as  was unable to find suitable ones of a low profile to avoid big lumps inside the fridge door which interfered with the thermal insulation. 

At the bottom of the cabinet is the cupboard which houses the fridge compressor, waste bin and other shelving.

And finally the completed fridge with extra containers and shelving.

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