Insulating Fridge

Submitted: Monday, Aug 09, 2004 at 17:11
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As reported previously we have had some problems with our fridge, particularly that the compressor would trip out immediately after starting if the voltage was not in the 12.7 - 13v range. Wanting to run some tests & at the same time to insulate the compartment I decided to take the fridge out. The testing finally revealed that the push on contact at the fridge terminal block was a little corroded & a working of this appears to have solved the trip problem although only the long term will confirm this. The insulation went well, because of the batons in the compartment it is necessary to use a few layers of insulating foam so I purchased sheets of various thickness & carefully measuring built up a full lining in the compartment. When the time came for re-installation I could not get the bloody thing back in! Talk about a trap for young players, on the base of the fridge the screws which hold the compressor in place sit proud by the thickness of the screw heads! This meant that my careful measurements were out by this amount but worse that the fridge could not be slid into the very snug insulated compartment as the screw heads just bound into the wood floor. In the end I fitted a thin galvanised plate on the floor so that the screw heads could side over same & had to shave away a section of the polystyrene roof. The whole compartment is now fully insulated & I am confident the unit will use much less power. Andy
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Reply By: Noosa Fox - Monday, Aug 09, 2004 at 17:13

Monday, Aug 09, 2004 at 17:13
Andy, I was having problems with my fridge trying to start and cutting out soon afterwards, but mine is only when the voltage is 12.3 or 12.4 volts. I was told to test the voltage at the compressor while it was starting, and I found that it quickly dropped to about 10.5 volts. Because of this the other device in the fridge that cuts it off if the voltage is too low to protect the battery came into affect and turned it off, so it was never going to start again until more voltage was put into the battery. In my van we have a Waeco transformer fitted so I solved the problem by going via the inverter and allowing it to run on 240volt supply which is in turn reduced back to 26volts. This does however by pass the low voltage protection built into the fridge. Our fridge had a problem with the thermostat and the resistor that is connected to the "C" terminal (I think without taking back off to check). This resistor detirmines what speed the compressor runs at. Without a resistor it was drawing about 2.8 amps but took for ever to cool fridge in hot climates, but with resistor in runs at between 5 and 7 amps depending on how long it has been running. I checked the instruction book on how the fridge should be installed and they recommend that it draws air under the front of fridge and exhausts it out the top, not via a vent top and bottom at the rear as most are installed. I then copied what Turist has done and closed off the external vents, hence preventing dirt getting on the condensor, and fitted vents on both sides of the bottom at the rear of fridge and vents directly above the top of the condensor. Since fitting this I have found that the fridge is working properly. It is my opinion that the fridges would be best installed with an air gap under the base plate that allows air to be drawn in as Waeco recommend and then exhaust it out the top at the rear of fridge, and I am considering cutting some of the timber from the top of the fridge and lifting it by 20ml to produce an air gap underneath and let it breath even better. I am not convinced at the need to provide extra insulation around the cabinet as it is really no different to a household fridge and that doesn't have extra insulation. (NOTE This is only my un-qualified opinion, and I have nothing to back it up one way or another) I learnt a lot about the Waeco fridges while mine was being repaired by the excellent Waeco service agent in Derby. All of their other agents that I have dealt with have left a lot to be desired. Brian
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Reply By: Andy1 - Monday, Aug 09, 2004 at 17:14

Monday, Aug 09, 2004 at 17:14
Brian Not wanting to go into too much detail I did not mention another issue which may have been part of the starting problem. Some time ago Anthony & Collyn commenced a discussion about voltage drop at the fridge, I measured ours at the time & it was a bit less than 1 amp. There were some suggestions that the BT wiring was too light but it looks to me like 6mm which should be heaps. When I was taking the fridge out I noticed that the connectors at the BT/Fridge cable interface connectors were a bit oversize & that the wires had only short tails so that in all probability the screw in the connector was not maximising the contact. I had planned to solder mine but when I put the soldering iron on it tripped the house earth leakage unit so I just used a longer tail on the fridge cable I would it onto the BT before tightening. The voltage drop at the connectors is now about 0.5 amp which seems quite acceptable. With regard to cooling, the fridge design seems to be such that the installed fan is configured to keep the electronics, rather than the compressor, cool. The heat exchange required to provide the necessary heat transfer is the coil where the heat removal requires as much air circulation as possible - logically the venting at the top is most critical although this brings the heat inside the van. I do not believe the dust is an issue, the condensor is a sealed unit, also I was very suprised how little dust has accumulated in the fridge compartment when I took the unit out. With regard to insulation I have to disagree, the air gap around the fridge will tend to be warmer than ambient due to the heat generated by the operation, even at ambient in the warmer months this is pretty hot & the fridge is only lightly insulated. I can not remember how to do heat transfer calculations but am prepared to base a case on logic. We have all had experiences with different insulation thickness on eskys & know that the thicker the insulation the less the heat loss per unit time. Engel in their recent models have significantly boosted insulation, portable fridges like Trailblazer (?) use significantly less power because of the much thicker insulation. How often does a household fridge cycle? When power is in finite supply in our vans we care, at home we really have little idea. QED. Only time will tell if the additional insulation has reduced power consumption. Andy
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Reply By: Deleted User - Monday, Aug 09, 2004 at 17:15

Monday, Aug 09, 2004 at 17:15
There are two ways a fridge loses cold or more rightly gains external heat that finds its way in through ....1. The door ... 2. The insulation. An example of insulation efficiency .... a 240 litre fridge with 50mm insulation gains a certain amount of heat through its insulation. For the sake of simplification lets say it gains 60 units of heat per 24 hr period. The same 240 litre fridge with 75mm insulation only gains about 40 units of heat which equates to 30% more efficient for a 50% gain in insulation thickness. The same 240 litre fridge with 150mm insulation (not practical for a BT cabinet but I'll give it to show the effect) only gains about 20 units of heat which equates to 60% more efficient for a 300% increase in insulation thickness. We also have a freezer sitting on top of our fridges, the loss of cold at least doubles with a freezer. It is a straight fact ...the thicker the insulation the less the compressor has to work to maintain the set temp because less heat is transmitted in through the walls. The duty cycle of the compressor reduces with 50mm of insulation verses 20mm because the fridge gains less heat through the insulation. There is another reason why I insulated between the wall of the fridge and the cabinet of the BT and that was to make the air flow over the condenser more efficient. The fridge in the BT is enclosed in a cabinet with an air gap all around, effectively making it a fridge in a box. This box is then vented on one wall with a low vent and a high vent, this rids the box of heat generated by the condenser via convection. Imagine enclosing the fridge at home in tightish box with only two vents for air flow. This heat is able to travel up and around the box before exiting at the top vent. This potentially heated the steel cabinet of the fridge and keeps the volume of the area quite large hindering convection action at the vents on one wall of the box. Insulating this area to the edge of the fridge cabinet stops the cabinet being exposed to condenser heat and reduces the area around the condenser to a much smaller, tall, funnel like shape with aids convection markedly through the vents. As battery consumption by the fridge is a direct relationship to compressor duty cycle ( time on/off per hr) it has to be a win-win situation for little expense and a bit of time. Our fridges really have very minimal insulation and this is most easily seen when the BT is in 40 deg heat of summer compared to 5 deg of winter the fridge works much harder (more battery consumption). If the insulation was better this difference would be much less ... Now !! If I could only stop the kids opening the door 100 times a day !! [wink] Brian, I cant see how my fridge can breathe from the front ? It is screwed all round by the fridge facia ...and the air has to get from here to the condenser ... do we have different types/models ? Are you bringing condenser heat into the BT ? Regards Anthony Explore this Great Land ...Do it Easy ...Tow a Bushtracker
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Reply By: Noosa Fox - Monday, Aug 09, 2004 at 17:16

Monday, Aug 09, 2004 at 17:16
Firstly, as in my first comment, these are only my un-qualified comments. I am not trying to critise anyone. Our 190 lt Waeco fridge has never worked properly since we have had it. I have taken it to Waeco agents in Emerald, Sunshine Coast, Katherine and finally Derby. Only the Derby one seemed to test it properly and fix the problems, well outside warranty so I had to pay. The first 2 in warranty period said there was nothing wrong with it. The main problem all along related to the Thermostat but when you read the manual it says how it is designed to be vented, (and that is NOT the way BT install them), and that dust on the condensor plate will cause inefficencies in the operation of the fridge. I checked the fridge and found that I had a large amount of bulldust all over the condensor plate and on everything else in the fridge cavity. This came from the standard fitment of the external vents top and bottom. When I cleaned the dust off everything it did appear to be working better. (If others are not getting dust in there, then all I can say is that maybe I am doing more off bitumen travel than most or maybe travelling at a different speed that caused it to get sucked in.) Turist told me how he had his new van fridge installed and how well it worked, so I copied what he did and blocked off the external vents. All I can say is that it now works perfectly with internal venting ONLY and that has been in northern parts of Australia in NT and Kimberleys. There is very little heat coming into the van, and infact to me it appeared that when the temperature outside was so 40C this was able to come in through the external vents, but with these closed the internal van temp was actually less than outside temp, so my new method of venting may well be more efficient. Only time will really tell, but both Bob and I are very happy with the way our fridges are now vented. My fridge is exactly the same as yours Anthony, and was installed in the same manner, but there is about 25 to 30mm that could be cut out from on top of fridge to allow an air gap, and this is what I am considering doing. My fridge and as yours is the same vintage, has a problem with the bottom hinge of the lower door. The hinge is a straight right angle and when travelling on rough roads this causes the backing plate that it screws into to bend and the door drops. This then allows more bouncing and the plastic inside the door gave out on mine and the replacement door was over $200. This has been solved on later fridges with the hinge having a second angle that goes under the fridge to prevent the bending. I think that you would be ewell advised to make a new hinge bracket that extends further down so that it pushes against the cabinet work and not only on the fridge cabinet. I will show you what I mean when we are at Copeton. Because my cabinet has given way and I had to change hinge sides, I will be replacing the fridge shortly and this is when I am planning to elarge the hole to give extra venting. I agree with Andy that the fan seems to be in the wrong place and this is why I have fitted another fan to blow air upwards when in really hot weather. Very little warmth can be felt coming out the vents. I have also had loose connections that prevented fridge from working. My voltage drop is only 0.3amp between battery and compressor when fridge is not operating. Try doing the test as the fridge compressor is just starting. You might get a surprise to see how far the voltage drops at this point. Ours is more than 1.5 volts lower when fridge first fires up compared to when it was idle just before hand. Brian
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Reply By: Deleted User - Monday, Aug 09, 2004 at 17:17

Monday, Aug 09, 2004 at 17:17
I have done some quick calculations regarding voltage drop in 6 sq mm wire. There are variables in each installation for sure but I've worked it on my BT as an average. When calculating voltage drop you must take into account the distance the current has to travel not only from the battery but back to it via the earth wire. I estimate the fridge power terminals are about 6.5 metres away from the battery as the wire travels... multiply this by 2 to give total distance current has to run.... = 13 metres. If we use Collyn's formula .... Drop in volts = (L x I x 0.017)/A where : L = cable length in Metres I = current in Amps A= cross section of cable in sq mm I have also assumed that the earth return is 6 sq mm also. The power feed to the circuit breaker box is larger than 6 sq mm but lets work on 6 sq mm for the total distance. I have done the calculations at 5, 6, 7, and 8 amp to cover fridge draw. 6 sq mm - 13 metre run - 5amp draw = 185 Millivolt Drop 6 sqmm - 13 metre run - 6 amp draw = 221 Millivolt Drop 6 sq mm - 13 metre run - 7 amp draw = 258 Millivolt drop 6 sq mm - 13 metre run - 8 amp draw = 295 Millivolt Drop This gives plenty of scope for the 6 sq mm to carry the current for the fridge. Andy's (and mine) voltage drop is caused by resistance so the reasons would be .... The wire is not 6 sq mm (differing wire insulations thicknesses sometimes give the impression of a larger gauge but the copper wire core is still small) ... there is always some resistance across circuit breakers .... there is also some resistance across terminal blocks ( one behind fridge - mine is soldered)... bad terminal contact etc. In a perfect world the drop would only be 150 millivolt ...500 millivolt is borderline .... and a 1 volt drop (1000millivolt) is unacceptable .... I'm happy to accept a bit of voltage drop as I have extra insulation ...terminal block removed ... and now have AGM batteries giving a constant 12.9 volt instead of 12.6 volt so I've gained 300 Millivolt there .... Andy, If you want to check the drop is in the wire from circuit breaker to fridge terminal ....add another 6 sq mm wire to the +ive feed from the fridge circuit breaker and run it out through window beside fridge and join into fridge +ive terminal and re-measure voltage again compared to battery ...if it improves markedly the feed wire is too small. Its very easy to run another across roof if you so desire ... obviously doing a voltage drop check at circuit breaker does the same thing. Regards Anthony Explore this Great Land ...Do it Easy ...Tow a Bushtracker
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Reply By: Turist - Monday, Aug 09, 2004 at 17:18

Monday, Aug 09, 2004 at 17:18
Hi there.
Just catching up on the fridge debate.
We did some testing on our fridge, took temperature readings in the cavity around the condensor and compressor.
In standard configuration, that is with external vents the temp in the fridge cavity was always around 10º higher than ambient.
ie, temp in van 26º, temp behind fridge 36º, temp in van 18º, temp behind fridge 28º

Current situation.
There are a series of 50mm dia holes in the floor of the fridge compartment to let air rise from the cupboards below.
There is venting on the rear top of the fridge box.
This creats a good convection current up the back of the fridge.
We have styrofoam insulation in the fridge box.

Temp tests now sow a 4º variation (fairly constant) betwen ambient in van and fridge cabinet.

Fridge works better, no dust in fridge box.
Can not detect any extra warmth in van.

I’m convinced.

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Reply By: Deleted User - Monday, Aug 09, 2004 at 17:19

Monday, Aug 09, 2004 at 17:19
Brian, If that much dust is covering the condenser you are right to vent it another way. It sounds like the venting was the least of your worries until the problems were sorted out. After your experience with the door hinge I wonder if the newer stronger hinge can be retro-fitted to the fridge cabinet ? And as for un-qualified comments, yours, like mine (I hope) are always welcome because that how things get discussed. The school of experience is a beauty ... the warning about the bottom hinge a prime example. Anthony Explore this Great Land ...Do it Easy ...Tow a Bushtracker
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Reply By: Andy1 - Monday, Aug 09, 2004 at 17:20

Monday, Aug 09, 2004 at 17:20
An Engineer mate tells me that in the heat loss formula insulation thickness is to the power of two so, all other things being equal, a doubling of insulation thickness is nominally a very significant increase in insulation efficiency. There is a slip of the pen in my second posting - I talked about voltage drop but typed amps in error. Turist - we have been contemplating a few holes at the top of the fridge box which does seem pretty logical but rejected the idea of internal air supply to the compartment, I had planned to fit a vent at the side, as in the hot weather it is usually warmer in the van than under the awning. I will follow your lead & take temperatures inside the condenser air space when it warms up a bit. With the extra insulation & this cool spell when I switched the fridge on to test the re-installation it hardly cycled once it cooled down. Andy
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Reply By: Turist - Monday, Aug 09, 2004 at 17:21

Monday, Aug 09, 2004 at 17:21
Andy our fridge is located on the left side of the van over the front end of the wheel arches.
This area, inside the cupboard around the wheel arch is surprisingly cool compared to the rest of the van.
In fact Judy stores the spuds and onions there and they don't go off.
Plenty of cool air to keep the convection current going.
Some are concerned that the warm air from the fridge will warm up the van but this is not the case.
A hand over the top vents can not detect a temp change.
Very rougly calculating the fridge would develop about the same amount of heat as a 50w light globe and then only while it is running.
Just got to let that heat escape, and preferably without external venting.

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Reply By: Dusky - Monday, Aug 09, 2004 at 17:22

Monday, Aug 09, 2004 at 17:22
Turist, My order has been placed for a BT due for delivery mid next year. Your analysis of dust through the fridge vents and the fridge venting internally is sound. So that I can advise BTI on fridge box construction so the fridge vents internally can you please supply more details how your fridge box is designed. Thanksyou, Dusky
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Reply By: Deleted User - Monday, Aug 09, 2004 at 17:23

Monday, Aug 09, 2004 at 17:23
Dusty, We collected our BT a couple of weeks ago, so our experience with the fridge is limited. We did see Brian sealing up his fridge vents and thought the idea of sealing dust out was sound, so we asked BT to leave ours unvented through the skin. All the struucture is there if we want to just instal the vents later. We had extra insulation installed aroung the fridge enclosure, but we have gone for the RDC190 which has extra insulation anyway (dimensions are W590x H1340x L610 compared to the BT standard HDC190 fridge which is W540x H1235x L565mm) I think all the extra dimension is insullation. The RDC is designed for yachts, and has vents above and below in its structure. We are pleased with it and consider the additional $500 worthwhile. Ask Wayne Thompson of BT for details of the Johnson installation. Cheers Robin and Ian
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Reply By: Deleted User - Monday, Aug 09, 2004 at 17:24

Monday, Aug 09, 2004 at 17:24
Hi everyone, What about using gold cables? Wouldn't gold's better conductivity be better? He! He! Macka
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Reply By: Deleted User - Monday, Aug 09, 2004 at 17:25

Monday, Aug 09, 2004 at 17:25
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Reply By: Turist - Monday, Aug 09, 2004 at 17:26

Monday, Aug 09, 2004 at 17:26
My fridge box is BT standard except for;
Styrofoan insulation sheets inside the box,
A series of 50mm holes in the box floor,
A pair of vents on the top rear of the box,
2 vents on the side/rear of the box, one top, one bottom.
And of course no external vents.

Took me some time to convince BT to do it this way but I believe that they have since done others.

Tracy will know the requirements.

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