Updated 10 February 2016
Making caravan fridges work as claimed is simple, cheap and easy – and their energy draw reduced. Most are badly installed and/or need better ventilation. Boat, camper trailer and motor home fridges too (and home fridges) rarely work as claimed or expected. This article shows why – and how to ensure they do.
Fridges do not generate ‘cold’. They pump heat from where it is not wanted to somewhere it does not matter.
Big fridges use more energy than small ones, but not in proportion to size. Doubling fridge volume increases energy draw about one and a half times, not twice. Where feasible use one larger fridge – not two smaller ones.
Some cold air is lost when a fridge’s front door is opened. Top-opening fridges lose marginally less. The heat seals of door-opening fridges must be perfect. If not, energy usage soars. If they are over three years old, replace them.
Making fridges work as claimed – energy consumption
Any fridge’s energy draw is directly related to ambient temperature. All use about 5% more for every 10° C above 25° C. The same applies to their set temperatures. Set fridges to +4° C, freezers to -18° C (some users settle for -14° to save energy). Let food cool before placing in the fridge. Keep bought frozen goods cold in a heat-insulating bag and put in the fridge as quickly as possible.Defrost anything frozen in the fridge section. Let warm beer first cool overnight. Keeping the fridge full reduces cold air falling out when opened. Leave gaps for air to move, but fill empty spaces with plastic bottles full of water.
Most fridges control temperature by cycling on and off. Energy draw is related to ratio of on/off times so one that draws more energy but is on less often, or for shorter times, may use less energy per day. Some new fridges run constantly, adjusting speed to maintain temperature. For any type of only their daily energy draw has meaning.
Making caravan fridges work as claimed from solar
Making electrical caravan fridges work as claimed from solar alone is totally feasible in temperate areas. A typical 40-110 litre chest and door opening electric fridge draws 0.7-1.0 amp hours/day per litre of their volume. Larger ones draw slightly less per litre. For any fridge, energy draw typically increases by about 5% for every 1° C above about 25° C. This typically requires 150-200 watts of solar, and 100-150 amp hours battery capacity per 100 litres of fridge volume. Alternator charging assists particularly if driving a few hours each day. See http://caravanandmotorhomebooks.com/dc-dc-charging/
Three-way fridges work well on gas, from the alternator whilst driving and 110/230 volts when available. Their energy draw – of 12-30 amps (at 12 volts), however, is far too high for solar. See below re ‘Climate Class’.
For making caravan fridges work as claimed competent installation is essential. Few are. Almost all can be improved by following that shown below. (When owners compare fridges – they are mostly talking about their respective competency of installation).
No caravan fridge will cool a carton of room temperature beer in an hour or two! Buy it cold and put it straight in the fridge. Fishers (particularly) tend to grossly underestimate the energy needed to freeze their catch. Power will be drawn continuously, doubling or tripling consumption, yet will still not freeze quickly. Doing this requires a generator powered chest freezer.
Correctly installed and sensibly used RV fridges will work as intended. Marketing however advises what a product may do, not what it cannot do. A fridge’s temperature range is thus shown in the technical data, but not necessarily in the brochure.
Gas and three-way fridges must suit the climate in which they are used. There may also be unrealistic expectations.
Tropical areas have less usable sun
A common error is to assume more solar input in semi-tropical areas. Solar input is mid-summer is 20%-30% less than many expect. It is hot all day and often all night, so fridges draw up to 50% more energy. Meanwhile solar modules lose energy through heat loss. Unless your existing solar system brings batteries to float voltage by noon on most days in temperate areas it has no chance at all of coping in tropical conditions.
Making caravan refrigerators work as claimed – installation
Few RV fridges are adequately installed, including many done ‘professionally’. Making caravan fridges work as claimed is usually possible: sometimes even better- and often at little or no cost.
It is usually easy to do but, in extreme cases, total re-installation may be required. A $550,000 motor home had one (450 litre) fridge totally enclosed and unventilated, plus a 300 litre freezer in an unventilated locker with its black front exposed to the sun. Both were connected by cable barely able to run LEDs. Neither would cool below about 5 degrees C. The RV maker refusefd to accept responsibility and blamed the fridge maker! Fixing the problem required a major rebuild of the kitchen area at a cost of over $10,000!
Whilst seemingly 100% obvious, a fridge must not be in direct sunlight. One character, who had his outside in Broome’s full tropical sun, complained: “my b..y mongrel Electrolux won’t keep my %#@^& beer cold.” He would listen to nobody (including me) who attempted to explain why.
Heat from a fridge must be allowed (or assisted) to exit the caravan (etc) such that it cannot re-enter. To do so fridges need a cool air entry at base level, and a hot air exit, ideally at roof level. Most fridges need baffles to direct cold air such that it can only flow through or over its cooling fins. The baffles can be made from aluminium, plywood or even heavy cardboard. They must be within a centimetre or two of the cooling fins. Rising warm air may need channeling so none is trapped.
The cool air vent can be at the side or through the floor (but not above or behind an engine’s exhaust outlet). Cool air must enter below the lowest cooling fin and exit well above the highest fin. The lower inlet can be a problem for off-road vehicles as a lot of dust will be sucked in. Here, some compromise will have to be made – such that the vent is closed off and air drawn in from within the vehicle whilst on dirt roads (but cooling will suffer as a result).
The warm air is ideally vented to and through the roof, or if not feasible, via a side vent well above that highest cooling fin. Some three-way fridges can tolerate 6° tilt, others only 3°. Electric fridges are less sensitive, but are best levelled.
The sketches (below) show the vital requirements for all types of fridges.
Upper Left: – the baffles are too short and need to be just below the cooling fins. Rising hot air is trapped in the dead air spaces – as shown. If not fixable (as at bottom centre or right), an extractor fan driven directly from a 5 watt solar module would enhance air flow. Upper right: – the upper air vent is far too low – hot air is trapped in the fins above it. Baffles are also needed. Below: How to install fridges correctly. Baffles really do help yet are rarely used. Note how rising hot air is channelled to the outside. This drawing is copyright: 2014 caravanandmotorhomebooks.com
In most installations a small extractor fan (as shown below) will assist. These work well as their cooling is most needed when it’s sunny. Some have an integral solar panel. Alternatively, those used in the larger desktop computers cost only a few dollars and can readily be run directly from a 5-10 watt solar module or the main RV 12 volt system. Fans are best used to extract warm air rather than pumping in cool air but the difference is minor.
Solar-powered extractor fans are readily available (Google for suppliers)
Electrical problems with 12 volt fridges
Most 12 volt fridges also have grossly inadequate cabling – many have only 25% of that required. Check by seeing if the fridge cools better on 230 volts (where relevant). Cable issues can be worsened by faulty fuse holders, and particularly cigarette lighter plugs and their associated wiring. Scrap all such plugs. Wire the fridge directly to the battery by the shortest possible route.
A certain way of knowing if cable is too small is to measure the voltage directly across the battery, then directly across the fridge. (Do this with the fridge door open to keep it cycled on.) Many caravan fridges have close to 1.0 volt drop. Accept no more than 0.15 – 0.2 volt drop.
Adequate cable makes an extraordinary difference to making caravan fridges work as claimed. For electric fridge to battery distance of less than four metres, use 4 mm² cable (AWG/B&S 11). Over four metres use 6 mm² cable (AWG/B&S 9). If over four metres, move the battery closer. Do NOT use the auto cable sold by auto parts and hardware stores without first reading about it below – or in more detail in Caravan & Motorhome Electrics.
Do also see DC-DC Charging – this ensure the caravan battery and fridge receive their full required voltage. Installing one of these can totally transform a caravan or camper trailer fridge.
Auto cable problems
Appliance makers specify required cable by its cross section in square mm. Auto cable makers (in effect) specify it by the size hole you can just push it through. They rate it by its diameter including insulation.
Auto cable sold as 4 mm is typically 1.8 square mm, but may be only 1.25 square mm. Many caravan electric fridge makers specify 4 mm square. But countless fridges are connected by that totally inadequate 1.8 square mm auto cable (less than half the minimum specified). No fridges wired that way work remotely as they should and usually can. Direct comparison is not possible for auto cable. Its size varies from maker to maker. One exception is that 6 mm auto cable (typically 4.59 square mm – or 10 AWG) can be substituted for 4.0 square mm cable.
Cable current rating trap
Cable ‘ratings’ (e.g. ‘50-amp’ etc) indicate only the current that cable can carry before it melts! It tells nothing about voltage drop (that is also a function of cable length). It’s useless asking most vendors about this. Few know it’s even an issue – let alone why. For caravans, locate the battery close as possible to the fridge. If alternator charged install a dc-dc alternator charger close to that fridge.
Never use cable lighter than advised above. If you do the fridge will never work correctly
Three-way fridges and climate class
Three-way fridges are designed to maintain cooling over tightly defined ambient temperature ranges. There are four such (CEN standard) Climate Classes. Those designated ‘SN’, and ‘N’ (Sub Normal, and Normal) work up to 32° C; ‘ST’, (Sub Tropical) up to 36° C. ‘T’-rated (Tropical) perform up to 43° C. A minor drawback (for some travellers) is that T-rated fridges do not work that well below 14°-18° C.
Only ‘Climate Class T’ work satisfactorily in climates such as north and north-west Australia (or tropical areas generally). Such fridges are marketed in Australia by Dometic and Chescold. These fridges have an unfair reputation for poor cooling but this is almost always due to buying one of the wrong Climate Class and/or poor installation. Three-way fridges will perform as claimed but must be installed as shown above to enable them do so.
Problems with three-way fridges
These fridges must used as the makers specify. It is not for example feasible to run them for long on 12 volts except whilst driving. Their electrical draw is far too high for solar or more than an hour or so battery operation. If used in a caravan, very heavy cabling is essential (ideally 10-13.5 square mm) all the way from the alternator to the caravan battery. Or and preferably by installing a dc-dc alternator charger as close as possible to the fridge battery in the caravan. Have at least 6 square mm cable from that battery to the fridge.
Some routine maintenance is required. In LP gas mode check the colour of the flame: it should be blue. If it is yellow (or the fridge works well on 12 volts but not on gas), it is probable that the baffle inside the flue is coated with soot. Soot etc may also have dropped down and affected the burner. Wearing safety glasses, and old clothing, use a powerful air compressor to clean that baffle. Then do likewise around the burner. Be aware this is a filthy job! You may prefer to have fridge repair specialist do it for you. This is preferable as it helps to have the LP gas pressure checked at the same time.
Whilst not common an LP gas fridge can sometimes suddenly stop working. This is usually due to a ‘vapour lock’ caused by the caravan being excessively out of level. This is usually fixed by turning it off, making sure the caravan is level (within 3 degrees) and turning the fridge back on after a few hours.
Cooling issues with gas fridges in imported RVs (or imported such fridges) can be that they were for LP gas different from that in Australia. The jets are likely to be the wrong size. Here, you need expert advice.
Making fridges work as claimed in cars and 4WDs
Making caravan fridges work as claimed in cars and 4WDs is more of a problem. Keep them out of direct sunlight, and leave an air space around the grill’s vent area. It is however fine to pack stuff close to or touching them – except for the types shown in the pic below (these must have a 50 mm air gap each side as the heat is dissipated from their sides).
All types of fridges can nevertheless be improved (some dramatically) by running a 6 square mm (8 AWG) cable from the battery to that fridge (a maximum of four metres away).
A few boat and RV fridges, such as this Australian designed and made Autofridge, dissipate heat from their side walls. These fridges need an air gap of 50 mm at each side. Pic: Autofridge Australia.
Fridge issues generally
Do not over-pack an RV fridge. Some space is needed to allow cool air to circulate.
Door seals leak after a few years. Check by inserting a strong strip of this paper (e.g. a banknote) between the door and the seal (at various places around the door) and see if it is gripped. If not then cool air will escape. These seals normally need replacing every three to five years. You can buy replacements from stores such as Clarke Rubber.
Fridges with external cooling fins benefit substantially by adding extra heat insulation. Some fridges however, such as the Intel and Autofridge, dissipate heat from their side walls. These ideally need a cool air feed at the base of their sides and must have an air gap (optimally of 50 mm) on either side and their top.
Making fridges work as claimed – summary
Particularly for boats, camper trailers, caravans and motor homes, you need the right fridge, competently cabled and installed.
Making caravan fridges work as claimed (or even better) – and energy draw actually reduced by is totally possible by making the above changes.
Except for the very cheapest fridges, dismiss claims of inherent deficiencies. Providing a fridge is appropriate for its proposed use, cooling problems are almost always due to installation failings. For domestic fridges, and fridges in cabins, virtually all of the above is relevant. It is however not likely that cabling will be an issue with a 110 or 230 volt fridge.
A great deal more on making fridges work as claimed is in my book Caravan & Motorhome Electrics. It even shows how to build your own fridge – that leaves commercial units for dead in cooling and economy. There’s also a lot of information about running them from solar in that book, and also Solar that Really Works!
If the fridge is large and in a large home or on a property consider also Solar Success.
If you found this article useful you are likely to find my books even more so. All are updated at typically yearly intervals (between print runs). Caravan & Motorhome Books does not accept advertising nor any payment for editorial of any kind. It covers the cost of all articles solely from the sale of the associated books.
See also our new Facebook page https://www.facebook.com/BooksByCollynRivers/