My Motorhome/Caravan Refrigerator is using Too Much Power
This is a very common comment I see in both emails and forum questions. Depending on the size of the solar/battery system, refrigeration can account for up to 70% or more of the total power requirements. In our motorhome we have a 220ltr low voltage, two-door fridge/freezer and a small (40ltr) chest fridge that becomes a freezer when the fishing has been particularly good. Together these two units consume about 40ah (at 24v) every day (80ah @ 12v). Why is it then that many people are reporting that their refrigerators are using more power than they expect?
The majority of portable fridges are powered by Danfoss compressors (or in some cases a Chinese made copy). These little compressors are amazingly efficient. The most common size of compressor is a called a BD35F – so let’s look at this compressor first. The BD35F will draw between 1.5 and 6.5 amps (@12v), depending on the speed (RPM) and the temperature. Generally, most fridges are shipped with the compressor configured to run at full revs all of the time – some have a switch to allow selection of high or low speed.
Ideally your fridge compressor should run for approximately 20 minutes before the thermostat stops the compressor (of course there are lots of factors that can alter that – ambient temperature, heat loading etc). The compressor will run less in the cooler night time conditions when the door is not being opened and more often and for longer in the heat of the day. A good basis for calculations is an average of 20 minutes run time every hour. This equates to about 53 amp hours every day (@12v).
If your caravan or motorhome refrigerator is using considerably more energy than this, or perhaps it is running nearly all the time, here are some possible causes…
- You have your thermostat set too low. This is very common. The sensor for the thermostat is normally located in the freezer compartment. Turning this down (often in an effort to get the beer in the fridge compartment cooler) will result in the compressor working overtime trying to freeze the items in the freezer compartment well below the recommended minus 18degC. A large build-up of ice inside the fridge compartment is another good indicator that you have the thermostat set too low. Place a digital thermometer inside the freezer (ideally one with the display located outside the freezer compartment). The correct temperature is minus 18 degC. The fridge compartment should be about 4 – 5degC.
- The seals around the door(s) are not completely sealing. You can test this with a piece of paper. Shut the door with the paper in the seal, if it can be removed without resistance, the seal is faulty – test right around both doors and replace if necessary.
- Airflow is essential. The fridge is designed to remove the heat from inside and get rid of it. If it can’t get rid of it efficiently, it won’t be able to remove it efficiently. There must be good air-flow around the cabinet and both under and behind the refrigerator. Some fridges are designed to dissipate the removed heat through the side walls – it is a BIG mistake to add insulation to sides of these types of fridges.
- If your fridge is running almost all the time, there is one other possible reason – if the compressor speed has been set to something other than full speed (3,500rpm) and the ambient temperature is quite high (say above 32degC), the compressor may struggle to bring the internal temperature down far enough to allow the thermostat to turn off. Check that a select switch has not been bumped.
- In addition to the points above, there are a number of common sense items worth mentioning:
- Don’t place hot food items directly into the fridge.
- Don’t allow the sun or other heat source to warm the exterior of the fridge.
- A full fridge will consume less power than an empty one (due largely to the loss of cold air when opening the fridge door).
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