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Common problems with solar or compressor fridges

Our experience is that in 99% of cases, problems associated with compressors on solar fridges are found to be related to an inadequate or faulty power supply to the fridge.

Things to know about the power supply:

When we buy a 240-volt domestic fridge, we do not have to worry about the quality of the electrical supply. All houses are wired to a standard that is suitable for even heavy-duty appliances, so the current drawn by a domestic fridge will not affect the power supply in the house. Indeed the power supply is always sufficient to run the fridge.

This is not always the case with a 12 or 24-volt solar system. The fridge runs off the house batteries via the cables that run to the fridge. The cables that run to the fridge must first and foremost be of sufficient diameter to carry the load required by the fridge, without the voltage dropping, at the fridge, when the load comes on.
Some typical examples of what can go wrong.
  1. A poor connection on the cable crimps and or a burnt-out switch may cause voltage drops in the cable, so even if the battery voltage reads correctly at the source, it may not read correctly at the end of the cable.
  2. A battery that has been damaged by deep cycling on a regular basis will lose capacity as the lead plates corrode from the deep historic discharges. Such a battery will show the following symptoms. (1) The battery will recharge quickly, a good battery should take several hours to recharge. (2) The battery may start to bulge at the sides if the 2 ends are deformed the battery is almost certainly history. (3) The battery may become a little warm when being charged, a battery should not be getting warm if charged by a good charge system. (4) The battery voltage will fall very quickly under load causing the fridge to become unreliable.
  3. Very occasionally loose contacts may occur on the fridge, especially in motor-homes and caravans, due to the constant vibrations in the vehicle. Great care is taken to ensure this does not happen, if you have checked all other issues as described above then, check contacts at the rear of the fridge and if they appear to be a little loose, it might be a good idea to hot glue the contacts to prevent further movement.
  4. The battery capacity of the solar system is too small. Sometimes the battery capacity of the solar system is ample to run the fridge through the summer when there is plenty of solar energy, however in the wintertime when the weather is overcast, the battery may not last between sunny days, this can be solved by adding extra solar panels and by using an MPPT type controller so that the battery is still charged even during poor weather conditions.
  5. A system with insufficient solar panels, for the demand on the batteries, will wreck the batteries and cost more money long term, vehicles are not always parked in full sunshine, when the panels are fitted, the technicians often make the mistake of calculating the potential energy supply of the panels based on the best case conditions. When a vehicle experiences shade the panels will not be able to bring the batteries up to full charge, That will also cause the batteries to fail. Some people will leave the fridge running 24/7, but if the vehicle is parked under a tree or in the shade of a building, it will only be getting sunshine part of the day. Consider all these factors before looking for faults with the fridge.
Battery Voltages and what they mean:

In a 12-volt system, 11.9 volt is a dead flat battery and 12.7 volts is a fully charged battery at rest. So the difference between a full and a flat battery is only 0.8 volt. It is easy to lose 0.8 volts in resistance through the existing wiring of the vehicle.

We sometimes see a battery voltage at 13.7. This is when the battery is being charged, through solar, alternator, or a 240-volt charger. When all the charge systems are disconnected, then the voltage should go down to 12.7 when at rest (nothing going in or out), a battery voltage lower than 12.7 indicates that the battery has not been fully charged yet or it is no longer very fit.

If we see a voltage of 14.9 or thereabout, then the solar system is going through its final stage of the charging procedure. This should only happen for about 90 minutes per day. If that voltage of 14.9 persists for more than 90 minutes then the system has a fault and you could damage your batteries by overcharging.

So if you suspect something is wrong with your batteries, be sure to check that the solar system is disconnected before checking the batteries. We have seen many "so-called experts" load test the batteries with the solar system still connected. The solar system will try to keep up as the load test is done, and this gives a false reading, naturally they think that the batteries are in good shape, however as soon as the sun goes down, the fridge experiences a low voltage supply and will turn off once again, as the batteries are once again depleted through the night.

The fridge comes on regularly

A fridge that is running regularly due to the factors below will have a shorter life cycle and will waste energy, and also shorten the life cycle of the batteries.

  1. First of all the fridge thermostat may be turned up too high. If the fridge has ice build-up at the rear, then the fridge temp is set too low. The fridge temp should be an average of about 4 degrees, which is hard to measure because the fridge maybe 0 degrees at the back but say 6 degrees in the door. These measurements will also vary as the compressor comes on and off, and as items are added and removed from the fridge. The best rule of thumb is that you should set the fridge so that the temp is just around the freezing point at the coldest point in the fridge.
  2. The ventilation behind the fridge is not sufficient. Compressor fridges work by removing heat from the inside of the fridge and discharging that heat by means of a condenser. If the condenser cannot get rid of the heat quickly enough, the fridge will keep running. Imagine the heat inside a motor-home could be 30 to 40 degrees in the sun when it is parked up, with little or no ventilation or air movement the condenser is unable to get rid of the heat, so the fridge tends to run longer. Other causes of poor cooling could be a build-up of dust and dirt on the condenser fins, preventing it from shedding the heat.
  3. In very rare cases the fridge may have lost gas. This will cause the fridge to run almost all of the time, but the temp in the freezer will not fall to below freezing.
  4. The door seal of the fridge may be damaged or not positioned correctly and this will cause cold air to leak out and the compressor will run more often. Place a torch in the fridge at night and check if you can see any light coming out the fridge seal. The rubber on a fridge door, can go hard and rigid over time, which causes a poor seal. To get a better seal warm up the rubber with a hairdryer, the rubber will become more flexible allowing the internal magnet to attach itself better to the fridge chassis and a better seal