Dometic fridge 12v supply puzzle

[ecliptic]

Not really.
Winter covers are just that, for use when the ambient temperature drops to about 8 degrees or less.

The only advantage of using them at other times is to stop, or reduce, the ingress of water or foreign matter into the void the fridge sits in, and when washing the van.

Properly fitted they are secure enough to stay on.

Fitting them in higher temperatures will reduce the effectiveness of the fridge, which is why people who have awnings which enclose the fridge often find that it stops working as it gets too hot, that is when extra fans sometimes are useful.
The fridge must have good air flow to work effectively, and fridges supplied in the UK are made to work in temperatures up to 30 degrees, above that, which is common in an awning, reduces the effectiveness.

Now that is interesting, Damian.

The temperatures I experience here in Western Australia can be significantly higher than 30C, and is why I have installed an extraction fan to improve airflow over the cooling fins. Could be I may have to put a second fan in, but time will tell.

Thank you for that gem.

 

[ecliptic]

For anyone who may not know, these fridges use a process called absorption to chill, and counter intuitively it actually needs heat to drive the system. Because the heat is applied to the outside of the refrigerant tubing its called "externally heated" and it doesn't care how that heat is made. So which ever heat source is used, provided the same amount of heat (Watts) is applied at the correct point in the cycle, the fridge will produce the same cooling effect.

There are some differences becasue the heat sources cannot physically be in exactly the same place but these are relatively small in comparison to the total heat input from each source.

The performance of the fridge is affected by a number of external factors, some of which will be more related to where the power is coming from. It will work best when it's stationary, correctly levelled and settled. This will be the case for use with mains power or gas.

The 12V supplied from a tow vehicle is normally only available when the outfit is coupled to the tow car when the engine is running. This is also usually when the caravan is in motion. The 12V may be reduced or interrupted if the electrical demands of the tow vehicle require power. The physical motion of fridge in the trailer may impede the correct flow of the refrigerant through the fridge. And when a fridge is towed the external air flow used to cool the condenser coil on the back of the fridge will be disturbed and may be less than ideal.

The consequence is a fridge when being towed is likely to be less effective at cooling down, the fact this only happens when its on 12V supply is not cause of the reduced performance, but just a practical coincidence.

Some of these fridges are used situations where the only power source is 12V, for example solar powered where no mains power is available (e.g. Storage of of some medical supplies in sunny climates) and they can be effective and durable.

Thank you ProfJohnL

Your insightful explanations are very helpful in understanding the "beast".

The motion and turbulence issues would definitely explain why the cooling effect seems to be less on 12v compared to 240v or gas.

Appreciated.