The fridge is probably one of the most important parts of your motorhome or caravan. It is essential for keeping your food from spoiling and your beer from getting warm.
In June, we were driving back from the UK to our home in south-east Spain. As we headed south and the weather got warmer, we noticed the fridge was staying on for longer and switching on more frequently. Our fridge is a compressor model, it only runs on electric and was sapping most of our battery capacity. In fact towards the end of the trip when we were hitting 40C the fridge would stop working because the voltage of the battery was too low. ie. all the battery did not have enough juice to keep it running.
What was going on?
So two problems. One was the fridge not coping with the temperatures and just giving up. Second, not having enough stored power in our battery because the fridge was having to work too hard.
According to the specs our Alpicool CR90 uses upto 60 watts of power when it is running flat out in temperatures above 25C. Watching the fridge in action, the compressor is running for about 50% of the time.
Time for some maths! (sorry!)
Apologies for this bit, but the maths is necessary to show how long a battery can power a fridge.
We have a 100Ah AGM leisure battery that gives us:
Total battery capacity 50% of 100Ah = 50Ah (we only want to use 50% of the capacity of a AGM battery without damaging it)
Total available watts 50Ah x 12volts = 600 watt/hours
Fridge power consumption is 60 watts so 600wh / 60w = 10 hours total running time
So our battery if it was perfectly charged could run our fridge for a measily ten hours! Now in practice, the fridge is not running all the time, only when the temperature rises above whatever temperature it has been set to. In our case about 50% of the time it was running. This gives you 20 hours for our fridge – not even enough to last a day – and assuming we are not using electric to charge devices, run lights etc.
If you have a Lifepo4 (Lithium) battery you can discharge to 80% which would give 16 hours total running time. Or a if your fridge only uses 45w then you would have 13 hours.
Hopefully you can see from all this, that compressor fridges use a lot of power – probably more than any other device in your motorhome.
Some ways to improve the situation
- In colder climates we have been able to just switch off the fridge at night times. I would not recommend this if you have lots of food, especially things like chicken as the temperature of the fridge will rise a bit.
- Increase the battery capacity. You can probably add a second battery without having to change the battery charger, assuming you have room. Also remember that even a modest AGM batter may weigh 25kg upwards. These things are full of lead and are really heavy!
- Increase capacity by changing to Lifepo4 (lithium). These have come down a lot in price. They also weigh a lot less. Depending on the age of your vehicle, you may need to upgrade your battery charger. At the very least you will need to change a setting so that it gets charged correctly. (Lithium batteries need different charging voltages to AGM)
What we did
In the end we did two things to help the situation. It is also possible we will switch to lithium batteries in the future, but we are going to see if these steps help first.
Firstly, we increased the thickness of the cables connecting the fridge to the battery. The cables that came with the fridge were AWG16 which for three metres of distance to the battery carrying 60w is too small. This means the fridge is unable to pull enough current from the battery which causes the voltage to drop. The fridge has battery protection in it, so if the voltage drops too much the fridge stops working. During normal use our fridge was dropping to 10.4v when the fridge was running, even though the battery was working well and fully charged.
By increasing the cable thickness to AWG10 the voltage when running never dropped below 11.9v. This fix cost about 11€ for some replacement cable from Leroy Merlin (a DIY store here in Spain).
The other thing we did was improve the insulation. Most fridges in motorhomes and caravans have very poor insulation compared to a domestic fridge. To make matters worse they are often in a space with lots of gaps and no insulation. On our fridge, you could feel the sides and the top getting cold when the fridge had been running for a while. This means the cold was escaping, and meant the fridge had to operate more often to maintain the temperature.
Again, we went to Leroy Merlin’s and bought some polystyrene insulation panels and spent about 8€. These can be cut easily with a craft knife and then were glued in place with silicon sealant.
The top of the fridge also got cold, and needed insulating, but there was no room above it so I used to reflective bubble wrap stuff that I had from another project. This is known as Reflectix in some places, and is pretty cheap.
When all the above was done. I put the fridge back in place and tidied up. Then switched on and monitored how often it was coming on.
Well I am happy to say that the fridge kept going for several days until I got bored with the experiment and switched it off! The fridge was running less than 20% of the time now instead of over 50%. Infact so much less that our 120w solar panel was providing enough power to keep pace with what the fridge was using. It was only at night when the sun was gone that it started eating into the battery.
Overall I am impressed! For less than 20€ we have made the fridge work much better. We may still upgrade to a 100Ah Lifepo4 in the future for the extra capacity, but right now our AGM battery is working fine
I hope this is helpful to someone having similar issues!