This article is aimed at extended trips in adverse conditions. Adverse for a fridge setup is high ambient temperatures, short drive times per day and long stationary periods. Engine switched off. Big loads of refreshments. (A six pack is a huge load for a 12 V fridge.) Then after all you want to keep the meat frozen.
It is very difficult to get straight answers in this field because of the lack of practical and technical knowledge and real understanding. Fault finding of a system as a whole is almost impossible as the experts mostly only partly understand their own system (The charging controller) and surprisingly little about how the rest of the items influence each other. The problems are normally much wider and if you cannot see the whole picture you will most probably misdiagnose the real issue.
The most common issues are bad installations, thin wires, bad connections, too small battery capacity, too low charging rate, expecting too much. Mostly because we do not really understand the requirements or we are trying to save some money. Something like cheap quality simply does not exist. Then again some mediocre systems can go for ridiculously high prices. On the other side of the spectrum there is the local solenoid system that is excellent for a very reasonable price. It gets a bad reputation from the industry because of bad installations, done by themselves. (Lack of technical understanding)
Figures used are rather arguable and many experts will want to use different figures. We have to have something and these are in my opinion a good guess from practical experience.
What does the power supplier offer?
Let us start with what is available and what we require when the circumstances are against us. The standard alternator and battery system in our vehicles is actually doing a sterling job in millions of vehicles and is efficient and reliable. The principles that works so well are well known and the batteries and alternators were designed to do exactly that.
Firstly the alternator is oversized to be able to draw all electrical equipment and charge the battery at the same time. To recharge a battery that has started the vehicle is normally achieved in 10 to 20 minutes.
Secondly an oversized battery is used. It should therefore never drain to a point where the battery will be damaged.
The battery supplies a high current for a very short period. Then it is recharged as quickly as possible.
Cable (Wire) is massively oversized and has pretty decent connections to avoid voltage drop as this will push up the ampere needed to do the job and will limit the charging rate to the battery.
Why is it not as simple as just adding another battery or two ? Most of the old timers started there 30 years ago when they decided to take refrigeration to the bush. It seemed so simple and anyone claiming that, has no idea what the pitfalls are.
The first issue was that the extra batteries had to be isolated when the engine stopped to prevent the starting battery from being drained, and that was only the beginning.
It may be easier to digest if we start with the common symptoms as you may experience them in the remote areas.
What does the client need?
By far the most common complaint runs something like ‘it worked perfectly for the first 3 or 4 days and then packed up’. What normally happens here is that the charging rate combined with the drive time was not enough to make up for the usage. Let us say you drive for 4 hours and have a charging rate of 15 A. This will give you a maximum of 60Ah (ampere hour) stored. Then you stop for 20 hours. The fridge guy claimed 1 to 3 A average per hour. Do not believe this for one second. They measured this under well controlled conditions. You most probably try to cool down a six pack (Coke) per day and ambient is around 30 degrees plus. This is a huge ask of the little 50 Watt compressor in your fridge. (For comparison a car aircon draws 3 to 4 kW.) It will most probably be running full taps most of the time. Therefore it will be drawing in the region of 6. 5 A max for most of the time. Lets say average is 4A. (This is very lenient and may well be too little in extreme conditions) The 20 hours at 4 A gives you 80 Ah usage. This is 20 A hour more than what you stored.
On day one you most probably started your stationary period with a full battery. On day two after your 4 hour drive you will start using the battery with a 20 Ah deficit. On day three you will start using the battery with a 40 Ah deficit and so on until the battery is depleted during your overnight stop. Once there it will not catch up again. Really a very logical and simple calculation that you should use to determine your requirements from a system before you decide to buy one. This is also the main reason for scrapped batteries.
Apart from a bad installation this is the most common problem out there. If you only do weekend trips you may never run into this problem even with an underperforming system.
What can we learn from this basic reasoning ?
Do not underestimate what you expect from the system, it will bite you.
Do not overestimate what you can get from a specific system.
Do not overlook what the car’s system has to offer. You may require a larger alternator but this is highly unlikely.
If your local expert cannot explain the above, find a better expert.