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AUXILIARY BATTERIES

ibatt4x4

The fitting of an auxiliary  battery in your vehicle is probably one of the first modifications you will make, running a fridge off your cranking battery is just not a good idea.
The biggest problem is most people do not understand electricity and the way we use it.
Following is an explanation of how batteries work for you to understand better.

How does a battery work?

This is a very basic battery, made up of lemons, coins and nails. All connected with wires and a led, the led lights up because of electric current that is flowing.

I am just referring to lead acid batteries here.

A battery does not generate electricity, but merely stores it to be used later. Once you have charged the batteries, it will store it in some chemical way, since Gaston Planté invented the lead acid battery, it is still the most effective and cheapest way to store electricity.

A normal 12Volt car battery, would normally consist of six electrochemical cells that can each deliver 2.1V, all together 12.6V. Inside each cell there are two lead plates that is isolated from each other. A positive plate, that is covered in lead dioxide and a negative plate that is covered with a spungy lead material. These two plates

are seperated from each other, by an electrolite, sulphuric acid and water. In a charged battery, the suphuric acid react with the negative plate and produces electricity. You can say that there are more negative ions to move to the negative plate and that causes it to have extra electrons to give off, and once you complete the circuit, you have electricity.  

A yellow skin of lead sulpfate forms on the plates until it is completely covered. The acid then turns to water and your battery is flat.

By charging the battery again, the process is turned around with the lead sulphate going back in the water and turning it into acid again. and your battery is charged up again.

Batteries are different!

Although the basic principal of working, for almost all batteries are the same, their respective construction differs in order for different applications. This gives each different type of battery different characteristics for different uses. 
the biggest differences are the plates size and thickness and the type of de-electricum that is used. They all have different recharge cycles and the amount of recharges they can handle.
CRANKING BATTERIES

This would be the normal batteries any normal car would have in, and their sole purpose would be for the car itself. To crank the engine when starting it and supplying electricity to various other systems of the car itself. This battery normally has the characteristic of being able to supply a high current for a short time to start the engine. It should have enough capacity to be able to crank the engine, way more times than what is necessary, and still have some extra charge left. However, it is not designed to be run flat too often, it has a lifespan of only so many discharges and recharges. BUT it has the ability to recharge to 100% over a very short period of time and be ready for the next crank.

Using such a battery as an auxiliary battery can work, if you choose one that have a large capacity ( Amp-hour rating) that you will not run it flat too often and that you do the maintenance on it very often. It is designed to be installed in the engine booth and can handle heat.  Cranking batteries typically has a recharge cycle times of between 50-80 times, being flatter than normal.                                                  

DEEP CYCLE BATTERIES

There are many different types of batteries, all with different characteristics and purposes. SOMEWHWERE, some very succesfull guy decided that we in the 4x4 industries needs to have DEEP CYCLE batteries, WRONG.

Deep cycle batteries were designed to be able to supply low power for a long time, run very flat and be able to regenerate again. So you would need less batteries for your backup. Yes, that is what we wanted, but here is the catch, THE CHARGING UP TIME of the battery is way too long. To get a deep cycle battery fully charged up, you would need a week. Yes it does get up to 80% within a couple of hours but then it trickle charges over the next couple of DAYS to get back up to 100%. Now there is your problem. When you are on an expedition and have your fridge running all the time, you are just draining the battery up to such a stage that your fridge is not running anymore. Having a superb solar system and the best alternator money can buy, it can not recharge the deep cycle battery fast enough. These batteries could be recharged up to 800 times.

HIGH CYCLE BATTERIES

A high cycle battery is a cross breed between a cranking batterey and a deep cycle battery. It can give high Amps but can also manage many recharges, although they do not like to be discharged to less than 75% of their capacity, this is a very important fact about them.

Using High Cycle batteries as your Auxiliary is fine but do keep in mind to add an extra circuit to prevent them from discharging to far.

These battery's recharge time is less than that of Deep Cycle batteries but still not fast enough for our application. Say you visit the Kgalagadi, you have your fridge running full time. Early morning your go on a game drive for 2-3 hours and your batteries regain some charge, now you come back to camp and make breakfast and open and close your fridge a few times. there goes the charge as the fridge has to run longer. And so your day progresses and by tonight when you have a few cold ones you have not really regained any charge.

This could partly be overcome by using a decent solar setup.

New technology

Lead Crystal Batteries

Lead crystal batteries have a very unique construction of various materials that works in basically the same way as lead acid, only better.

As in during the charge and discharge cycles, the electrolite solidifies into a white crystalline powder. This results into a high performance safe battery. This battery could be used to replace most other lead acid applications.

These batteries have a much better life span as they can take a good couple of thousand recharge cycles and they are not bothered by being run down completely. Their recharge time is also about 5 times faster than their lead acid counter parts. They can tolerated heat well by having a working temperature of up to 65 degrees Celsius.

All of these facts makes it the ideal battery for our application but the only problem is the price.

I bit the bullet quite a number of years ago and bought one, I still have the same battery and haven't had a days problems with it. No fancy extra circuits needed, just connect and go. 

AGM Batteries

The AGM stands for Absorbent Glass Mat. The sulfuric acid is absorbed by a very fine fiberglass mat, making the battery spill-proof and robust, it means that there is fiber glass in between the plates that absorbs the acid and protect the plates. This makes the battery spill proof and very easy to install and transport. They are also a lot lighter than normal lead acid batteries.

One of the biggest advantages of AGM batteries is that they recharge considerably faster than other batteries making it very plausible for our application. Further more they have a recharge cycle of up to 8000, times that they can be recharged.

However, they are very sensitive to overcharging, and that will require a special intelligent split charging circuit that you can set to AGM. This is very import as it will determine the lifespan of your battery.

Another disadvantage is that they do not like heat and should be installed away from the engine compartment, the ambient temperature should not exceed 49 degrees.

Charging of these batteries

The charging of batteries is a science on its own altogether. Basically what you need to now is that the average car's alternator, only supply 13.6 Volts. And your battery would typically need 14.4 Volts to recharge fully. You should make absolutely sure of what the specific auxiliary battery installed in your vehicle's charging voltage should be. In that case it is best to install a DC - DC converter to get the correct Voltage. There are very smart DC - DC converter chargers on the market lately, see if you can find one that could be set to the specific type and size of your auxiliary battery.
Solar Panels

Adding a solar panel to your system could just be the guarantee that you not run out of battery power. Depending on where you are planning to go, what the average ambient temperature is and how big your fridge/ freezer are will all have an influence on what your power requirement would be. But the general rule of thumb is to get a 12 Volt, 100 watt solar panel, that should be sufficient to charge your battery. Use it with a charge controller, also set to the correct voltage or working in conjunction wit your DC  DC charger.

A solar panel has the unique feature of generating electricity when exposed to sunlight. They are very fragile and needs to be treated with care. When you put it out in the sun make sure that there is no shadows on the panel and it is fully exposed to the sun and as close to perpendicular as you can possibly get. Also make sure that your solar panel is as clean as possible. If you are standing for the day you should move the panel every so often as to keep it exposed to the sun to its full potential.

Battery charger

Connecting a 12 Volt power supply to any of these new age batteries is just as bad as to mow the lawn with nail clippers.

The best is to buy a decent smart battery charger with dedicated settings for recharging specific batteries. 

All batteries recharges basically with the same sequence, first it would need a constant high voltage over a length of time, depending on battery type. Then in the second stage the battery would need a constant voltage of not higher than 14.4Volts. This stage is very important as this is where the battery stores the most of it's power.

The third stage is a trickle charge where with a very low current the battery is being topped up to the brim with charge.

All of these stages have different length of time depending on the type of battery.

There are quite number of smart chargers on the market, make sure to get one that can charge your specific battery

Keep in mind

Strong enough? 

Please keep in mind that the power requirements, alternator,  installed in your vehicle, were designed to charge a standard size cranking battery and to drive the wipers, normal lights and other electronic equipment.

In the mean time you have added more driving lights, compressor, fridge and a concrete mixer.

There is a very good chance that your alternator will not be able to handle all the required amps. You need to confer with your auto electrician and calculate your requirements to see what size alternator you require.

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Get insurance!

Make sure that every extra connection from both batteries, do have a fuse, and that it is the correct size!

Put a 100A fuse directly where the wire that

charges the extra battery leaves the main battery and another 100A just before it gets to the auxiliary battery. Every other appliance that is connected, must have a fuse leaving the auxiliary battery and before it gets to the appliance. 

You could also have one wire that goes to a distribution box, also fused twice, and from there all the respective fuses. It is very important as this can easily cause an electrical fire in your vehicle.

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Thick enough?

Make sure your wires used for all auxiliary power is thick enough, if it is not the required power will not reach the battery or your appliances, resulting in your auxiliary battery never being fully charged.

Get a proper Voltmeter and first measure the voltage on the main battery, whilst the engine is running. Now measure the voltage across the poles of the auxiliary battery, if there is a difference of 0,2V or more, you have problems. 

You can use the following guidelines to work with:

  • 16mm² for auxiliary in the engine compartment.

  • 25mm² for auxiliary on the back of a bakkie or in the boot of a station wagon.

  • 35mm² to the trailor.

Also lay an extra wire for the negative, it is not a good idea to use the chassis as an earth.

Contact?

Make sure to use crimped lugs for all connections with the colour coded crimp sleeving on, red for positive and black for negative. Make sure that your battery clamps are clean and that they make

​good contact, it is a

common problem that battery clamps come loose. You can use hot water or even better hot water with bicarbonate of soda to clean the poles.

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Compressor.

Any compressor will draw a lot of power, do NOT connect your compressor to your auxiliary battery but rather connect it directly to your main battery, it will drain your auxiliary battery very quickly and then you have warm beer.

Connect it to the main battery and have the engine running whist you are using it, that way the power will come from the alternator.

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