More things to think about.
A very important thing to consider is where you are going to place your battery/s, standard open wet cell batteries give off hydrogen gas (a very explosive gas) when they are charging and discharging, so just throwing them under a seat or in a cupboard is far from ideal, and just down right dangerous.
AGM (Absorbed Glass Matt)
be seriously considered here, please check out my article on >>AGM
Charging your auxiliary batteries from your vehicles charging system.
Charging your auxiliary batteries from your vehicles charging system can be done with varying degrees of success, it depends on the type of battery, the type of battery isolator, and very importantly the size of the cable connecting the batteries.
Please read my article
Another consideration is keeping your batteries charged when you have 240v mains power available.
Briefly put, the standard cheaper automotive charges that you use to charge your car battery with will not do the job very well at all, besides not charging them properly, they can and often do contribute to the early failure of batteries.
On the other hand smart multi-stage chargers are specially designed for charging all batteries, and are essential for fast, safe, and full charging of deep cycle batteries (and any battery for that matter), and will ensure you get the best correct operation and life from them. Unlike the cheaper automotive chargers, multi-stage smart chargers truly deliver the amps that they say they will, i.e. if it’s a 20 Amp charger it will deliver 20 Amps for as long as the battery can accept it, and only backs off when the battery is about 80 – 90% charged, and then the charger drops into the adsorption stage where the voltage stays the same and the current backs off for final charging, more >>here<< on these great chargers.
Wiring and Cable.
Without going into too much detail here one of the biggest mistakes made by a lot of people, including way too many so called professionals, is under sizing the wiring/cabling, this includes some auto electricians, and sadly quite a few manufactures of caravans and motorhomes etc.
In many cases it’s not them just trying to be cheap either, it’s ignorance, and with an industry as old as this one is, it’s unbelievable that we still have such a huge problem.
Collyn Rivers wrote a good article on this subject and it’s well worth reading >> found here<<
A very basic explanation would be, the larger the current draw the larger the wire needs to be, and the further the distance the wire needs to run, the increasingly larger again, the wire needs to be.
What you can, and can not use off 12 volt batteries.
Simple 12v lighting and most other 12v appliances are easily run from 12v batteries, and through an inverter (makes 240V AC from 12V DC) for the likes of 240v TV's, laptops, small chargers for cameras cordless drills etc, lighting, dvd players etc, there is an almost endless list of things that you can run from an inverter.
But come to any sort of heating device, now these consume huge amounts of power, things like jugs, toasters, microwaves, hair dryers, it’s not really practical to run these sort of devices from your batteries for anything but a very short length of time, and even then it will cost a heap extra for the much larger inverter needed to drive these things.
Running the likes of the things mentioned above for longer periods can be done, but in most cases the cost of the extra equipment to allow you to do it would give most bank managers heart failure.
And don’t even think about running Air-conditioners from your batteries, it just can not be done without a road train full of batteries and solar panels. Quick example, small A/C running 12 hours a day = 35 large solar panels, 16 large batteries, cost = $25,000.00
If you really need to run an Air-conditioner or any heavy draw items while away from mains power, then you really do need to think about a generator.
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