
| Auxiliary
Batteries are used to operate appliances while you are away from mains 240v power,
and so you dont run the risk of compromising you vehicles main starting battery (jump or push starting your vehicle is not much fun and best
avoided dont you think?)
People have been using and charging auxiliary batteries in their cars and caravans with varying degrees of success for over a century. For most of us the days are long gone when all we needed from our auxiliary battery was a small amount of power for a bit of lighting and maybe a radio. These days we expect much more, we like to run lights, TVs, DVDs, pumps, fridges, winches, charge camera batteries and mobile phones etc, even microwaves, some of us like all the luxuries of home when we go camping. So over the years our demands on the humble auxiliary battery have increased to the point that we need much more useable energy, and over a longer period of time, and we need fast and safe ways to recharge them. Many of the old ways used to charge these batteries are now antiquated, and they mostly never did the job well anyway, nor were they conducive to long battery life either. So lets look at what we need to build a system that will
deliver the best performance for our hard earned dollars. Whats needed. Well I guess a good place to start would be an auxiliary battery, then we need an efficient way of charging this battery using the cars alternator, and most importantly a way of isolating it from your starting battery so that it is not compromised, to do this we use a battery isolator, and then all thats left is some cable to connect it all up, simple eh, well it is simple as long as you use the right bits, and put it together the right way Auxiliary Batteries. Basically you should be thinking about how big a battery can you fit, and less about how small and cheap a battery you can get away with, the larger the battery the less percentage wise you will be draining it, and the longer it will last both in power usage and battery life, with the extra advantage of more capacity when needed.Hot Tip Batteries love being fully charged, they dont like being discharged at all, they like it when you only take them down to 50% of their capacity and then top them back up soon after, they will lose capacity and die quickly when left discharged for long lengths of time. Deciding on what size and type of Auxiliary Batteries to use is really a whole other story, please read my article on AGM (Absorbed Glass Matt) batteries www.fridge-and-solar.net/agm.htm The Battery Isolator. The battery isolator is a device that allows the cars alternator to recharge the auxiliary battery while protecting the cars starting battery from discharging, if these batteries are simply linked together you run the very real risk of draining them both to a level that you can not start the engine, and there are many other reasons why you should not do it this way.So hence we have the battery isolator, there are many different methods used to isolate the batteries, most use some form of solenoid, this is an electronic switch that can handle large (charging) currents, much more than standard switches can, and they are operated by applying a small amount of power to them, this is turn actuates a solenoid that links the batteries together so that large currents and be passed between the batteries. There are many ways to operate these battery isolators, some much better that others. The cheapest way is that you manually turn them on and off, I call these idiot switches, because sooner or later some idiot (and Ive been there) will forget to turn the switch on (no charge goes into the aux battery) or off at the right time (and then the starting battery gets drained as well).Another way of doing it is to have the solenoid turn on as soon as you start the engine up, and turn off when you shut down the engine, this has been the cheap way of doing it for many years, but its far from ideal. I believe the best way for most situations is to use a VSR (voltage sensitive relay) activated solenoid, and the one I like the best and use is one of the most inexpensive ones, it does the job very well, and as good as, and sometimes better than many of the very expensive ones too. The Redarc Smart Start battery isolator and how it works.
When you start your engine the Redarc
works by first letting your starter battery recover its charge, it lets it achieve
13.2 volts, at this point that battery has about as much charge in it as it's going to
get, once the Redarc sees this 13.2 volts it closes the contacts on the solenoid, this
links both batteries together for charging purposes.
The next thing the Redarc is looking for is 12.5 volts, in other words you have shut down your engine and started to draw power from the batteries, so very quickly the voltage across both batteries will fall to 12.5 volts, as soon as the Redarc sees this voltage it will open the solenoid contacts and isolate the batteries, leaving your starting battery for starting and your auxiliary battery for auxiliarying ;-) The Redarc Smart Start battery isolator is rated at 100Amps constant duty with a surge capacity of 400Amps, it has silver contacts unlike some of the cheaper ones that have copper (silver is much better), the Redarc also has spike protection so it wont upset the delicate electronics on newer vehicles, the Redarc is on SPECIAL and is priced at $139.50.The Wiring & Cable. Wiring this is without doubt where many people get it wrong and end up with a system that may work, BUT barely, and nowhere near as well as it could and should, doing it right can double the useable capacity of your auxiliary batteries over and above what many people normally have, and help them charge much faster and last longer too. Understand that when charging from vehicle alternator one of your biggest enemies is voltage drop, you need to have the highest possible voltage at the auxiliary battery, this will allow it to charge as quickly as possible, and as fully as possible. Some standard set-ups I see regularly that have been fitted by the so called professionals is where they use twin 6mm auto cable (really 4.59mm˛), this is next to useless for fast deep charging. A very basic explanation would be, that the larger the current draw, the larger the wire (cable) needs to be, and the further the distance the wire needs to run, the increasingly larger again the wire needs to be. Water and power analogies work well here, so think about it, if you want to fill a bucket full of water fast, do you use a hose the size of a straw, or a ˝ inch garden hose, what one do you think will fill the bucket quicker? I always suggest a minimum of 6 B&S (13.5mm˛) cable here for linking batteries, Battery placement. A very important thing to consider is where you are going to place your batteries, standard open wet cell batteries give off hydrogen gas when they are charging and discharging, this is a very explosive gas, remember the Hindenburg, there is no problem if you are putting the auxiliary battery under the bonnet of your vehicle, or mounting it somewhere on the chassis with good ventilation to the open air.Just throwing them under a seat or in a cupboard is far from ideal and just down right dangerous, even worse some people place battery chargers and even inverters next to these batteries, just think about that for a moment, a hydrogen producing device next to a possible spark producing device, I guess some people just don't know or dont think! Wet cell batteries must be housed in a properly vented area, and must be well vented externally away from any ignition source and from human habitat areas, hydrogen gas rises so sealed battery enclosures should be vented externally top and bottom. If you need to place batteries inside vehicles, then AGM batteries should be seriously considered here as they are totally sealed, AGM batteries if placed in an enclosure only need to be vented to atmosphere not necessarily vented externally. Putting AGM batteries under the car bonnet is fine as far as safety goes, the only consideration here is that AGMs and Gel batteries should be kept away from the extreme temperatures of turbochargers, and if they must be placed close to the turbocharger then heat shields should be used. How to wire it all up.Now this is much simpler than most people think, it is not complex, and as long as you take care almost anyone can do it. Some tips * Do not install the Mega fuses until the last thing, when you have completely finished all the cable runs and tightened up all connections. * Although not always totally necessary (some people can use the chassis for earth return), but it really is best to run the earth/negative cable all the way between the start and auxiliary batteries, for the extra few dollars in cable it really is worth it. When running the cables between the batteries you should take great care with where you place the cable, making sure that it wont rub or be cut through, also be careful to keep it clear of sharp corners etc, and if the auxiliary battery is going to be placed anywhere other than under the bonnet, you should seriously consider using a protective covering like split convoluting tubing and secure it well with clips or cable ties at well spaced intervals.The cable should also be protected against short circuit, and I have found the most economical way to protect the cable is with Mega fuses of 100A, an all too common mistake made by many people and even some auto sparkies is that they only fuse at one battery (normally the starting battery), but the cable needs to be protected from both ends, i.e. a fuse at both batteries, after all it is being feed from both batteries. If your auxiliary battery is in a caravan or trailer then the standard trailer lights connectors are way too small for the 6 B&S cable, and cant even come close to handling the high currents for effective battery charging, so here we use 50A Anderson plugs (Pictured below). All cable lugs used with the 6 B&S cable are far too big to be crimped with standard crimping tools, so they should be crimped by an auto electrician, or you can solder them if you have a gas torch, they do take a lot of heat to solder on properly. As you can see in the picture of the the
Redarc battery isolator, it has two wires coming from it, one blue and one black, and it
has two terminals for attaching heavy cable, now the blue wire is rarely used, so lets
forget about that one for the time being, the black one is simply an earth that should be
secured under one of the screws that you mount the Redarc to the vehicle with. Below are some examples of how an auxiliary battery set-up may be done, but there are many many other combinations that can be done to suit almost all needs. |
This is a basic layout for those
that might install an auxiliary battery in the back of their vehicle.
This for those that might install an auxiliary battery under the bonnet of their car.
This for those that might install an auxiliary battery in their Caravan or camping trailer.

On
the right of this photo are two examples of the Anderson plug, a very well designed plug
for connecting heavy cable together,
incorporating no gender, both connecting plugs are identical, they can not possibly be
hooked up wrongly,
so there is no risk of shorting out the batteries in the dark, they are also self
cleaning, so a bit of mud won't worry them,
the price for these is now only $10.00 each, and you need two
to make a connection.

These are Mega fuse holders and a
100A Mega fuse,
The 100A Maxi fuse is $8.45, and the in-line holder is $19.95,
while the block holder is $34.95, and you need either one of these at each battery.

The larger cable is the required 6
B&S (13.5mm˛) and matching lug, note the wire above it,
that's the 6mm (4.59mm˛) Auto cable used by many to do the job, it's just not up to it at
all.
The 6 B&S cable is $5.50 per Mtr, and you need enough red and black to run between
both batteries.
If you need more information please don't hesitate to contact me.
Val Rigoli
Fridge & Solar
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