We all love to sink our teeth into a good DIY project, and the way technology is going these days you can bet your bottom dollar you’re going to end up hip deep in an electrical job at some point or another. The thing is, any 12V project – particularly installing a second AGM deep cycle battery –  has the potential to cause hours of dramas out on the tracks if it’s not done right, not to mention the risk of causing an electrical fire too. Plus, the rigors of off-roading is particularly harsh on electrical equipment, which means you’ve really got to go the extra mile to ensure your next 12V project will go the distance. With that in mind, we’ve put together ten top tips to ensure your workmanship is ready for the scrub. You’ll find this advice to be incredibly useful for just about any 12V DIY you hook into. After all, when you get it right you’ll enjoy years of trouble free service and a real sense of pride every time you jump in your truck.

If you get it right, installing a deep cycle battery into your vehicle is one of the most rewarding 12v jobs you can do – and the truth is, as long as you know the basics, it doesn’t have to be that hard, either! This article is the first in a two-part series where we take an in-depth look at the right tips and tricks you need to know to properly install an AGM battery for camping into your 4WD.

THE RIGHT WIRE

When it comes to selecting the right 12V wiring for the job, the current rating and voltage drop are the two main things to consider, and are especially important when you install a 12v deep cycle battery. An electrical wire’s current rating is usually a very optimistic number. You’ll find in most 12V circuits we actually need much larger wire than this to minimise the amount of voltage drop, which naturally increases the longer the cable stretches.

To calculate voltage drop with copper cable, you simply multiply the wire’s length in metres by the current draw through it by 0.017 and then divide that number by the cross sectional area of the wire. So if you use seven metres of 4mm wire to power up your 4WD’s 12V fridge, and it draws a maximum of 5 amps, You’d use the following formula:

Voltage drop= Length x Current x 0.017
                                       Area

So, plugging our numbers into the formula gives us:

7 x 5 x 0.017 = 0.595

Then you’d divide by 4mm, giving you:

0.15 (rounded up) voltage drop.

So if there’s 12V at the battery, there’d only be 11.85V at the fridge

Note that this formula is accurate at 25°C. Voltage drop increases with heat roughly 0.4% for every degree above 25°C. Voltage drop is incredibly important when it comes to a camping AGM battery, as if you get this wrong, the battery will never properly charge.

FUSIBLE LINKS

The purpose of a fuse is often misunderstood. Their real purpose is to protect the wiring between the battery and the actual load (accessory), not to protect the load itself. If wires from a deep-cycle battery aren’t protected, a short circuit can cause high currents to flow, which overheats the wire potentially causing a fire. With all the bumps and vibrations out on the tracks, our trucks have a much higher chance of damaging the wiring and causing a short circuit. With this in mind, the fuses rating should be less than the current rating of the wire, the idea being you want the fuse to burn out and cut the power well before the wire does.

In 12V automotive wiring, all fuses should be located as close as practical to the AGM dual battery’s positive terminal to minimise the amount of wire that’s not protected by the fuse.   

SOLDERED TO PERFECTION  

Soldering is one of the most common ways to permanently connect wires together or to connect wires to terminals to connect to your deep cycle battery. If done correctly it forms a durable, low resistance and corrosion free joint, which is exactly what a 4WD needs if it’s going to last.  

Your choice of soldering iron is absolutely vital, as many a poor solder joint has been caused by a soldering iron with insufficient heat capacity. If it hasn’t got enough power it can’t heat up the joint properly, which actually creates a high resistance joint that’s prone to complete failure at some stage. These are often called ‘cold joints’.

CRIMPING LIKE A PRO

Despite what some might think, crimping can actually be every bit as good as soldering if it’s done correctly, and it definitely has a place when talking about installing a second deep cycle battery into your vehicle. In fact, if the terminal has a double crimp; one for the wire and another for the insulation it’s even better. Using the wrong sized terminal in relation to the wire’s diameter is the main cause for this method to fail. A loose fit is simply bad news on bumpy off-road tracks. You’ll need to use a proper crimping tool, not a pair of pliers to allow the terminal to crush down nice and tight on the wire, and terminal insulation. Note that different jaws are needed for insulated versus uninsulated terminals of the same size. It’s vital to strip the wire down to the correct length as stripping off too much insulation will usually cause the insulation crimp to fail and the wire to later break due to mechanical fatigue. That’s the last thing you want – you’ll be there thinking your deep cycle battery is flat, when in truth it’s your connections that have failed!

For a successful joint, the soldering iron must be pre-heated to operating temperature, and the tip must be clean and freshly tinned with solder. If in doubt, wipe the tip clean on a rag and re-tin before attempting the joint. The tip then needs to be in contact with all parts that are to be soldered together to ensure that everything gets hot enough for the solder to flow through and adhere. Do this, and you’ll ensure proper flow of electrical power from your auxiliary camping battery into your 12v appliances.