That is the perfect equation, as the 20A fuse will burn out before the 25A wire will. As an example, say you've got 25A wire and a 20A fuse. When you have a short circuit across a wire, it will burn out whatever has the least ability to carry that current – namely a fuse. As you may well have guessed, this isn’t ideal. If you remove the globe and connect the positive to the negative wire, the wire in the system attempts to do the same thing - become a resistor, and it glows white-hot. It starts to heat up, the amount of energy it uses is controlled by its resistance, and it glows white-hot – creating light. The globe itself is an appropriate load, in that it is essentially a controlled short circuit – the filament within the globe is basically a resistor it receives power from the positive and negative. If there wasn't a resistance (load) on the circuit, everything would melt. Positive attaches to one side negative attaches to the other. The simple analogy is to think of your average halogen/incandescent light globe. Also, if something goes drastically wrong inside an accessory you've wired into your four-wheel-drive they can internally short circuit, and achieve the same result. Think, touching the positive wire to the chassis or body which will create a short circuit (and some impressive sparkly 'arklys'), whether on purpose or by accident.
In a nutshell, a contacting of positive and negative without an appropriate load on it will create a short circuit.
Next up, let's look at what causes electrical fires. That power is unidirectional, meaning it runs from the positive on your battery, through to an electrical item (such as your fridge), and then back to the negative on your battery (or to the chassis/body that's connected to your negative terminal). These are fused usually at the fuse box, or inline at the battery terminal with a fuse-able link in most cases, or sometimes with an 80+ Amp fuse at the battery. In contrast, the positive is directly back to your battery by a rather heavy gauge wire to carry the current. When your alternator is generating power, it is earthed via the alternator housing to the engine, via an earth strap, back to the battery. All the positives end up back at the positive terminal of your battery. Negative is usually connected to the chassis, body and motor by way of earth cables or straps. On your battery, you'll have a Positive (+) terminal, and a Negative (-) terminal. When your engine is running, it's also turning the alternator, and this generates AC power, that is then converted to DC power (by a bridge rectifier), which in turn charges your battery and provides additional power for the vehicle's electrical accessories so far, so simple.
That means power flows in one direction only (unidirectional) and we've only got to deal with positive and negative simpler than Active, Neutral and Earth in an Alternating Current (AC) system (like your house). The first thing we need to understand is how the electrics in our four-wheel-drive work which is a 12-volt Direct Current (DC) power system. Auto-electricians are a lot cheaper than having to replace your four-wheel drive. So with that in mind, I’m going to offer up some of these lessons and tips to hopefully stave off disaster for you.ĭespite offering up some magic tips and tricks articles over the years, I want to re-iterate if you're not comfortable playing with your 12-volt system, leave it to an expert. My old man was an electrical engineer, so he explained to me the value of how a fuse in the right spot could keep you from burning your vehicle to the ground when you're installing 12-volt bits and pieces. There is much more to it than that if you want to do things safely, and stop your rig from burning to the ground.
Red goes to positive, black goes to negative, and things light up and start working as they should. Sure, putting in a UHF, installing some lights, or swapping out the plug on the back of our Travel Buddy 12-volt ovens or fridges from the ciggy plug to an Anderson plug is pretty straight forward. I think it's time we sat down and talked about what is possibly the single most crucial component to keeping our four-wheel-drives safe - fuses.
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