jts tips and tricks

How to pick the right cable size for 12 volt

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Cable type and size is something that is quite controversial amongst 4wdrivers , caravaner’s and motor homers. Choosing the right cable is important because the wrong cable could cause all sorts of issues from voltage drops to undercharging your battery. The cable we need to use for our 12 and 24 volt projects is an automotive cable known as AS Auto Cable. Household electrical cable will work to a certain extent but the thicker copper strands mean that the cable is not as flexible and in a moving vehicle overtime can crack and break.

The most common sizes used in low voltage systems are 3,4,5,6 mm as well as 8 and 6 B&S. Automotive cable is measured in its overall diameter including the insulation.

At JTS we keep to a standard of where we use a particular size cable. Depending on distance 3 or 4mm cable is normally the best for most interior lighting. For fridges and 12volt sockets 6mm works well and if distance is extended we will even jump up to 8 B&S so that voltage is not compromised.

jts wiring diagramSizing up cable for you project can be a little difficult if you’re going to do the math yourself. To determine the cable size you will need to know the distance of the cable, the current draw and the acceptable voltage drop which is .36v in most 12volt applications. Using a chart like this one will be much quicker and easier.

Charging batteries through an Anderson Plug is the largest issue we face Day to Day in our workshop. We see a lot of vehicles that have been wired up with 6mm cable to charge a battery in a caravan and camper. A battery can take up to 30amps of charge which will struggle using 6mm cable over the distance of a vehicle and camper. There will be a voltage drop as well as the chance of the wiring getting hot causing even more issues. We use 6 B&S for Anderson plugs when not using a DC-DC charger. This will help with getting as much as possible to the battery without losses. When we use a DC-DC charger we can drop down to 8B&S as the charger itself will overcome voltage drop by pulling power in to the battery.

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