Battery Cables

In an ideal world your cable should be sized to achieve a maximum of 3% voltage drop along it’s length to ensure safe, effective and efficient power delivery and operation. That will limit the amount of power being dissipated along the cable to less than 3% of the power being delivered and will also ensure that any fuse protecting the circuit or device has adequate power to do it’s job quickly and efficiently.

Selecting the right gauge wire for your car battery is crucial for safe and efficient power transmission. All you need to know to calculate what gauge cable is best suited for your application is the amount of current required and how long the length of cable will be.

There are several ways to determine how much current flow is required for a given device. Always start by consulting the specifications page of the manufacturer’s operating manual, as most manufacturers will specify the peak power consumption of the product therein. Alternatively, if the device has a fuse, then simply double the value of the fuse. For example, if the device has a 10-Amp fuse then 20-Amps is a relatively safe bet for maximum current flow. If the device to be powered has a continuous and consistent current demand, such as a light or heater then you may be able to find the current draw using a multimeter, however be sure not to exceed the maximum rating of the meter. If the device has a motor, note that the startup current will surge much higher than the continuous load. If in doubt, consult a suitably qualified auto electrician or contact the manufacturer for cable sizing advice.

Armed with the required current flow and the length of cable, you can use an online calculator like that found here to calculate the minimum cable size you need to ensure a voltage drop of less than 3%. The output will be in metric, however you can easily use the cross reference chart found here to find the imperial gauge (AWG) equivalent.

Setting up a dual battery system requires the right cable size to ensure both batteries are connected effectively, and with minimal voltage drop at peak power. Follow the process of calculating current demand using the procedure outlined on the previous question.