Calculating the wire size you need to connect your camper van’s leisure batteries ultimately depends on how much power you intend to draw from the batteries. The more power you require, the thicker the batteries will need to be. That is because more power means more current (amps), which means more heat generated inside the wire. And if the wire is too thin, the copper wire will burn through the insulation and potentially create a fire in you van.
When calculating the size of the battery wires, we prioritize safety above all else. We don’t want you selecting too thin of a wire for your power demands and subsequently putting you and your camper van at risk. That’s why we take a systematic and conservative approach to help you arrive at a wire size that is appropriate for connecting your van’s leisure batteries together.
In this post, we provide a simple 5 step guide to help you calculate a safe battery cable size for your camper van.
If you ready, let’s get to it.
Calculate Maximum Watts From 12V Devices
The first step to determining your leisure battery wire size is to calculate the maximum wattage draw from all your 12V devices. To do this, you need to know the wattage rating for each of your 12V devices and assume that all these devices will be running at the same time. If you don’t know the exact wattage ratings of these devices, that’s OK. To help you, we list a table below with popular camper van 12V devices and their individual wattage ratings.
Your job is to make a table and list out all your devices and their watt rating. Then, add up all the watts together.
In our van, we have 12 LED lights, a fridge, 2 smartphones, a vent fan, heater, and more. Assuming all our devices are running (or charging) at the same time, we estimate all our 12V devices draw about 250W.
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Identify Your Inverter Watt Rating
If you will be wiring a power inverter (120V) to your batteries, you need to identify the watt rating of your inverter. Most inverters are rated for either 1000W, 2000W, or 3000W. But you should double check yours to make sure.
We will assume that at some point, you will utilize the max potential of your inverter.
In our van, we have a 2000W inverter, so we assume that our inverter’s max potential power draw is 2000W.
Add The 12V Max Watts & Inverter Watt Rating
Now, take the sum of the 12V watts and inverter watt rating to get your final maximum wattage power draw. This is the combined value from step 1 and step 2.
Knowing your max wattage usage is important because you will know what the maximum power your battery wires could potentially transmit. This will help you to appropriately size your battery cables.
In our van, all our 12V devices together draws about 250W. Our inverter is rated for 2000W. Therefore, our theoretical maximum power draw is 2,250W.
Divide Max Watts By 12
Next, take your maximum watts and divide by 12, which is the operating voltage of your leisure batteries.
We do this because you need to know what is the max potential current (amps) that is being transmitted through the battery wires. Remember, it is current (amps) that determines how much heat is generated inside an electric wire.
Watts (W) = Current (A) x Volts (V)
Our theoretical maximum watts is 2,250W. When we divide our max watts by 12, we get 187.5 Amps.
Calculate Battery Wire Size From Chart
Now that you know the maximum current (amps) that can potentially flow through your battery cables, refer to the table below to determine the ideal leisure battery wire size for your van conversion.
Note: For safety, 6 AWG wire is the minimum wire size we recommend. Additionally, wire size recommendation assumes each wire segment will be less than 4 feet long.
Max Current (Amps)
Since our maximum potential current is 187.5 Amps, our ideal battery cable size is 2/0 AWG.
...Or Just Use This:
Our Recommended Battery Wire Size
If you’ve read our camper van wire size guide, you’ll know that we like to err on the side of caution by over sizing our wires. That’s why for most van conversions, we recommend getting 2/0 AWG wires to connect the leisure batteries together if even you only have modest power demands. We love peace of mind.
(Note: This assumes you are using no larger than a 2000W power inverter.)
In our own van conversion, we use 2/0 AWG wires from EWCS to connect our batteries. These cables are made of thick stranded copper wires and are insulated with tough EPDM rubber that are resilient to overheating. Protecting our van and ourselves is critical and we don’t trust just any wire. We recommend getting one of the best, high quality wires in the business. Check out their website for more information.
Safety is a top priority. This ultra flexible, premium copper cable is wrapped in tough EPDM insulation and handles 175+ Amps of 'continuous' current. This is PLENTY for most camper vans. Get peace of mind with this wire.
We hope you found this battery cable size calculator post helpful. For more van conversion information, be sure to check out our van conversion guide homepage, with over 75 useful build articles. Additionally, when you’re ready to put together your electrical and solar system, be sure to download our wiring diagram eBooks. They’re completely free to use.
If you have any questions, don’t hesitate to email us at the address listed in our footer.