Calculating your van’s ideal leisure battery cable size depends on how much power (Watts) you intend to draw from the batteries. The more Watts you require, the thicker the wires must be (assuming constant voltage). This is because more Watts (W) means more Amps (A). And more Amps means more heat is generated inside the wire. If the wire is too thin, the copper wire will get hot enough to burn through the insulation and potentially create a fire in your camper van or RV.
When calculating the size of the battery wires, we prioritize safety above all else. We don’t want you selecting too thin of a battery cable and subsequently putting you and your camper van at risk. That is why we take a systematic and conservative approach to help you find a wire size appropriate for connecting your van’s leisure batteries.
In this post, we discuss the factors determining wire size, provide an easy-to-use battery cable size calculator & chart, and even show you how to DIY your wire size calculations.
Let’s get to it.
Factors That Determine Battery Cable Size
The amount of amps flowing through a battery cable is the ultimate factor determining the wire size. The more amps, the larger the wire size required to dissipate the heat generated.
But what determines how many amps pass through the battery cable? There are two main factors.
- Maximum power draw of electrical system
- Operating voltage of battery bank
1. Operating Voltage of Battery Bank
For most camper vans and RVs, the operating voltage of the battery bank will be either 12V or 24V. You will need to choose which voltage to go with. Generally, a battery bank operating at 24V will need thinner wires than a 12V battery bank.
Deciding your operating voltage can get a bit technical, but if you want to know more, check out our 12V vs. 24V leisure battery voltage to help you decide. In most cases, we recommend keeping it simple and going with 12V.
2. Maximum Power Draw of Electrical System
The more power (watts) your electrical system will demand, the more amps there will be, which requires a thicker battery cable size. A camper van running only a modest amount of electrics will require significantly thinner wires than an RV that wants to power a water heater, air conditioner, and television.
Battery Cable Size Calculator (Simple Method)
Below, we provide a simple calculator to help you determine your ideal battery cable size. This is intended for people who are not interested in making detailed calculations and want a sizing solution that works for them.
(Skip to the next section if you want to do your own calculations)
For the calculator to work, you only need to input two pieces of information.
- The wattage rating of your inverter
- Whether or not you will have a DC system (most likely you will)
Note: The calculator below assumes your battery’s output is 12V (not 24V).
DIY Battery Cable Sizing Instructions (Advanced Method)
In this section, we show you how to calculate the maximum amps.
If you are not sure how to calculate the maximum theoretical amps that can be transmitted through your battery cables, use our step-by-step instructions below.
Step 1: Add Wattage From All DC (12V/24V) Devices
First, list all the DC devices in your camper van and identify the maximum power draw (W) from each device. This includes your LED lights, vent fan (on max speed), fridge, water pump, etc. Then, sum up all the individual watts to get the maximum power drawn from all your DC devices.
Example: In our camper van, the theoretical max wattage draw of all our DC devices is 304 watts.
Step 2: Identify the Operating Wattage of Your AC Inverter
If you will be wiring a power inverter to your batteries, identify the watt rating of your inverter. Most inverters are rated for either 1000W, 2000W, or 3000W. But it would help if you double-checked yours to make sure. Save this wattage number for Step 3 below.
Example: In our camper van, we use a 2000W inverter.
Step 3: Sum Up the DC and Power Inverter Wattage
Add the max DC wattage (Step 1) and inverter wattage (Step 2). This is the maximum power draw of your electrical system.
Example: For our camper van, we add 304W and 2000W to get 2,304W
Step 4: Divide Wattage by Your Battery’s Operating Voltage
Take the combined wattage from Step 3 and divide this figure by your battery’s operating voltage. (In most cases, this voltage is either 12V or 24V.)
The resulting amount is the maximum amount of amps that will flow through your battery cables.
Example: We utilize a 12V battery bank, dividing 2,304W by 12V to get 192A.
Step 5: Calculate Battery Wire Size From Chart
Once you have calculated your maximum amps, refer to the chart below to help you identify your ideal battery wire size.
Example: Our maximum potential current is 192 Amps, so our ideal battery cable size is 1/0 AWG.
You should know that you can always oversize your wires for added safety. Although we could have gone with 1/0 AWG wires, we decided to purchase 2/0 AWG wires instead. We did this for added safety and to future-proof our battery cables in case we wanted to upgrade our inverter to power larger devices.
Recommended Battery Cables
For all battery cable sizes, we recommend going with the Windynation brand. All their wires are made in the USA from 100% stranded copper conductors. These cables are highly flexible for their thick size, which is essential when building an electrical system in tight spaces. Additionally, their EPDM rubber wire jackets resist extreme heat caused by high-amperage power transmission.
The video below reviews the 2/0 AWG battery cable from EWCS. We love the EWCS brand, but Windynation sells the same quality wire (we’ve compared them) for substantially less money. It’s a no-brainer.
We hope you found this battery cable size calculator post helpful. Check out our battery size calculator post if you do not know how many batteries you need for your electric system build.
For more van conversion information, check out our van conversion guide homepage, which has over 75 helpful build articles. When you’re ready to assemble your electrical and solar system, download our wiring diagram eBooks. They’re entirely free to use.
If you have any questions, please post a comment below.
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