12. 12v DC Electrical System | Design & Installation
The central point of any van conversion is the electrical system, which powers everything from your morning coffee to your evening podcast. This is the heart and soul of the van build. Electrical systems can typically be broken up into two systems; the 12v DC system and the 120v AC system. In this step of our build, we will go through the planning and installation of the 12v DC system. This system is the most important, and will power most functions including; lighting, heat, the fan, water pump, the fridge, cell phone booster, auxiliary charging ports, and even an onboard air compressor.
Table Of Contents
Getting Started
Understanding Your Power Needs
Before setting up the electrical system, it’s crucial to understand your power needs. Take stock of all the devices and appliances you'll be using in the van. Consider items like lights, a refrigerator, a laptop, and charging stations for your gadgets. Determine the wattage each device requires, which is often listed on the product or in the user manual. Add up these figures to get a clear picture of your total power consumption. Keep in mind that not all devices run simultaneously, so factor in usage patterns as well.
Once you've assessed your power needs, it's time to calculate your total energy consumption. This is typically measured in watt-hours (Wh) or amp-hours (Ah) per day. By estimating how long each device will run daily, you can sum up their energy usage to estimate your daily consumption. This step ensures that your system wont be underpowered, allowing you to avoid potential problems down the road. My forecasted usage is relatively low with the Fridge being my largest consumer.
Another major consumer to consider is air conditioning. 12v Air conditioning units can draw 100-250ah a day. Solar panels keep heat off the roof and convert that heat into useable energy so I am planning to forego a roof top air conditioner in favor of more solar panels. I also find cross ventilation to be more than adequate in most situations. For the rare times where I could need AC, I can always just start the van for a bit or go for a little drive to use the cab AC.
My total projected daily amp hour usage is around 110ah on the high end. Here are the total daily amp hours of each component individually.
My Amp Hour (AH) Usage
Fridge - 23-50ah per day
Lights - 3ah per day
Water Pump - 6ah per day
Maxx Fan - 2ah per day
Electric Kettle - 12ah per day
Electric Cooktop - 15ah per day
Additional Combined Loads - 30ah per day
With a forecasted total of 110ah a day of consumption, I can now start to plan the system. With one 100ah battery, we know that with no method of charging, we would outrun the battery during a single day of use. The bigger the battery bank, the longer we can extend this out, or extend our “off-grid”/ “boondocking” time. After evaluating this and considering space limitations for the batteries and other electronic components, I decided the most feasible and likely option will be a 300ah battery bank. In tandem with the future planned charging systems, this should be enough to stay of the grid nearly indefinitely.
(As a general rule, you'll want at least 200Ah of batteries for moderate energy use or 400Ah+ for high demand.)
Creating a Diagram
The best way to start building the electrical system is by creating a detailed wiring diagram to plan out the full electrical layout. This blueprint will guide the installation and serve as a reference for any future modifications. It also helps visualize the entire system and brainstorm the path of electricity throughout the system allowing you to make adjustments and refine the system before installing. This can help streamline the overall system keeping wiring short, neat, and well organized. Planning the system out on a diagram also helps see the appropriate locations to place breakers and fuses to minimize risks and safeguard against shorts or overloads and ensure a safe and efficient electrical system. This diagram is my complete plan. It includes the 120V AC system, 12V DC System, and my Plumbing plan. I also broke each system out separately into smaller diagrams that are easier to evaluate and work from during installation. While designing these diagrams I was able to answer many questions and mitigate many electrical issues. This process helped decide exactly which components to purchase, where they would be mounted, and even identify tools I would need for the work.
Recommend Electrical Tools
Having the right tools for the job always makes a big difference, but I find it extra important for electrical. The main tools needed are Wire Strippers and Wire Crimpers for the various sizes of wire you will be working with. Using the proper wire strippers ensures precise cuts that remove the outer insulation without damaging the underlying conductors. This precise stripping ensures optimal electrical conductivity and connection reliability. Wire crimping tools are designed to create a strong, reliable bond between the wire and the terminals, preventing the wire from pulling out which can cause a short circuit or even a fire. Both tools are easy to use and make the work much easier. For this van build and install, I will be using 4/0, and 14 Gauge wires. These strippers and crimpers will cover all of our needs for the entire van build including the 120 AC electrical system and Solar Charging System installs.
Battery System
When building a van RV, selecting the right battery system is crucial for ensuring reliable power supply during your travels. The two main options are Lithium-ion and Absorbed Glass Mat (AGM) batteries. Each has its own advantages and drawbacks.
Absorbed Glass Mat (AGM) VS. Lithium
Lithium Batteries - Lithium batteries are known for their efficiency, lightweight design, and long lifespan, making them ideal for those who prioritize performance and are willing to invest upfront. They can be discharged nearly complete without damage and re-charge quickly, which is beneficial for off-grid camping. This means that a 300ah battery, has 300ah of actual usable energy. Lithium batteries are not susceptible to voltage sage like AGM batteries allowing more versatility of use with appliances like coffee machines and electric stoves. They can be more expensive however, and require temperature regulation in freezing conditions. Charging lithium batteries when the temperature is under 20°F can damage the batteries.
Offer more usable capacity
Significantly lighter
Have a longer lifespan
Charge faster and more efficiently
Take up less space due to higher energy density
AGM Batteries - AGM batteries are typically more budget-friendly than lithium batteries and can operate in colder temperatures without additional insulation or heating. AGM Batteries start to breakdown when the charge is under 10.5 volts. This means the useable capacity of an AGM battery is actually half of its total amp hours. So the useable amp hours of a 300ah battery bank is actually 150ah. Dropping the capacity below that will start to damage the batteries. The other major drawback of AGM batteries is voltage sag. Electrical loads can sag the total voltage of AGM batteries well below their actual stored capacity. This voltage sag can impact small appliances and electronics that are common to RV and van life such as cooking appliances and can trip the low voltage cutoff points. They are also heavier and have a shorter lifespan compared to their lithium counterparts. That said, AGM batteries are suitable for van builds, and can be a solid option for part-time users or those on a tighter budget.
Less expensive initially
Perform better in extreme temperatures, especially cold
More readily available and familiar technology
Understanding these differences can help you make an informed decision based on your specific needs and budget constraints. For full-time van life or frequent use, lithium batteries are the better choice due to their superior performance and longevity.
Armed with the energy consumption data from above, and knowledge about the differences between lithium and AGM batteries, we can now focus on choosing the right components for our electrical system. I am starting my system off with Three 100ah AGM batteries for a total of 300ah (150ah of usable energy), with the intent to replace them toward the end of my build with a 300ah self heating lithium smart battery. 150ah will be plenty of energy for how I will be using my van throughout the build and its early adventures. Switching to the lithium battery later will be more about the ability to run small appliances reliably than increasing my usable capacity though that will certainly be a welcome benefit.
Wiring & Installing the Batteries
Before we can wire our battery bank, we need to make sure we get the right size wire and a couple additional parts.
300a ANL Fuse - The first component coming from the battery bank will be a fuse. We will want this as close as we can get it to the battery bank. If any wire or component in the system shorts out, this fuse will melt disconnecting our battery bank and isolating it from the rest of the system. This is a must-have safety feature. This fuse will be on the positive cable coming out of the battery bank. We want this fuse close enough that the hot battery cable coming into it will be too short to ground itself to anything if it were to become disconnected. This three pack is a good value and leaves extras in case you get a bad one or accidentally short circuit the fuse during install.
Master Shutoff Switch - After the fuse, we will place a rotary switch. This ON/OFF switch will be our master switch for all the power in our system allowing us to isolate the batteries. We want to place this switch somewhere that will be reasonably accessible if needed.
Bus Bars - Bus bars allow us to connect multiple cables together in a clean, organized, and safe way. Our ground wire from the battery bank will go straight to the end terminal on the ground (black) bus bar. Our positive battery cable will go from the master switch to the end terminal on the positive (red) bus bar. The remaining posts on the bus bars are where our other components will now be able to connect to our battery bank. The components include our DC Loads (lights, fan, heater, etc.) through a fuse box, and our charging methods such as our solar charger or DC to DC Charger. These 6 post bus bars offer plenty of room for all your components with some extra for future proofing.
Wire - Choosing the right gauge wire is important to prevent energy loss and fire hazards. Wire that is too small can overheat. 1/0 gauge wire is the smallest to go for the battery cables. Larger wire from here has less resistance and is more effective. It is more expensive, and in many builds it may be unnecessary. For reference, the 300ah AGM battery bank I mentioned above could not power my 120v electric kettle, a portable single cup coffee machine, or a single burner electric convection stove from a 3000w inverter. The voltage sag from the appliances would bottom out the system. In comparison, when the 1/0 gauge battery wires were replaced with 4/0 gauge, all three devices can be operated. The 120v electric kettle boils water in 3 minutes while sagging the system down to 10.5v during most of the runtime. As mentioned above, this would not be a factor with lithium batteries, but is a great reference for understanding the resistance and effectiveness difference between cable sizes. It is equally important to route the cables on the shortest runs possible. In short, the thicker and shorter the cables, the more efficient the system.
The wire on the left is the 1/0 Gauge, and the wire on the right is the 4/0 Gauge. You can see a substantial difference in the size. The larger gauge does come with a much higher price, but depending on your electrical needs, the difference in electrical resistance is worth it. Think of these as straws that you have to breath through. Its much easier to breath through the larger straw.
The first step in installing the system is mounting the batteries. Mine are going in a cabinet so their is nowhere for them to slide or move to in any direction. Mounting them in my case pretty much consists of placing them in the cabinet. We can also create the wires and connect the three batteries together. Remember, we want these wires to be as short as possible.
(Make sure all the cables are cut and stripped cleanly, the cable connectors are properly crimped, and the joints are covered and secured with heat shrink. For added safety and good practice, place the heat shrink to cover the connectors up to the start of the lug holes. If a lug comes free, the exposed wire will still be covered by the shrink and help avoid additional danger or a short.)
When it comes to wiring the batteries we have to decide whether we want to wire them in series or parallel connections. Both methods have their advantages and are used in different scenarios depending on your power needs.
Series - In series wiring, batteries are connected end-to-end, with the positive terminal of one battery linked to the negative terminal of the next. This configuration increases the overall voltage of the battery bank, maintains the same amp-hour (Ah) capacity as a single battery, and results in a higher voltage system (ex. 24V from two 12V batteries). Series wiring is beneficial when you need a higher voltage system, which can be more efficient for certain applications.
Parallel - Parallel wiring involves connecting all positive terminals together and all negative terminals together. This method maintains the same voltage as a single battery, increases the overall amp-hour capacity, and allows for greater current draw and longer runtime. Parallel wiring is commonly used in most van and RV setups, as it provides more capacity while keeping the standard 12V system. I will be wiring my battery system in parallel.
Next we will identify the location for our fuse. This needs to be close to the battery so that if it were to disconnect, the positive cable from the battery cannot ground itself to anything. A short after the fuse will melt the fuse, but a short in front of the fuse can be harmful and even cause a fire.
Mount the master shutoff switch in an accessible place, but close to the main battery fuse to keep the cables short. Make a cable to connect the fuse to the switch.
Find a suitable location for the bus bars. Try to keep these close as well for short cable runs, but keep in mind they will be connecting to several additional devices. Once mounted, connect the ground bus bar (black) to the battery banks ground lug, and the positive bus bar (red) to the master switch.
Ensure all connections are tight and secure.
A clean, organized wiring job is important not just for aesthetics but also safety and maintaining your system. Taking the time to properly install cables, connectors, fuses, and grounding will pay off in the long run with a reliable, safe, and efficient electrical system.
Wiring & Installing the 12V System
With the batteries installed, we are on to the fun part of connecting our DC loads. These are all of the components and accessories that require 12V power to operate. The most common is the lighting, heater, water pump, and the fan. The 12V system in my van build is a lot more robust and will also power a cell signal booster, the fridge, an air compressor, accessories lighting, and several USB DC port panels for charging devices.
12V DC Electrical Loads
Lighting - There are a lot of lighting options to choose from these days. I am using these recessed 12V LED interior RV lights. These are highly energy-efficient, consuming only about 3w per light at full power while providing bright and long lasting illumination. These lights are designed specifically for use with 12-volt power supplies, making them ideal for RVs, boats, and off-grid homes. Their low voltage operation not only enhances safety but also reduces energy consumption, which is crucial for conserving battery power in mobile living spaces. They are dimmable and offer a customizable temperature control from 2700k to 6000k. Both features are controlled by a clean and compact remote control. The lights will all be wired together and controlled from a rocker switch centrally located in the van for easy access.
This 4 gang switch panel will be flush mounted between my front and rear upper cabinets on the drivers side of the van. This will place the panel about center and with easy access from anywhere in the van. The switches will control the main ceiling lights (above), and in the future, under cabinet mood lighting, in cabinet lighting, and the cell signal booster.
Similar switch panels will be used to power the air compressor from rear of the van (single switch), and the fridge, water pump, and water tank heaters from the kitchen galley (3 gang switch panel). These circuits and panels will be covered in more detail during those specific installs. For now, I will pre-run the wiring for each system so it is staged and ready.
3 Gang Rocker Switch Panel
The single 12v Socket Port will be mounted inside the kitchen galley behind the Fridge. The Fridge will be powered by 12v DC and operate from a standard cigarette lighter plug. This port will be controlled from a switch on the 3 gang rocker switch panel in the kitchen backsplash allowing me to turn the fridge off when not in use or when the van is going to be sitting idle for awhile.
USB/ DC Panels - These 4 in 1 USB and 12V socket panels will be placed in the back wall of my upper cabinets, and one in the drivers side wheel well box out to give me options for charging and powering devices. These panels are fully customizable, but come pre set up with a master on/off rocker switch (allows me to isolate the ports to avoid parasitic draws when not needed or not being used.), a voltmeter for checking the available capacity of the battery bank, a USB socket, and a 12v DC socket. For my in cabinet panels, I will replace the voltmeters with a USB 3.0 & PD charging socket to give me additional ports. The panel in the rear wheel well boxout will retain the voltmeter giving me a way to quickly check battery capacity from the rear of the van.
This 4 in 1 square panel will be mounted in the kitchen backsplash. This panel will keep the voltmeter giving me a convenient place to quickly see the battery capacity. Having 12v and USB power available in the kitchen backsplash allows the ability to run 12v appliances and is a great place to plug in USB devices to charge on the countertop or next to the rear bed.
This single voltmeter will be mounted in the headliner above the rear view mirror. This will give me a quick way to check the capacity of the cabin battery bank from the drivers seat without having to get up, or while driving down the road.
With our DC loads identified, we can start to plan the wiring. All of these components will be organized into circuits that are fed from a fuse block keeping things clean and orderly. The fuse block will be in the electronics cabinet near the batteries and bus bars.
Wiring & Installing the 12V Electrical System
Blue Sea Fuse Block - This is a robust and versatile fuse block that features 12 circuits capable of handling blade-style ATO/ATC fuses ranging from 1 Amp to 30 Amps, with a maximum total amperage of 100 Amps per block and a voltage rating of up to 32 volts DC. This fuse block is constructed from marine-grade materials to withstand harsh environments, making it ideal for RV and van applications. The fuse block will distribute power from the bus bars out to all of our DC loads/ circuits.
8 Gauge Wire - The fuse block is being connected to the bus bars with 8 gauge wire cable. 8 AWG cable provides an optimal balance of current capacity and voltage drop for many marine and automotive applications. This wire size can typically handle around 40-50 amperes, which is sufficient for powering multiple 12V accessories and devices. We will wire the negative lead of the fuse block directly to the ground bus bar (black). The bus bar connection will use 3/8 Ring Terminals, and the Blue Sea fuse block will use 1/4 Ring Terminals.
60 Amp Circuit Breaker - The positive side of our fuse block will connect to a 60 Amp DC circuit breaker. This connection will use the 1/4 Ring Terminals. The other side of the circuit breaker will run directly to the positive bus bar (red) and connect with the 3/8 Ring Terminal. This circuit breaker provides overcurrent protection and allows us to disconnect power from the batteries to all DC loads quickly with the push of button for maintenance or troubleshooting.
The next steps involve connecting and wiring all the DC circuits within the van. For all of these circuits we will be using 14 AWG wire cable.
14 Gauge Wire - 14 AWG wire can safely handle up to 15-20 amps, which is sufficient for most 12V accessories and lighting circuits in RVs. It's thick enough to minimize voltage drop over typical RV circuit lengths while still being relatively easy to work with and fit into tight spaces. 14 AWG wire is compatible with common 15-amp fuses used in RV electrical systems. It offers better durability and resistance to vibration compared to thinner gauges like 16 AWG, which is important in mobile applications. It also provides future proofing opportunities for potential upgrades or additions.
Ring Terminals - The 14 Gauge wire will connect to the fuse block with these #10 14 AWG Ring terminals. These ring terminals provide a stable and secure connection between the wire and the fuse block, ensuring continuous power flow and preventing disruptions that could impact device performance.
Spade Connectors - Each 12V device will be connected to the circuit with 14 gauge spade connectors. Spade connectors allow for quick and simple connections with easy disconnection. The Rocker Switches, Volt Meters, and USB/DC Ports all receive direct input from spade connectors for an easy install. These spade connectors are also great way to join the lighting fixtures.
Wire Connectors - These 14 AWG wire connectors are great to have on hand during the electrical system install. In some cases, we may want or need to join two wires without the need to disconnect them such as with the spade connectors. Most of our wiring will not require these, but they are good to have on hand in case they are needed.
We’ll start by running wires from each fuse block circuit, out to the 12v loads following our planned wiring diagram.
Main Cabin Switch Panel - As outlined above, this panel will be located in between the upper cabinets on the drivers side centrally located in the van. The 4 rocker switches will control the main cabin lights, mood lights, the in cabinet lights, and the cell signal booster. We will route 4 separate 14 AWG wires from our fuse block to this switch panel. Each of our 4 switches will be connected to their respective devices. At this stage of the install the ceiling lights will be the only load connected. The other 3 switches will be wired and the wire will be staged where appropriate for the future installs.
Kitchen Switch Panel - This panel will be located in the kitchen backsplash and control 3 loads; the fridge, water pump, and water tank heaters. The backsplash will be fabricated yet in the future so this panel will be wired and staged in the area (ensure the wires are long enough to reach the future location). Route 3 separate 14 AWG wire from the fuse block to the kitchen panel switches. Run wire from the first switch to where the water pump will mount. Mine will be just to the rear of the passenger side rear wheel well. Run wire from the second switch to the water tank for the tank heaters. The last switch is for the fridge. My fridge will be built into the kitchen galley and pull out on drawer slides. The 12v Fridge plugs in with a standard 12v DC cigarette style plug. I will put the 12v DC socket port inside the backwall of my galley and connect it to the remaining rocker switch with the 14 AWG wire.
Direct Circuits - The remaining DC loads are all direct circuits and will not be switch operated. These loads are; the Maxx Air Fan, the Diesel Cabin Heater, and all my 12v Socket/ USB Port Panels. Route separate 14 AWG wires from the fuse panel to each of these. The port panels can be combined on one circuit. I am combining mine into two circuits, one circuit serving port panels on each side of the van.
Make a diagram for the usb panels with the switch
Secure the wires in place, ensuring they are not exposed to sharp edges or excessive movement. Once everything is connected, put fuses in the appropriate fuse slots for the currently installed loads, power up your system and conduct a thorough test. Check each component to ensure it's working as intended, and make any necessary adjustments to optimize performance.
Final System Testing
Before embarking on any van life adventures, conduct a comprehensive final test of the electrical system. Begin by powering up all devices and appliances, and monitoring their performance to ensure everything operates as expected. Pay close attention to any unusual behavior, such as flickering lights or overheating components, and address these issues promptly.
In addition to individual component tests, perform a full load test by running all devices simultaneously. This will help you determine if your system can handle peak demand without compromising performance. If any issues arise during testing, troubleshoot and resolve them before hitting the road. A thorough final test will provide peace of mind and ensure your van is ready for off-grid adventures.
Whats Next/ Future Planning
Building out a van takes a lot of different steps some of which need to be completed before others can be started. The process can be tricky. The heart of our electrical system is installed and functioning but many features are unusable, temporarily placed, or not installed yet. With the system functioning and the wires ran, we can now start shifting our focus to several other key components of the van build.
Remaining Components - Remaining components of our 12v electrical system yet to be installed are our cell signal booster (which will go in the drivers side upper cabinet near the front), our diesel heater, an aur compressor (which will be controlled by a rocker switch on the rear of the electrical boxout), and our kitchen galley which will contain our fridge and our backsplash switch and DC/USB port panels.
Future Proofing - The bus bars for this install offer 6 lug posts. We are currently using one for the incoming power from our battery bank, and a second post connecting that power to our Blue Sea fuse block to distribute to our 12v circuits. That leaves 4 open posts which future proofs our system for additional incoming or outgoing power. 3 of these posts will be used for incoming power to charge and maintain the battery bank. These include; a solar controller for roof mounted solar charging, a shore power battery charging connection. and a DC to DC charger to distribute excess power from the engines alternator to the cabin battery bank while driving.
Future Considerations - Additional considerations include system monitoring. Monitoring systems can keep an eye on many things through the use of shunts and sensors. I will be installing the Simarine Pico Blue system which can monitor; indoor, outdoor, and battery temperatures, incline and level of the van, water tank level, and many aspects of the electrical system including isolating each load individually to evaluate and monitor its specific electrical draw. This is done with shunts that are placed inline with the circuits coming from the fuse block. For future considerations such as this, keep space free near the fuse block for mounting the additional shunts and components.
