Electrical Installation
1. Basics of Electricity
There are two types of electrical energy; direct current (DC), and alternating current (AC). DC runs in one direction so it requires a positive and negative wire, and AC moves in an ‘alternating’ direction so it only needs one wire. Batteries typically run on DC, which has a lower voltage (12 volts), so most appliances for RV’s and cars are designed for DC. Most appliances you use at home run on AC (120 volts). You can run AC appliances from a 12V battery if you use an inverter.
To figure out how many solar panels (Watts) and battery capacity (Amp-hours) you need, you should first figure out how much energy you plan to use in a given day. The easiest way to do this is to make a spreadsheet with: a list of appliances you plan to use; the voltage and amperage they require; and how much time you plan to use them per day. My ebook comes with a template spreadsheet that has formulas already incorporated to calculate the watt-hours and amp-hours as well as information to then calculate fuse and wire sizing.
Before getting into the nitty-gritty of a full-scale electrical setup, it’s possible to go simple without any solar panels or additional batteries. There are lights and other small appliances that are battery powered (like these lights: link, and this fan: link). A phone and laptop can be charged from a car battery with a cigarette lighter inverter when the vehicle is running (link). A fridge is the main power sink for vandwellers; a cooler (link) can keep food cold if you don’t mind buying ice once a week or so.
2. Battery Selection
The 3 types of batteries that are commonly used for mobile homes are 6V flooded lead acid batteries (link), 12V deep cycle AGM batteries (link), and 12V lithium-ion batteries (link).
Flooded lead acid batteries are the cheapest option, but since they are filled with fluid acid, they require regular maintenance and the batteries need to be properly vented to the outside of the vehicle.
Deep cycle AGM batteries don’t require any maintenance or venting, but cost a little more. Lead acid and AGM batteries shouldn’t be regularly discharged below 50% of their total capacity. Their recharge ability will degrade over time if they are frequently discharged below and stored below that level (about 12.1V), and they won’t last as long. To account for this, you should double the amount of Ah you plan to have.
Lithium-ion batteries don’t require maintenance and the power can be further depleted without having to worry about recharge. However, they are the most costly option at about $900 for 100Ah, compared to $170 for a 100Ah AGM battery.
3. Power Sources
The most obvious power source is solar since it uses a free renewable resource, although a solar setup can become expensive. A standard 100W solar panel (link) is about 2’ x 4’ and usually costs around $100.
There are flexible solar panels (link) that have a very low profile, making them stealthier than rigid solar panels. However, they cost more and are more prone to issues with internal connections, so they may not last as long.
Solar panels require a solar charge controller to regulate the voltage going from the panel(s) to the battery system. There are two types of solar charge controllers: MPPT (max power point tracking) and PWM (pulse width modulation). PWM solar charge controllers (link) don’t work well with high voltages, as they can become very hot.
MPPT charge controllers have a higher initial cost but work more efficiently, so the additional energy stored will make up for the cost. This solar charge controller (link) also comes with an MT-50 battery meter that shows the voltage and amperage that is coming in from the panel, going out to any appliances, and is stored in the batteries.
The solar panel wires will likely need to pass through a cable entry housing (link) to enter the vehicle and solar panel extension cables (link) to reach the charge controller, which are connected by MC4 connectors using MC4 tools (link). Solar panels connected in parallel need MC4 branch connectors to connect wires from multiple solar panels to a single wire going to the solar charge controller (link).
An alternative to a solar setup is a VSR (voltage sensing relay), or battery isolator. A VSR (link) uses a car alternator to charge a leisure battery, but prevents the appliances from running your car battery too low.
4. Power Distribution
To connect the battery system to any 12V DC appliances, you’ll need a positive and negative bus bar (link), which is a metal strip that distributes electricity. The positive bus bar would be a fuse block (link) with a fuse for each connection to protect the wires and appliances from getting overcharged and potentially heating up, which can cause a fire.
Fuse block on the left, negative bus bar on the right
An inverter converts 12V electricity to 120V. There are MSW (modified sine wave) and PSW (pure sine wave) inverters. MSW inverters (link) are cheaper than PSW inverters (link), and work for simple systems that don’t have any delicate electronics or audio equipment. It’s safer to use a PSW inverter for computers and TVs, and they don’t produce a buzzing noise like MSW inverters do.
You get an inverter with 3 prong outlets and run extension cords to any AC appliances. If you’d like to have a wall outlet, you can buy a desk grommet (link), which is similar to an extension cord but can easily be installed to have a clean finished look.
5. DC Wiring
To connect all the above components together, you’ll need wires of different sizes, or gauges. The higher the gauge of wire, the thinner it is. Wires should be slightly larger than necessary as they can create heat if they’re too small. Wire sizing is covered in my ebook.
Wires typically come in red or black to signify if they are positive or negative. Here are links to low cost, high quality wiring: 4 gauge; 6 gauge; 8 gauge; 10 gauge; 12 gauge; 14 gauge; and 16 gauge.
6. Connections
You’ll need some tools and materials for making all wire connections. First you’ll need a wire stripper (link) and wire crimper (link) to attach terminals to the wires. You’ll also need electrical tape (link) to protect the connections. There are different types of terminals (link) based on the receiving terminal that the wire will connect to.
Terminals come in red, blue, or yellow; these colors are made for different wire sizes. For a single wire, red is for 22-18 gauge, blue is for 16-14 gauge, and yellow is for 12-10 gauge. Twist connectors (link) are used for connecting two wires together.
Typical crimper tools aren’t made for wires larger than 10 gauge. For larger cables you can use a lug hammer crimper (link) to connect them to lug terminals.
Working with electricity is obviously dangerous. A multimeter (link) can be used to check if a wire is active, as well as measure its voltage, amperage, and its polarity.
The DC device that’s likely to be used the most is a USB outlet. You can install an outlet with 2 USB sockets (link), or a 4 in 1 panel (link) that has a cigarette lighter socket, a dual USB socket, a simple voltage meter, and a switch.
7. Fuses
Typical crimper tools aren’t made for wires larger than 10 gauge. For larger cables you can use a lug hammer crimper (link) to connect them to lug terminals.
Working with electricity is obviously dangerous. A multimeter (link) can be used to check if a wire is active, as well as measure its voltage, amperage, and its polarity.
The DC device that’s likely to be used the most is a USB outlet. You can install an outlet with 2 USB sockets (link), or a 4 in 1 panel (link) that has a cigarette lighter socket, a dual USB socket, a simple voltage meter, and a switch.
8. Switches and Relays
Aside from fuses, battery switches (link) can protect you if you ever need to do electrical work after installation is complete. A DC rocker switch (link) can be added to any DC appliance.
There are dimmer switches (link) that can be used for 12V lights (link), which can be intense at full brightness. It’s nice to be able to adjust the light to a low setting in the mornings or at night.
Another kind of switch is a DPDT switch (double pole, double throw; link), which can reverse the polarity of the electricity powering an appliance. This is useful for a vent fan made to extract air, so it can be used to blow air in like a ceiling fan. DPDT switch wiring is covered in my ebook.
A relay is similar to a switch, although it is electrically operated. It can be used to switch something on or off depending on the time, temperature, etc. I installed one for my mini freezer so that it can be used as a fridge; at a certain temperature read by a 12V temperature controller (link), the relay (link) shuts off the freezer compressor and inverter to save energy. I used a mini freezer instead of a mini fridge since they are made to have better insulation. This makes the freezer about as efficient as an expensive 12V fridge.