This winter I've been working on a pretty intimidating project; building my own campervan that functions as a remote office. The project involved delving into several disciplines I had little to no previous experience with, such as carpentry, insulation, electrical engineering and interior design. It was a long and tedious process and needless to say I have gained a lot of respect for people who are profficient in these crafts.
The aspect of the van that for sure required the most research and knowledge was the electrical stuff. Batteries, cables, fuses, circuit breakers, inverters etc etc. A bunch of scary words, and I was pretty sure this had to be outsourced to a professional to make sure my van didn't explode. However, I have always been curious about how these things work, given that these systems exist virtually everywhere, so I decided to have a crack at it myself. With caution of course.
It turns out that electricity isn't as complicated as it seems, it's actually pretty frickin' awesome. Wiring my battery to my roof fan and turning it on without catastrophic failure gave me a sense of accomplishment I haven't felt in a long time. Therefore I would like to share my experience and try to explain how simple electrics work and how one can setup an off-grid electrical system with relative ease. My system is not a super complicated one, but it allows me work from my van using only solar power.
I will begin with some theory and then show my system in detail.
Amps, Volts and Watts
Scary words, aren't they? So what are they really?
In an abstract sense, they collectively describe how much electricity your system is using. In reality, they describe how many charged particles that are moving through your system at a time. I like to use the water hose metaphor to make it more understandable. Volts is the pressure of the water. Amps is the hoses width. Watts is the combination of Amps and Volts, equaling to the amount of water moving through the hose.
Usually in a Direct Current (DC) system, the power output of a typical battery is 12 Volts. Electrical components will always come with a given Watt usage. My roof fan for instance uses 30 Watts at 12 Volts. How many Amps does this equal to? Easy. Divide the Watts by the Volts and you will get the Amp usage. 30 W / 12 V equals 2,5 Amps. I therefore need a cable that supports 2,5 A or else my fan won't receive enough power.
My battery is a 100 Amp hour battery. What does this mean? It means that I can use 100 Amps for one hour. Or 1 Amp for 100 hours. If I leave my roof fan on, which we found uses 2.5 Amps, this means I can run my fan for 100 Ah / 2.5 A = 40 hours. That's how easy it is to calculate battery lifetime. Divide the total amount of Amp hours in your system by used Amps.
AC / DC
A cool band, but also cool technologies. The roof fan, lights, USB charging port, and solar panel in my van all run in a Direct Current (DC) at 12 volts, so they easily connect to my battery using the red and black cables that stick out of them. Red connects to the positive of the battery and black connects to the negative. My PC needs to run in an Alternating Current (AC) at 230V. For this we need an inverter. You connect a red and a black cable (DC) from the battery to the inverter, which has a socket that outputs 230V like in a house socket. My inverter uses only 4W by itself, and my mac that I work on uses around 90W, so I'm using an inverter that supports 250W.
Before I show you my entire system, we need to talk about safety.
It's no secret that electricity can be dangerous. Cables can catch fire and expensive equipment might break. That's why there are some things you need to calculate correctly, depending on your usage; cable width, fuse size and circuit breaker size. The cables need to be thick enough to support the amount of Amps that run through them, and the fuses and circuit breakers need to have an Amp limit that is low enough for them to break the circuit if the load gets too high.
Alright, let's move on to my system.
The diagram below shows all the components in the system and how they're connected.
My lovely little system includes the following components:
Solar panel that produces 160W
Solar panel regulator that controls the charging of the panel and prevents it from overcharging.
100 Ah Lithium battery with built-in BMS, heating and bluetooth so I can monitor the temperature, voltage and battery percentage on my phone
Dometic roof fan - 60W
Roof light - 4W
Water pump - 96W
USB charger port - 24W
230V inverter - 4-250W
The 12V components are all connected to the battery via a blade fuse holder distribution board. This is really useful because you only need two red and black cables connected to the battery itself, and all the other devices can be connected directly to the board. This also provides a centralized location for the fuses, so they are easy to keep track of and replace if needed. It makes the system tidy so you don’t get that many connections to the battery itself, and allows for an easy way to add more devices in the future. I’ve used 6 mm2 cables between the solar panel, the distribution board and the inverter, and 1,5 mm2 cables between the distribution board and the various 12V devices. I learned how to size my cables using this video by YouTuber Greg Virgoe. He provides a nice table of cable sizes required depending on the load size. The table is shown below:
In order to connect the cables to the various components, you need to use cable lugs and a crimping tool. The bolts of the battery, circuit breakers and distribution boards are usually of different sizes, so I recommend getting a crimp terminal kit.
Fuse and circuit breaker sizing
Another video from Greg gives a great introduction to how you should install your devices with the correct fuse sizes. He explains that you should use a fuse that has 25% more Amps than the maximum Amps your device can output.
For my system, almost all the devices were installed with 2,5A fuses because of the low amount of Watt usage. The water pump gets a 10 Amp fuse (not shown in the picture).
Thats basically it. If you have questions regarding my setup or anything really, hit me up on twitter. Thanks for reading!