In the 1800's electricity was as enigmatic as dark matter is today; it was primarily used by magicians to stun an audience. But in 1879 everything changed when Thomas Edison invented the lightbulb - within a few decades every house and street corner was lit. Unfortunately, to most people electricity remains enigmatic. This Campervan Electrics Explained article will teach you the most important things you need to know about electricity (as it relates to van conversions). By the end of the article, I guarantee you will have learned some really interesting information and be for more informed about how to wire up your campervan electrical system (or even your house). We will cover AC and DC current, how to measure electricity (amps, volts, and watts), how electricity is stored, how electricity flows from solar panels and to appliances, and also how we size wires and fuses.
I'm Shane, I've been teaching people to convert campervans for many years, I'm the author of The Van Conversion Newsletter, the van conversion instructor at Udemy, and the proud owner of a beautiful self-build campervan called Beans. So let's jump in and have a look at campervan electrics explained!
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Index
Note: Before we hop in, you might want to grab yourself a wiring diagram which you can get for free by signing up to The Van Conversion Newsletter (suggested, but not mandatory 🙂 - wiring diagram gets sent to you straight away).
How electricity flows
Let's start with the basics.
Electricity is the flow of electrons. When electrons are "lost" from an atom, the free movement of these electrons constitutes an electric current. Electricity travels through wires - a metal conductor (copper is most popular) that is sheathed by an insulator (rubber). The rubber insulator blocks electrical force from passing through it.
We can think of electricity flowing through a wire like water running through a hose. Water can flow in the middle, but it can't escape.
Alternating current (AC) vs. Direct current (DC)
There are two kinds of electric current: direct current (DC) and alternating current (AC). Electrons move in one direction with direct current (batteries produce direct current). Whereas in alternating current, electrons flow in both directions.
Direct current
Direct current electricity flows in one direction: out the Negative (-) side of the battery, to the appliance, and back into the Positive (+) side of battery. In a DC system, positive wire is typically coloured red, negative wire is typically coloured black. Car batteries are DC, typically 12v (12 volt).
We can think of this movement of electricity like a river; it only flows in one direction.
Many van conversion electrical appliances will be 12v DC, such as the fan, heater, or lights.
Alternating current
With alternating current, the electrical force vibrates rather than flows. This is known as oscillation. In an AC system there is no positive or negative, current is instead transmitted through these vibrations. We can think of this like waves across an ocean: force moves, but the water does not.
AC electricity does not just flow in one direction, indeed it periodically reverses direction.
Mains electricity is AC, ie. the electricity you use in your house. In North America 110v is typically used for AC, whereas in Europe 230v is used.
An AC household appliance (eg. a kettle) will have 3 wires running to it: Live (brown), Neutral (blue), and Ground (green & yellow).
When converting a van, you will likely want plug sockets (so you can charge your laptop to watch netflix...). These plug sockets are AC.
Converting AC into DC
We can convert DC into AC using an inverter - most people will want to install one of these. Related guide: Campervan inverters
We can convert AC into DC using a converter (battery charger) - if you want to setup shore power for your van (eg. plug into mains at a campsite), you will also want one of these. Related guide: Split charging.
Measuring electricity: Volts, Amps, and Watts
Volts and Amps
We measure electricity using three terms: volts, amps, and watts.
Voltage is the pressure of the electricity flowing through the wire; it is the force ready to be used (energy potential). Amperage is how much electricity is flowing through the wire.
If we think again in terms of our garden hose analogy, voltage is the pressure of the water (even if the tap is turned off, there is pressure there ready to be used). Amperage is how much water is flowing through the hose.
Voltage tells you all about compatibility - what appliance you can hook up to the source; a 110v appliance can hook up to a 110v source.
The thickness (diameter) of the hose is very important, it determines how much water you can transport. Similarly the thickness of the wire is very important. If the wire is not thick enough, it will generate heat (Energy has to go somewhere and so heat is generated - conservation of energy principle).
Watts
Watts is what we get when we multiply volts and amps; it is the total energy running through the system.
Let's say we have two hoses: the first is narrow with high pressure, the second is fat with low pressure. If we could still fill a bucket in the same amount of time with these two hoses, we would say they have the same wattage. If for instance we have two solar panels, the first produces 10v and 1a, and the second produces 1v and 10a, we would say they have the same wattage.
Wattage describes how much power overall the system is using.
How to calculate Volts, Amps, and Watts
Calculating volts, amps, and watts is very simple.
Watts = Volts X Amps
Volts = Watts / Amps
Amps = Watts / Volts
So if we have an appliance that doesn't say one of these values, we can very easily figure it out.
Storing electricity: Batteries
Battery capacity (Wh and Ah)
A battery is a device that stores chemical energy, and converts it to electricity on demand. This is known as electrochemistry. To put it more simply: electricity is stored in batteries. Related guide: Leisure batteries for campervans
Watt hours (Wh) are used to describe the capacity of a battery - ie. how much electricity they can hold. Watt(W) X hour(h) = Watt hour (Wh). You might be familiar with kWh (kilowatt hour) from your home electricity bill (where 1000w = 1kW).
Amp hours (Ah) are also used to describe batteries, but are less descriptive. A 100Ah battery can produce 100a for 1 hour. Or to go back to our analogy, the hose can give 100a of pressure for 1 hour.
For example, Tesla have two powerwall batteries:
24v battery with 250Ah capacity
12v battery with 500Ah capacity
Though the Ah of both batteries look very different, the Wh is actually the same (and the most descriptive of actual capacity):
24v X 250Ah = 6000Wh
12v X 500Ah = 6000Wh
So, using wH is the best way to compare batteries. In fact, we should always use Wh!
Given our battery, how long can we run our appliances for?
Finding out how long we can run our appliances for given the battery we have can be a very useful piece of information.
For example, let's say that we have a 100w load in total - the sum total of all our van appliances we expect to run at a given time (fan, fridge, heater, etc.). Let's also say we have a 1500Wh battery. Taking these two parameters: 1500Wh / 100w = 15 hours. We can expect to run our appliances for roughly 15 hours before running out of electricity.
In a nutshell: use volts and amps to figure out watts. Then use watts with time to figure out watt hours, then you can use this to figure out battery size, how long it takes to recharge, and how long you can use this battery to charge you appliances.
Van conversion Electrical Circuits: Parallel vs. Series
If we have multiple appliances (eg. lights), we can choose to wire them in series or parallel on the same circuit. Depending on how we choose to wire them, the voltage or amperage will change.
In a parallel circuit, we connect all the positive and negatives into one wire. If instead you "daisy chain" them, that is series.
Parallel:
Voltage stays the same, but the amperage does not.
eg. If we wire up four solar panels in parallel that are 10v and 10a. Our voltage output will remain the same, but our amperage output will increase to 40a (4X10a).
Series:
Amperage stays the same, but the voltage does not.
eg. If we wire up four solar panels in series that are 10v and 10a. Our amperage output will remain the same, but our voltage output will increase to 40v (4X10v).
Sizing a sample solar system for a van conversion
Battery capacity
Let's say that we have two 130Ah 12v sealed lead acid leisure batteries in our van. We wire them in parallel, giving us a total of 260Ah capacity. This equates to 3120Wh in total (12v X 260Ah).
However, because these are lead acid batteries, we can (should) only discharge them by 50%, meaning we can only use 1560Wh of power from our batteries.
Quick note: If we discharge sealed lead acid batteries more than 50% frequently enough, we will greatly reduce the number of charging cycles we get from the batteries. In contrast, Lithium batteries can be emptied to about 80% without problem (though they are far more expensive).
Solar panels
Let's say we purchase 4X 100w solar panels online. We look at their data sheet, and see that each panel is 17.2v and 5.82a under ideal circumstances. We are buying four, for a total of ~400w. We wire our solar panels in series, bringing our voltage up to 68.8v (17.2v * 4).
Given our 400w of solar power flowing to our 12v batteries, we now need to size our solar charge controller. A solar charge controller keeps the battery from overcharging by regulating the voltage and current moving from the solar panels to the battery. Broadly speaking the solar system looks like so: Solar panel(s) -> Solar charge controller -> Leisure batteries.
First, we must figure out how many amps at 12v our 17.2V solar panel set will actually produce. From this information, we can see that our solar charge controller must be able to handle 400W/12V = 33.7a. So we should to buy a solar charge controller that is slightly bigger, for example a 40a solar charge controller.
How long will it take the solar panels to charge our leisure batteries?
Given the above information, we know we have to fill up 1560Wh of battery using 400W of solar power. So: 1560wH / 400 watts = 3.9 hours
However, solar panels typically only output 70% of the rated wattage. This is primarily due to the angle of the sun. So: 1560wH / (400W * 0.7) = 5.5 hours
Fuse and wire sizing
Wire sizing
To calculate the size (diameter) of wire needed in a system we need two variables:
The length of the wire (distance to the appliance AND back)
The amps the wire will be carrying
When we have these two pieces of information we can plug the variables into the wire size calculator over at http://circuitwizard.bluesea.com/ or consult the BlueSea diagram below (the formula for wire sizing is quite complex, so use these tools instead!). Related guide: Campervan Wiring.
AWG (American Wire Gauge) and mm² (cross sectional area) are the units of measurement used to describe wire size. AWG is used in North America, mm² is used everywhere else.
For van conversions (and vehicles in general) we should be sure to use stranded (flex) wire rather than solid wire. There is less chance the wire will break when being bounced about.
Here is the wire sizing I used in my conversion (you can get a free wiring diagram of my system by signing up to The Van Conversion Newsletter):
12V appliances: 14AWG
Solar panels to solar charge controller to batteries: 8AWG
Batteries to inverter: 2AWG
Batteries: 0AWG
Fuse sizing
A fuse is a small wire that heats up at a certain amp rating. If too many amps go through, it will disconnect. It is a self-destructive switch that protects both the appliances and the wire.
It is important that we size the fuse correctly to prevent a fire; the fuse should be smaller than the wire - it should blow before the wire does. Related guide: Campervan fuse boxes.
To calculate the fuse size, we should calculate the total amp rating of the appliance and add on a ~25% buffer.
For example, let's say we have eight 12v puck lights which are 3w each. The amp of each light would be 3w / 12v = 0.25a. We have eight of them so: 0.25a X 8 = 2a. We want to give ourselves a 25% buffer, so we will choose a 2.5a fuse for this system.
Fuses vs. Breakers
Both fuses and breakers protect a circuit. A fuse is single use (self-destructive), whereas a breaker is more like a switch: when it is tripped it can be reset.
Just to really nail this point home, remember: A wire that is too small will give off more heat and not be as efficient (energy converts to heat). Better to size up.
Next step: Wiring Diagram for your van conversion
We've covered all our bases for the electrical knowledge you should know for a successful van conversion. Now that you understand the campervan electrics, the next step is running through an in-depth van conversion wiring diagram. I highly suggest you read this article which runs through my system at length including wiring up shore power, a split charge relay, solar power, AC and DC appliances, and much more.
Conclusion
I truly hope you found this Campervan Electrics Explained Article useful! Boy did we cover a lot! Volts, Amps, Watts, Fuses, Wire sizes, AC/DC, Solar, and batteries. You are now well equipped to build out a kickass campervan electrical system in your own self-build! Don't forget to subscribe to The Van Conversion Newsletter for everything you need to get started with your own van conversion (I'll send you a free wiring diagram when you sign up).
Be sure to check out the rest of the Electrics Guides. Related articles include: Campervan wiring diagram explained, campervan fridges, 12v campervan lights.
If you're converting a van but unsure of how to do it, you could also check out the Van Conversion Course on Udemy. In the course, you'll learn directly from me how to convert a van into your dream home - no prior experience needed!
Until next time,
Shane ✌️