Not everyone who builds a campervan is an electrician or has a background in engineering, but it is possible to learn enough to understand the basics. A lot of people get very intimidated by the electrical stuff; they hear Volts, Watts, Amps, kiloWatt-hours, Amp-hours and it goes in one ear and out the other.
But it can be very useful to have a basic understanding of how your van’s electrical system works, even if you have someone else install it or buy an all-in-one system. One time we were camping with one of our van friends and she told us that she had basically only been camping in sites where she could get shore power because she thought she was draining her battery down every time she camped without it. She had a friend with a background in electrical engineering install her van’s electrical system, but he had not really explained how it worked to her. We looked over her electrical system together, and talked through some of the basic things she needed to be keeping track of, and she came out of the whole discussion feeling a lot better about her van’s power system.
The Waterfall Analogy
My favorite way to give a basic overview of electrical systems is with an analogy. We recently (April 2019) went to Yosemite National Park. As you might know, Yosemite is famous for its stunning waterfalls. Some of our favorites from our visit can be found in this Instagram post. I will use the waterfall analogy to explain the relationship between Voltage (measured in Volts), Current (measured in Amps), and Power (measured in Watts).
There are numerous adjectives that could be used to describe the waterfalls in Yosemite, but one that comes to my mind is “powerful.” So what makes a waterfall powerful? Let’s focus on arguably the two most famous waterfalls in Yosemite: Yosemite Falls and Bridalveil Fall.
Yosemite Falls is one of the tallest waterfalls in the world at a whopping height of 2,425 ft. It is a site to behold as the water crashes onto the rocks below. So, one measure of the strength of a waterfall could be its height; the taller the waterfall the more powerful it will be. However, as you might also be aware, Yosemite Falls does not flow all year and is usually dried up by August. A dried up waterfall isn’t exactly what I would call powerful, so maybe the height of a waterfall isn’t the best measure of how powerful it is.
Bridalveil Fall is another incredibly iconic Yosemite waterfall. It is described as thunderous, and standing at the bottom you will get drenched by the mists it creates. However, Bridalveil Fall is only 617 ft high, roughly a quarter of the height of Yosemite Falls. But it flows almost year round, while Yosemite Falls dries up by August. So another descriptor of the power of a waterfall could be how much water is flowing.
We have now come up with two descriptors that describe the power of a waterfall: the height and how much water is flowing. So how do we relate this back to electrical systems?
The voltage of an electrical system is analogous to the height of the waterfall. But higher voltage does not necessarily mean higher power out of the electrical system. When we first bought our battery for Dolly, we plopped it down in the back of the van, and it sat there for a while not connected to anything. Basically, during this period, it was Yosemite Falls in the summer time: not flowing.
As you may have guessed, the current of an electrical system is analogous to the water flow of the waterfall. Without current (or water flow), there is no power. Conversely, you cannot have any current (water flow) without voltage (height).
So now we can write an expression relating power, voltage, and current:
Power = (Current) × (Voltage)
P = IV
[Watts] = [Amps] × [Volts]
If either term in the expression is zero, the power is zero.
Energy and Power
There is one more topic that I think you should be familiar with regarding your electrical system: Energy. The relationship between energy and power is:
Power = (Energy) / (time)
or…
Energy = (Power) × (time)
Why is this important? Because a battery is an energy storage device, not a power storage device. When selecting a battery, the capacity is most commonly expressed in Amp-hours (Ah). I really wish this wasn’t the case, because Ah is not a unit of energy, and that is what batteries are storing. But, this is what the industry mostly uses, so we are stuck with it. A less commonly used unit of measurement of the energy of a battery is the Watt-hour (Wh) or kiloWatt-hour (kWh = 1000 Wh).
The relationship between the Ah and the Wh is obtained from the first equation introduced relating power, current, and voltage:
[Watt-hour] = [Amp-hour] × [Volts]
[Wh] = [Ah] × [V]
So if you buy a 200 Ah, 12V battery, the Watt-hours of the battery are calculated as (200 Ah) × (12 V) = 2400 Wh = 2.4 kWh.
Every electrical item that you connect to your battery draws power when it is on. To calculate how much energy is consumed, just multiply by the number of hours that it is used. For example, a device that uses 100 Watts when turned on will consume 100 Wh of energy when used for 1 hour.
So now you have a bit of background, and hopefully feel a little more comfortable with the whole topic of electrical systems. There is a lot more information that you can learn, but what we have covered so far will help you get started.