If, like us, you hardly have any experience in working with electrics, it can be a very daunting task to set up your own electrical system in your campervan. It might even be tempting to postpone it till later.
However, if you’d like to build your van as efficiently as possible, setting up the electrics is one of the first steps you’ll have to deal with. If you’ve nicely covered up the inside of your van with insulation and cladding, how will you manage the wiring of the cables? Right, you’ll have to tear part of it down, which is a shame of course.
In our conversion, we’ve started by tackling the rust (which you can read all about here). After that, we started fitting and installing the subfloor.
Our next step will already be the installation of the first part of our electrical system on the roof of our van: the solar panels and the Maxxfan Deluxe. But in order to determine the amount of watts in solar panels we need, we first have to figure out more about our electrical demands.
We have to make an overview of all electric appliances that we plan to use in our van. This in turn will help us size our batteries and solar panels.
Finding the right information needed to set up our electrical system can be quite difficult and at the least a time consuming task. Over the past months, we’ve done extensive research into all details that come into play.
By sharing what we’ve found, we hope to help you in sizing the batteries for your campervan, and to show why postponing this task is not necessary at all!
In a future post we will explain other parts of our electrical system, such as the installation of the solar panels and setting up the wiring.
Making a list
In order to find out how many watts our solar panels should have, and how large our batteries need to be, we started off with setting up a list of the electrical appliances we plan to use in our campervan. For more information on the terms watts and watt hours, check out our blog post about our general electrical diagram.
After we were done setting up our list, we needed to find out how much power each of these appliances consumes. For the fridge, fan and some others, we were lucky to find some values online. For most objects however, we ended up empty handed.
To determine the power requirements for the remaining appliances, we bought a little wattmeter for just a few bucks. These are really great, we’d definitely recommend acquiring one if you’re planning your solar setup!
All you have to do is plug the watt meter into a socket in the wall, plug the appliance into the watt meter, switch on the appliance, and read the amount of watts it is using.
Our watt meter also has an option to calculate the total amount of power the appliance consumed for the duration it is plugged in. This can be handy if you need to know the total amount of power consumed to charge your phone for example.
Collecting everything into a structured spreadsheat
So at this point, we know which appliances we are planning to use, and how many watts or amps everything consumes. It doesn’t matter if you can only find the amount of amps an object uses. You can easily calculate the amount of watts as long as you know the voltage, by using the equation we’ve mentioned previously; amps x volts = watt.
All that is left now, is to determine for how long we think we are going to use each of the appliances per day. At best, this will just be an educated guess. Nevertheless, it is necessary to figure this out in order to proceed with further calculations.
Every estimation was taken quite generously. Some appliances have different settings or other reasons for them to use a variation of electricity depending on circumstances. For the fan for example, we noted the maximum amount of time we would ever use one speed setting on a given day.
Whilst we determined everything we were using and how long the items would be used each day, we noted the information in a structured spreadsheet to have a clear overview of our planned power usage. Additionally, to makes things easier further down the line, we split these appliances into two categories; 12 volts and 230 volts.
Here we can see how much power our 12V and 230V appliances use, and what our total planned power consumption will be. We are however not finished just yet.
The leisure batteries used in campers are, as far as we are aware, always 12V. So if we would like to use 230V appliances in our camper, such as a laptop and blender, we need to convert 12 DC to 230 AC. DC stands for direct current and AC for alternating current.
Generally, you can compare AC to a Sine wave; which is the most frequently occurring type of AC:
This type of current periodically reverses its direction. In the up curve of the sine wave, the current flows in a positive direction, and in the down curve, the current flows in a negative direction. Or in other words the current alternates, making it an alternating current (AC).
DC current can simply be represented by a flat line. It delivers a constant current flow in one direction. Simply said, a direct current (DC).
This knowledge can be of help in choosing the type of converter we need. We’ve found a lot of disagreement within the camper community on which type of converter to use.
Two types of converters
Appliances are developed with an AC following a sine wave in mind. However, less expensive converters use a simpler way of representing the alternating current. We’ve found that there are basically two types of converters.
The first is a pure sine wave converter, which uses a sine wave equal to that of your standard AC. The second type is called a square wave converter, also known as a modified sine wave converter.
This type of converter uses blocks (get where the name comes from?), to represent a sine wave. This results in quite a jerky interchange from a positive to a negative current and vice versa, opposed to the smooth sine wave.
We’ve also come across inverters that use more than two steps to switch from a positive to a negative current. This type will resemble the sine wave much better already. However, with four steps, you’re still far away from a smooth curve. This would require many more. Due to the simplified representation of the AC current, they are much cheaper to make.
Disagreement within the camper community
We were unable to find a unanimous opinion on whether or not the square wave converter represents a sine wave well enough. We’ve found people saying that their appliances work perfectly on the cheap square wave converters. But we’ve also read about people stating that either their appliances started making a buzzing sound, did not work properly, or even broke.
When we use our common sense and compare a sine wave pattern, for which the appliances are built, to what the square wave inverter puts out, although we do not know all the ins and outs, we would argue that a sine wave inverter is the better way to go.
We’re not the type of people that just want to take chances. We need quite a small inverter, therefore the difference in cost between a pure sine wave and a square wave inverter is not too big, around 60 euros. The chance of breaking a laptop or other appliances is not worth the risk for us.
So what does all of this mean for the sizing of our batteries?
The type of converter does not influence the answer to this question that much per se. But the particular converter you’ll choose does. During the conversion from DC to AC, part of the energy is lost through the surroundings through heat by the converters. This means that we’ll have to put more energy into the converter than we need to power our 230V appliances.
A higher power consumption
Using a converter thus causes for an increase in our total watt hours.
The efficiency of the converter we plan to buy is 85%. This means that 15% of the energy it converts will get lost.
To take this efficiency in to account in our calculations, we need to divide the total watt hours of our 230V appliances by this efficiency factor, which for us is 0.85. So the total watt hours for our 230V equipment increases to:
Finally, we’ve come to the battery size
The total amount of watt hours we think we are going to use on a daily basis is thus about 962 watt hours. Is this then the battery size we need?
Well, in theory you could go with a battery of that size, but it won’t last you very long. This has to do with something called the depth of discharge of a battery. This is a measure for how far you’ve drained your battery. 0% means a full battery, and 100 % means it’s completely drained.
But that is of course not all that’s to it.
What this figure shows, is that how farther the battery is discharged (x-axis), the fewer total charge cycles it can handle (y-axis). This is however not a linear relationship. As you can see, this graph shows an exponential decrease. A discharge from 20 to 30% results in a decrease of 2400 cycles, compared to 900 cycles for a discharge from 50 to 60%.
If you do not want to buy a new battery each half year, you’re best off not leting your battery get fully drained each charging cycle.
Generally, people use a value of 50% for the depth of discharge as a limit. This does however differ between different battery types and batteries. Gel batteries for example are known to be much more resistant to discharging than semi-traction batteries. AGM batteries are somewhere in the middle.
For simplicity, we’ll use a depth of discharge of 50% in this example.
When using a depth of discharge of 50%, we cannot let the battery to be drained further than 50% of its total capacity. This would thus mean that we will need twice as much watt hours in our battery than our total watt hours. This comes down to:
This is the minimum value we need in our battery. We however would like to have some leeway. We would like to be able to store a little extra power on sunny days to use as a buffer on cloudy days. So for us, a last addition to our calculation is to double our total watt hours:
The capacity of batteries is usually expressed in amps though. So lastly, we need to convert our watt hours back to amps using the equation we’ve explained in the beginning of this blog post (amps x volts = watt):
You’re still with us? Great! You’ve made it to the end. We’ve now finally calculated our specific planned power usage. For our power consumption, we would thus need a battery of at least 321 amps. Or, two batteries with 160 amps.
We really hope that by explaining our approach towards sizing the battery, and by sharing our findings, you’ll have an easier time calculating your own! So you can spend more time on the more fun parts of building you own camper. Such as making the lay out, or designing your own kitchen!
If you have any tips or additions, please let us know in the comments below!
Did you like this blog post and want to read more? Click here to go to our main campervan conversion page! Here, you can find a neatly organized list of all blog posts related to our van conversion project.