Our autonomy and comfort depend a lot on the electrical system of our DIY camper van conversion. No power means no fridge, no lights, no heat, no fan, no Instagram = no #vanlife as we know it! Therefore, we want our electrics and wiring to be robust and reliable.
Designing the electrical system was an intimidating and a sensitive topic, especially since we did not know much about it and we had to start from scratch. The more we read about it, the more complicated it seemed. It quickly became obvious that we had to educate ourselves and that we had to make a bulletproof plan before doing any physical work.
This page was created to capture and organise our toughs, our notes and to pave the way that would lead us to our final electrical system design (and hopefully help others going the same route as us!)
This post is about the design process. For the actual installation of our electrical system, we recommend you to read the following post:
DISCLOSURE: This post contains affiliate links, which means that if you click and commit to buy one of the product links, we will receive a commission fee. The price you pay remains the same, affiliate link or not. Buying through our affiliate links is a great way to say thanks if we were of any help in your van conversion! We only link to products that we personally bought or researched throughout.
- 1- What Do We Expect From Our Electrical System?
- 2- Power Consumption
- 3- Battery Bank
- 4- Charge Sources
- 5- System Monitor
- 6- Battery Bank Sizing
- 7- Logical Diagram
- 8- Detailed Diagram
- 9- Electrical Wire
- 10- Fuses and Breakers
- 11- Conclusion
1- What Do We Expect From Our Electrical System?
- Power all of our “fixed” loads (fan, lights, fridge) and power our “external” loads as well (phones, laptop, etc)
- Charge from solar, van & from shore power
- Have an inverter for occasional & modest use of 120V
- Be completely autonomous in full-sun condition and have a few days autonomy in absence of solar power and driving (no charge source)
2- Power Consumption
Our power consumption will dictate the “size” of our components (solar panel, battery, inverter, etc). Let’s make a list of our loads and calculate how much Ah (ampere hour) we will draw in total each day.
|Load||Description||Measured Instantaneous Consumption
|Calculation Assumptions||Calculation||Daily Consumption (Ah)|
|Fridge||Novakool R5810||4.0A||24h per day @ 35% duty cycle||4.0A * 35%*24h=||34Ah|
|Lights||3W LED Recessed Pucks (10) controlled by dimmer (2 zones)||1.3A (total 10 lights @ 100% intensity)||4h per day @ 80% intensity||1.3A*80%*4h=||4Ah|
|Fan|| Maxxfan 6200K
(10 power settings)
|0.2A@1, 0.4A@2, 0.5A@3, 0.8A@4, 1.1A@5, 1.5A@6, 2.0A@7, 2.6A@8, 3.3A@9, 4.4A@10||24h per day @ 3 average||0.5A*24h=||12Ah|
|Hot Water||Mr Heater BOSS XCW20||Guesstimate…||1Ah|
|Load||Description||Measured Instantaneous Consumption (A)||Calculation Assumptions||Calculation||Daily Consumption (Ah)|
|Fridge||Novakool R5810||4.0A||24h per day @ 20% duty cycle||4.0A * 20%*24h=||20Ah|
|Lights||3W LED Recessed Pucks (10) controlled by dimmer (2 zones)||1.3A (total 10 lights @ 100% intensity)||8h per day @ 70% intensity||1.3A*70%*8h=||7Ah|
(10 power settings)
|0.2A@1, 0.4A@2, 0.5A@3, 0.8A@4, 1.1A@5, 1.5A@6, 2.0A@7, 2.6A@8, 3.3A@9, 4.4A@10||0.4A*12h=||4Ah|
|Hot Water||Mr Heater BOSS XCW20||Guesstimate…||1Ah|
|Air Heater||Webasto Air Top 2000 STC||Guesstimate…||20Ah|
Our daily consumption is similar for summer & winter because in winter the fridge draws less power, but it is balanced by the Webasto air heater that needs some electrical power.
120V loads consumption can be measured using a “Kill A Watt”. The Kill A Watt is plugged into the 120V outlet, the appliance plugged into the Kill A Watt and then the consumption will be displayed.
3- Battery Bank
We just determined that we will draw about 55Ah daily. Does it mean that, to have 4 days autonomy, we need a 55Ah*4days = 220Ah battery bank? No! There are more variables to take account of… keep reading the whole page and we will size the battery bank afterward…
3.1- Temperature de-rate of the battery bank
If you know someone that owns an electric car and uses it during winter time (let’s say a Canadian friend), you probably know that his/her car will do about half the kilometers than in summer (Canadian winters are cold AF & we still use the metric system. wait what?). Batteries are much less efficient in cold weather. The exact loss will, of course, depend on the battery temperature, but we will assume 30% less efficient as a general rule. For example, a 210Ah battery bank will actually deliver 210Ah*70% = 147Ah. Or, we could say that our daily consumption of 55Ah is in fact 55Ah*1.3 = 72Ah. We have to keep that in mind.
3.2- Charging a frozen battery
First of all, unlike water, a battery will not freeze at 32F (0°C). The freezing temperature of the battery depends on the depth of discharge. As the state of charge in a battery decreases, the electrolyte becomes more like water and the freezing temperature increases. It is very important to make sure your battery stays fully charged in extreme cold weather. If a battery freezes, it can damage the plates and container leading to a potential explosion. A frozen battery must NOT be charged! Consult your battery manual.
As a guideline, this is extracted from our Rolls Battery Manual:
|Depth of Discharge
3.3- Depth of Discharge
The cycle life of a battery is directly affected by the depth of discharge. What is the depth of discharge? It is how deeply the battery was discharge during one cycle. Let’s say that a fully charge battery is 100% and a fully discharged battery is 0%. If we draw 30% of available capacity (from a fully charged battery), the depth of discharge is 70% (there is 70% of Ah remaining before the battery is 0%).
For AGM batteries, it is recommended not to go below 50% depth of discharge to maximize the battery life (it might be different for different type of batteries).
So, if one’s consumption is 55Ah daily and has a 100Ah battery bank, it means that at the end of the day the depth of discharge is 45Ah/100Ah = 45%? Well, not exactly… because the battery bank will get charged throughout the day by solar or by driving the van or by getting power from shore power. In fact, we observe our minimal depth of discharge in the morning just before the sunrise. Indeed, we dont have any charge source during the night. What we experienced so far is a depth of discharge of about 75-95% in the morning cause by the loads that run overnight (fan, fridge, air heater and some lights).
3.4- About battery types
There are many types of battery available. Let’s play PROS and CONS :
- Cheapest battery type available
- High maintenance (needs to be filled periodically with water and kept in a vented compartment)
- Similar to Flooded lead-acid but the gel wont spill as easily
- Similar to Flooded lead-acid
- Must be charged at low rate
- Low maintenance, good low-temperature performance
- Expensive to buy (but good value in the long run)
- Light, low maintenance, low self discharged
- Unstable, Expensive
4- Charge Sources
If we had no charge sources at all, we would require a 220Ah battery bank to hold 4 days @ 55Ah daily consumption (in summer). In fact, we would require 440Ah if we dont want to go below 50% depth of discharge! Fortunately, there are multiple ways of recharging the battery to minimize the battery bank.
4.1- Solar Power
Harvesting power from the sun feels a bit like cheating to us; this is the exciting part of the electrical system! It is free to use, but it is not exactly cheap to setup at first.
4.1.1- The Panels
How many watts?
As a general rule of thumb, a 100W solar panel can generate about 5A/hr at peak power, that’s about 25Ah per day (sunny, summer day, best-case scenario).
We calculated previously that we will draw about 55Ah per day; it would be nice if the solar panel could provide at least that amount of power… We need 55Ah\25Ah*100W = 220W solar panel(s) to compensate exactly for our loads draw. Well, a bit more actually if we account for cold temperature de-rate & cloudy weather. However, solar power is not our only power source! When driving the van we will get some power from that as well; we have to keep that in mind…
Monocrystalline or Polycrystalline?
We read quite a bit about that and came to the conclusion that, these days, the quality of the solar panel (manufacturer) is more important than the type of the panel. If you want to learn more about that, Google is your friend! To start, here is a good article.
Should we use 1 large panel, or 2 smaller panels?
At the time of our research, we could buy one 300W or two, let’s say, 160W panels for 320W total. The cost of the 300W is generally higher than two smaller one, but is it really if you account that you need additional hardware to connect the two panels together (cables, connectors, junction box, etc…)?
One larger panel instead of two smaller ones:
- Simple to install (no junction box and connectors)
- Higher working voltage = lower amperage = minimise lost
- Large physical size
- Higher working voltage = use of MPPT charge controller recommended ($$)
Partial Shading is Evil!
When locating your panel(s) on the roof, ensure that no partial shading will be induced by any others component (fan, A/C, etc). Shading of just one cell could completely “block” the output of the panel! Many panels now come with bypass diodes that will allow the current to flow “around” the shaded cell(s) and therefore minimize the effect of partial shading.
A panel will deliver more current if oriented directly towards the sun. On large commercial solar plant, the panels are mounted on a motor-driven device that will optimized the orientation of the panel automatically throughout the day. Obviously, there is no such device for a van roof (until when?) BUT it is possible to add a tilt kit similar to this one:
Adding a tilt kit will obviously add weight and slightly raise the panel(s). The worst part, for us, is that you have to climb on the roof to adjust the panels… knowing that we will be mostly on-the-go, we don’t feel that tilting the panels are worth it. But that’s us. The Wynns are doing a GREAT job at showing the effect of tilting the panels:
Wait for it!
We chose to install two panels of 160W* each, for a total of 320W. This is quite a lot of power, but we’re not messing around here! We had the roof space and we don’t feel like expanding later. Since we are using a PWM charge controller, we connected the 2 panels in parallel; this will keep the nominal voltage of the panels near the voltage of the house battery (12V).
*Update 2017: Grape Solar do not make the 160W panels anymore. It’s been upgraded for 180W panels with very similar physical dimensions!
Our Solar Panels Installation:
From now on, we will use 320W solar power in our calculation. This should provide 320W\100W*25A= 80Ah of charge per day during summer, 30 Ah of charge per day during winter (guesstimate, time will tell for winter).
4.1.2- The Charge Controller
How many amps?
Charge controllers are rated based on the amount of amperage they can process from the solar panels.
Solar Panel Max. Watts / Solar Panel Max. Voltage = 320W / 18.5V = 17.30A
AMPS x Surge factor = 17.30A x 25% = 21.62A
Therefore a charge controller of at least 22A is required.
PWM or MPPT?
MPPT are the latest thing in solar charge controllers. They will be more efficient than PWM in cold temperature, partially sunny day and if the voltage of your solar panels are superior to the voltage of your battery bank. However they consume a small amount of power for themselves and are more expensive than PWM. The debate rage about the MPPT efficiency over PWM, but it is believed to be around 10%-20% more efficient depending on the conditions.
See Bogart Engineering take on MPPT vs PWM charge controller debate here (see FAQ “C1″)
MorningStar MPPT vs PWM comparison.
Side-to-side, real world testing of MPPT vs PWM charge controller here.
We also considered:
4.2- Charging while driving
4.2.1- Inverter + Battery Charger
This is the setup we selected. The idea is to connect an inverter to the van battery (when driving, the van 230A alternator easily overcome the inverter draw). Then, this inverter will power a battery charger/converter to charge the house battery.
Our Pick (inverter):
We also considered:
Why the inverter + battery charger setup? Because we use a Smart Battery Charger/Converter that will provide a nice 3 stages charge profile to the house battery. When we are not driving, we can use this same Battery Charger/Converter to charge the house battery from shore power. Neat! In addition to power the Battery Charger, the inverter can also be used to power occasionally some 120V loads.
The disadvantage we experienced with this setup is that we often forget to turn on the inverter before driving. To overcome this, we bought a small remote for the inverter. No big deal! Also, this setup might not be ideal for someone who use their inverter a lot when parked, since there is a risk of draining the van battery…
About using an inverter
An inverter will convert DC power to AC power. There will be a loss in the conversion from 12V to 120V of around 15%. So it is better to minimize the use of an inverter. If possible, get a universal 12V power adapter; they are quite common for laptop and such.
We bought this one from Amazon and are really stoked about it! It works as it should, it has quality feel and the design is quite nice 🙂
How to check the actual wattage of an appliance (or how to avoid overloading your inverter!)
Most often, the wattage of an appliance will be much higher than the manufacturer claims… to check the actual wattage of an appliance, use a Kill A Watt:
Modified vs Pure Sine-Wave Inverter
Good explanation here. This is a must-read if you need to choose between the two.
4.2.2- Battery-to-Battery charger
This option is quite popular these days as it is fairly simple and plug-and-forget. The battery-to-battery charger is plugged between the van battery and the house battery. It will provide a nice 3 stages charge profile. No need to turn on the device, it will turn on by itself when the van battery is fully charged and the van is running!
We did not go this route (but hesitated a LOT) as the battery-to-battery charger is not cheap and we still had to buy an inverter + a battery charger/converter (for shore power).
4.2.3- Direct connection to alternator (via an Automatic Charging Relay)
It is possible to charge the house battery from the van alternator via an Automatic Charging Relay (ACR). The ACR will automatically combines the van/house batteries during charging and isolates the van/house batteries when discharging and when Starting engines.
4.3- Shore Power
4.3.1- Battery Charger / Converter
If you did not skip the previous parts of this page, you understand that this is what we are using. If not, go through section 4.2 above (charging while driving, inverter + battery charger/converter)!
4.3.2- Inverter / Charger
An inverter / Charger is actually one device (plugged to your house battery) that will, first, act as an inverter and, second, charge the house battery from a 120V source (shore power). It is quite convenient, but we passed because of the price.
5- System Monitor
A system monitor is not mandatory, but we strongly recommend it. Depending on your model, it will display the house & van battery voltage, amperage coming in/out of the house battery, % battery left, amperage used since last charge, etc, etc. You will learn a lot from the monitor on: 1- the impact of shade on solar (and help you choose the right parking spot) 2- the impact of your load(s). This will help you better manage your energy. One of the most popular option out-there is the Bogart Engineering Trimetric TM-2030. This is the one we’re using in our system, because it will “pair” with our charge controller and this will increased the smart features. It might be fugly, but the electrical geeks out there know that this is a very well engineered product.
6- Battery Bank Sizing
Back on the battery topic. We now understand that if the charge sources were properly chosen and sized, the battery should (normally) get a full charge everyday (by solar and/or driving and/or shore power). So what dictate the size of the battery then? I would say overnight discharge + cloudy days + rough buffer + the price you are willing to pay…
We finally went for a 210Ah AGM battery. In summer, at sunrise, the battery will be 75%-90% capacity depending on what happened the night before (driving late generally means a full charge when we go to bed). At noon, the battery is generally fully charged from solar depending on the weather. For winter, time will tell…
The concept here is that there is a lot of variables to take account. We went on the safe side by choosing a medium-large battery bank (some people go up to 300-400Ah).
We also considered:
7- Logical Diagram
Before going any further, we drawn a logical diagram of our electrical system. We still refer to it very often.
(Different requirements would generate different system designs… this one works for our needs!)
While parked, the 12V loads can be powered from either (shown in order of preference)
- shore power (if available)
- the house battery (should be the case most of the time)
- the van AGM batteries (if the house battery is running low)
While driving, the 12V loads can be powered from either
- the van (full house battery, enough solar power)
- the van, via the house battery for extra charging power (low house battery, weak solar power). We’re thinking this will be especially useful during winter when the solar power is limited.
8- Detailed Diagram
We did not want to waste time on that at first, but we are so glad we did it. When doing the actual physical installation of our system in the van, we realized how important it was to prevent messing up. Things will not clarify during the installation… the physical installation is quite overwhelming and referring to the diagram gave us a lot of confidence. When we first turned the switches on, we were not afraid to blow everything up 🙂 To this day, we printed a copy and leave it in the van at all time.
(click on products for more info!)
The image above is best seen on desktop… Click here for full-size high-resolution image (best for mobile!)
9- Electrical Wire
9.1- Wire Diameter (AWG)
Selecting the correct electrical wire diameter is crucial for the system performance and safety. The maximum current and the voltage drop need to be taken into account to select to appropriate diameter.
9.1.1- Maximum Current (capacity)
For a certain wire diameter, there is a maximum current carrying capacity of a wire. Going over that capacity would create a safety issue (i.e. bigger current requires bigger wire diameter).
9.1.2- Voltage Drop
There is a loss of energy (voltage drop) as current moves through passive elements (wires, terminals, etc) of an electrical system. The wires are a big contributor to the voltage drop and this should be taken into account when designing the electrical system. How? By selecting the appropriate diameter; the bigger the diameter, the smaller the voltage drop. Generally, wire diameter should be selected to provide a maximum of 3% voltage drop for critical loads (panel main feeder, inverter, electronic) and 10% maximum voltage drop for non-critical loads (lightning, fan, etc).
9.1.3- Selecting the correct wire diameter
The inputs are:
- Nominal Circuit Voltage (hint: it’s 12V)
- Load Current (it normally written in the owner manual of the load)
- Length of Wire (hint: you need to add the positive AND negative wires! For example, a load located 10 feet away from the battery would require 20 feet length of wire)
- Allowable Voltage Drop % (critical VS non-critical loads, see section 9.1.2 just above)
The outputs are:
- Recommended wire diameter
- Maximum current capacity of the wire (for reference)
9.2- Wire Crimping (connecting wire)
There are many ways to connect wires together. We will go straight to the point here, the best way to do it is crimping. Crimping will deform the connector into the wire and ensure a solid permanent mechanical connection with low resistance. To crimp, you need good tool and good connectors (heat shrink recommended):
Do not use pliers for crimping! Do not use cheap connectors! You will get poor connections that will not last in time and could create safety issues.
9.3- Wire Installation
For safety sake, the wires should not be installed loose and unprotected; as opposed to a house, there is a lot of vibration and movements that will damage the wires in the long run.
The wires should be routed through Split Loom Tubing (make sure to buy several diameters) attached with zip ties:
The Split Cable Loom should be secured with Nylon Cable Clamps on wood:
The Split Cable Loom can be secured with Zip Ties Mount Adhesive on metal. Make sure the surface is cleaned (isopropyl alcohol works great) and warm enough.
10- Fuses and Breakers
Fuses and breakers are essential in any electrical system! It will protect the circuit wires and the components against over current and ultimately fire. If you blow a fuse during your system installation (we did a few times), it means that you just avoided a potential failure or fire! Nice!
Each load should be fused according to it’s current maximum normal draw. Consult the owner manual of the load. This is achieve through a fuse box such as:
The fuse will drive the wire diameter selection. For example, if wiring a load that draw 5A and a fuse of 15A is used, you should choose a wire capable of (more than) 15A! This is safety matters.
Breakers are similar to fuses, except that if it blows it is possible to reset it without replacing it. Fuses generally blow faster than breakers and therefore fuses are preferred for sensible electronics. We added a few 40 amp breakers in our system. Why? First, to avoid having to use big electrical wires. Indeed, our fuse block is capable of 100A; even if we know that we will never draw 100A, we need to size our wires for 100A ($$$). By adding 40A breakers, we can size our wires for 40A. We can also turn off portion of the system by switching a breaker off (for example, turn off solar panels to display on our system monitor the draw that the loads are pulling. Or the opposite to display the charge that the solar panels are providing).
Here is a more complete article about this topic: http://www.12voltplanet.co.uk/fuses-guide-uses.html
The design of the electrical system is not an easy task. Make sure to clearly define your own requirements and design your system accordingly!
There is a lot more to what we covered here, be we hope this will get you started!
Did we missed anything??
(Very) Related Article:
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Hello! We’re Isabelle and Antoine, a couple dreaming of being on the move and we’re seeking for the ride of our life. We bought a Ford Transit van, we’re converting it to a campervan and we are now selling our house to make our dream a reality. We are sharing this in hope of inspiring and helping others to follow their dreams too!