Electrical systems. Probably the utility I care about having in the van the most - more than running water or propane heating, since both of those are nice to have, but not nearly as essential to me as lighting, refrigeration, ventilation and charging my devices. Well, plus the fact that both the water pump and the propane heater need power to operate in the first place.
My build is not too dissimilar to many others, so this isn't going to be an extensive essay, but I do want to talk about my equipment choice, some safety aspects, and what informed my system design overall.
When you're building out something like this, it's helpful to know why you are doing it. Obviously, I want to have lights inside the van, but an electric system needs to do so much more than that. Here's what I need mine to power:
- LED lights
- Ventilation fan
- Propane air heater
- Electric water heater
- Laptop/phone chargers
- LTE Router
- Motorised awning
- Electric kettle
- Potentially: Microwave, toaster oven, induction stovetop/hob
That's a pretty decent list, and while most of those are not huge power draws, the kettle pulls in a good kilowatt, and an induction stovetop would pull 1.8kW. That's getting to the higher end of what you can design a system to service in a small van, so it's important to make sure we get it right.
The other consideration is autonomy - how long should the van be able to work away from the grid? Many bigger RVs are incapable of doing very much without a permanent electrical hookup, but I'd like the van to work for a full week without plugging in, using just batteries, solar power and the alternator occasionally.
Voltage wise, the van runs two voltage subsystems:
- 12V DC, for powering most of the basic systems (heaters, fan, fridge, lights)
- 110V AC, for powering the more powerful kitchen appliances
At the heart of the system, then, are the batteries. There's two main chemistry choices for batteries here:
- Lead-acid batteries. This is the traditional "car battery", and modern AGM style ones are pretty decent and reliable, but still heavy and can't be drained below half charge without damage.
- Lithium-Iron-Phosphate (LiFePO4) batteries. These are much lighter than lead-acid batteries and can be drained entirely, but are much, much more expensive.
Given my autonomy requirements, I went for two 100 amp-hour lithium-iron-phosphate batteries - giving me far more power in a small space than any lead-acid option could provide. It's not without cost, though, as these batteries are $800 each. I'll buy a third eventually, and I've left space for it.
The two batteries are wired in parallel, so they essentially act as a big 200Ah battery.
My system has three ways of charging the batteries:
- Solar power, via a MPPT solar charger
- Alternator power, tied into the Transit via it's Customer Connection Point and a DC-DC charger
- Shore power, via a standard 15 or 20 amp US electrical outlet
Each of these goes via a different charging device, but all the charging devices, the batteries, and the main loads are all just wired in parallel onto a big set of bus bars. The power flows to where it's needed, and it's fine to have multiple charging devices sending out power at once.
The solar power comes from the two 175W panels mounted on the roof, which feed down inside the van to the MPPT solar charger. This takes the variable voltage and wattage the panels provide (as the sun conditions change) and converts them down into a steady voltage that is much better for the batteries and the other devices on the circuit that all expect something around 12V.
The alternator power is emitted from the Transit's electrical system - it's smart enough to only give you power out of the Customer Connection Point when its own starter batteries have enough charge. It goes into a DC-DC charger that makes sure the voltage flowing into my system follows the correct charging curve, but that's only isolated on the positive side. The ground of the van and my system are shared, and tied into the vehicle chassis.
Shore power comes from the grid (usually) via a standard electrical socket. In the workshop, this is just the workshop's power and how I keep the van charged while I'm working on it; outside, this is likely to be from a camping spot that has an electrical hookup, like you find in larger campgrounds.
Shore power flows into the Victron MultiPlus inverter-charger, where it actually goes two ways - one way through a rectifier circuit to go charge the batteries, and a second way into the van's 110V system. When the shore power is not present, the MultiPlus seamlessly swiches to inverting the battery power up to 110V AC and into the van's 110V system. Both of these jobs share some components, and having them in one box allows seamless switching, which is why they're combined.
All three sources of power that can't be unplugged - the battery, the solar panels, and the alternator - have isolator switches, so I can isolate them off and safely work on the electric systems without risking a short-circuit. It's hard (but not impossible) to electrocute yourself with 12V, at least, but the 110V system has a much higher arc/electrocution risk, so I make sure that the isolators and the breakers are off.
Wires, Fuses & Sockets
Wire size is very important, to prevent your wires from overheating, melting, and maybe starting a fire. With 110V AC, you can get a lot of power down a relatively small wire - in the US system of AWG, AWG 14 is more than enough to take 15A (so, around 1.6kW). With 12V DC, however, you need a MUCH bigger wire to take this level of power (which at that voltage, is 137 amps).
For this reason, it's important to size all the wires properly. The inverter, being capable of 3000W of power draw, has giant AWG 2 cables to it (as do the batteries), and the electric water heater has AWG 10 wires, for example. Then, for every circuit, you have to fuse it at the rating that the thinnest wire in that circuit is capable of, so there are MEGA fuses for the big circuits (solar charger, alternator charger, etc.) and then a smaller DC fuse block for the smaller circuits - a 3A fuse for the garage lights, or a 10A fuse for the fridge.
On the AC side of the system, the same thing applies, but here we can use breakers rather than fuses. The van uses two 15A GFCI breakers, which as well as tripping when there's too much power draw, will also trip when it detects current flowing out down the live wire but not back along the neutral (thus preventing a decent number of scenarios where you're electrocuting yourself).
For DC loads, most are hardwired in, but there are cigarette-lighter style sockets by the main seats and up in the overhead cabinets to allow plugging in USB-C chargers or similar. AC only runs to sockets - two near the seats, one next to the kitchen prep area, and one next to the spare work surface above the fridge. These sockets have built-in USB sockets too, since it's really not much harder to add those in when you're buying new electric sockets.
The battery has a shunt installed on its negative side that measures the exact power flow in and out of it - it's a lot more accurate than estimating battery remaining via measuring the battery voltage.
The shunt, inverter-charger and solar charger all tie into a Cerbo GX, which is Victron's monitoring system and the reason I bought all-Victron gear. The Cerbo has a little touchscreen that tells you power system information and where power is flowing, can tie into an internet connection and relay power information up to the VRM portal so you can see it anywhere, and also plugs into wired tank level sensors and bluetooth power sensors.
I also wanted to make sure my temperatures and wire sizing was sensible, so I ran the system under rather heavy load for an hour or so and then used an infrared camera to measure the temperatures of all the main system components. The battery cables got up to about 30°C, which is well within spec, and while the wires to my electric water heater were fine, there was a 70°C hotspot near its fuse that went away with some reseating.
There's still more wiring to be done - up into the ceiling for the lights, for example - but most of the main system is now done and tested. The solar panels got 230W from the winter Colorado sun, which given they're not tilted is pretty decent. The alternator sends over about 300W, and shore power gives about 1500W with the current limiter I have set up (I don't want to push a full 20A through a single socket right now).
That charges the batteries in a few hours, and heating a full 6 litres of water in the water heater - the biggest single power draw over time - only draws down about 15% of the battery power. With sensible use of hot water and other big power draws, plus 5 hours of good sun each day, that easily allows for a full week off-grid.
Once I've used the power system on a few trips I'll see how it fares and if I need to add more battery capacity, but in terms of pure power ability I think things are good. Hopefully!