Camper Electrical

Moving on with the camper project (see this for more info), I'm dedicating this post to a discussion of the camper electrical system.

Electricity is complicated, except when it isn't, but oftentimes it may appear it isn't when it is. Put another way, I put a lot of effort not only into determining my needs but also ensuring everything is installed correctly and safely. I've spent a ton of time researching my options and ensuring I have everything wired up properly, and then I'm checking my work with friends who are more knowledgeable about electricity than I am. DON'T assume I'm the world's expert on RV/camper electrical systems, and please PLEASE make sure to do your own research before copying anything I'm doing (or hire a professional to do it for you). And by all means, if you see me doing something wrong feel free to reach out - I promise I will not be offended by you trying to help me!

Disclaimer over, let's dive in!

Here's my simplified wiring diagram for the entire camper shell. "Simplified? That's a mess of lines and little boxes with even littler text crammed in 'em. That's not simple!" Well, it's actually not too bad. Let's start with some core concepts for the folks who aren't electrically inclined.

First, it's valuable to understand the relationship between Volts (V), Watts (W), and Amps (I, but also A, for some reason). With DC systems, that's simply V*I=W. This describes the instantaneous load on a conductor or electrical system, kind of like the speedometer of a car (and in fact these measurements are often displayed with "swinging needle" analog or digital gauges very similar to a speedometer).

Also note that Watts and Amps can be time integrated. With no math whatsoever, what this means is that you can measure usage, generation, and capacity with time-integrated units. For example, my batteries have a capacity of 600 amp-hours. If a load draws 100 amps consistently, then the batteries can power that load for 6 hours on a full charge (in theory anyway). My two DC/DC chargers can draw 50A each (100A total) from the alternator to charge the batteries, so it should take 6 hours to fill the 600Ah capacity of the batteries while driving the truck.

Is it really that simple? Haha, no, of course not. First, your loads are never going to be nice round numbers, and they're going to fluctuate. Some loads are pretty consistent (for example, the toilet will draw a few amps constantly to power a small extractor fan, and that load shouldn't change much). Some loads will obviously be turned on and off (things like the water heater, water pump, and fan) - they'll draw some amperage when on, and no/very little amperage when off. And some loads will draw higher amperages on startup, then settle down once they're running (the AC unit and diesel heater fall into this category). Second, you're going to have small losses all over the place, plus loads that still have a small draw even while inactive. Batteries lose capacity over time, and a charger rated at 50A might only deliver 46A. But these concepts are still useful for planning and visualization purposes.

For example, I have 600Ah of capacity and 300A of draw on my various loads. That means I could run EVERYTHING at FULL POWER for two hours. Well, except that's the sum of the breaker ratings for all of those loads, meaning the actual draw should be about 80% of 300A or about 240A, so I should get 2.5 hours of runtime. Well, except the batteries may not deliver the full 600Ah promised, so back to about 2 hours. Well, except I wouldn't be likely to run the AC and Diesel heater together, so that's more like 165-210A depending on what I'm running. Well, except I might be generating some passive solar and/or plugged into shore power, so I'm using 165-210A but bringing in 50-100A, so my net draw is 65-160A.

Like I said, complicated even when it seems like it's not.

Hardware

Let's talk specific hardware. Some key components:

Victron Orion 50A DC/DC Charger (x2): these provide the bulk of my charging. I upgraded the truck to a 250A alternator from the stock 145A model, so I have a 100A "surplus" that these chargers can use to top off the camper batteries. They have some nice features, chiefly a sensor that automatically detects whether the truck is running and disables charging if not (no worries about accidentally draining the driving batteries overnight). Basically, if I drive the truck for 6 hours, I should have full batteries (or, if I'm driving the truck but running the camper AC, I'll net maybe 50A and fully charge the batteries with 10 hours of driving).

Victron Smart IP43 Charger: Provides 50A of DC charging from a "shore power" connection (ie, a 120Vac wall outlet). This will give me the ability to grab a charge overnight at a campground or RV park or friend's driveway, and more importantly let me keep the camper charged when parked. Note that this provides 50A at 12V DC, which thanks to my stellar explanation we know is 600W, but it draws from a 120V AC power source. That means we can take 600W / 120V and get 5A of draw on the AC side. In other words, I can use this connection not just for battery charging but also to provide some AC power inside the camper when parked (but only an additional 10A of 120V AC power).

Victron MPPT 100 50 PV Charger: For solar charging. Solar is an interesting beast, because the output from solar panels is rarely fixed. Panel output depends on temperature, orientation relative to the sun, cloud cover, shading, and a number of other factors. Remember that time integration in terms of power? Well, a solar array's production is going to fluctuate, so we're going to have to work with a daily average. Right now I'm looking at 4x Renogy 150W CIGS 12V panels, which would give me 600W of PEAK production (back to math, that's 600W/12V=50A of PEAK solar production). If I get 12-14Ah average over the course of a day, I would be very happy with this setup (as a bonus, they'll produce the most power when the truck is getting hammered by the sun, so they work to offset the AC's heavy draw).

12V 300AH Lifepo4 Battery (x2): The heart of my energy storage. These two batteries are wired up in parallel to provide 600Ah of capacity at 12V. They feature built-in battery management systems rated at 200A (meaning the battery bank can charge or discharge at 400A total, well in excess of my planned charge/discharge rates). Since they're lithium they're much lighter than a comparable lead acid battery, which is appreciated in a smaller camper build like this. Victron BMV700 Battery Gauge: Gives me a reasonably accurate estimate of total battery capacity, using a shunt on the negative busbar. I'm going to do some custom monitoring on my charging and larger loads, but this will be my source of truth for the overall battery state of the camper. "Oh no, we're at 20% power, no hot showers tonight if we want to keep the fan going all night long", that sort of thing.

CT220RMV-HS5 Contactless Current Sensors (x8): these will monitor the amperage in (from charging sources) and power out (from my four largest loads). I could go the extra mile and pair these up with voltage readings to get true power, but I don't really care that much. The goal is just to make sure systems are producing/consuming power in line with their ratings. If I see my DC/DC chargers are only outputting 10A and the battery gauge shows 50% battery state of charge, it may clue me in to a problem with the alternator or DC/DC chargers before something breaks.

Various breakers, disconnects, fuses, etc: these provide the ability to isolate parts of the system from one another (eg, I can disconnect the alternator from the DC/DC chargers, or disconnect loads from the batteries while still letting the chargers do their job, or disconnect everything from the batteries to service the rest of the electrical system or put the camper in storage). The breakers and fuses protect against over-draw conditions, where a broken component tries to pull more current than it should. This can cause fires, so it's and important protection feature. All of these various protective items add a TON of complexity to the wiring diagram, so I'm breaking them out into individual diagrams.

Various loads: The loads should be pretty self-explanatory here, with all the basics and comfort features I wanted. My big draws are an AC unit (75A startup, 40A in eco mode), the diesel heater (30A startup, 5A once running), a 750W inverter (unlikely to draw more than 200W at once) and the water heater (40A). On the smaller load side, I have the interior lighting, roof fan, a Raspberry Pi with cameras and a LCD screen, the water pump, 20A for a USB-C charging station (two USB-C devices at once, at up to 60W combined), and the toilet extractor fan (keeps the camper smelling nice and fresh inside).

What's next?

I have my general wiring diagram complete, and about 90% of my parts. I still need to purchase wire, breakers, fuses, and suitable mounting for the above. I also have to work out all the details of the busbars and distribution panels, as well as mounting. A lot of that is going to depend on the camper shell layout, and while I have a rough idea of what those dimensions look like I'll need to wait for the final product to actually install everything.

There's still a lot of work to do, thank you for following along so far!