Example DIY Camper Van 24V Electrical System (Internal BMS batteries)

In this post we’re going to discuss a popular topic these days – 24 Volt electrical systems. This system offers some benefits compared to the traditional 12 Volt electrical system detailed in our original camper van blog post. This post includes a detailed wiring diagram and system bundle needed to put together a very reliable and robust electrical system for your camper van that is capable of extended off-grid adventures and powering just about anything you throw at it…including more efficient use of those power-hungry rooftop air conditioners.

What’s different?

Well the battery bank is 24 Volts instead of 12 Volts, obviously. Except the system has 12 Volts too. Let’s un-confuse things.

Looking at the 24 Volt example wiring diagram as compared to the 12 Volt example wiring diagram, all of the key features and components are quite similar between the two systems. There’s still a Victron Multiplus inverter/charger, one or more DC-DC (alternator-based) chargers, solar capability, an optional Victron Cerbo communication center, the ability to use shore power, and a load center for AC & DC. Victron, other battery manufacturers, air conditioner companies, and large segments of the camper van and marine industries have long supported 24 Volt equipment. While the 24 V system looks quite familiar, each equipment model has been carefully selected for compatibility with a 24 Volt house (domestic) battery system.

So why is there still 12 Volts then? Because some popular equipment in our vans still only operates on 12 Volts. We’re looking at you MaxxFan (at the moment, anyways). But we’ll explain shortly why this additional wrinkle is not hard to overcome, and more importantly why considering a 24 Volt system may be a better choice for some vanlifers.

Also different in this 24 Volt system is a new product from Victron, the Orion XS 1400 DC-DC charger. The XS 1400 operates in 12 or 24 Volt systems, can charge up to 50 Amps, and supports parallel operation like existing Orion XS chargers.

Why is 24 Volts better?

Efficiency is the name of the game for a 24 Volt system. Higher voltage systems are well suited for large DC loads like rooftop air conditioners. On our website we’ve already shown how much more efficient DC air conditioners can be over traditional AC air conditions. But take a closer look at the specifications on some of our air conditioners or the comparison spreadsheet. In particular, let’s look at air conditioner capacity in BTUs versus power consumption. The Nomadic Cooling X3 offers a great example, where the 24 V X3 and 12 V X3 have the same rated power consumption, yet the 24 V model has a rated cooling capacity that is 12% higher! Why? Because the air conditioner operates more efficiently at the higher operating voltage. Other air conditioner brands and models show similar efficiency benefits.

Since an air conditioner may be the single largest, sustained load for an off-grid camper van, improvements in efficiency are a big deal for maximizing your battery capacity.

While some van products don’t run on 24 Volts yet, and we’ll get back to those, you will find that a majority of your DC system can operate natively at 24 Volts. Of course this includes your Victron components like the Cerbo and chargers, but you can also find refrigerators, water pumps, LED lighting, fans, and host of other equipment working at 24 Volts.

While we’re harping on efficiency, let’s not miss out on a chance to consider a little Physics. By increasing the house voltage to 24 Volts over 12 Volts, the required current is reduced by 1/2. Resistive losses in your cabling (commonly referred to as I²R losses), have been reduced significantly (almost by 1/4, due to the I² factor). Note that we say almost 1/4, because with the reduced current you’re likely to use smaller cable gauges for lower cost and easier wiring. Smaller cable gauges do have higher resistance per foot, however not by a factor of 2 given the range of cables we’re using. So reduce by 4, increase by less than 2, blah blah blah…using 24 Volts gives you less losses (greater efficiency) and smaller cables. That’s a win.

Better equipment performance and less cable losses with smaller/cheaper cables, those are the main reasons why a 24 Volt system may be the right choice to maximize your battery capacity and improve your off-grid experience.

Things to consider:

So why are we not talking about a 48 Volt system here? Good question. And maybe we will be. 48 Volt air conditioner performance and efficiency is a great reason to consider a 48 Volt system over 12 Volts (and 24 Volts). However, many of the other camper van items (like refrigerators, possibly the second highest power consumer in most systems) are not readily available at 48 Volts. For now, we’ve found that 24 Volts offers a significant improvement with a majority of the system running at the house voltage, avoiding having to turn around and run most of the equipment at 12 Volts anyways.

Included in this system is a Victron Orion 24/12 Volt converter. With as many loads as possible running natively on 24 Volts, the 70 Amp 24/12 converter is more than sufficient for most customer’s needs. You need to be mindful that there is now a 24 Volt distribution center (using one or more Lynx distributors as shown in the example wiring diagram) as well as a 12 Volt distribution center (shown using our favorite WFCO combined AC/DC load center). For this system, we think that the improvements in performance offset the small increase in components required to use both 24 Volt and 12 Volt equipment simultaneously.

Solar charging is readily supported on a 24 Volt system, and most Victron MPPT chargers automatically select the house voltage. Because the MPPT chargers require a PV voltage higher than the house battery voltage to initiate a charge cycle, solar selection is a tiny bit (and we really do think it’s tiny) harder to select. Most customers can use two or more solar panels (typically in series), and there are 24 Volt solar panel options out there, like this one from Newpowa, where customers using only a single panel or desiring a parallel panel configuration can still effectively utilize solar.

48 Volt solar charging is a little more limited in this case, primarily because rooftop DC air conditioners necessarily compete with space for enough panels. There are not a lot of options for 48 Volt panels that fit on camper van rooftops, so multiple 24 Volt panels in series are typically needed. While solar charging for a 48 Volt house system is possible, it’s another minor reason why a 24 Volt system may be a good compromise right now.

Tips

If you Bring-Your-Own-Battery, programming your system at 24 Volts will be similar to the steps we’ve shown with our 12 Volt internal BMS system. Programming examples include the Multiplus and Cerbo GX configuration, where you’d carefully replace 12 Volt specifications with appropriate parameters from your 24 Volt battery manufacturer.

If you select the Epoch Elite batteries as part of bundle, the batteries include a cable for connecting the batteries to a Cerbo GX. Most customers will want to take advantage of these features, using the following steps as part of the installation:

• Set the battery DIP switches per the manual, representing the battery configuration and total capacity of the battery bank in your system.
• Install the communications cables per the battery manual, specifically making sure that the INV-labeled end of the Victron cable is connected to the Cerbo GX. Daisy chaining of multiple Epoch batteries is done with the CAN-labeled cable. Terminators are not required.
• Taking note of which VE.CAN port on the Cerbo you’re connected to, ensure that the CAN profile is correctly set: Console(Remote Console) > Settings > Services > VE.Can port # > CAN-bus profile > (select the CAN-bus BMS LV (500kbit/s) setting)
• Assign the Cerbo to use the Epoch BMS as the battery monitor (see note below): Settings > System Setup > Battery Monitor > select (Epoch BMS name) on CAN-bus. Alternatively, if you installed a Victron shunt, you would select that shunt as the battery monitor.
• Configure DVCC. When using the DVCC, you need to assign Epoch as the controlling BMS on the Cerbo: Settings > DVCC > Controlling BMS > select (Epoch BMS name).

NOTE: The Epoch batteries will aggregate multiple batteries into one battery BMS/shunt to be displayed & utilized by the Cerbo GX. An additional system shunt is not required, but through testing, we have discovered that the internal BMS will not register current below 1 Amp. There will be a SOC drift of unregistered current resulting in an actual SOC that is lower than the reported SOC. The solution is to install a Victron shunt and to use that as the battery monitor yet still use the Epoch BMS as the controlling BMS in the DVCC settings. Epoch is aware of this issue and have stated that they are working on the issue.