Self-Sufficient Caravan Project

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1

Hello everyone,

I’m Dirk, and I’ll soon be getting my new caravan, so I’m already starting to plan the off-grid setup. It’s probably all a bit over the top, considering everything I want to install, but hey, I enjoy this sort of thing. I’m hoping I might be able to get some advice here in case my plans aren’t entirely correct or there’s a better way to put them into practice.

So, what am I planning? I want to make my new caravan so self-sufficient that, when I’m away, I can run the coffee machine and perhaps even switch on the air conditioning.

To do this, I’d like to install a Victron MultiPlus II 12/3000/120 in the caravan. For storage, I was thinking of using two LiFePO₄ batteries (12 V, 165 Ah, 200 A BMS) connected in parallel. The display and so on are obviously part of the plan too, but for now I’m mainly concerned with the wiring, specifically the cable cross-sections and fuses.

Why do I want to install a MultiPlus at all? Well, in the past it has happened a few times that you only get 6 A at a campsite, which isn’t very much. That’s why I’d like to install the MultiPlus: I can limit the input current (shore power), protecting the campsite’s circuit breaker from tripping, and if I do need more power, the MultiPlus can draw on the batteries as well.

So, here’s my plan:

The two batteries mentioned above are to be connected in parallel. I would first run cables of the same length from both batteries to a busbar. The cable cross-section from each battery to the busbar would be 70 mm², with the length being less than 1 metre. Each battery would be protected with a 250 A MEGA fuse installed shortly after the positive terminal.

From the busbar to the MultiPlus, I would use either 95 mm² cable or, as Victron specifies in the manual, 2 × 50 mm². I would protect this cable with a 350 A fuse installed shortly after the busbar; this run will also be less than 1 metre long.

The caravan’s standard 12-volt supply and the mover would also be connected to the busbar, but I don’t want to consider those components here.

So, my actual question is: are the planned cable cross-sections and fuses for the battery → busbar → MultiPlus connection OK, or should I use smaller fuses or change the cable cross-sections?

Thanks for your help.

Best regards,
Dirk

2

Hello,
What you unfortunately don’t mention at all is how you intend to charge the batteries and how long you then plan to remain self-sufficient.

3

So, to start with, the batteries are meant to be charged by one of those portable solar panels, but I haven’t looked into it any further yet. Otherwise, when shore power is connected, the batteries will be charged by the MultiPlus again.

At first, I’ll only be off-grid for around two or three days at a time. Maybe longer later on, but I can’t say for certain yet. I just want to lay the foundations for it now, which is why I’m going for the MultiPlus rather than simply using a small inverter.

4

To start with, get 2–4 truck starter batteries and test them.

If you fit lithium batteries, choose ones whose BMS can be configured in the Cerbo (Battery CAN).

5

Plan for 24 V! Half the cable cross-sections will be sufficient. And if you want to charge via PV at some point, smaller or fewer charge controllers will be enough. Make sure that the battery is approved for installation in vehicles. And that it has Bluetooth.

6

Are you planning to run the full 3,000 W continuously, or do you normally need less? How much power does your air conditioner or coffee machine use, as they’re likely to be your biggest consumers? Do you need to be able to run both at the same time?

Ultimately, that determines the fuses and cables.

7

Sorry, that won’t work; they’re definitely too heavy for caravans.

How can I find out whether the batteries have a BMS that I can register in the Cerbo?

24 volts will be difficult to implement, as 12-volt components also need to be powered, such as the caravan’s onboard electronics at around 300 watts, and the mover, which requires up to 125 A.

So it’s rather unlikely that the MultiPlus will constantly be required to deliver its full continuous output (2,400 W), but it could happen briefly.

The air-conditioning unit uses around 1,000 watts at full load, although it only needs that at the start; afterwards, it should require around 500 to 700 watts. The coffee machine is rated at 1,500 watts.

8

Hi Dirk,

I have essentially exactly the same kind of system in my caravan. However, I built the batteries using EVE MB31 cells. I put four of them in a case made from phenolic-faced plywood panels and secured them together, and used a 123SmartBMS as the BMS. It has a cable, so it can be integrated seamlessly into the Victron system. I have two of these battery packs in total (giving me around 8 kWh of storage altogether). Each battery is connected to the busbar with a 50 mm² cable and protected by a 150 A fuse. The MultiPlus is also connected with two 50 mm² cables and protected by a 150 A fuse. The MultiPlus draws 200 A at full load, so that’s 100 A per battery pack.

On the roof I have two 250 W panels (just standard panels intended for domestic installations; mine are simply already 12 years old), plus a portable 200 W panel. The PV is connected via one SmartSolar charge controller each.

While driving, the charge controller installed by Hobby (Toptron) charges via the permanent live and the charging live, at around 140 W.

We use it to run a coffee machine, a small washing machine and a small oven for bread rolls and so on, and we’ve even baked a cake. We don’t have air conditioning because we always travel north; this year we spent three weeks in Sweden, and the caravan didn’t use shore power even once.

We also run the absorption fridge on 230 V while driving and on the ferry.

If you have any questions, just let me know. I can also send you some photos.

9

Just a quick question: you’re building the whole thing yourself, so why are the batteries and the inverter so far apart? Can’t you put them right next to each other?

Another question: why do you want to fuse the inverter twice? You’ve already got fuses right by the batteries.

10

For example, via the compatibility list:

11

Yes, I’m building the whole thing myself. Naturally, I’ll try to install everything as close together as possible, but since the caravan isn’t here yet, I’ve initially assumed around 1 metre per run. Once the caravan is on site, I’ll of course try to find a place where I can keep the cables as short as possible. The figure given above was more about the maximum length, and whether the cable cross-sections and fuse ratings would work in that case.

I don’t want to use the fuses to protect the inverter directly, but rather the cables between the individual connections. I wanted to play it safe, hence the additional fusing.

Yes, I had already looked at that list, but I mainly found storage systems intended more or less for domestic use, making them too large and too heavy for a caravan.

12

Hello Laertes,

thanks, your post is helping me a lot. But I have one more question: you write 150 A per battery, which is clear, but regarding the connection

busbar → Multiplus,

you used 2 × 50 mm² cables. Did you install a 150 A fuse on each cable, or did you connect both cables to a single 150 A fuse?

13

150 A per battery to the busbar. That makes a maximum of 300 A. That’s absolutely no problem for a 50 mm² cable; it doesn’t need to be separately fused, even if the second cable were to come loose for whatever reason. It would only introduce additional losses and potential points of failure.

14

Dirk, is this planned for a towable caravan or for a camper?

Be aware of the weight of all components.

The batteries is about 160kg and the inverter with all cables another 40kg. Also the MP-2 is not silent and may generate a lot of heat under larger loads.

I doubt if this is a proper solution for a caravan.

15

The title says it quite unambiguously: caravan.

WHAT?!?
A 12V LiFePO4 with a capacity of 165Ah weighs between 15 and 20kg, depending on the model…

According to the datasheet, the MP2 weighs 19kg. I don’t believe that the cables, RCD, fuses, etc. would add a further 21kg…

That’s certainly true; a MultiPlus might be better suited to this.

16

Hello Dirk,

Yes, each battery → busbar is protected by a 150 A fuse, and both cables from the busbar → MultiPlus are also protected by 150 A fuses.

As for the weight, my EVE batteries weigh approximately 25 kg each.
The MultiPlus, including all the cables, weighs around 23 kg.

As for the noise, I previously had a cheap inverter whose fans kept coming on even under the lightest load and were clearly audible. I didn’t hear the MultiPlus 2 once during the entire holiday. The coffee machine is much louder when it’s running, as are the blender and oven. When only 300–400 W is being drawn, you can’t hear anything at all. I installed everything under the seat bench and couldn’t even feel the humming.

17

Yes, the larger the cells, the less weight you get per Ah.
25 kg for 314 Ah is a good ratio. :wink:

Which exact model are you using?

18

I’ve got the MultiPlus2 12/3000/120 + Cerbo GX MK2 + Smart MPPT 150/70 + Smart MPPT 75/15.

For the display, I’m using a 7-inch Android tablet.

The MultiPlus uses between 11 and 13 W when running at no load, by the way. We switch it off via the display whenever possible. You could also enable the energy-saving options. I tried both settings, but they cause problems because, for example, the coffee machine only draws a lot of power while heating up. There have been occasions when the MultiPlus switched off during the brewing cycle.

19

That was just out of curiosity, thanks…
Personally, I don’t have a 230V installation in my motorhome; my coffee machine runs on gas, and if it gets too warm inside, I go outside. Everything else has been switched over to USB-C, but that’s absolutely not meant as a judgement — everyone has to and should decide for themselves what they need and what they don’t…

20

And now the fuses get to play poker to see which one blows first. What’s the point of this double protection?