Help Litio system RV

DIY
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1

Hi everyone, thanks in advance to anyone who can help me. I own a Carthago C-Tourer I 145 RB LE motorhome based on a 2025 MY Mercedes Sprinter (2000 cc, 170hp) equipped with a Smart Alternator. The motorhome came from the factory with a lithium battery setup and a Lippert DC-DC charger.

Since I need to run my Truma Aventa Compact air conditioner while driving, I would like to upgrade the electrical system. My plan is to replace the factory DC-DC charger with two Orion XS 50A units connected in parallel, current-limited to 35A each in order to protect the OEM alternator. I want to replace the original lithium house battery with two 200Ah batteries (I am not using Victron batteries due to the high cost). To monitor them, I will use a SmartShunt 500A. To simplify the wiring and ensure proper fusing, I will use a Lynx Distributor M10.

Finally, I would also like to add a Cerbo GX so I can monitor all system parameters via the VictronConnect / VRM app.

In the attached wiring diagram, you can see how I planned the setup. I say “planned” because this is a DIY project; I am gathering information and advice from more experienced users, but I am not sure if it is entirely correct.

I also have a few questions that I haven’t been able to find answers to:

  1. Is it correct to connect the negatives of both the house battery and the starter battery to the same busbar, or should they be connected differently?
  2. Are the factory Mercedes cables going to the starter battery properly sized for the maximum alternator output? Specifically, can they handle the extra 50A from the new DC-DC chargers? (I am saying 50A instead of 70A because I will be removing the Lippert charger, which already had its own current draw).
  3. Since the starter battery has an OEM device attached to it (which I assume is a factory shunt), should I ground the system negative directly to the vehicle chassis?
  4. The factory DC-DC charger uses a D+ signal wire. Do I need to connect this D+ wire to both Orion XS units?
  5. Is there an easily accessible D+ connection point in the cab area, under the dinette, or under the driver’s seat?
  6. Do you notice any mistakes or potential improvements in my diagram?

Thank you all for your patience in reading through my questions. I hope that with your help, we can successfully build this new system.

Litio diagram
Litio diagram1714×1291 342 KB

2

You want to save money on the batteries but use a second Orion XS and then limit that to 70A total? Are you sure those 20A are worth the ~300 bucks? Also depending on how fast you want to build that, there is a 70A Orion XS announced. The manual and datasheet are already available on the victron site, so its full release cant be too far out.

  1. The starter battery is already connected to the vehicle body, so you can likewise connect the house battery negative busbar to the vehicle body as well.
  2. I would hope they are, but you got the vehicle at your disposal, so if you want to know for sure then you would have to measure the cable gauge. Id say in general the cabling is properly rated, but maybe keep an eye on things if you end up drawing those 70A for the whole ~3hrs it takes to recharge those 200Ah again. They may not be made for that kind of constant load
  3. You dont need to do anything with the starter battery negative, the body is already connected
  4. Not necessarily, the Orion feature an engine shutdown detection which works nicely if its setup properly. Otherwise you can use the D+ plus signal.
  5. No idea, probably not. D+ isnt that common anymore now that everything is bus-controlled
  6. I personally would consider using a MultiPlus instead of a Phoenix. The added cost is not much but the ability to charge both house and starter battery (through the trickle charger output) is worth it to me. You also may want to plan a fuse spot for an MPPT, but i guess if you want to add one in the future you could combine the two Orion outputs onto one fuse.