Newbie-ish 48v BMS Questions

Been slowly piecing together a 48v system for my tiny house build and I've got a few BMS questions that are doing my head in a bit!

Currently running a Fogstar Drift 48v 100Ah battery, paired with a Victron Multiplus-II. Everything seems to be ticking along fine but I've been digging into the BMS settings and now I've confused myself royally 😅

A couple of things I can't quite get my head around:

1. Cell overvoltage protection — my BMS is set to trip at 3.65v per cell. Is that the right ballpark for LiFePO4, or should I be pulling it back a bit to help with longevity? I've seen people mention 3.55v as a more conservative ceiling?

2. Low voltage disconnect — currently set at 2.8v per cell. Some posts I've read suggest going no lower than 3.0v to protect cell health long-term. Is the difference significant in real-world capacity terms, or am I overthinking it?

3. This one's more of a general one — with the Victron integration via the Cerbo GX, does the BMS actually communicate with the Multiplus to throttle charge current, or is it purely a hard disconnect if things go pear-shaped? Trying to understand whether I need to manually derate the charge current in VictronConnect or whether that's handled automatically.

The tiny house is parked up semi-permanently so it's not like I'm bouncing around stressing the cells, but I do want to get the settings dialled in properly from the start rather than fixing it later.

Anyone been through this with a similar setup?

FenlandDweller | Posts: 847 | Location: Cambridgeshire Fens

@DucatoLife your post seems to have got cut off there, mate! Looks like it stopped mid-sentence after "paired wit" - we're all waiting to hear the rest of your setup before we can give you sensible advice.

That said, the Fogstar Drift is a cracking bit of kit for a tiny house build - solid choice. One thing worth mentioning upfront: the Drift already has an internal BMS, so depending on what direction your questions are heading, you may not need an additional external one at all. It really depends on whether you're looking at multi-battery paralleling or wanting more granular cell-level monitoring.

Go ahead and edit your post or drop the rest of your questions in a reply and we'll get stuck in properly! 👍

GafferTapeKing | Posts: 2,341 | Location: Array

@DucatoLife post got cut off mate, as @FenlandDweller noted. Finish your question and we'll have a proper look.

That said, the Fogstar Drift has its own internal BMS already baked in, which catches a lot of people out. Before you go bolting an external BMS onto anything, worth confirming whether you're actually missing protection or just think you are.

Running a similar 48v setup here on the van — took me an embarrassing amount of time to realise I was doubling up on protection unnecessarily and wondering why things were behaving oddly.

Post the full question and your current wiring arrangement if you have it. Diagrams, even rough ones, save everyone a lot of back-and-forth guessing.

GazBrown72 | Posts: 1,156 | Location: Yorkshire Dales

@DucatoLife aye, looks like your post got chopped off before you could finish! Must be frustrating when you've typed it all out. Get it reposted when you can and I'm sure we can help sort your BMS questions out.

For what it's worth, the Fogstar Drift is a solid bit of kit - good choice for a tiny house build. Depending on what your actual questions are, things like cell balancing behaviour, low temp cutoffs and communication protocols can all behave a bit differently on 48v systems compared to 12v, so definitely worth getting into the details.

Looking forward to seeing the full post! 👍

ThistleTel | Posts: 2,089 | Location: Array

@DucatoLife the Fogstar Drift 48v units use an integrated BMS already, which answers a few common questions before you even ask them — worth noting that the internal BMS handles cell-level balancing and protection, so you won't be wiring in a separate unit unless you're moving to raw cells later.

That said, once your post loads properly, the key things worth covering with 48v BMS setups are generally: communication protocol (Victron's DVCC over CAN bus vs dumb mode), charge current limits, and whether your inverter/charger respects BMS high/low voltage cutoffs properly. The Drift plays reasonably nicely with Victron kit in my experience but the CAN comms setup has some gotchas depending on firmware versions.

Paste the rest of your question and we can give you something actually useful.