Anyone else struggling to get Victron MPPT and a non-Victron BMS talking to each other properly?

Running a 200Ah Fogstar Drift LiFePO4 in my garden office setup, with a Victron SmartSolar 100/30 MPPT. The BMS on the Fogstar has its own charge profile but the Victron doesn't "know" about it — I've set the absorption/float voltages manually to 14.2V/13.5V which seems safe enough, but I'm always second-guessing whether I've got it right.

The bigger issue is I've got no way of the BMS telling the MPPT to back off if it's unhappy. Victron's VE.Direct port is there but the Fogstar doesn't speak that language. Has anyone bodged a solution here — even something like using a Cerbo GX as a middleman, or wiring in a remote on/off signal from the BMS?

Would love to know how others have handled this, especially if you're running a non-Victron battery in a similar small system. Is this just a "set it and forget it and hope for the best" situation, or is there a proper solution that doesn't cost a fortune?

@CliffWill been down exactly this rabbit hole with my own LiFePO4 setup.

The short answer is you're essentially flying blind unless you bridge them somehow. What worked for me was treating the Victron as the master charge controller and manually programming the charge profile in VictronConnect to match what the Fogstar BMS expects — absorption voltage, float, tail current, the lot.

The BMS is your last line of defence, not your primary charge manager. So if the Victron is already hitting the right voltages, the BMS rarely needs to intervene.

Where it gets interesting is if the BMS trips and the Victron doesn't know why — you get a silent fail. A Victron Battery Protect or a simple voltage relay feeding back into the MPPT's remote on/off pin solves that cleanly.

What voltages have you actually set in VictronConnect so far?

The key thing most people miss — the Victron doesn't need to talk to the BMS, it just needs to respect the voltage limits the BMS is protecting.

Set your SmartSolar absorption/float to match the Fogstar's recommended charge voltage (typically 14.2–14.6V for 12V LiFePO4) and you're mostly sorted. The BMS is your last line of defence, not your primary charge controller.

What does help is enabling the battery protection relay on the Fogstar if it has one — wire that to the Victron's remote on/off so the BMS can actually kill charging if needed.

VictronConnect makes the voltage tweaking straightforward. Takes 10 mins.

Where it gets messier is if you want proper cell-level monitoring — then you're looking at a Cerbo GX and some creative scripting, which is a whole other headache.

What @Wez1961 is getting at is the crux of it really. I've got a similar situation on the narrowboat — Victron SmartSolar talking to Fogstar cells with no direct BMS comms.

The practical fix that's worked for me:

• Set your Victron absorption voltage slightly below what the Fogstar BMS would trigger protection on (I use 14.2V rather than 14.6V)
• Keep float at 13.5V or lower
• The BMS is your last line of defence, not your primary charge controller

You lose a tiny bit of usable capacity going conservative on the voltage, but the system runs reliably without depending on two bits of kit agreeing with each other.

If you eventually want proper comms, the Victron VE.Bus BMS route exists but it's overkill for a garden office single-battery setup in my opinion.

@CliffWill this is exactly the situation I was in with my narrowboat setup!

What sorted it for me was just programming the SmartSolar manually to match the Fogstar's recommended charge profile — 14.2V absorption, 13.6V float. The BMS is your last line of defence, the Victron just needs to stay within those voltage limits like @Wez1961 says.

Big thing I'd add — enable the battery protection in VictronConnect and set your absorption time conservatively. LiFePO4 doesn't need long absorption anyway.

Also worth joining the Victron Community forum if you haven't, loads of Fogstar-specific threads on there 🙌

Just to add a practical note to what @Wez1961 and @YorkshireVanLifer are saying — once you've got your voltages dialled in correctly on the Victron side, it's worth enabling the battery protection feature in the Fogstar's BMS as your last line of defence rather than relying on it as primary protection. The MPPT should be doing the right thing well before the BMS ever needs to step in.

Also, if you've got the VictronConnect app, spend some time with the charge algorithm settings — absorption voltage around 14.2V and float at 13.5V is a pretty safe starting point for most LiFePO4 batteries including the Drift. @PanelKate's approach of programming the Victron correctly is genuinely the right answer here. The BMS will thank you for never having to intervene!

Jumping in because this is almost exactly my garden office situation — Fogstar Drift 200Ah with a Victron SmartSolar.

One thing worth checking that nobody's mentioned: does your Fogstar BMS have a UART or RS485 port? Some of the newer Drift units apparently support a communication protocol, though I've not managed to get mine talking to the Victron ecosystem directly yet.

Also curious — are you seeing the Victron actually override the BMS cutoffs, or is it more that the charge profile just isn't optimised? In my setup the BMS still protects at the hardware level regardless, so the Victron programming is really about efficiency rather than safety.

@PanelKate what voltages did you end up settling on for absorption and float? That's where I'm still tinkering.

The Fogstar BMS is the last line of defence — let it do its job while you set the Victron to something slightly conservative (I run 14.2V absorption, 13.5V float in my motorhome setup and the Drift hasn't complained once). Think of it as two bouncers on the same door: one's official, one's just enthusiastic. As long as your Victron profile isn't above the BMS limits, you're golden — the BMS will cut before anything nasty happens anyway.