RahVolt BMS/Inverter CAN/R485 question (charge but no discharge)

Had this exact faff with my tiny house setup last year — turned out the RahVolt BMS was set to "charge only" mode via CAN because the inverter wasn't receiving the discharge enable flag properly. 🔋

Worth checking a few things:

• CAN vs RS485 — are you actually using the right protocol for your inverter? Some combos need one or the other, not both active simultaneously, or you get conflicting signals
• BMS discharge enable signal — pop into the BMS config and confirm Discharge Enable is actually being broadcast; mine was stubbornly set to 0 until I manually toggled it
• Termination resistor — 120Ω at both ends of the bus, no arguments, just do it; half my grief was a missing terminator on the inverter end
• Cable pinout — RS485 A/B lines get swapped more often than anyone admits publicly

What inverter are you pairing it with? If it's Victron, the DVCC settings in VenusOS can override your BMS discharge limits entirely, which is a separate headache. Fogstar cells or something else in the pack?

Also, have you tried monitoring the CANbus traffic with a cheap USB analyser? Costs about a tenner and immediately shows whether the BMS is even talking — saved me about three days of head-scratching.

Others here have probably wrestled with RahVolt's rather optimistic documentation too, so chip in if you've cracked it! 👇

Classic case of the BMS playing gatekeeper while the inverter stands outside in the rain like a sad labrador. 🐕

@CotswoldCruiser had the right diagnosis — worth double-checking your DVCC settings in Victron if you're running that combo, as it can silently override the discharge parameters coming through CAN. Had this exact headache with my motorhome build; Fogstar battery was perfectly happy but the Multiplus just refused to pull from it until I forced the correct BatteryLife state in VE.Configure.

Also — RS485 or CAN, pick one and stick with it, running both simultaneously on some RahVolt units causes the BMS to throw a wobble and default to charge-only as a safety fallback.

Double-check your CAN termination resistors — my Victron Multiplus threw a similar wobbly until I realised one end of the bus was floating like a lost balloon at a funeral. 🎈

Great shout from @CotswoldCruiser — worth also checking which CAN profile your RahVolt is actually broadcasting. Some of these units ship defaulted to a generic Pylontech-style profile rather than their own native protocol, and if your inverter is listening for something slightly different, the discharge enable frame just gets ignored silently. No fault codes, no drama, just... nothing happening. Dead frustrating.

Also, what firmware version are you running on both ends? There was a known handshake issue in earlier RahVolt firmware where the State of Charge reporting was slightly out of spec, which caused some inverters to interpret it as a fault condition and refuse to discharge as a precaution. Updating both sides sorted it for a few lads on here previously.

If you can share your CAN log or parameter screenshots that'd help narrow it down quickly. 👍

Good timing on this thread — I've been wrestling with something similar on my motorhome build with a Fogstar Drift battery and a Victron MultiPlus-II.

One thing nobody's mentioned yet: have you confirmed the baud rate matches on both ends? My setup was silently failing because the BMS was running at 250kbps and the inverter expected 500kbps — no error thrown, just the discharge flag never arriving properly.

Also worth checking — is your RS485 cable properly shielded and grounded at one end only? Picked up interference on mine that was corrupting packets intermittently, made fault-finding a nightmare.

What firmware version is your RahVolt on? There were known CAN handshake bugs in earlier releases that caused exactly this "charge only" behaviour regardless of your profile settings.

Great points all round here. One thing I'd add that hasn't been mentioned yet — have a look at your RahVolt's DVCC settings if you're running it through a Cerbo GX or similar. Sometimes the BMS is correctly sending the discharge enable flag over CAN, but DVCC is overriding it and capping discharge current to zero because it's pulling conflicting data from a second voltage source. Caught me out for a good fortnight!

@JG_VanLife — worth knowing that Fogstar Drift batteries use a slightly different CANbus protocol variant, so double-check whether your inverter has a specific Fogstar profile available rather than generic PYLON, as that mismatch alone can cause exactly this charge-only behaviour. Usually buried in the inverter's BMS protocol dropdown menu. 🔧