Probleme mit Victron + Biwatt Nest R2 (Sodium-Ion) – MPPT regeln ab, keine volle PV-Einspeisung

Interesting timing on this thread — I've been down a similar rabbit hole recently with my cabin setup.

Been trialling a sodium-ion battery (not the Biwatt, but a similar chemistry unit from a smaller Chinese manufacturer) alongside my Victron SmartSolar MPPT 150/45, and I'm seeing the MPPT throttling back PV harvest well before the battery is actually full. Frustrating when you're watching perfectly good sunshine go to waste.

My suspicion is it comes down to the charge profile parameters not being a great fit for Na-ion chemistry. These cells have a slightly different voltage curve compared to LFP — the absorption knee is in a different place, and if Victron's algorithm is interpreting that as "nearly full," it'll back off early.

A few things I've tried or am looking at:

• Custom charge profile via VictronConnect — manually dialling in absorption and float voltages specific to the Na-ion spec sheet
• Checking the BMS comms — if the battery BMS is talking to the MPPT via VE.Direct or CAN, make sure the BMS isn't sending a premature charge current limit signal
• Firmware — both the MPPT and any Cerbo GX you've got in the loop. Worth ruling out

The BMS comms angle feels most likely to me honestly. If the BMS is broadcasting a reduced charge current request, the MPPT will obey regardless of what your manual settings say.

Anyone else running Na-ion with Victron kit in a UK off-grid context? Particularly curious whether anyone's got this working cleanly with a Cerbo in the loop.

@WingAndPrayer curious which unit you ended up with — sodium-ion is still pretty niche over here in the UK.

The MPPT throttling issue rings true with any battery that has a flatter voltage curve than lithium. Victron's absorption/float thresholds are tuned around LiFePO4 assumptions by default, and sodium-ion sits in slightly different territory.

Worth checking a few things in VictronConnect:

• Absorption voltage — may need nudging down
• Tail current setting — sodium-ion tends to reach full charge earlier
• BMS communication — if there's no DVCC handshake happening, the MPPT is basically flying blind

My shepherd's hut setup had similar curtailment grief until I got proper DVCC sorted over VE.Can. Made a significant difference to harvest figures.

What does the BMS on your unit actually expose? That's usually where sodium-ion compatibility falls apart with Victron kit.

@WingAndPrayer @DodgyHermit — sodium-ion is on my radar for the shepherd's hut build actually. The wider temperature tolerance vs LiFePO4 is appealing given it's not a heated space year-round.

Quick question though — when you say the MPPT is throttling back, have you confirmed the battery BMS is actually communicating charge parameters correctly to the Victron? I've seen setups where the MPPT just defaults to its own internal voltage curves because it's not receiving proper data over VE.Direct or DVCC.

Is DVCC enabled in Venus OS? That's often the culprit when things don't play nicely with non-standard chemistries — the MPPT basically doesn't know what the battery actually wants.

What's the battery's recommended absorption voltage? Sodium-ion tends to sit at a different window to lithium and if Victron's profile is mismatched it'll throttle well before full charge.

@DodgyHermit @PikeTom — mine's a unit from a Chinese manufacturer I sourced through a freight forwarder, so not exactly a household name here yet! Happy to share details via DM if useful.

One thing worth flagging for your shepherd's hut build, @PikeTom — the charging profile is the critical bit. Sodium-ion typically wants a slightly lower absorption voltage than lithium, and if your MPPT doesn't have a user-defined profile, you'll likely hit the same throttling issues the OP is describing. I had to fiddle with the Victron's custom battery settings for a good while before things settled properly.

The temperature tolerance advantage is genuinely useful though — I've had no issues through some properly bitter nights that would've had a lithium pack sulking.

@DustyWanderer that freight-forwarder route is exactly where things get complicated — what BMS protocol does yours expose? That's the crux of the issue for me with my van build. I've been trying to get a sodium-ion unit to communicate properly over the Victron VE.Can bus and the BMS UART settings are just not documented anywhere in English.

@PikeTom the temperature tolerance argument is genuinely compelling for an unheated shepherd's hut — sodium-ion's low-temperature discharge performance is measurably better than LFP. But has anyone actually verified the charge profile parameters against what a Victron SmartSolar will accept without custom scripting?

Specifically: what absorption voltage ceiling are people using, and are you relying on the BMS to cut off, or dialling the MPPT back manually? The Victron documentation is frustratingly vague on non-lithium chemistries.

@FormerMariner1 raises the real crux of it — BMS protocol compatibility is where I've lost days of my life troubleshooting.

On the boat I'm running a Victron MPPT 100/30 and when I introduced a non-certified battery last summer, the MPPT kept throttling back exactly as the OP describes. Turned out the MPPT was seeing voltage curves it didn't recognise and defaulting to a conservative absorption ceiling.

What actually helped me was switching to battery voltage sense via the VE.Smart network rather than relying on the MPPT's own terminals — it gave Victron a cleaner picture of what the battery was actually doing.

Whether that translates to sodium-ion chemistry is another question entirely. If the BMS isn't communicating state-of-charge properly over whatever protocol it's using, the MPPT is essentially flying blind and will protect itself by curtailing output.