Is there a good way to detect MPP Mode limiting reason?

Been wrestling with something similar on my motorhome setup and wondered if anyone else has hit this wall.

Running a Victron MPPT 100/30 with 400W of panels, and I've been trying to automate when certain loads kick in — water pump, 12V compressor fridge, that sort of thing — based on what the controller is actually doing at any given moment. The MPP operating mode field looks like the perfect trigger, but it's frustratingly blunt as a diagnostic tool.

When it shows the controller is limiting/clipping, it doesn't really tell you why. Is it:

• Battery full and absorbing?
• Panel output genuinely exceeding what the controller can handle?
• Temperature throttling on the MPPT itself?
• Something else entirely?

Each of those scenarios calls for a completely different response from my automation logic. If it's a full battery, I want to shed load somewhere useful. If it's thermal throttling, maybe park in shade and wait. If it's wiring or a controller limitation, that's a maintenance flag.

I've been poking around in VictronConnect and looking at what's exposed via VE.Direct, but the granularity just isn't there natively from what I can tell. Some folks have cobbled together inferences using battery voltage + current + temp sensors, but that feels like guesswork dressed up as logic.

Has anyone managed to build something reliable around this — whether through Venus OS, Node-RED on a Cerbo, or even just logging and pattern-matching after the fact? Or is there a smarter parameter combination I'm missing that effectively triangulates the reason rather than just the state?

Curious what others are doing, especially those running more complex setups than a single motorhome.

Hey @SteveWhite70, great question and one I've spent way too long puzzling over myself!

The Victron MPPT does expose quite a bit via VE.Direct or the Bluetooth VE.Direct dongle. If you're pulling data programmatically, the MPPT field in the VE.Direct protocol tells you the tracker state (Off, Voltage/Current limited, MPP etc.), and crucially the CS (charge state) field helps narrow down why it's limiting.

Combining PPV (panel power), I (charge current) and V (battery voltage) you can usually infer whether you're hitting the 30A current limit versus absorption voltage limiting versus just poor irradiance.

If you're on Home Assistant or similar, the Victron integration surfaces most of this already. Are you using any home automation platform, or going more bespoke with the serial data directly? That'd help me point you in the right direction. 🙂

Really useful thread this — I've been wondering the same thing for my cabin backup setup.

One thing I've been curious about: does the off reason field in the VE.Direct protocol give any useful granularity here, or is it too coarse to distinguish between absorption limiting vs temperature derating vs input power limiting?

I've got a Victron MPPT 75/15 and occasionally notice the reported panel wattage seems artificially low on warm afternoons, but I can't tell from VictronConnect alone whether it's the battery that's full or the controller throttling due to heat.

Has anyone managed to correlate the OR register values with actual limiting behaviour in practice? I'm considering grabbing a Raspberry Pi to log everything properly, but would love to know if the data is actually meaningful before I invest the time.

Had this exact headache on my motorhome last summer. Worth checking the CS (charge state) register via Modbus alongside MPPT mode — cross-referencing those two gave me a much clearer picture of why the controller was throttling.

On my 100/50 I found the absorption voltage ceiling was the culprit most of the time, not panel output. Easy to miss if you're only watching one register.

If you're using Node-RED or similar, a simple flow comparing PPV (panel watts) against P (output watts) with the charge state logged gives you a decent audit trail. Fogstar cells with tight BMS cutoffs can also muddy the picture — worth ruling that out first.

Really interesting thread this — I've got a similar thing going on with my static caravan setup, Victron SmartSolar 100/50, and I've been poking around in VE.Direct trying to make sense of it all.

Silly question possibly, but has anyone looked at combining the MPPT field with battery voltage trends over a short rolling window? I was wondering if you could infer the limiting reason that way — if voltage is already high and absorption's kicking in, that's one story; if it's mid-afternoon and output's just... flat, that's another.

Also does the Victron app's "history" page expose anything useful here, or is it genuinely just the raw Modbus registers @WildTinker mentioned that give you the granularity you'd need? I keep meaning to dig into Node-RED for this but haven't quite got there yet.

Great thread. On my narrowboat I've got a similar setup and spent way too long staring at VictronConnect wondering why my panels were loafing around like they were on a Bank Holiday.

One thing worth looking at beyond CS is the MPPT register (0x0200) — it'll tell you whether the controller is actually tracking or