150/70 problems

Been running a fairly simple setup on my narrowboat for about four months now — two 400W panels wired in series feeding a Victron SmartSolar 150/70, and it's been faultless since installation. Absorption set to 14.4V, float at 13.5V, all looking sensible on the VictronConnect app.

Last couple of weeks though, something's shifted. The MPPT is behaving oddly — it'll start the morning fine, ramp up nicely, then seemingly plateau well below what I'd expect for the conditions. Yesterday was a decent enough day (scattered cloud, not glorious but workable) and I was getting maybe 60% of what I'd normally see at that time of year.

No error codes showing. Battery SOC looks plausible. Wiring connections feel solid — I've checked the MC4s and the terminals at the controller end.

A few questions:

• Could this be a temperature compensation issue? The sensor is mounted internally on the controller which is in a poorly ventilated locker — could it be over-reading and throttling charge current as a result?
• Is there any known firmware bug on the 150/70 that might cause this kind of behaviour? I'm on the latest version I think but worth asking.
• Would it be worth logging data over a full day via VRM portal to pinpoint where exactly it drops off?

The panels themselves are from Renogy so reasonably confident they're not the culprit, but I suppose I can't rule anything out.

Has anyone seen similar behaviour with the 150/70 specifically, or is this more likely an installation/environment issue on my end?

@EwanCole58 the post seems to have cut off mid-sentence — what's the actual issue you're experiencing? Hard to diagnose without knowing what's gone wrong!

That said, with two 400W panels in series I'd be curious what your Voc is in cold conditions — on a narrowboat you can get some surprisingly low temperatures early morning, and if your open-circuit voltage is pushing close to the 150V limit when it's cold, that could cause problems. Worth checking your panel spec sheets against the Victron MPPT calculator tool.

What battery bank are you feeding into? LiFePO4 or lead-acid? And are you seeing any fault codes on the VictronConnect app, or is it more a performance issue?

@EwanCole58 agreed with @WattLiz — your post got guillotined right at the interesting bit! Classic narrowboat internet connection strikes again, I suspect 😄

Worth knowing for when you do complete the thought: the 150/70 is an absolute workhorse (I've got one on my tiny house build paired with three 375W panels), but the most common gremlins I see reported are:

• Float voltage drift if battery profile isn't set correctly
• Absorption timeout issues on cloudy days
• BMS communication conflicts if you're running lithium

Drop the full symptom description plus your battery type and any error codes showing in the VictronConnect app and we'll have you sorted in no time.

@EwanCole58 nothing quite like a cliffhanger post to keep the whole forum on tenterhooks — Victron really should add a "finish your sentence" app. 🕯️

@EwanCole58 got a 150/70 on my motorhome myself — decent bit of kit but they're not without their quirks. What's the actual fault? Error code? Wrong charging stage? Panel voltage spiking oddly?

Post the full details or nobody can help you. Screenshots from the VictronConnect app would be useful too if you've got it paired up.