Verliere den Arbeitspunkt

Been noticing something odd with my Victron SmartSolar MPPT 100/20 lately and wondering if anyone else has seen similar behaviour.

I've got a couple of 175W panels wired in series feeding into a 200Ah Fogstar Drift LiFePo4. On clear days everything tracks perfectly — the controller hunts for the MPP and settles nicely. But I'm seeing what looks like the controller losing the operating point intermittently, particularly in the mornings when irradiance is still building, and occasionally when clouds are breaking up after a heavy overcast period.

What I mean specifically: the VRM app shows the panel voltage suddenly jumping well above where the MPP should be, power drops off sharply, then after 30-60 seconds it recovers and re-locks. It's almost like the MPPT algorithm gets confused and overshoots badly during rapid irradiance transitions.

A few things I'm unsure about:

• Is this a known quirk with the 100/20 firmware, or is it more likely my panel configuration causing it?
• Could the LiFePo4's relatively flat charge curve be contributing — i.e., the battery isn't "pulling" enough to keep the tracker anchored?
• Would adjusting the absorption voltage or charge current limits in VictronConnect help stabilise it?

I've updated to the latest firmware already. Panel wiring looks clean, no partial shading issues I can identify.

Anyone running a similar Victron + LiFePo4 setup who's seen this kind of tracking instability? Curious whether it's a software/settings issue or something more fundamental about how these controllers behave under variable UK conditions (which, let's be honest, is basically all conditions here).

Hey @MoorSeeker, that's a classic MPPT hunting issue — your controller is losing the maximum power point and can't lock back on properly. A few things worth checking:

First, have a look at your wiring connections — any loose terminals or dodgy crimps can cause just enough resistance to throw the tracker off. Also worth checking whether your panels are getting any partial shading, even something subtle like a vent pipe shadow in the morning.

On the Victron SmartSolar specifically, pop into the VictronConnect app and check your battery absorption voltage settings. If they're set too high relative to your actual battery state, the MPPT can oscillate trying to balance things out.

What's your battery bank — lithium or lead-acid? That'll make a difference to the troubleshooting approach. Also, what firmware version are you running on the controller?

@MoorSeeker a few things worth checking before assuming it's a controller fault:

1. Partial shading — even a tiny shadow on one cell throws the whole series string off. MPPT struggles to find the true peak when the IV curve has multiple humps
2. Loose connections — had this exact issue on my cabin setup last summer, turned out to be a slightly dodgy MC4 connector causing intermittent resistance
3. Battery state — if your 200Ah bank is near full, the controller should throttle back, but sometimes it hunts rather than settling cleanly

What firmware version are you running on the SmartSolar? Victron pushed some MPPT algorithm updates a while back that helped with hunting behaviour. Worth checking via the VictronConnect app.

Also — are you monitoring via the app? The live graph will show you exactly when it's dropping the power point, makes diagnosis much easier.

Something I haven't seen mentioned yet — check your panel connections with a thermal camera or even just your hand on a sunny day. I had a similar hunting issue with my shepherd's hut setup (two 200W panels, Victron SmartSolar 100/30) and it turned out to be a dodgy MC4 connector causing intermittent resistance. The MPPT was constantly chasing a moving target.

Also worth logging via the VictronConnect app if you haven't already — the history graphs will show you exactly when the hunting occurs. Mine was worse in the morning when temperatures were shifting rapidly.

@EmmaEdwards82 makes a good point about shading. Even the shadow from a TV aerial drove me mad for weeks before I spotted it.

Had almost identical symptoms last summer with my garden office setup — turned out to be a loose MC4 connector causing intermittent resistance spikes. The MPPT was chasing a moving target basically.

One thing nobody's mentioned: check your battery absorption voltage setting in the VictronConnect app. If it's set too high for your battery chemistry, the controller can oscillate weirdly near the top of charge as it tries to maintain the absorption phase. Took me ages to spot that one.

Also worth enabling the "tail current" setting properly if you're on AGM or lithium — makes the transition to float much smoother and stops that hunting behaviour @StormyNomad described.

Download the mppt history from VictronConnect and look at the yield graph — any sharp dips mid-day usually point to connection issues rather than controller firmware problems.