I’ve ran into the first issue I don’t know how to fix myself

Something similar had me scratching my head for the better part of a fortnight last spring.

I'm running two Victron 100/50 MPPTs off a mix of panels — nothing exotic, just some Renogy 200W units and a couple of older 300W panels I picked up second-hand — feeding into a 300Ah Fogstar Drift LiFePO4 bank with a SmartShunt keeping tabs on everything.

What I noticed was the SmartShunt's state of charge drifting further and further from what the MPPTs were reporting in VictronConnect. Some days it was a 12% discrepancy by mid-afternoon. Not catastrophic, but deeply unsettling when you're trying to trust your system.

Turns out the culprit was the synchronisation between the two controllers — they weren't networked together via VE.Smart, so they were essentially making independent decisions about absorption and float. One would drop to float while the other was still pushing, and the shunt was getting confused about what "full" actually looked like.

Enabling VE.Smart networking through the Victron app so both MPPTs could see each other's data sorted it almost immediately. The charged voltage threshold on the shunt also needed nudging to match what the batteries actually needed rather than the default.

Worth asking — are your controllers talking to each other, or are they operating blind? And have you double-checked your tail current setting on the shunt? That's often the quiet troublemaker nobody mentions.

Curious whether others have seen similar drift issues with parallel controllers on a shared bank. Feels like this comes up more than the manuals suggest it should.

@MoorHamish sounds like the post got cut off mid-sentence — what are you actually seeing? Error codes, weird charging behaviour, panels not producing expected output?

A few things worth checking with mixed panels on dual MPPTs:

• Are your panel strings matched by Voc within each MPPT?
• Check the MPPT history in VictronConnect — absorption time and bulk/float transitions tell you a lot
• Any BMS comms involved, or standalone?

Had something similar on my garden office setup — turned out one string had a dodgy MC4 connector causing intermittent dropout. The MPPT was logging it as normal behaviour which made it genuinely annoying to track down.

Drop the full setup details and any VRM screenshots if you've got them — much easier to diagnose properly.

@MoorHamish classic move, cutting off your own post like my Victron cuts off charging at 2am for no apparent reason 🔋

@MoorHamish while we wait for the rest of that post to materialise, two MPPTs on mixed strings is a classic recipe for one unit doing all the heavy lifting whilst the other one lounges about — check your VictronConnect history graphs and I'd wager they're wildly asymmetrical, which usually points to mismatched Voc rather than any actual fault.

@OldSailor makes a fair point about the mixed strings, but I'd also be looking at whether those two MPPTs are set to the same absorption/float voltages. Had exactly this nonsense on my static van setup last summer — both units technically "working" but fighting each other like a pair of drunk uncles at Christmas because one was set 0.2V higher than the other. Victron Connect makes it dead easy to check, at least.

@MoorHamish finish your sentence, mate. We're all just guessing in the dark here. Error codes would narrow it down considerably — screenshot from VictronConnect would be ideal if you've got it paired up.