I've got a bit of a head-scratcher on my hands. Running a 12V lithium system on the boat (100Ah Fogstar Drift) and I'm trying to add two secondhand 24V panels to the two 12V panels I already have. The existing setup uses a Victron SmartSolar 100/20, which has been rock solid, but I'm not sure whether to wire the new panels in series, parallel, or just get a second controller entirely.
The maths is doing my head in. If I series the 24V panels together I'm pushing Voc well over 60V before I even factor in the cold-voltage spike, which would likely exceed the 100V input limit in winter. And mixing the 12V and 24V panels in any configuration seems to invite current imbalance problems — at least that's my understanding.
Has anyone actually run a mixed-voltage string through a single MPPT and got it working sensibly? Or is a second dedicated controller the only clean answer here? Wondering whether something like the Victron 75/15 would be a cost-effective way to handle the 24V panels separately rather than faff about trying to make one controller do everything.