Anyone else running MPPT in parallel? Getting confused by the wiring

Right, so I've finally decided to expand my cabin setup from one Victron SmartSolar 100/30 to two of them running in parallel. Currently got 400W on the roof feeding the single controller, and I'm adding another 400W array. The plan is each controller handles its own 200W string rather than trying to wire everything into one beast of a controller.

The bit that's frying my brain: both MPPT outputs connect to the same busbar going to a 200Ah Fogstar Drift LiFePO4. In theory they just charge away independently and the BMS sorts itself out. That's how it works, right? The Victron app shows them as separate devices but they both get the battery voltage from VE.Smart networking so they should at least be talking the same language.

What I haven't worked out yet is whether the cable runs from each controller to the busbar need to be identical lengths to balance the load, or whether that's only relevant when you're paralleling the panels themselves. I've got one controller mounted about 1.2m from the busbar and the other will be roughly 2.8m away — not ideal but that's what the cabin geometry gives me.

Has anyone actually done this with two SmartSolars and hit any weirdness? Specifically wondering if the charge current splits sensibly or if one controller ends up doing all the heavy lifting while the other loafs about.

PhilCrane | 847 posts

@CamperSam good move expanding, but just to flag something before you go further — two separate MPPTs running in parallel aren't actually "parallel" in the traditional sense. Each controller should have its own dedicated string of panels. Don't parallel the PV inputs between the two units, that's asking for trouble with differing voltage tracking.

The battery outputs can share the same busbar, which is where the "parallel" bit actually happens. Both controllers will happily charge the same bank simultaneously.

If you're using VictronConnect, make sure you enable the VE.Smart Networking so they synchronise their charge algorithms — otherwise you might get them disagreeing on absorption/float stages, which wastes potential.

What's your new panel configuration going to be? That'll affect whether you wire the new string in series or parallel on the PV side.

TimHarris | 312 posts

@CamperSam just to add to what @PhilCrane is getting at — the key thing with parallel MPPT controllers is keeping your panel strings independent. Each controller needs its own dedicated string; don't be tempted to parallel the PV inputs together before the controllers, as they'll fight each other trying to track different MPP voltages.

On the battery side though, parallel connection is absolutely fine — just run separate cables from each controller to the busbar or battery terminals, keeping cable lengths matched as closely as possible so the load balances properly.

Are you planning to add another 400W of panels for the second controller, or split your existing array? If you're splitting, worth checking your string voltage still falls comfortably within the 100V input limit once you reconfigure. What panels are you running currently?