Battery charging with a converter and solar panel at the same time?

Running both at the same time is totally fine — done it loads. The key is having a decent MPPT controller that plays nicely with whatever else is charging the battery simultaneously.

My setup runs a Victron SmartSolar alongside a mains converter and they sort themselves out without any drama. The MPPT just sees the battery voltage rising and backs off naturally. Same principle applies whether it's a converter, alternator, or wind turbine chucked in the mix.

Few things worth checking though:

• Combined charge current — make sure your battery can handle the total from both sources. Check your BMS limits if you're on lithium (Fogstar Drift cells, for example, are pretty specific about max charge rates)
• Voltage settings — both sources should ideally be set to the same absorption/float voltage, otherwise one will be fighting the other
• Converter quality — some cheap converters have terrible voltage regulation and can cause issues. Proper battery chargers with IUoU profiles are far better than basic PSU-style ones

The Victron app is brilliant for monitoring what's actually happening in real time, so you can see both sources contributing and check nothing's misbehaving.

What converter are you using and what battery chemistry are you working with? That'll probably change the advice a bit. Lithium and AGM behave quite differently in this situation.

@CurrentAffairs96 broadly agree, but I'd push back slightly on "totally fine" as a blanket statement. It depends heavily on your battery chemistry.

On my shepherd's hut setup I had a Victron SmartSolar MPPT running alongside a mains converter, and with lithium (Fogstar Drift cells) it was fine — the BMS sorted out any disagreements between charge sources.

With AGM though, I had issues. Two controllers both trying to push into the same battery at absorption stage got messy — one kept resetting the other's voltage curve.

The real key isn't just a decent MPPT, it's making sure the charge sources can communicate or at least not actively fight each other. Victron's VE.Smart networking helps if you're running multiple Victron units, but mixing brands is where it gets sketchy.

What converter are you actually running?

@ExPostie is right to pump the brakes — ran my Victron SmartSolar alongside a converter for months thinking I was a genius, until the battery decided to have a little meltdown and remind me who's actually in charge 🔥

@MoorKev curious what actually went wrong on your setup — was it voltage feedback causing the MPPT to back off unnecessarily, or something more dramatic?

The bit people miss is that the battery sees a combined current from both sources simultaneously. Where it gets hairy is if your converter is a cheap unit outputting a noisy DC profile — some of the budget units (looking at you, random Amazon specials) effectively fool the MPPT's battery voltage sensing, causing it to prematurely drop into float when the bank isn't actually full.

Running my Victron SmartSolar 100/30 alongside a Victron IP22 charger on my narrowboat, they communicate via the VE.Smart network and actively coordinate. That's the proper solution — shared voltage/temperature sensing across devices.

If you're mixing brands without any communication protocol between them, at minimum ensure your MPPT has good battery voltage sensing and isn't measuring mid-busbar where converter noise corrupts the reading.

@ForestBoater @MoorKev — relevant question. Had something similar on my static van. Victron SmartSolar kept throttling back because the converter was holding the battery voltage artificially high, so the MPPT thought it was nearly full when it wasn't. Wasted a good chunk of solar capacity for weeks before I cottoned on.

Worth checking whether your MPPT is reading battery voltage at the terminals or somewhere else in the circuit — cable voltage drop can skew things badly too.

What converter are you actually running? Some of the cheaper units don't regulate cleanly and that causes all sorts of grief. I've seen Renogy MPPT controllers handle it better than expected, but it's not a given. Is there a BMS in the loop as well?