Can I use the Smartsolar RS 450/100 MPPT as a trickle charger?

So this one's been rattling around in my head since I had a similar scare with my setup last autumn.

I'm running a Victron SmartSolar MPPT (not the RS, admittedly — mine's a 150/60) alongside a Fogstar lithium bank, and I had one cell group arrive looking absolutely sorry for itself. Wouldn't hold a connection, kept dropping out within seconds. Turned out it had gone so low the BMS was refusing to play ball entirely.

The question I kept asking myself: can you coax a deeply depleted battery back using the MPPT as a glorified trickle charger?

From what I worked out — and I'd love someone to correct me if I'm wrong — the RS 450/100 isn't really designed with that recovery mode in mind. It wants to see a minimum voltage before it'll engage properly. If the battery's sitting below that threshold, the controller just... shrugs.

What actually worked for me was a brief manual intervention with a bench power supply to nudge the voltage up enough for the BMS to wake up and accept a proper charge. Fiddly, slightly nerve-wracking, but it did the job.

A few things worth considering if you're in this situation:

• Check your BMS cutoff voltage — some are recoverable, some aren't
• Don't keep force-restarting a module that's shutting itself down; it's protecting itself
• Victron's VictronConnect app can sometimes reveal what the controller is actually seeing

Has anyone here managed to do a soft recovery purely through the SmartSolar RS? Curious whether the absorption settings can be tweaked low enough to make it viable, or whether you always need an intermediate step.

@ValleyOffGrid the RS 450/100 is very much overkill for trickle charging, but it'll handle it fine — Victron's BatteryLife algorithm does a decent job of managing low-SOC situations without hammering the cells.

The thing people miss is setting the absorption and float voltages correctly for your battery chemistry. Get those wrong and you're not "trickle charging," you're just slowly cooking your bank.

What battery are you actually running? If it's lithium (Fogstar Drift or similar) the RS will talk to it via VE.Smart networking and handle it properly. Lead-acid is more hands-on to configure.

My 150/60 on the shepherd's hut sits doing next to nothing most of winter and I've never had a problem, just had to tweak the float voltage down a touch.

@ValleyOffGrid worth noting that the RS 450/100 uses a different architecture to the standard SmartSolar range — it's a synchronous buck converter rather than the traditional design, so behaviour at very low loads can differ slightly.

That said, I ran my 150/85 at trickle levels all winter on the motorhome when it was parked up, and Victron's low-current handling is genuinely solid. Set a proper float voltage for your battery chemistry and it'll just sit there doing its job.

The bigger question is why you'd use a £600+ controller for trickle duties. If it's already installed and handling your main array, great — let it do both. But if you're buying specifically for trickle charging, a SmartSolar 75/15 would do the same job for a fraction of the cost.

@ValleyOffGrid good point about the autumn scare — worth mentioning that the RS 450/100 has a minimum input voltage threshold to consider if you're running it in low-light or trickle conditions. The panel array needs to exceed battery voltage by a decent margin before it'll even begin operating, so if your panels are undersized relative to the controller you might find it simply doesn't engage at all during those grey winter mornings. Not a dealbreaker, just something to plan around. Also make sure your VE.Can network is properly configured if you're integrating it with a GX device — the RS series communicates differently to the standard SmartSolar units and I've seen folk catch out by assuming the Bluetooth app behaves identically. It doesn't, quite.

@PYQ_Power that minimum input threshold is worth expanding on — the RS 450/100 needs around 120V to wake up, so if you're running a modest string in winter UK conditions, you might find it simply won't kick in on overcast days. That's the real practical gotcha for trickle charging scenarios.

I had something similar on my shepherd's hut setup — not with the RS, but low-irradiance mornings in November meant my controller sat dormant longer than expected. Worth checking your Voc at low light against the controller's start voltage before assuming it'll top up your batteries on grey days.

The Victron VRM portal will show you exactly when the controller was active vs idle — genuinely useful for diagnosing whether your array is even feeding in during those marginal conditions.