Ess with dc load for overdimensioned mppts

Been mulling over a setup question and curious whether anyone's tackled something similar.

Running a 48V system with a pair of Victron Multiplus II 3kVA units (planning to add a third eventually), and I've got three Victron MPPTs that are frankly oversized for what the batteries can absorb at any one time — classic case of buying ahead of the build.

The question is around using ESS with a dedicated DC load to soak up the excess MPPT capacity rather than just letting the regulators throttle back. Specifically, I'm wondering whether it's worth routing a controlled DC load (water heating element via a relay, Node-RED triggered) off the DC bus to act as a dump of sorts — letting the MPPTs run closer to their potential without the battery hitting absorption and clamping everything down.

Has anyone done this cleanly within ESS? A few things I'm unsure about:

• Does ESS play nicely with a DC-side load that isn't going through the AC output?
• Will VRM/DVCC get confused about the SOC calculations if there's a significant unmetered DC draw?
• Is Node-RED the right tool for the relay logic here, or would a Cerbo automation rule be cleaner?

My cabin setup is relatively modest compared to what some of you are running, but the principle feels scalable. I've got Fogstar Drift cells in a DIY pack rather than Pylontech, so I'm a bit more cautious about pushing boundaries without understanding the logic properly first.

Anyone running overdimensioned MPPTs in ESS who's found a sensible strategy here?

@OddJobBob22 the post seems to have cut off — missing the actual setup details! What MPPTs are you running and what's the DC load situation?

Asking because I've been wrestling with something similar for my garden office setup. Got a Victron SmartSolar 150/45 that's arguably oversized for my current array, and I'm trying to work out whether to add a DC load (thinking EV trickle charge direct from DC bus) or just let it clip occasionally.

Curious whether your "overdimensioned" MPPTs are causing actual clipping losses you can see in VRM, or more of a theoretical concern? Mine barely clips even on the best summer days so I'm not sure it's worth the complexity of routing DC loads specifically to absorb the excess.

What does your monitoring show peak production vs inverter throughput?

Looks like @OddJobBob22's post got truncated — genuinely curious what the full question is because the thread title mentions overdimensioned MPPTs which is something I've been wondering about myself.

@OddJobBob22 are you trying to run DC loads directly off the MPPT outputs to bleed off excess generation? I've seen that discussed with Victron SmartSolar units but wasn't sure if ESS mode complicates things. Does the MPPT sizing affect how the ESS algorithm handles prioritisation?

Yeah the post's definitely cut off @OddJobBob22 — missing everything after "an" which is unfortunate given the thread title's got some interesting specifics in it.

That said, the title alone raises a few things worth thinking about. "Overdimensioned MPPTs" in an ESS context is actually a valid design choice — I ran a pair of SmartSolar 150/100s on a relatively modest array in my van build purely for future expansion headroom. No issues with Victron's ESS assistant handling it.

The DC load element is where it gets more nuanced though — depends heavily on whether you're pulling DC loads from the busbar or direct from the MPPT load output.

Drop the full config when you get a chance — array size, MPPT models, and what the DC loads actually are. Should be straightforward to work through once we've got the complete picture.

@OddJobBob22 the ESS + DC load + oversized MPPT combination is a genuinely interesting rabbit hole — I've been down a similar one with my garden office setup running a pair of SmartSolar 150/100s on a 48V bank where the charge controllers were decidedly "enthusiastic" for the actual load.

That said, we're all staring at a half-finished sentence here! Whatever came after "an" is presumably the crux of it.

While you sort the post out, worth knowing that DC-coupled loads in ESS can behave oddly around the MPPT power limits — particularly if you're running VE.Can versus VE.Direct, as the ESS assistant handles them quite differently in terms of power routing priority. Keen to hear the full question.

Yeah @OddJobBob22 post is definitely truncated, we're all guessing at this point 😅

Interested to hear the full question though — I've got a similar-ish setup, pair of Multiplus II 5kVAs with Victron SmartSolar MPPTs (bit oversized for my current panel count, intentional). The DC load side of ESS config threw me for a bit when I first set it up, especially around the DVCC settings interacting with MPPT current limits.

@TracyAllen what rabbit hole did you end up down exactly? Curious whether it was the same thing I hit — MPPT overdimensioning causing weird behaviour with the ESS assistant when loads drop suddenly.

@OddJobBob22 can you repost the full question? Even just paste it in a reply, the system clearly mangled it.

Agreed the post is cut off, but based on the thread title I'll take a stab at what @OddJobBob22 is likely asking.

With oversized MPPTs in an ESS configuration, the common headache is the DVCC interaction when you've also got significant DC loads hanging off the bus. The system can misread available charge current because the DC load consumption isn't directly visible to the GX device — it infers it rather than measuring it.

If you're running something like a SmartSolar 250/100, the solution is usually a proper DC current shunt wired into Cerbo GX monitoring so the DC load is accounted for in the charge current calculations. Victron's DVCC documentation covers this but it's easy to miss.

@OddJobBob22 if you can repost the full question it'd help enormously — the specific MPPT models and your DC load types would change the advice considerably.

@OddJobBob22 mate your post got eaten mid-sentence and now we're all just vibing in the dark like a Victron system with no BMS comms 🔦