Recent changes to the Factor 1 rule

Been reading through the updated Victron docs on this and noticed they've quietly revised how they explain the Factor 1 rule — specifically around whether you're working from the VA rating or the actual watt (real power) rating of your inverter/charger.

Previously I think a lot of us were just looking at the kVA figure on our Multiplus and using that as the baseline. The updated guidance seems to anchor things more clearly to the real power output at 25°C, which does actually make a difference depending on which unit you've got.

For my setup on the static — running a Multiplus-II 48/3000 — it's not a massive shift in practice, but I can see it causing confusion for anyone sizing a system from scratch or deciding whether they need to upsize their inverter/charger to accommodate a larger battery bank.

The practical question I keep coming back to is: are most people here sizing their charger capacity based on VA or watts? And has anyone had to reconsider their battery bank size (or the inverter itself) off the back of reading the revised page?

Feels like one of those things that's always been a bit ambiguous in Victron's documentation and they've tried to tighten it up — but I'm not sure the new wording is all that much clearer for someone coming to it fresh.

Worth discussing, especially for anyone planning a new build or an upgrade over winter. Curious whether installers are seeing this come up with clients too, or if it's mainly a DIY concern at this point.

@Lee1996 the distinction matters enormously in practice. Victron have always been a bit cagey about whether Factor 1 applies to the VA rating or the actual watt output of the inverter, and the revised documentation does clarify this — but only if you read the small print carefully.

On my narrowboat I have a Multiplus 12/3000, which is rated 3000VA but realistically delivers around 2400W continuous. Factor 1 means your battery bank should be at minimum 3000Ah at 12V using the VA figure — not 2400Ah. Victron's support confirmed this when I queried it directly.

The critical bit most people miss: this is a minimum recommendation to prevent the charger overwhelming the battery's acceptance rate, not an optimisation target. What specific revision in the docs triggered your question — was it the section on parallel configurations?

@Lee1996 @DefenderAdventure — worth clarifying that Factor 1 is applied against the inverter's VA rating, not the apparent power of the load itself. Where people get caught out is assuming their charger's power factor corrects the equation in their favour — it doesn't, at least not from the MultiPlus's perspective.

In my shepherd's hut build I sized accordingly: 3kVA Multi, max 3kW charger input. No exceptions. Victron's position has always been that exceeding this risks the transfer relay, regardless of what your actual watts are doing.

The revised documentation does seem to soften the language slightly, but I'd treat that as clarification rather than a loosened restriction. If Victron support tell you otherwise in writing, brilliant — but I wouldn't deviate from the 1:1 ratio based on ambiguous wording changes alone.

@LesWood78 got there before me on the VA point, so I'll spare everyone the repetition.

What I will say is that this bit me properly when I was building out my van setup. Had a Multiplus 12/3000 and assumed I had headroom I didn't. Ran the numbers wrong, charger went into protection, took me an embarrassing amount of time to work out why.

The revised Victron docs are actually clearer than the old ones if you dig into the footnotes — they've been more explicit about apparent vs real power in the context of Factor 1 compliance. Whether that's because enough people were getting it wrong or some regulatory nudge, I couldn't say.

Point is: always work from the VA rating on your inverter spec sheet, not whatever figure you've got in your head from the marketing blurb. Learned that the hard way.

Cheers @GafferTapeKing — curious what you were about to get into there before you cut yourself off, because I think the bit that often gets glossed over is the practical consequence when you're running a charger with a poor power factor.

Your actual usable charge current can end up noticeably lower than the nameplate suggests once the inverter/charger is doing its sums against that VA ceiling. I've seen people scratching their heads wondering why their 30A charger isn't pulling 30A when the Factor 1 limit is the culprit.

@Lee1996 — which specific part of the updated docs flagged this for you? Worth knowing if Victron have actually changed the guidance or just reworded something that was always there.