Multiplus and Smart IP43 Charger in the same system

DIY
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1

I have a complete 12V Victron setup in my RV:

  • Four Smart Lithium batteries

  • Lynx Power In

  • Lynx Smart BMS

  • Lynx Distributor

  • Cerbo GX

  • BatteryProtect for the RV loads

  • Two MultiPlus 3000 units (because it is a US 50A split-phase RV)

  • Several MPPTs

I have discovered a few limitations with the setup.

Because I have two legs, the MultiPlus units can only be placed into Charge Only mode when connected to 240V split-phase service, not when connected to 120V single-phase service.

I also found that in normal inverter/charger mode, the lowest AC input current limit I can set is 7.5A. Unfortunately, my storage location only allows me 5A. There is a single 20A circuit shared between four RVs, so each RV is limited to about 5A.

That leads to my first use case: storage charging.

The second use case is boondocking and moochdocking. We do a fair amount of both, and I would love to be able to get more charging capacity than just 10A while moochdocking.

Here is what I am considering:

If I install a Smart IP43 Charger 12/50:

  • I could use it in storage because it should stay under the 5A limit

  • While moochdocking, I could plug it into a separate outlet and gain an additional 50A of charging into the battery bank

My question is:
Will this work properly in my setup, or will the Smart IP43 Charger and the MultiPlus units conflict with each other, even though everything is connected through the Cerbo GX?

2

A VE.Bus configuration setting can solve that

No problem, but the charger won’t be DVCC controlled so configure the charging voltages properly and it will be fine.

3

For transparency, this system was originally installed by Off-Grid Power Systems. Based on that experience I would prefer to get additional independent opinions from others familiar with large Victron split-phase RV systems.

Can others confirm whether running a Smart IP43 charger alongside dual MultiPlus units in a DVCC-managed system is expected to work correctly in this use case?

4

Charge-Only mode is only indirectly connected to having both phases present. The main point is if the mains is in an acceptable window. This also counts for On mode, since if the mains is not accepted the system will not switch to mains. One of those conditions is if every MP in the system has an accepted mains voltage present.

What Ed means with that is disabling the option “Switch units as group” in the VE.Bus System Configurator. This will allow the system to accept a single phase mains input. So you could connect to 120V mains, the respective MP would switch to mains while the other stays in inverting mode. It does have its drawbacks, for example depending on the load all the charge current that the MP with mains voltage can produce might be consumed by the MP without mains, leaving effective no charge current for the battery itself.

Just because the limit can only be set down to 7.5A does not mean that the system always consumes those 7.5A. At least i hope not, otherwise our interpretation of RV storage is vastly different. But for example theres also the possibility to limit the charge current in DVCC. This indirectly also helps to reduce the AC current.

What is this 10A, AC input limit? Why only 10A? It cant be an MP limit, so its an external limit, then i struggle to see how an additional charger helps with that, that 10A limit is still there.

Depends on how you define correctly. Does the MP system still work? Yes. Can the Smart IP43 charge the batteries? Yes. Can the batteries accept the full charge current of potentially 290A DC (2x 120A from the MPs and 50A from the IP43)? Possible, but you did not specify the exact battery type.

A Smart IP43 charger can not partake in DVCC, it will only use its own internal charge settings. So for example, it cant react to any current limit the BMS wants to see. Its possible that the BMS will reduce the charge current through DVCC because a cell voltage is getting high. Because of this, you would need to use the ATC output on the BMS to switch on/off the charger. Thats all the control the system then has, on or off, no gradual current reduction

5

When PowerAssist is enabled (the default), Victron has a minimum that the AC input current limit can be set. However, if PA is disabled the Multi will allow lower limits. We have NodeRed flows that we provide customers that quickly allow them to toggle PA, change current input limits, and set upper and lower SOC thresholds for Ignore AC to give them some ESS controls without running ESS. These NodeRed flows are presented via Victron’s Virtual Switch in GUI2.

6

Thanks, this explanation was extremely helpful. I think I understand the concepts much better now, although I may still be misunderstanding some aspects of how split-phase behaves when connected to single-phase shore power through a standard RV dogbone adapter.

What I am now trying to better understand is this:

With a standard 50A-to-30A RV dogbone, both L1 and L2 are effectively fed from the same 120V source, correct? If so, do both MultiPlus units normally see valid AC input and transfer/charge together even though true split-phase 240V is not present?

If that is the case, then I may have misunderstood the practical effect of disabling “Switch units as group.” I originally interpreted it as allowing one MultiPlus to accept shore power while the other remained inverting, but now I am not clear under what real-world conditions that would actually occur in a typical RV setup using adapters/dogbones.

My actual use cases are:

  1. Storage with a very limited shared shore source

  • The storage facility installed a single 20A circuit shared across four RV spaces

  • Technically that works out to roughly 5A per RV, but considering continuous-load guidance I am really trying to behave more like a good citizen and stay closer to ~4A continuous

  • I still occasionally want to use the RV normally for a few hours while there

  • I am fine with the battery bank carrying most of the temporary load

  • I mainly want the system to slowly recover whenever loads are reduced

  1. Moochdocking at friends’ homes

  • I intentionally limit what I pull from any single household circuit

  • My thought was that a Smart IP43 12/50 on a completely separate circuit could provide additional charging capacity into the battery bank without increasing the load on the primary shore connection feeding the MultiPlus units

  1. Supplemental charging while driving

  • Potentially powering the IP43 from the truck during travel days

  • I realize 50A DC is not huge relative to the system size, but it still seems potentially useful as supplemental charging

Regarding the DVCC side of this, thank you for pointing out the limitations there as well. I do understand that the Smart IP43 would not participate directly in DVCC current regulation and that the Lynx Smart BMS would only really be able to control it through the ATC output as an on/off mechanism.

I had already been exploring using the ATC output to disconnect AC power to a Blue Smart IP22 12/30 charger through an external relay/contact setup. However, once I priced out the relay components, enclosure, wiring, protection, and the additional installation complexity required to do that cleanly and safely, the total system cost and effort started approaching the cost difference between the smaller Blue Smart charger and stepping up to a Smart IP43 solution anyway. Once I also factored in installation labor at typical shop rates, the economics started favoring the cleaner integrated approach pretty quickly.

At that point, the Smart IP43 12/50 started looking attractive not simply because of charge rate, but because it potentially simplified the overall system architecture while also supporting multiple use cases.

That is part of why the IP43 seemed attractive to me:

  • higher charging capacity

  • simpler overall installation

  • more compact overall solution

  • fewer external relay/control components

  • potentially useful across multiple scenarios instead of solving only one narrow problem

At this point I am mainly trying to determine:

  • whether I am misunderstanding how the dual MultiPlus units behave on single-phase shore power in the first place

  • confirm whether the IP43 approach is actually a reasonable fit for these use cases, since it sounds like it may be

  • whether changing the VE.Bus “Switch units as group” behavior would materially help in these specific scenarios

7

I dont know, im european, to me feeding the same single phase voltage coming from the grid into both phase conductors of a splitphase plug is silly. But thats another discussion.

If thats how it works then im not certain how the system would behave once “Switch as group” is disabled. I assume it is the same behaviour as when only L1 has grid voltage present. That the L1 MP, which has the master role in the system, will synchronize to the incoming grid voltage, which then means that the slave MP on L2 has no acceptable grid anymore (becuase they are 180° out of phase) so the L1 MP would switch to grid while the L2 MP would remain inverting. Im sure @OGPS tried that already and can tell if thats true or not.

Thats correct

I think the main issue is that i misunderstood what single phase shore power practically means for you. I assumed that this means only L1 will receive grid voltage, not that you apply that voltage to both L1 and L2. It should not matter however, the outcome should be the same.

If its reasonable or not is something you have to decide for yourself, the technical limitations we already discussed, albeit not completely detailed since we dont know if the battery bank could handle the full 290A of all charging sources.

I think it would help in the case of single phase grid supply, but if you decide on installing the IP43 anyway, then personally i would try with that one first. Using the MPs grid connection when splitphase is available while only using the IP43 if singlepahse is available. Since disabling “Switch as group” can be done relatively easy down the line should you still see the need for it

8

That actually helped clarify something important for me conceptually as well.

North America uses a center-tapped split-phase system:

  • L1 to Neutral = 120V

  • L2 to Neutral = 120V

  • L1 to L2 = 240V

  • L1 and L2 are 180° out of phase

Most of Europe uses a standard single-phase system:

  • Live to Neutral = ~230V

So in the North American RV world, 50A service is 120/240V split-phase, while 30A service is 120V single-phase. A standard 50A-to-30A dogbone commonly feeds the same 120V hot onto both L1 and L2. That means both legs still see 120V to neutral, but they are now in phase with each other instead of 180° apart.

I am guessing the split-phase MultiPlus configuration is aware of whether the incoming legs are in phase or 180° out of phase, and that this likely influences some of the transfer and synchronization behavior.

What I am now wondering is whether keeping the MultiPlus units grouped together is actually important specifically because of this behavior.

My current thinking is that if both MultiPlus units independently saw the same dogboned 120V source and “Switch units as group” was disabled, there could potentially be situations where both units attempt to utilize the configured AC input limit independently, even though they are really sharing the same physical upstream source.

For example, if the AC input current limit were set to 10A and both units independently attempted to utilize that allowance from the same dogboned 120V source, total draw could potentially approach 20A and trip the upstream breaker.

So I am starting to suspect that grouped behavior may not just be about synchronization elegance, but also coordinated management of a shared upstream AC source in the North American split-phase RV world where campgrounds commonly offer only 30A service.

Historically, North America adopted 120V residential distribution very early, before higher-voltage residential systems became the global norm, and we largely evolved from there rather than fully transitioning to ~230V systems later.

9

Thats the easy part and known to me. The specific detail i was missing was that funny adapter.

Yes and no. The RV side of electrics is very much only single phase, but the grid as a whole, and how houses are supplied for example, three phase 230/400V is common as well. Depends on the country however. Some countries supply three pahse into every house no matter how small, some only supply industrial stuff with three phase.

Now we’re starting to mix topics. The AC input limit is only indirectly tied into this, and i would leave it away for now.

The fundamental thing is, if you supply the same voltage to both L1 and L2 MP, only one of them can use it. Theres no way both of them can use it at the same time, due to the 180° shift that needs to be kept on their outputs. Remember, once an MP has switched to mains, then both its input and output will be the same. Theres no way to let both use the same single phase grid voltage with essentially 0° angle between the two ACin, for both MP to switch to that AND to keep the 180° phase angle on the ACout. So the situation that could beg the question of “Whats going to happen if both share the same single phase input” does never happen.

10

You are getting into a very important distinction now, and I think your understanding is mostly correct.

The MultiPlus-II 2x120V models are somewhat unique specifically because they were designed around the North American RV and marine market, where:

  • true 120/240V split-phase exists sometimes

  • but pseudo-split-phase via dogbones is also extremely common

  • and many coaches distribute loads across two legs without actually needing true 240V loads

Here is a cleaned-up way to explain it to him without over-asserting anything that still needs confirmation:

I think I am finally starting to understand where some of the confusion came from here, specifically around the North American RV use case and the MultiPlus-II 2x120V models.

The MultiPlus-II 2x120V units seem somewhat unique to the North American RV/marine market because they need to operate across several very different real-world scenarios:

  • true 120/240V split-phase shore power

  • 120V single-phase shore power through 50A-to-30A dogbones

  • generator inputs

  • and pure inverter operation

In the North American RV world, many 50A coaches do not actually require 240V loads internally. Instead, they simply distribute independent 120V loads across two legs for balancing purposes.

What makes this interesting is that, during inverter-only operation, my understanding is that the two inverter legs are not necessarily behaving like a true utility-derived 120/240V split-phase source. Instead, each MultiPlus is effectively powering its own independent 120V leg from the shared battery bank.

However, when true split-phase shore power is present, the system can synchronize to and pass through a proper 120/240V split-phase input.

That distinction may explain why some of the RV-specific configuration options exist in VE.Bus System Configurator, including things like “Ignore phase rotation” and “Switch units as group.”

From the RV perspective, these systems have to deal with situations where:

  • both legs may receive the same 120V phase through a dogbone

  • both legs may receive true 180° split-phase shore power

  • or the system may be fully inverting with no shore at all

So I am starting to suspect the North American RV behavior of these systems is more nuanced than a traditional permanently-fixed split-phase inverter installation.

11

I know the difference between two MP running in 180° splitphase and a 2x120 model, which was never up for discussion here since you dont have one. Splitphase isnt that special, outerworldly concept some people make it to be, its just two phase with 180° angle instead of 120°. Feel free to continue here, but im done talking to chatGPT

13

My original post, without any cleanup:

“YOu are no talkign to ai, you are talking to a human that does a bad job typing and uses modern tech to clean things up and try to make their thoughts clear. i am very sorry for offending you. everything you have said compared to what information I can find, here in north america there is some way to set two 120v Multiplus into the same type of mode as one MultiPlus-II 2x120V. it sounds to me like you are saying that is not true, that is where my confusion comes from. I am simply trying to understand what is going on here and it seems nobody knows or is willing to help understand.”

I gave that to ChatGPT and said: Please clean that up for me, keep it tight because this guy doesn’t like AI, so I don’t wnat to burden him with too much reading, if he is willing to compare the two:

From ChatGPT:

You are not talking to AI, you are talking to a human that does a pretty terrible job typing and uses modern tools to help clean things up and make thoughts clearer. I am sorry for offending you.

Everything you have said generally lines up with the information I can find. Where my confusion comes from is that, here in North America, there appear to be configuration options that allow two standard 120V MultiPlus units to behave similarly in some ways to a MultiPlus-II 2x120V setup, particularly in RV environments where 50A split-phase and 30A single-phase service are both common.

It sounds like you are saying those are still fundamentally different behaviors and architectures, which is completely fair. I am simply trying to understand exactly where those differences are and how Victron expects these systems to behave in the various RV shore-power scenarios.

I am not trying to argue with you. I am just trying to understand the system better, and honestly some of the Victron behavior around North American RV setups seems difficult to find clearly documented.

At the end of the day, my goal is to put things out there which are easier for others to understand. I would love to know what about my AI cleaned up posts bother you. The reason I ask is because you are not the first person to push back on me trying to clean things up and I want to get better at putting out my thoughts that don’t offend others.

14

Sam, I will say - just be human. As most reasonable humans these days, no one in a technical forum such as this takes kindly to the use of LLMs in any substantial form, and we can all tell when it’s being used. AI hallucinates, lies, knows nothing at all, destroys the environment, encourages people to forget how to use their own brains, and is never entirely correct about anything.

Be human, learn as a human, interact as a human, and grow as a human. It’s okay if you’re a bad typer.