Multiple MultiPlus inverters on main and sub DBs

Morning everyone. New user here. :wave:

I’m really enjoying reading posts here and learning things from all of you. I hope you can help with some questions I have regarding Victron MultiPlus inverters.

Here is some background about my property for context. The house and the garage are 50+ meters apart in my property. The garage has a sub DB connected to the main DB in the house via a 40 amp double pole isolator on each side. The garage sub DB contains an earth leakage, breakers for inside lights, outside lights, garage door openers, general plugs (for tools and a fridge), a pool pump and a wellpoint pump.

The garage also contains a wall mounted network rack with the fiber ONT, router, security gateway, a POE switch (for cameras, access points and a wireless bridge to the house).

The main DB in the house has the Eskom feed, an earth leakage, the usual breakers for lights, geyser, stove and plugs for all the usual stuff. The house has another POE switch for cameras, access points and the other side of the wireless bridge.

My wife and I both work from home full time so require internet to be running in order to minimise the disruptions caused by load shedding. That means I need both those POE switches, bridges, access points and internet gateways up during load shedding.

I used to have 2 x 1000 watt, 1200Wh standalone UPS devices with LiFePo4 batteries to run those loads. One in house and another in the garage to run everything we need. They worked great until a few weeks ago when the one in the house stopped working after a load shedding session. :cry:

I returned the faulty unit and got a full refund. So now I only have one UPS in the garage and even if I could get stock (which I can’t), I don’t think it’s the right solution for me going forward. I don’t really like extension cables running all over the place with UPS devices lying on the floor. The setup works OK in the house as everything I need to power is close together so could use a multi-plug but the garage was not so simple so had to run multiple extension cables all over the place.

We are going to be doing some renovations to the house in the near future and part of that is to create a space to deploy inverters, batteries and everything else needed for solar. I plan to use Victron MultiPlus-II 5000 inverters, the appropriate MPPT charge controllers, solar panels, GX devices and everything else needed to get that working.

Instead of buying a new standalone UPS, I am considering putting a smaller MultiPlus 1200, MultiPlus 1600 or MultiPlus II 3000 inverter and battery in the garage to act as the UPS for the critical garage loads to replace the UPS that is there. I would then get everything wired up correctly and it would both cleaner and safer. Then I can move the “old” standalone UPS currently in the garage to the house and use that until we do our renovations and deploy the solar kit with the bigger MultiPlus-II 5000.

I can easily do the garage side now but can only do the house side after the renovations as there is no real space in the house to install anything like inverters and batteries safely right now.

So, after that long preamble which has hopefully created enough context for my scenario, here are my questions:

  1. Considering the layout of the DB boards in the house, will there be any issues in having a different spec MultiPlus on each DB board when the house kit is deployed in a year or so? The house would have it’s own and the garage would have it’s own. They would be separate inverters with their own batteries and (presumably?) their own GX devices but the house and garage do share a common electrical connection via those isolators.
  2. There is an opportunity to deploy 3 or 4 solar panels on the garage roof to charge the batteries in the garage and provide power to the pool pump, wellpoint and everything else in the garage. Would doing this complicate things in any way or should I skip that and just do solar in the house? The solar opportunity in the garage would be much smaller than the one in the house as the roof space is much less but there is still some power to be generated on that roof - it’s a big garage.

Sorry for the long post. Hope you can help my decide what to do before I start looking around for kit and an installer for the garage equipment.


There is really no reason to buy a small Multiplus for your garage when the larger 5kVA should be able to handle both garage and home once it is installed in the home.
So if you know that is the way to go in future, just buy the 5kVA just buy it to use in the garage and then move that unit to the home and main DB when the renovations are done.

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The AC cabling is pre-existing and will already be rated for the current and the associated voltage drops.
Two independent systems will be extremely frustrating and result in a load-juggling nightmare.
If one roof is big enough for all the PV, @Louisvdw’s suggestion is suitable and I agree with it.

However, if you need both two roofs that are remote from one another to provide sufficient PV real estate then there will be a problem.
Then there is no pre-existing dc cabling and dc-coupling back to a single inverter will be an expensive proposition:
If this is your situation, I suggest a second AC-coupled inverter (at the garage) electrically downstream of a smaller hybrid inverter ( at the house).
This will be the most elegant and cost-effective solution and use pre-existing cabling whilst still allowing load-sharing flexibility.

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I did consider this but I’m not 100% sure the 5kVA is enough for both the house and the garage. I know that I can parallel the inverters if I need more power but am a bit worried about buying one now and then when I need to add another unit in the future then I can’t find a matching unit to create the pair. I have read in a few places that one must get the same model and they can’t be too far apart in terms of age due to natural component changes Victron will make to the line over time and then one has compatibility issues. Not sure how true this is?

I need to put a bit more time and effort into sizing the house side of things. I did a fair bit of measurement on the garage side to understand power usage. The garage getting it’s own inverter is appealing to me if it can work as that is a bunch of loads off the house inverter but it needs to work obviously. :slightly_smiling_face:

Not sure what you mean by load-juggling? Will each inverter not see themselves as grid connected and not really be aware of each other?

Never even considered an AC coupled inverter or micro-inverters. Thanks, I will do more reading on this possibility.

Welcome, Nullable.

When you grid-tie, it makes no difference when the loads exceed 5kva (4kw). Eskom supplements that.
When there is no Eskom, only then the 5kva may be enough, or not. You load profile “seems disciplined”.

Also keep in mind:
The bigger the inverter, the more panels … the bigger the battery bank required.

Just my 2 cents.

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If you are uncertain, then buy the GX device with 2x ET112 energy meters and monitor both location’s power usage. It will upload the data to the VRM cloud and you can review the past.

There is a few images of what you can see in my install page Install in the Southern Cape

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You stated you wanted to minimize disruptions during load-shedding.
So by definition, the inverters cannot see themselves as grid-connected during load-shedding as there is no grid during load-shedding,
That is when both systems will go out of phase with each other and have to function according to the individual generation limits of each system.
The two systems cannot be wired to share loads because of this lack of synchronism (even though the inverters will be in phase when the grid is present).
On top of this, the state of charge of each battery will have to be managed.

I believe this will become frustrating to manage very quickly on two small systems.

This contrasts with a downstream AC-coupled PV inverter that does not require a battery and will maintain synch with a battery inverter even during load-shedding. It will contribute to the loads and even charge the other inverter’s battery.
(Caveat: There are still rules regarding inverter sizing to be followed).

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@Nullable_Type , this is what Phil is saying. I had the same question a while back.