question

I think you could set one up to be the "Grid" for the other. You'd want to disable charging for the slave though, otherwise it would use AC from the primary to charger the batteries they are both using.

Essentially both are standalone, then set the relay on one ot turn on or off the other as needed using the assist.

This is just an idea, I could be very wrong headed on this.

Hi,

Thanks @Elimac for starting this topic, I landed on this page as I was looking for more information on such a setup.

Indeed, I have similar requirements for my boat with electric cooking, wanting to have the benefits of redundancy, flexibility and reducing the standby consumption to a minimum: as written in the manuals, parallel operation has the disadvantage of disabling the low-consumption search mode. The idea was to have one inverter always on in search mode for every day use and then to turn the other one on when cooking.

This is the answer I got from a Victron representative when I asked if switching from parallel to standalone mode would be easy to do on the fly and what would happen if one of the 2 Multis in parallel was switched off :

Unfortunately, what you are asking is not possible.

Setting up a system for parallel operation requires changing several software settings in both the master and the slave after which they can be parallel connected.

The process cannot be automated.

If you switch off a slave in a parallel system, the master will shut down in fault mode.

One possible solution would be to split your loads into groups that are powered by an appropriately sized inverter (e.g. if there are light load electronic equipment, you could power these from a small inverter)

This solution does not really suit me as this would mean that I would not be able to take advantage of the 'smaller' inverter to power the high loads as well, leading to a bigger inverter on the high load side. I don't like having 2 separate AC circuits on board either.

I insisted that my request was passed to the engineers for a possible future improvement (however I don't think it will happen shortly if it happens!).

When asked about the 'serial' configuration suggested by @neondeddy the answer was:

You are not the first to ask about this configuration.

The answer from Victron remains unchanged: the MultiPlus is not intended to be cascaded like that and you may get unexpected behaviour.

Basically it is an untested configuration and Victron do not endorse it as a proper way to use the product.

It is therefore clear - and understandable - that Victron will not guarantee it will work this way.

However, it looks like some people have successfully used this setup. Here is a video where the owner explains how he has put 2 Quattro 5000 inverters in series without mentioning any issue about it (from 9min onwards if the timestamp I added to the video url below does not work), except that Victron does not recommend doing it:

In the end, I can't see why it would not work, and seeing a working installation is encouraging. The advantage would be that you don't need to have exact matching inverters, and the one that is always on can be smaller than the 'secondary' one. I imagine that the caveat is to be able to play with the power assist current threshold in case the big inverter heats up, or set it low enough so that it never does...