stijn avatar image

Expanding an off grid system

Hey all!

New to this. Have an off-grid system with a Phoenix MultiPlus Compact 24/1600/40 and 4 Victron AGM 12V 220Ah. 2s2p. This is equipment from 2008 so the batteries are getting old. I ordered some 2V traction batteries to replace them. I would like to have more power though...

So I was thinking of buying a MultiPlus 48/5000 to use the old AGMs in a series setup until they are completely dead and replace them later on with more traction batteries. I would also buy extra panels and extra MPPTs to be able to charge everything. I would connect all the solar to the 48V AGM battery bank and its 48/5000 and wire the AC-out of the 48/5000 to the AC-in of the 24/1600/40. A cascading setup. Can I do this? Or would the 24/1600/40 try to charge the 48V battery through the AC-out of the 48/5000? Can you disable this? If I also buy a Venus GX, could I monitor and control both with one device?

Any suggestions?

cascading inverters
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3 Answers
wkirby avatar image
wkirby answered ·

A cascade is not going to provide you with much benefit. The 48V Multiplus is going to be permanently charging the 24V one's batteries. If you take 1600W off the 24V Multiplus the 48V one will have to supply that power plus losses. I can see what you are trying to do though, keep good equipment working. You'd be better off running them independantly for different purposes. Naturally this would mean splitting up MPPTs and solar strings, it starts to get complicated.

48V is the way to go though, would you not consider selling your old Multiplus to fund new kit instead? Which brings us to the question about monitoring your old Multiplus. Probably not if it has 18xxxxx firmware, then no, not at all, 19xxxxx firmware, yes with limitations. The limitations will annoy you next to your new shiny 26xxxxx firmware in your 48V Multiplus.

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stijn avatar image
stijn answered ·


Thanks for your reply. I am bound to the 24V system by a 24V wind turbine. I left that out as the question was getting long already. I would love a 48V system but it would mean selling everything and starting all over. Waste of money. I'll consider running two separate systems. Sad I cannot find a good use for the AGMs.

The reason I thought about this is that the 1600VA from the 24/1600/40 from PowerAssist plus the 3600W pass-through from the 48V system would give me a nice powerboost, without stretching any of the two battery systems. During the day this wouldn't be a problem if I feed in enough solar to the 48V system. At night would be different as I would just drain the 48V system trying to recharge the 24V system. Maybe I could install a switch to switch off the AC connection between the 2 at night?

On more thing, would the 24V system try to charge the 48V system through the AC-out of the 48/5000? Thought I read this somewhere in connection with AC-coupled Fronius inverters. That would be an option too to get more power...

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Hello, It could be worth thinking about reliability through simplicity.

Why not boosting your wind turbines 24V to 48V? It would be really interesting how your wind turbine is implemented in your system.

Best Regards,



The wind turbine is connected directly to the battery which is protected against overcharging by a Morningstar TS60 in diversion charge control mode, i.e. before 29,6V it starts dumping current into a dumpload and if/when it reaches 29,6V all electricity generated is dumped into the load. Looking into changing this resistor to an immersion heater. The windturbine maker, FuturEnergy, even sells one specifically for this purpose. Will change the setting on the TS60 to 28.8V so that I can use the electricity from the solar as well, right before my batteries go into absorption.


The Morningstar TS60 is capable of 48V, according to quick specs.


The TS60 is not an issue as you stated. The issue is the turbine itself, it is winded for 24V. So with a DC-DC converter which I could put between my turbine and a 48V battery, it would work. Would loose 10% though...

We did some kind of X crossing here ;o)

Yes we did! Thanks for helping me out! Much appreciated!

One more would I raise the turbines voltage?

Could use this...

Wind turbine is a 1000W. Wouldn't that be very inefficient? 90% according to the datasheet...

You would need a generator producing a higher voltage, well this might not be the most expensive part of the wind system. ...just thinking.

A DC converterter is not 100% efficient, but it could be worse. Depending on model...

Don't really feel like taking apart a perfectly working wind turbine, cutting through the perfectly-sealed, weather-resistant housing to get to the generator...if I do this it will be a converter I guess...

...and you maybe need another dump load solution too, when changing the generator.

I would indeed. Thinking now of just keeping the 24V system as it is and adding a grid tie solar inverter, like a fronius. Any idea what happens when you connect them to the AC-in? I only read about the AC-out. I assume the 1:1 rule still applies, so again my weak inverter might limit me here, but are there any other drawbacks you know of? Thanks!

Of what kind of drawbacks do you think off?

As said, the 24V inverter is old. Maybe I can not get it to work with the Fronius. I might have to use the frequency shifting option, even if I attach it to the AC input...don't know...

Elimac avatar image
Elimac answered ·


I have a similar plan myself!

I currently have a 24V system with 3kva Multi and OPzS 500Ah battery bank. The system if off-grid, but I can charge from grid if necessary, so the AC-in is connected to my grid supplyer.

The house is divided in several circuits, each with its own MCB. I diverted many circuits (lighting, IT, TV, etc) to my offgrid system, while maintaining higher-load circuits still on-grid (whasing machines, motors, etc).

I intend to get another Multi, this time 48V, new battery and have its own MPPT and Venus device. The AC out of this new system would go to a new MCB board, but one circuit would feed the older Multi.

Now, the important thing is how to program the behaviour using the "ignore AC" switch of each multi and also make the second one (in the cascade) work sometimes in passtrough (not charge bank, just let AC flow in to out). So, during sunny days, each Multi would have no AC on its input. In the night, I could make the first work from grid (charger enabled) and pass AC to second (charger disabled). After 1st bank charged, I could enable 2nd unit charger and charge the older bank. I could also not enable the AC in of first and charge the 2nd bank from the 1st, but seems rather silly...

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@Elimac Aha! That is interesting. In software there is an ignore AC switch? Or do you hope there is one? I have no acces to the VE software for the moment so i can't check for myself but that would open up some nice possibilities! I hope all the things you plan to do are programmable! For instance, is it possible to program a MultiPlus to be just inverter during the day? Or to be just charger at night? Thanks for the reply!

What I would love is to have charger/inverter during the day and just inverter at night. If I would program the second downstream MultiPlus like this, I could charge the batteries during the day with solar, while enjoying the extra power that the pass-through function and the PowerAssist function give me. At night I would just use both battery banks without one trying to charge the other one...problem solved...or am I missing something?

Yes, I am doing just that! My multiplus is inverting only in daylight and charging at night + AC passtrough. This is in Winter with long nights. In the Summer I may let it invert 24/24h.

There is the AC ignore switch in VE configure options (Virtual Switch tab), but I am currently using assistants:

And using the following manual:

I think it could of use to you!

1545496014077.png (17.8 KiB)

Anyway, I think the missing link to your desires is to put Victron in passtrough only mode. There was a way to do that in Venus, I have submitted a question about it recently, it can also be of your interest:

With these two pieces of information toghether, I think you could be pretty close to what you want.