Joos Louw avatar image
Joos Louw asked

Multiplus II 5000 Application and Questions


I'm planning and understanding what I need from a high level design before I start talking to qualified installers in my area.

I'm in Cape Town/South Africa and we have load shedding daily and outages between 2-8 hours a day. So I'm looking at a MultiPlus II 5000 GX, MPPT RS 450/200, 1 or more 51.2V 100Ah LiFeP04 batteries with onboard BMS (Victron compatible) and ±15 x 545W PV Panels totaling ±8kW max output.

Working from home I want to design/split my load circuits into 3 categories, Critical Loads (Office, IT equipment, Fibre, WiFi and networking with average 1.4A max 2.5A), Essential Loads (Lights, house power points, small appliances, fridges and freezers) and Non-Essential Loads (Pool pump, geysers, heat pumps, aircons).

My idea is that I have my Critical loads on ACOut1, Essential Loads on ACOut2 and Non-Essential on the same circuit as ACIn.


  1. Can the ACOut2 relay be controlled to switch off if no grid, no solar and battery SOC is say less than 30%? That way I can keep at least my Critical loads running off battery a little longer.
  2. Is there a benefit of having a MultiPlus II + Cerbo vs Multiplus II GX?
  3. In this configuration, can excess solar be used to supply the Non-Essential loads to save on grid or alternatively feed-in to grid (with the correct meters and approval)?
  4. The MPPT RS spec on its DC Output charging power is confusing. 4kW per tracker but its max total is 11.5kW. Can someone explain this? I assumed the 450/100 will be to small for my application?
  5. On the City of Cape Town approved inverters dated 2023-01-06 (link below), the MultiPlus II 5000 is listed but not the GX model. Compared to the MultiPlus II 3000 GX where both models are listed. Is the 5000 GX in the process of being approved or can you consider the 5000 and 5000 GX to be the same inverter model with just the addition of the GX functions?

Thanks in advance

City of Cape Town approved inverters 2023-01-06

Multiplus-IIESSmppt rs
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2 Answers
nickdb avatar image
nickdb answered ·

Sign up to and go through the tutorials, it will provide a good overview.

A dedicated cerbo is better as it has better connectivity and performance, there is next to no difference in cost.

By default AC2 drops with loss of grid.

Batteries are the most important part, 100AH is way too little for that inverter, it is about discharge/charge current, not capacity.

Use the mppt sizing tool on the victron site to help with your mppt's.

There is no difference with the GX variant, it is the same inverter and thus certified, it just has an embedded GX in the chassis.

A good installer (use victrons site to locate one) will help you through all of this.

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Joos Louw avatar image Joos Louw commented ·

Thanks nickdb.

I watched most videos in professional training sections.

I know the default setting of the ACOut2 is off when grid fails. My question is can you program it to only drop out when grid out and battery SOC is less than XX%. I did watch Victron videos on the ESS and relay assistants, but they only briefly mentioned the ACOut2 relay can be programmed but no detail on what criteria can be used.

Regrading your comment on battery, I stated “1 or more”, but noted.

I used the MPPT calculator but it seems to have incorrect specs on the SmartSolar RS models. It uses 80A as max MPPT output current vs 100 or 200A as per the datasheet.

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nickdb avatar image nickdb ♦♦ Joos Louw commented ·
You can use relay assistants to control AC2 OUT. It was something I was going to tinker with but I eventually decided to use smart switches/timers etc and control that via Node Red (if needed). Then everything can be left on AC1 so you have the option of using it when there is excess solar etc.

I just find assistants too rigid as they aren't easily adjusted remotely and many aren't well documented.

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Joos Louw avatar image Joos Louw nickdb ♦♦ commented ·
Thanks nicdb, that is a different take on the problem. I will keep it in mind.
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daniel-feist avatar image
daniel-feist answered ·
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Joos Louw avatar image Joos Louw commented ·
@Daniel Feist these are very informative, thank you.
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