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Gavin avatar image
Gavin asked

Whole house backup through Multiplus II

Good Evening everyone,


I have been planning a system for ESS, and wondered what extra costs would be needed to make the system into a whole house backup.

My initial research shows that the Multiplus is capable in providing Pass-Through and UPS functions.

The plan would be to place a Multiplus II 5000va between the meter and the Consumer Unit. However the Grid feed is 100amp, and the diversity calculations on the CU come up at approx 75amp.

Is there an option to have an external ATS that can work alongside (or replace) the internal 50A ATS of the Multiplus.

I have a feeling that you are going to tell me to buy 2x Multiplus 5000va to run them in parallel for a combined 100amp PassThrough.


Many Thanks

Gav


Multiplus-II
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wkirby avatar image
wkirby answered ·
How are you splitting your loads up?

Even if you stayed inside the 50A passthrough but are over the ~20A capacity of the inverter then the inverter would be overloaded, shut down and not be providing the UPS function that you wish when the network goes black.
For backup UPS functionality, the inverter needs to be sized to accommodate all of the loads that you want from it.
So either split up your loads or think about a larger Quattro or yes, parallel two or more MultiPlus.

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Gavin avatar image Gavin commented ·

Hi WKirby,

Thanks for taking the time to comment.


There is no plan to split the loads. The CU is inside the house and would be too much work. The aim of the installation is ESS first.

Grid outages are a rare occurance here so this is not essential. Its more of an annoyance to me that I will have all of the components needed to power the house, but when wired in parallel they cannot function without power to AC-IN.

During an outage we could manually reduce our load to stay within the limits of the Multiplus.

In an ideal world I would just purchase an external 100A ATS which the Multiplus could control, but I am not sure if this type of solution exists.

Thanks

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wkirby avatar image wkirby ♦♦ Gavin commented ·

The the only option is to choose the product to suit your needs.

What about the older MultiPlus 5000 which does have a 100A transfer switch?
Only caveat that comes to mind is grid code compliance which these older units do not comply. This is only really a problem if you actually need ESS. For pure UPS functionality then you don't need ESS and then you don't need grid interaction and you don't need the grid compliance.
https://www.victronenergy.com/upload/documents/Datasheet-MultiPlus-inverter-charger--800VA-5kVA-EN-.pdf

If you do want to use ESS and the older units don't comply with your grid code then you need one of the new units the "II" units.
The you need MultiPlusII 8000VA which has a 100A transfer switch.
https://www.victronenergy.com/upload/documents/Datasheet-MultiPlus-II-inverter-charger-EN.pdf

Why no external ATS?
This is because it is almost impossible to guarantee current sharing between any given product and an external ATS. How much current goes through internal ATS and how much goes through the external ATS is completely unknown when the two products are unknown and almost certainly not the same resistance for each path.
This is why Victron locks the capability to use multiple units to only exact same models so that the current path is known to be the same resistance for the units and then the current will share close to 50/50 for two parallel units.

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Gavin avatar image Gavin wkirby ♦♦ commented ·

Thank You,

I'll check the specs of the 8000 model. This might be the simplest option.

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