question

johnsmith avatar image
johnsmith asked

2 x Multiplus 48/3000 vs 1 Multiplus 48/5000 UPS off Grid, generator option

I already have a spare Multiplus II 48/3000.

Apart from the obvious reasons is there any reason to favour 1 Multiplus II 48/5000 over 2 x Multiplus II 48/3000 in parallel? This is for a single phase application as a UPS backup function for whole house, with charging battery bank from grid when power resumes, also have MPPT DC PVs off grid to charge bank during day.


This will be for a small house with 800W continuous load, peaking at 4000W for 15 minutes and occasionally 8000W for 30 seconds? the property has Gas mains and LED lighting, LED TV etc, , so the electrical loads on average are not huge.


1. I either buy another Multiplus II 48/3000 and put into parallel with existing unit I already have.

2. Buy Multiplus II 48/5000 and use stand alone with possibility of buying another Multiplus II 48/5000 in the future for parallel operation. Using the Existing Multiplus II 48/3000 to charge the battery bank independently off grid with with generator, also giving me independent single phase for any other dedicated circuits.

3. Continue with adding up to 3 Multiplus II 48/3000 in parallel if needed.


I like the idea of redundancy as I know Victron equipment will be getting harder to find next year when load shedding starts and would not like to be down if a dedicated unit fails and leaves me with no power until the unit is repaired or I can buy another (if available).


My experience in life always tells me that multiple smaller ones are always better that 1 big one!

I would prefer opinions from people who have had actually done the install and have it running and have experience of the real life pros and cons.


cheers




Multiplus-II
2 |3000
Toggle Comment visibility. Current Visibility: Viewable by all users

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

2 Answers
Kevin Windrem avatar image
Kevin Windrem answered ·

Parallel systems are much more complicated to set up. All wiring must be same length to properly load share. In a failure situation, the failed unit must be completely removed from the system and the remaining unit reconfigured for solo operation. Switches to isolate the AC input, AC output and DC connection to each Multi would be needed, but then you'd need to reprogram the Multi.

When starting from scratch, I'd recommend a single, larger unit over a parallel system if reliability is the goal. In your case, you already have one unit so the choice is more complicated. You need to consider the revenue for selling the existing unit.

1 comment
2 |3000
Toggle Comment visibility. Current Visibility: Viewable by all users

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

johnsmith avatar image johnsmith commented ·
@Kevin Windrem Just bought a 230V MPII 10K. 100A transfer switch and no overhead to worry about. Thanks for the input.
0 Likes 0 ·
Kevin Windrem avatar image
Kevin Windrem answered ·

With grid, the Multi will pass power up to the preset AC input current limit and the inverter will ADD to that to supply the load. Assuming a 120 volt system, the Multi 5KVA will supply at most 40 amps so with an input current limit set to 30 amps, you loads could pull up to 70 amps. If at that point, the grid fails, the inverter will attempt to supply all 70 amps. It will do so for a short period of time until an overload or battery drops below its low voltage threshold. The Multi will then shut down. No damage will occur. What constitutes an overload is not easily to specify in a data sheet. Here is a detailed description of what constitutes an overload:

https://www.youtube.com/watch?v=4SXtGIx0x5w

You can manage overloads to some extent by connecting some non-critical loads to the AC 2 output. This output will receive power only when the grid is present. That's the default behavior but you can add "assistants" to the Multi firmware to provide additional control.

2 |3000
Toggle Comment visibility. Current Visibility: Viewable by all users

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.