'UPS' function only, MP2 + 5kWh LFP battery, no PV

DIY
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Hello,

I’ve posted a few ideas earlier and taken on-board feedback, specifically using a 5000VA unit purely for its motor-starting capacity. I’m closer now to purchasing parts so just need a sanity check. We’ve already covered the load application in my older posts - a 1.25 kW (230VAC 5.2A) water pump that runs intermittently during rainfall. Power must be maintained to that under all circumstances without human intervention. There’s a backup pump but I don’t see that both would ever run together.

I’m happy that the battery is large enough from an energy perspective. I’m hoping it’s also enough for the MP2 from a start-up power perspective, that being 250ms.

The 5kWh 48V LFP battery will have a 125A fuse and 100A CB acting as an isolator.

In the PDF drawing it’s the stuff in the box at the lower-left that’s relevant, along with some house rewiring to exploit the UPS past just supporting the pump.

As I’ve explained in the drawing notes I’d like to use a generator-type ATS around the Victron AC input and AC-1 output to bypass it automatically if for any reason it’s not outputting AC when the grid is down. It’s the same switch model I use for my existing generator system and works well in that application. In this case the neutral is passed around it to maintain the MEN.

The MP2 will feed the existing generator/ATS system which will simply pass it through to the pump. In the case where no power is provided the generator/ATS will automatically handle pump power requirements. That system is proven but the long term goal is to remove it and rely solely on the MP2 and battery once I become confident of its reliability.

  1. I need to be confident the Victron application is feasible before I call my electrician as they will bill me for any time they spend on it. I’m fairly confident they will be happy with this wiring arrangement but doubt they know anything about commissioning an MP2. I’ll have a USB cable on hand and a PC with the config program. As best as I know my grid provider (“lines company”) requires an application to be lodged for every install but I know they already ‘type-approve’ the MP2.
  2. Legally I can’t use grid power for my own initial testing. As such, is it feasible to set the mains input to the non-specific setting initially so that I can test functionality (charging the battery, switching to inverter output, etc) using my (alternator-type) generator as an off-grid system?
  3. Once that’s done, my electrician would wire it to the house, configure it for “NZ-grid” and sort out the paperwork.
  4. As I’ve mentioned in my other posts my grid power is very reliable. If the MP2 is needed the pump will run intermittently, just 1 minute per each 3 mm of rainfall. I’m confident the cabinet cooling will be adequate even if it were in continuous operation.

29-06-2026 Block Diagram.pdf (4.4 MB)

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34 views and no one has anything to add?

All I really need to know is “can I set the grid to non-specific for testing” and then later, when the electrician connects it up, to “NZ” without any roadblocks?

There’s no local Victron expertise and I need to plan my installation before splashing out NZ$1600 for an MP2.

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Hi @KiwiME - I’m one of those lurking in the shadows, not commenting, and i’m not an expert, so here’s some comments:

  1. I find the block diagram confusing, specifically regarding what are inputs and outputs on the various devices. and what the signal direction is. I’ll try to give you some examples below. Usually there’s labelling of the specific wire (Live (or Hot), Neutral, Ground/Earth) and terminal connections. Also, the convention is usually schematics have a flow, top down, left to right.
  2. Relays - there are a few relays in this diagram. I don’t know where they get L/N exactly and what terminals and contacts are being used.
  3. The relay at E2 has “N.C.” which is probably Normally Closed, but I can’t tell whether NC is to the left or right. eg to the LED or the Fan temp controller. Where is Common terminal that feeds the N.O. and N.C.? Where is power to the coil, and what energizes it eg is it coil energized by the output of the MPII ? the Live coming in?
  4. With Geya G2R (at D2) - it looks like you’re using the grid as the least likely to fail, and the MP-II as the more likely to fail device. Why not let the MP II do its job? I reread what you’ve said a few times, and am not on the same page, so I figured I’d keep quiet :wink:
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Buzzy, thanks for commenting as it gives me some impression to what others are seeing.

This is just a block functional diagram to present the concept as it fits into the house wiring. Point to point switchgear wiring will be documented on another drawing once I settle on the design. I don’t really need feedback on the cooling arrangement, luckily that’s my expertise!

The GEYA ATS will connect the Victron whenever that source is present irrespective of grid power. If it sees power at the grid but not the Victron it will switch to the grid. If there neither are present it stays in place as it needs power to switch. I have one of these on my generator and it works well and has the correct EN standard required here, not too common with these cheaper switches.

I doubt anyone has used an ATS in this way but my application requires that power is always available to the critical load whenever possible and with no manual intervention. I’m confident this arrangement will work. If the Victron is reliable the switch will never change state. If I need to switch-off or remove the Victron, it will allow power to bypass without any re-wiring.

My major concern is how I can test the functionality of the Victron + battery with a spare pump before calling my regular and very-expensive electrician. There seem to be no electricians with Victron expertise available locally on this part of the island but if I can test the system off-line first then the rest should be relatively easy.

I read a post some time ago that the grid setting cannot be changed, once set. I need to set it to ‘no specific grid’ first to run it off my generator, then set to NZ-grid later when connected up by the electrician.

Thanks again for commenting.

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Here’s a (possibly bad) idea: Why not start your tests with the system configured as Off-Grid (not using ESS or Grid Code for Loss of Mains detection e.g. no power going back into the grid from AC In)? You could start with D1 MCB off, so no power gets into (or out of) MP II AC In.

That way you could check the batteries and inverter and can handle the pump starting current etc.

And you could always contact your dealer for the Password if you decide to set / change the NZ grid code.

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Ok, thanks, those are type of details I’m not familiar with and need to plan for.

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Its a long post, which makes it hard work. I think the issue is engagement.

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By default the Victron units come with no gridcode set, since thats what you would use in mobile or backup only installs.

A gridcode is only necessary if you want to feed energy back to the grid from the DC side. Since this is not the case here, you dont have to set a gridcode.

9

Im a bit confused as to why you put the MP2 infront of the ATS that switches the Genset.

So in this config, whenever the grid fails, the MP2 will take over, until the battery is empty, and then the genset will take over.

I personally would put the MP2 behind the Genset ATS and then use the genset start/stop from the MP2 as well. So in the event of a gridfailure, the MP2 will take over, and once the battery is low it will start the genset, to both supply the load and recharge the battery.

Optionally, you could use a Quattro instead. ACin1 from the genset, ACin2 from the mains, no other ATS needed (apart from the bypass if you really want that)

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A good question. I’d considered that logical option initially but I was told that I had to set the MP2 to “NZ-grid” in order to connect to our grid, even if I don’t export. I’m still not clear as to whether that is true but I do know our lines companies (the entity who deals with grid subscribers) is very fussy about this sort of thing since that safety is software/firmware-based.

Following that, if and when the diesel generator runs, I was told that the Victron would quickly disconnect the generator because the alternator output is relatively sloppy compared to grid power.

The solution offered was to use a Quatro which can handle both inputs. However the Quattro is not on the NZ type-approved list at this time even though it’s much the same as an MP2.

So, the next idea was to use a Deye 5kW hybrid inverter which has a separate gen input and is type-approved. It’s another NZ$1400 over the 5kVA MP2 and not well supported here. But another issue arises in that (by electrical code) the genset must be hard-wired to maintain the N-earth bond without leaving a live N pin at the appliance inlet, an oddity unique to NZ. The arrangement in the photo (which has a detachable genset) is allowable for a generator as it establishes a new N-earth bond locally.

But the reason I’m reluctant to go that route anyway is that the long-term intent is to remove the generator/ATS from use and rely solely on the MP2 + battery once I determine it’s reliable. I don’t really need the generator at all since my grid power is quite reliable. The battery has enough energy for what I need it to do.

Since the gen is already installed and signed-off, I may as well leave it in the system for the next year just in case something goes wrong. The way I have it wired after the MP2 provides that extra backup without complicating or changing the design of the MP2 system. Thanks for responding though!

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3FE290D8-324A-4406-85FA-F178E24D9575_1_201_a3213×5712 3.6 MB

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Yeah, I can certainly understand that but small details are what’s important in engineering. Thanks for commenting though.

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Thanks for your comment. My understanding is that my electrician need to apply for permission to connect the MP2 to the NZ grid and even if I’m not exporting. It would certainly be easier if that was not the case! I’d assume that means also setting the MP2 grid type to NZ.

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Thanks all for the recent comments. As suggested I’m going to test the MP2 powering the load off the battery first as that is the only aspect I’m not 100% certain about. If that works I can have my electrician go ahead with wiring the complete system to the house and make the grid setting once only.

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That’s understandable, but it’s also worth remembering that view count doesn’t necessarily reflect the number of people who are able to contribute. Of those 34 views, how many are engineers with relevant experience? And beyond that, everyone here is a volunteer contributing in their own time. As i mentioned its a long post.

Sometimes the right person simply hasn’t seen the thread yet, or those who have don’t feel qualified to comment.

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Thanks. I have a direction to follow now. I have the steel enclosure, a DC fuse and the battery is on order. I’ll order a DC circuit breaker/isolator, the MP2 48/5000 GX, a programming cable and AC switchgear in a few days. Will have to see about DC cables, may just buy a crimper as it’s not easy getting stuff custom made here.

I have a spare pump to load-test the inverter + battery. If that passes I can wire the switchbox and call in the electrician. I was hoping to be able to also charge the battery off my generator (off-grid) but don’t want to mess up the grid configuration just for that.

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While thats possible due to NZ regulations, theres no technical reason from the Victron side. The MP (with no feed back to grid) is simply a load to the grid, just like the pump is.

I also need to apply for permission to connect an MP to the grid when its done with a solid connection, but if its not exporting then its a load and permission is only necessary due to the rated power.

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Thanks for the clarification. In your case would you need to configure the grid setting to your provider or can it be left as non-specific?

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No, since its a load, there is no gridsetting. Installing a 3kVA MP would be the same as installing an additional 3kW oven/hob or something (or exchanging an old oven by a new one with higher power rating)

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Hi Paul, Radek here.

I’ve read your " system description " and had quick look at your diagram too.

Seem to me that you’re enough capable of such design, so I wouldn’t try to dispute what you’re doing and how.

I live in Banks Peninsula and from your description I’m getting that you’re also based somewhere down here in South.

What I would like to do is offer few views from my side. Firstly I need to indicate that I’m minimalist while finding solutions and always trying simpliest approach.

1 - for your load needs (as described) I’d go with MP2 /3000 which is capable of surge capacity of 5.5 - 6kW , and lot cheaper then 5000 too.

2 - as someone here already recommended, would use MP2 internal switching capability ( without GEYA - for simpler/ more reliable design ), and if you really need device to bypass MP2 for maintenance, use manual changeover switch

3 - crimped high current cables made to order I’m getting from here, and they have fast reasonably priced service, perhaps they may have solution for you too

4 - regards of testing your system before permanently connecting it to NZ grid, I would use isolating transformer, seem no need to mention for it to be sized appropriately.

Have nice evening

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Hi Radek,

Thanks for taking the time to look through my plans. I’m actually in Napier but did live in Christchurch for 5 years while slogging my way through engineering school long ago. I also enjoyed exploring the unsealed roads around Banks Peninsula on my trail bike back then, 1975-76. I do remember having to stop and unfreeze my mittens on the bike’s muffler as it was quite chilly in winter. It’s hard to imagine that it was 50 years ago.

I’m all about simplicity as well and when I get a bit overwhelmed I do try to reduce the scope of the problem, which I’ve done in the attached schematic. I could do a lot of useful things with this system but I’m trying to restrict it to only supporting the stormwater pump. My grid supply in the Napier CBD is quite reliable but having a pump operable at all times is critical for my two ground-floor retail shop tenants as there is no natural drainage.

Regarding the MP2 sizing, I was originally considering the 3kVA but advice here in my first post led me to the 5kVA. As you have seen I’ve measured the pump draw (a dry start) at 23A for 250 ms. There are 2 identical pumps but I don’t expect more than one to run at any time since each has more than enough capacity to cover the highest-likely rainfall rate. The second is considered a backup.

The LFP 5 kWh battery is spec’d at “50 A recommended, 100 A maximum discharge”. It’s already on order and expected any day now.

Looking at the basic power conversion and (optimistically) assuming 95% efficiency, that’s (230/48 x 23)/0.95 = 116 A at the battery for 1/4 second.

So, I’m already in trouble with the battery rating and to get past that can only rely on:

a) DC-bus capacitance,
b) some time-based wiggle-room in the battery rating,
c) or power limiting from the inverter allowing the motor to start slower.
The next size battery, 10 kWh, would fit in the box if it came to that but for one-third of the cost I could fit a smaller pump.

Regarding MP2 capacity, specs for the 3kVA unit indicate peak power is 5500 W, say 24 A, just enough, although the fault current rating of 32 A for 1 sec suggests that it would be fine. But the maximum rated battery discharge current of 75 A is way too low, only relating to 15 A at the pump where I need 23 A.

At least the 5 kVA MP2 can pull 100 A out of the battery and provides a better chance. Essentially that’s how I got pointed to that model.

Since just about any appliance that natively starts a 0.75 kW motor would have similar startup demands, and I don’t see many complaints along that line, one or more of the above points must be coming into play.

Regarding the use of the ATS, what led to that is the understanding that if the MP2 is ‘off’ the incoming AC is no longer transferred to AC-OUT1. That risk is unacceptable and the ATS nicely cures it for about $100. The key is that there may not be anyone around to flip a manual switch. The ATS also has a manual setting, but not the centre-off typically found in a bypass switch.

I’ve got the two software applications installed and will familiarise myself with the settings. I’ll probably order the MP2 5kVA in the next few days as I don’t see that I have any other choice than to carry out a test and deal with the results.

Thanks again for your input!

Paul

Specific considerations.pdf (7.6 MB)