Axpert invertors

[superdiy]

A while ago I had another idea which is unfortunately flawed, but maybe it sparks something else.

I thought of bonding the input and output neutral. Since the output floats I am pretty sure you can bond the output neutral to the input and it also takes care of the grounding problem both on batteries and on Eskom. Current won't flow in the 'house' neutral when running off batteries because that is not part of the closed electrical circuit. The only problem I can think of is when your mains trip - then your house neutral is not bonded to earth any more and when the inverter kicks in you sit with the floating neutral problem again.
Maybe my studies/memory is letting me down here, please shoot holes as required

That sounds like the best solution to date. My main switch only disconnects Live, so I will not have the floating Earth issue described here if the main switch trips.

Technically this must work without a problem in all scenarios:
1) Eskom is available and the inverter input is internally switched to the inverter output by means of a relay. That means that the input and output neutrals are bonded inside the inverter. There is also a bond between Neutral and Earth on the input of the inverter - that bond would be before the main ELR and since the Neutral in and Neutral out is bonded inside the inverter, there is a bond between Neutral and Earth on the inverter output as well.

2) Eskom is unavailable or PV power supplies the load or both, in the case of a true hybrid (e.g. infini). You create a Neutral Earth bond on the inverter output to prevent a floating earth and to ensure that the ELR on the inverter out functions properly. By creating a bond between Neutral and Earth on the inverter output and since the Neutral Earth bond on the inverter input is still in place (the Neutral Earth bond before the main ELR) and the inverter input Earth and output Earth is connected in the installation, you are actually bonding input Neutral to Output Neutral on the inverter.

In 1) above and when you create the N-E bond on inverter output in 2) above you actually have the inverter input and inverter output Neutrals bonded in both situations and by bonding them permanently you do not have to bond the Neutral and Earth on the inverter output only when Eskom is unavailable.

 

[superdiy]

I thought the infini does not have the floating neutral problem? Maybe I remember incorrectly.

I've tested that last night and can confirm that there is no Neutral - Earth bond when the utility (Eskom) is disconnected from the inverter input. N-E read about 80V and L-E read about 150V - earth was definitely floating.

 

[Getafixx]

My main switch only disconnects Live, so I will not have the floating Earth issue described here if the main switch trips..

In that case I can't see a problem. Comments?

 

[greg_SA]

A while ago I had another idea which is unfortunately flawed, but maybe it sparks something else.

I thought of bonding the input and output neutral. Since the output floats I am pretty sure you can bond the output neutral to the input and it also takes care of the grounding problem both on batteries and on Eskom. Current won't flow in the 'house' neutral when running off batteries because that is not part of the closed electrical circuit. The only problem I can think of is when your mains trip - then your house neutral is not bonded to earth any more and when the inverter kicks in you sit with the floating neutral problem again.
Maybe my studies/memory is letting me down here, please shoot holes as required

I'm pretty sure you won't get a COC this way, as your inverter isn't completely isolated from the grid when it is a power source (battery mode).

 

[Gnome]

Got my Axpert today (switching form Cotek SK1000 with a c/o relay to Axpert MKS 5kVA).

New Axpert seems to come with a USB port:


My Axpert is in another room and it is in a cupboard, so I have this "sub-db" which is wired to the Axpert (and back to main-db).
Not 100% done with it yet (I know the earth wire is taped, I didn't have that colour )


Getting ready to change my main db:
Yes I know, it is a mess right now...

 

[Getafixx]

I'm pretty sure you won't get a COC this way, as your inverter isn't completely isolated from the grid when it is a power source (battery mode).

I'm happy to concede if it's non compliant. But can you perhaps explain why it's not a good idea from an electrical point of view? I'm just curious.

 

[Getafixx]

Got my Axpert today (switching form Cotek SK1000 with a c/o relay to Axpert MKS 5kVA).

New Axpert seems to come with a USB port

Yes. Mine also has USB, no serial. Enjoy the install! It's a fun project

 

[Gnome]

I'm happy to concede if it's non compliant. But can you perhaps explain why it's not a good idea from an electrical point of view? I'm just curious.

Split neutral required

Yes. Mine also has USB, no serial. Enjoy the install! It's a fun project

Thanks, feel like a kid again (building lego )

 

[superdiy]

Split neutral required

When an ELR is installed on the inverter output (after the N-N bond) the Neutral coming from that ELR will go to the second Neutral bar, which needs to be split / isolated from the first / primary Neutral - that means that Neutrals will be split. As was mentioned before, this SANS diagram is "high level" and does not describe everything in detail.

To date, the Neutral-Neutral bond solution is the only solution which will work in every scenario (I can think of) - every other suggestion had a flaw of some sort. I'm all for a discussion and open for other suggestions - I would really want to have a proper solution to this and I think all of you want that too.

 

[scottwday]

Got my Axpert today (switching form Cotek SK1000 with a c/o relay to Axpert MKS 5kVA).

If you ever feel the urge to take things apart I'd love to see a photo of the underside of the comms board (the one with the RS232, USB and dry contacts.) It's just two screws

There are a bunch of different versions of that board, and I'm interested to see if the "2015" board is compatible with the older ones. So far I've got photos of most of the other versions here

 

[Gnome]

If you ever feel the urge to take things apart I'd love to see a photo of the underside of the comms board (the one with the RS232, USB and dry contacts.) It's just two screws

Yeah I think I will. I'm still busy sorting out some of the extras. Like my cupboard needing more support for the 104kg of batteries (yep 26kg each).

Once I start installing I'll do more playing around.

I think I'll let my Raspberry Pi do some data logging for me and do a web interface. Since software development is my day job, may as well incorporate it into this

I'll happily release source code but that will be for the future (probably going to do it in RoR).

 

[scottwday]

Yeah I think I will. I'm still busy sorting out some of the extras. Like my cupboard needing more support for the 104kg of batteries (yep 26kg each).

Once I start installing I'll do more playing around.

I think I'll let my Raspberry Pi do some data logging for me and do a web interface. Since software development is my day job, may as well incorporate it into this

I'll happily release source code but that will be for the future (probably going to do it in RoR).

Awesome, If you're looking to do a web interface it'd be handy (for me at least) if it used thingspeak.com as the backend because I've already got my 'dongle' sending data there...

 

[Gnome]

Awesome, If you're looking to do a web interface it'd be handy (for me at least) if it used thingspeak.com as the backend because I've already got my 'dongle' sending data there...

No I'll probably do a ruby on rails "website" that is hosted on the Raspberry Pi. Which I can just port forward so I can access it from the internet.

Generally speaking tho, my apps use APIs so there is no reason you wouldn't be able to change it to upload the data yourself.

Either way, it'd be a git bug project.

 

[Getafixx]

I got the following from this thread on 4x4community.co.za:

For what it's worth, this is an extract from SANS10142-1 relating to the neutral - earth bond

7.12.3.1.3 Where alternative supplies are installed remotely from the installation, or from one another, and where it is not possible to make use of a single neutral bar which is earthed, the neutral of each unit shall be earthed at the unit and these points shall be bonded to the consumer's earth terminal (see 6.12.4).
The supply from each unit which supplies the installation or part of the installation, shall be switched by means of a switch that breaks all live conductors operating substantially together (see annex S), to disconnect the earthed neutral point from the installation neutral when the alternative supply is not connected (see also 6.1.6).

 

[Gnome]

I got the following from this thread on 4x4community.co.za:

So what they are saying is:
- Alternate supply should have its earth and neutral bonded at the supply
- You must break both the live and neutral when switching the supplies.
- Your alternative supply earthed neutral must be disconnected from the supply when not in use

The last point is pretty much what we have been discussing. If you aren't using the alternate supply (eg. running in bypass mode), your bond should not be present.

IMO it is safe to tie the ground and neutral at your inverter permanently, provided:
- Your neutral and earth bond at the inverter is of the same gauge of your incoming neutral wire
- For some houses that would mean 10mm (or more) wire which I doubt will fit in the inverter terminals...

 

[superdiy]

So what they are saying is:
- Alternate supply should have its earth and neutral bonded at the supply
- You must break both the live and neutral when switching the supplies.
- Your alternative supply earthed neutral must be disconnected from the supply when not in use

The last point is pretty much what we have been discussing. If you aren't using the alternate supply (eg. running in bypass mode), your bond should not be present.

IMO it is safe to tie the ground and neutral at your inverter permanently, provided:
- Your neutral and earth bond at the inverter is of the same gauge of your incoming neutral wire
- For some houses that would mean 10mm (or more) wire which I doubt will fit in the inverter terminals...

They've also mentioned and referred to all the options discussed in this thread already, but as discussed here, all of the proposed connection options were flawed in some or other way. I've created an account in that forum and I'm just waiting for approval, then I'll post a comment in that thread and see if we can get a proper solution to the problem.

The Neutral In to Neutral Out bond, on the inverter, still looks like the most promising option.

 

[Gnome]

On a completely separate note:

I've created a Ruby library for the Axpert (Ruby = works on all OSs). It works well but I just want to create a CLI component for the library before I release it.

Some issues I've run into is:
- The documentation on the internet is very flimsy. People keep referring to the hex of the serial commands but I've found they have little use. You are sending bytes over the stream and receive bytes back. Not sure why using hex to represent it is so tempting.
- The USB on my Axpert shows up on my Mac as composite device. Haven't spent time to figure out how to use it. At this point I used a serial -> USB converter because I knew how it works. Coded and tested on my Mac but I'll test on Windows and Linux to make sure it works as expected.

My next steps:
- Turn the library into a daemon that collects data at 500ms intervals and writes to a text file
- Create a web-application that listens to the text file and updates a web GUI to show the results

Ideally I'd like the ability to show my stats over time, as reported by the Axpert.

I realize the Axpert may not be the most accurate but it is something.

 

[Virge]

Hi All,

I have a silly question. Why the 5KVA Axpert supports only 3000W photovoltaic panels in total? Is it not a 4Kw inverter? Then it takes only 3 strings of 300w PV which is below 3000w. Can I hook to it 12 x 300w Renesola in 4 strings?
And if not, can I add PVs to a total 4000w with an extra MPPT charger?
Thanks.

 

[superdiy]

Hi All,

I have a silly question. Why the 5KVA Axpert supports only 3000W photovoltaic panels in total? Is it not a 4Kw inverter? Then it takes only 3 strings of 300w PV which is below 3000w. Can I hook to it 12 x 300w Renesola in 4 strings?
And if not, can I add PVs to a total 4000w with an extra MPPT charger?
Thanks.

Not a silly question...

In short, in PV mode, the Axpert can only utilize 3000W from the PV panels, but in battery mode it can supply a load of up to 4KW or 5KVA.

You can combine your PV panels in any configuration you like, but the open circuit voltage of the PV array may never be more than the max PV input voltage on the inverter, which is 145V. Each string of PV panels should also consist of the same type and size (e.g. Jinko 300W) and number of PV panels in order for the MPPT to work optimally. If you add more parallel strings, the inverter will utilize whatever it can up to a maximum of 3000W.

No, you cannot add an additional (MPPT) charge controller to the configuration, because the additional charge controller will fight with the Axpert when it comes to charging the batteries etc. etc.

You can however add more Axpert inverters (of the same model) in parallel and add PV panels to each of the inverters.

 

[Virge]

Thanks, then 9x300W will be (very tempted to use the roof surface to the max) but 12 x 250W will be a better choice.

Cheers