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Axperts in parallel


Chris Hobson

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37 minutes ago, Nonlinear said:

1. Have you found that the RCT and Mecer are able to operate in parallel successfully, if so, which firmware versions did you use to allow parallel operation. From my reading here it seems (in my case) both would need to be running 72.40.

2. Is the Mecer an actual Voltronic inverter or only a clone. My concern is that I may not be able to get the firmware versions updated to allow parallel operation if it is a clone. 

The Mecers are real Voltronics. 

My understanding is that you will need 72.70 on your existing machine, and 74.XX or whatever comes with the 5 kW model. 

I'm starting to think that 72.70 is the last firmware to have some sort of backwards compatibility with respect to CAN bus message formats. 73.00 and some others don't seem to have that legacy support any more. The 5 kW models must presumably have this legacy support. So even if you don't need the old CAN bus message formats, if one firmware has it, then the others need to have it as well, else you get a fault code 71 (firmware version inconsistent). 

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11 minutes ago, Coulomb said:

My understanding is that you will need 72.70 on your existing machine, and 74.XX or whatever comes with the 5 kW model.  

Thank you sir!

I must have misread your posts on Aeva and here. I was under the impression that for older PF0.8 inverters like mine the highest I could go would be 72.40 but I stand corrected.

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1 hour ago, plonkster said:

Official rebadged Voltronic. Not a clone.

Thank you. I am relieved, I don't want to muck about with this, things are already complex.

As a side question (if it is OK), I really like that picture of your new DB, and will be looking into some of the distribution blocks too, what is the ACDC code on those? Also, the Gewiss breakers, are they DC rated? The ZAR/USD exchange rate is killing me and I'm hoping to find an alternative to the Carlings I have now?

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1 minute ago, Nonlinear said:

distribution blocks too, what is the ACDC code on those?

https://www.acdc.co.za/pages/product-individual?BKB251

2 minutes ago, Nonlinear said:

Also, the Gewiss breakers, are they DC rated?

Yes, that particular one is.

https://www.acdc.co.za/pages/product-individual?GW92152

The guys at the shop won't know. But I downloaded the spec sheets from the internet. They are rated 55V per contact, multiply that by the number of contacts, so mine is rated to 110V, which is ample for a 24V system. I didn't buy mine from AC/DC though, but the price shown on that link is a good one.

It might be good for yourself to also check my work, in case I got it wrong :-)

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5 minutes ago, plonkster said:

It might be good for yourself to also check my work, in case I got it wrong :-)

Unlikely!

I think newb versus supreme master says it all.

I trawled the Gewiss site a bit and downloaded the MT60 datasheet as a start and they are indeed rated at 50VDC. That solves my problem on the DC output side but unfortunately not on the PV side, voltages are well above 50VDC in that case. I will do a bit more trawling though...

Thanks. Much appreciated.

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Just now, Nonlinear said:

not on the PV side

On the PV side I have 1000VDC fuse holders that open up in a safe manner (the high voltage is wired to the top side where you cannot touch them when the holder is open).

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11 minutes ago, Jaco de Jongh said:

If that Engineer of yours signs this off, Can you please post his number in this thread, I am sure a few of us can use his services. :D

Not a chance. "They" all claim that allegedly the cables must be in trunking, active or passive vent on the battery box, panels earthed ... list goes on.

Fact that I never have heat issues, THAT slips their observations!

I must have a combiner box. On that one I told them to take a hike, here, let me help push you ... I have disconnects and basta ... they reluctantly went quiet on that point ... for now.

So I asked, lighting. Lighting strikes the panels, explain to me how earthing helps that? Or are you after recurring business, seeing as there is now a direct path down to the DB?
Shocking oneself on the roof ... it is a metal roof for pete's sake! Explain that one to me I said.
They call on select research, I gooi back select research ... we are still negotiating on earthing. :-) 

And what if I want to change something, mmm, must I undo all the trunking ... AGAIN ... or is it the recurring business thing again?

Did not get anywhere I tell you, they are as stubborn as SWAMBO when she has a really big bee in her bonnet.
SHE, obviously(!), is loving it, the way "they" pull that piece of art apart. Gmpf. 

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11 minutes ago, plonkster said:

On the PV side I have 1000VDC fuse holders that open up in a safe manner (the high voltage is wired to the top side where you cannot touch them when the holder is open).

Ditto. I'm a very nervous solar explorer so I have fuses on positive & negative per string, positive & negative per array (combined string) and DC breakers per string and per array. Belts and braces perhaps but I'd hate to set my house on fire.

On second reading of the Gewiss datasheet though I see they do provide a rating for 2 in series so that may be a solution in my case because (according to the datasheet) that takes the rating to 100VDC which is sufficient in my case.

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13 minutes ago, The Terrible Triplett said:

claim that allegedly the cables must be in trunking, active of passive vent on the battery box, panels earthed

I don't care too much what people say about that, I prefer my cables in trunking anyway. No need to vent the batteries (if an LFP needs venting you have bigger problems).

Earthing panels is one of those "it depends" things. The rule is that if there is live and a neutral going from your DB to the panels in some possible way, then there must also be an earth going along with it. Where the PV enters through the DC bus, and there is an isolated boost stage between that and the AC side, there is no direct path to the panels, and hence the earth need not be interconnected, and in my opinion should not be interconnected. This doesn't mean that it is not a good idea to earth the panels to their own spike though!

13 minutes ago, The Terrible Triplett said:

must have a combiner box

Again details are vague. Combiner boxes are for parallel strings, for brining them together. If each string is on its own MPPT, there is little reason to have a combiner box. Some might insist on having it anyway so that you can have a lightening arrestor in the same box. The one guy I spoke to said the DC fuses I have in would suffice. I guess I'm still going to find out :-)

13 minutes ago, The Terrible Triplett said:

Shocking oneself on the roof

Can happen with those high voltage PV inverters that don't have an isolated boost stage. Re the general rule... with those units there IS a path back to the DB, you must earth, and if there is a ground fault it could electrify the structure.

11 minutes ago, Nonlinear said:

On second reading of the Gewiss datasheet though I see they do provide a rating for 2 in series so that may be a solution in my case because (according to the datasheet) that takes the rating to 100VDC which is sufficient in my case.

They show you exactly how it works a few pages on. If you have an isolator in both the positive and negative lines (switching both simultaneously) you are already safe to 100V.

Edited by plonkster
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4 hours ago, plonkster said:

The rule is that if there is live and a neutral going from your DB ...

Off grid ... there was no Solis at that discussion.

4 hours ago, plonkster said:

No need to vent the batteries ...

Hydrogen venting out of battery box.

4 hours ago, plonkster said:

If each string is on its own MPPT ...
DC fuses I have in would suffice. 

2 x fused incoming arrays to 2 x MPPT's. Disconnects on wires and Brad Harrison on cables.
Basta with the combiner box.

5 hours ago, plonkster said:

Can happen with those high voltage PV inverters ...

This I can accept. Thank you.

But, now that I am going grid tied, ag ok, they can earth them ... but only because of grid tied!

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13 hours ago, Nonlinear said:

Hi Chris et al,

I'm new here and I hope this is not regarded as a thread hijack. I'm intending expanding my setup and it is very similar (if not identical) to your setup, in that I also have an RCT 5kVA/4kW (currently running) and plan on putting it in parallel with a Mecer 5kW/5kVA (not yet running). I have two very general questions thus:

1. Have you found that the RCT and Mecer are able to operate in parallel successfully, if so, which firmware versions did you use to allow parallel operation. From my reading here it seems (in my case) both would need to be running 72.40.

2. Is the Mecer an actual Voltronic inverter or only a clone. My concern is that I may not be able to get the firmware versions updated to allow parallel operation if it is a clone.

Any help, advice or further information on your particular installation would be much appreciated.

Thank you.

Your questions have largely been answered but for completeness I will add what I have done.

  1. Axperts have been successfully paralleled. The only thing I battled wth was getting setting 28 into Parallel Mode. You need to switch the unit off to make the changes.
  2. Mecer is Voltronic rebranded product. I used @Coulomb's updated firmware (72.70c).

Looks like it's mostly covered.

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1 hour ago, Chris Hobson said:

Your questions have largely been answered but for completeness I will add what I have done.

  1. Axperts have been successfully paralleled. The only thing I battled wth was getting setting 28 into Parallel Mode. You need to switch the unit off to make the changes.
  2. Mecer is Voltronic rebranded product. I used @Coulomb's updated firmware (72.70c).

Looks like it's mostly covered.

Thanks Chris, and others. Much appreciated, now I have some peace of mind on both my breaker problems and firmware worries. Now all I need is to buckle down and get the rest of the install done.

I want to re-read the posts here and elsewhere (and on MyBB, 4x4 and Aeva) with respect to earthing and neutral. I have measured continuity across my neutral bars while the inverter is on solar and I'm not sure I understand how that can be. Does the Axpert bridge incoming neutral and outgoing neutral? Anyway, before I make any more bold statements I want to review this issue and possibly start a new thread.

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10 minutes ago, Nonlinear said:

I want to re-read the posts here and elsewhere (and on MyBB, 4x4 and Aeva) with respect to earthing and neutral.

No need, here you go ... :D

image.png.e2a9f1b3087679f6f444d7a22efc7a85.png

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On 2018/08/21 at 9:36 PM, Nonlinear said:

I want to re-read the posts here and elsewhere (and on MyBB, 4x4 and Aeva) with respect to earthing and neutral.

Hi NL

It is relatively simple if you can consider PE (Protective Earth) is an "low resistance alternate pathway for stray currents back to source". When grid is your supply your earth needs to be bonded to grid neutral and when in inverter mode the earth needs to go to inverter. The fact that neutral is bonded to a earth spike  is to ensure don't have a floating neutral and that the neutral's potential is zero with respect to the physical earth reducing the risk of electrocution. You can always get shocked on the live but since neutral is a low resistance pathway back to source.

One can use the Axpert's dry contact to achieve this switching the bonding of the earth of circuits supplied by the inverter  from inverter to grid.

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14 hours ago, Chris Hobson said:

One can use the Axpert's dry contact to achieve this switching the bonding of the earth of circuits supplied by the inverter  from inverter to grid

Why not bond grid and Axpert Neutrals together instead of switching?

The possibility of grid surges damaging Axpert perhaps?

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12 minutes ago, Colin said:

Why not bond grid and Axpert Neutrals together instead of switching?

The possibility of grid surges damaging Axpert perhaps?

Well this is exactly my setup, although unintentionally due to (I think) the Axpert. In my case the neutral is bonded to the grid side, I've checked both during grid bypass and during PV generation. Considering that my neutral is bonded at the incoming DB to earth (I checked) effectively this means my neutral is always bonded to earth. I have significant surge protection I think: an SPD on the incomer, an SPD on the feed before the inverters and a DC SPD on each array combiner box. I also have an E/L as per the SANS requirement (and diagram in the 2018 rev) and I have a DC GFP per array. However, all of this is useless if I've gotten the earthing and bonding wrong. In my case I have a pretty old Axpert so I think it means I would need to put in a separate contactor if I want to explicitly bond earth to neutral on the outgoing side of the Axpert. Also, if the latter is the best approach I would need to install a separate earth spike in a good location which is not so easy in my location (but not impossible). In general I've tried to follow SANS to the letter and used the NEC guidelines where they are more stringent.

Edited by Nonlinear
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15 minutes ago, Nonlinear said:

earthing and bonding

Basic rule: The earth conductor is only allowed to carry fault current, no working current, at least to the point where it is bonded. For a TN-S system that means only fault current all the way back to the transformer. For TN-C-S or PME setups, where you might have a bond and possibly an earth stake where it enters the premises, it means no bonds after this point.

If your inverter bonds earth to neutral itself when in inverter mode, and you have all your earths interconnected (as you should), and you also have your neutrals connected together, then the inverter will create a second earth/neutral bond higher up, which is technically incorrect.

I am not an electrician, and I know it is common to bend the rules a bit, but in my mind you don't bond the grid and inverter neutrals, and you use a earth relay to create a bond when in invert mode. That's the proper way to do it.

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Come to think of it, if you don't have an earth relay in the inverter, but you bond the inverter and grid neutrals together, then the inverter benefits from the existing earth/neutral bond while in inverter mode, plus you avoid creating another bond. Which is good. But there is one problem: If you open the big 60A (or larger) isolator otherwise known as the main switch... you lose the neutral, and the bond.

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Just a warning of multiple earths. If you have a ground lightning strike you set up a momentary voltage gradient radiating around your lightning strike. So in theory you could have current travel up your earth cable through your system and down through the second earth as your earth wiring provides a lower resistance pathway compared to the soil. 

Some folk seem to think grounding is for lighting protection. Lightning is usually  300 000 volts and anything between 5000 and 50 000 Amps. That little bit of wire is not going to conduct that  amount of electricity.  Remember earthing is a pathway for stray current back to source (Plonky has just made reference to this) .  The one time it does help is when there is an inductive surge created by lightning which then gives this a pathway to ground. Even so I have seen inductive surges blow surge protection devices at the same time spider arcing up the walls and generally frightening the living daylights out of everyone in the house.

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On 2018/08/21 at 12:43 PM, plonkster said:

Official rebadged Voltronic. Not a clone.

Thank you, Plonkster and Chris (I wish I knew how to do that blue link thingy),

I agree wholeheartedly, earthing is not for lightning strikes but rather to protect people from accidental contact. Also, as Plonkster said, in my case (for reasons unknown) the neutrals are bonded throughout, which is fine until someone opens the main switch while PV is on. Our main switch has never been tripped and only once or twice switched, but there is a first time for everything. My problem is (as already pointed out) if I now bond earth to neutral after the inverter (as suggested) I create a second bond which is a no-no according to SANS. So the only solution (that I can see) is to figure out how to disconnect the neutrals when in "off-grid" mode and to simultaneously bond the earth and neutral. 

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13 minutes ago, Nonlinear said:

I wish I knew how to do that blue link thingy

You mean how to quote? Highlight the text, and click "Quote selection". The javascript is a bit wonky so sometimes you have to do it twice before it works.

You can also select the first word, then use shift+arrows to go as far as you want to. This does not suffer from the do-it-twice issue.

Selection_213.png.ac2c64d3a6322dc7bf00a0ca5415cd4d.png

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25 minutes ago, Nonlinear said:

(I wish I knew how to do that blue link thingy),

It is here, the blue like thingy ... and other options if you want.

Click on the grey heart bottom right of the posters post you want to like, say thanks etc.

image.png.2f2608fa0cd0493e82e5010e07ea7d8b.png

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