One consideration that I've found to be valuable is ensuring the parallel comm cables(inverters and batteries) are equal length. This may even potentially be a more important consideration than AC lines being equal length.
On Wed, Oct 29, 2025, 9:19 AM jay via RE-wrenches < [email protected]> wrote: > It seems like the inverters are not actually communicating for them to be > so far off from each other. > > jay > > On Oct 29, 2025, at 8:58 AM, Dave Tedeyan via RE-wrenches < > [email protected]> wrote: > > Jay, > It is a grid tied system, and I am seeing this behavior while the grid is > present. I have not been able to take a closer look to see if this happens > during a grid outage. I am not even sure there has been a long enough > outage yet as these systems are fairly new. > > And to be clear, these systems are generally working as expected. Even > though this strange circulating current seems to happen many days, each > system has only thrown the CA-DC link overvoltage error once. > > Cheers, > Dave > > On Wed, Oct 29, 2025 at 10:43 AM Jay via RE-wrenches < > [email protected]> wrote: > >> These issues described here is this for both on and off grid? >> >> Jay >> >> On Oct 29, 2025, at 7:41 AM, Dave Tedeyan via RE-wrenches < >> [email protected]> wrote: >> >> >> William this is really good information, thanks for sharing the technical >> perspective. >> >> I have two sites with two of these inverters and both of them are >> exhibiting very similar behavior. On Friday, I was out at the other one to >> wrap up a few things. While I was out there I verified some of the things >> that Midnite tech support suggested like making sure that the AC wires to >> each inverter's grid in and cables are the same length and also from the >> battery bus bar to each inverter are the same length. This was actually a >> bit surprising to me, considering with lead acid it is more important to >> have the battery cables from the bus bar to the batteries be the exact same >> length and the cables to the inverters did not matter as much. >> >> Based on what we were talking about last week, I removed the N-G bond in >> the disconnect for the solar, but I have not yet gone looking for other N-G >> connections in the way that Jason suggested. I have not gotten a CA-DC link >> overvoltage error, but I have still seen some of the symptoms. It is not as >> bad as the other site, but what I notice on the monitoring is that in the >> late afternoon/early evening one inverter shows an unreasonable amount of >> solar (with power going into the grid and into the battery), while the >> other inverter shows low solar (with a ton of power coming out of the >> battery going to the load and the grid), and the battery SOC drops very >> quickly down to the discharge end SOC (on grid) setting of 85%. >> Jason and William, do you know whether any faulty wiring with N-G >> connected in loads on the non-backed up side will affect the system the >> same way? Or is it mostly just important to check for any neutrals >> connected to ground on the backed up loads side? >> >> Jason, as to why a supply side connection - I was under the impression >> that a Power Control System just effectively limits the amount of power >> that can be sold to the grid. But on a standard 200A service, that limits >> you to about 7.7kw of sell back. I would not want to limit the system that >> much for a roughly 20kw system, even if more than the 7.7kw can go to >> powering loads and battery charging. In the Midnite monitoring, it is >> pretty easy to limit the grid sell back with the "maximum feed in grid >> power" in the Power Control settings. >> >> Cheers, >> Dave >> >> On Sun, Oct 26, 2025 at 8:51 AM William Bryce via RE-wrenches < >> [email protected]> wrote: >> >>> All >>> >>> Most modern all-in-one (AIO) inverters are designed around a non-isolated >>> high-voltage DC bus. This design is what allows manufacturers to advertise >>> higher output numbers — for example, “15–18 kW” — while the inverter may >>> only deliver 12 kW during nighttime operation when PV isn’t contributing >>> (it is also cheaper to build). Without the shared non-isolated DC link, >>> these power-boosted daytime ratings wouldn’t be possible. >>> >>> A DC-bus overvoltage fault almost always points to one of two issues: >>> >>> 1. >>> >>> Improper system design >>> 2. >>> >>> Wiring and installation mistakes >>> >>> Off-Grid Example >>> >>> A common DIY mistake is pairing a large solar array (because glass is >>> cheap) with a relatively small battery (not as cheap). >>> When the battery is full and a large load suddenly turns off, the excess >>> energy has nowhere to go. The inverter throttles back, but the stored >>> energy can still push the DC-bus voltage up rapidly. If the inverter didn’t >>> protect itself, the capacitors would be at risk — so it shuts down with an >>> overvoltage error. This is also common when using a large retrofitted AC >>> coupled array. >>> Grid-Tie Example >>> >>> In grid-connected systems, DC-bus overvoltage is typically caused by wiring >>> mistakes, some common examples are: >>> >>> Multiple neutral-to-ground bonds >>> >>> Reversed hot/neutral at outlets >>> >>> A single inverter is usually more forgiving. However, stacked inverters must >>> share phase, neutral, and grounding relationships precisely. Any mis-wiring >>> can create circulating currents. That circulating energy is not >>> accounted for in the inverter’s internal power calculations, so the DC-bus >>> voltage rises unexpectedly — and the inverter shuts down for protection. >>> >>> A DC Link Overvoltage error is usually not an inverter defect — it’s a >>> system design or system wiring problem 99% of the time. Ensuring proper >>> neutral/ground bonding, correct polarity, adequate battery capacity, and >>> proper commissioning is critical to reliable AIO operation. >>> >>> This behavior is not unique to the MN AIO — all AIO inverters using a >>> non-isolated DC-bus topology share the same fundamental protection >>> limitations. >>> >>> Inverters are getting more complex to deal with the new rules and >>> utility requirements, this causes reliability issues as we move (or pushed) >>> to full integration with the grid. Because you know we all want the >>> utility to have full control over our systems! >>> >>> On Sat, Oct 25, 2025 at 9:51 AM Jay via RE-wrenches < >>> [email protected]> wrote: >>> >>>> I had an issue with a EG4 inverter and tech support was an insistent >>>> that there was multiple ground neutral bonds in the system. Fully off grid >>>> system with no generator. >>>> It wasn’t the issue but it seems like these inverters are sensitive to >>>> it. >>>> >>>> Is the inverter internally bonded, not that I’m aware of or what I’ve >>>> measured. >>>> And so I can’t figure out what it’s measuring between N/G to have a >>>> potential issue. >>>> >>>> Maybe someone can explain? >>>> >>>> Jay >>>> >>>> >>>> >>>> On Oct 24, 2025, at 6:49 PM, Dave Tedeyan via RE-wrenches < >>>> [email protected]> wrote: >>>> >>>> >>>> Thanks all for your thoughts here. It seems that the general consensus >>>> so far is that the N-G should be bonded in the solar main disconnecting >>>> means when doing a supply side connection (even if it is not technically a >>>> separate service). When talking with Midnite Power, we made it very clear >>>> that we were talking about a N-G bond in the inverter combiner / solar main >>>> disconnect, and not the backed up loads panel. And being that NY is still >>>> on 2017 code (only going to 2020 next year), with the ambiguity in the code >>>> I am probably okay to undo the N-G connection in the main solar disconnect. >>>> >>>> In this case specifically, we are backing up only a small subset of >>>> loads in the house. The reason for the two inverters is because there is >>>> about 24kw of solar. There is also a manual transfer switch to normally be >>>> able to power the loads off the inverters, but to be able to switch to >>>> powering the loads off the main panel in case of service needed on the >>>> inverters. The neutrals in this system are all connected together, and I am >>>> not sure if that could cause issues. It is probably difficult to explain >>>> all the details in words, so I am copying part of the three line diagram >>>> here. The second picture is the conductor and conduit schedule. >>>> >>>> Tom, I get it that the error sounds like it is on the DC side based on >>>> the words, but when I talked to Midnite about it they were pretty clear >>>> about it being due to multiple N-G bonds and they did not mention that it >>>> could have anything to do with the DC side. >>>> >>>> Jason, that is a good idea as well to check the loads that got moved >>>> over to see if there are any other inadvertent N-G bonds on the premises. >>>> This also similar to what Midnite suggested, which was to lift the N-G bond >>>> in the main panel and then see if they are still bonded somewhere else. It >>>> seems like it can be a slow process to track that down with power cut to >>>> the house, but that might be what I have to try if removing the N-G bond in >>>> the solar main disconnect does not help. >>>> >>>> So, my main questions to anyone who has an opinion here are two fold: >>>> 1. Do you bond the N-G in general in the main solar disconnect for a >>>> supply side connection? >>>> 2. Specifically with the Midnite AIO inverters, has anyone else had >>>> issues with this "CA-DC link Overvoltage error" due to having a second N-G >>>> bond in the house? (one in the main service panel, and one in the solar >>>> main disconnect if it is a supply side connection). Or have you seen this >>>> error and found that it was caused by something else? >>>> >>>> Cheers, >>>> Dave >>>> >>>> >>>> >>>> On Thu, Oct 23, 2025 at 5:25 PM Jason Szumlanski via RE-wrenches < >>>> [email protected]> wrote: >>>> >>>>> I agree. It is not a separate service. It is a "tap" of the existing >>>>> service (I use that term loosely here). The additional service disconnect >>>>> for the supply side interconnection should have L1, L2, and N >>>>> connected ahead of the premises main disconnect with no EGC. There should >>>>> be a N-G bonding jumper in the PV service disconnect. Then there should be >>>>> no N-G bonds downstream of both the premises main disconnect and the PV >>>>> service disconnect. >>>>> >>>>> Basically, it's the same as two main disconnects running from a meter >>>>> enclosure. Each of the service disconnects has a N-G bond required. >>>>> >>>>> Some AHJs (the crazy ones) require an EGC between the enclosure where >>>>> the supply side connection is made and the PV service disconnect. This >>>>> creates a parallel fault path, and should not be allowed, in my humble >>>>> opinion. >>>>> >>>>> Now it sounds like you might be doing a partial home backup. The issue >>>>> there is that sometimes the loads or enclosures you moved over the backup >>>>> load panel have inadvertent N-G bonds. Sometimes it's as simple as someone >>>>> who got creative and used a ground as a neutral in a switch box. I say >>>>> simple, but that can be hard to track down. >>>>> >>>>> When Midnite said to remove it from the inverter distribution panel, >>>>> they were probably talking about the protected loads panel. >>>>> >>>>> I think more information is needed. >>>>> >>>>> >>>>> >>>>> Jason Szumlanski >>>>> Principal Solar Designer | Florida Solar Design Group >>>>> NABCEP Certified Solar Professional (PVIP) >>>>> Florida State Certified Solar Contractor CVC56956 >>>>> Florida Certified Electrical Contractor EC13013208 >>>>> >>>>> >>>>> On Thu, Oct 23, 2025 at 11:03 AM Tyrone Houck via RE-wrenches < >>>>> [email protected]> wrote: >>>>> >>>>>> My interpretation, and the way it was explained to me by both Ryan >>>>>> Mayfield and Kyle Bolger(several years ago at this point, popular opinion >>>>>> may have changed since). Is that it is not a seperate service. >>>>>> It is however required to have a ground-neutral bond( though in my >>>>>> opinion pointless and redundant as there is a bond in the enclosure where >>>>>> the tap is made). If it gives you any issue, ensure as close to equal >>>>>> potential to the grounding electrode as possible(and make sure your >>>>>> neutral >>>>>> is appropriately sized). I personally don't see the point but it is an >>>>>> NEC >>>>>> requirement >>>>>> >>>>>> >>>>>> >>>>>> >>>>>> On Thu, Oct 23, 2025, 6:08 AM Dave Tedeyan via RE-wrenches < >>>>>> [email protected]> wrote: >>>>>> >>>>>>> Hi All, >>>>>>> >>>>>>> For years I have understood that when doing a supply side >>>>>>> connection, you are supposed to bond the neutral to ground in the solar >>>>>>> service disconnect. I have a Midnite AIO system with two inverters (set >>>>>>> up >>>>>>> as a supply side connection) that recently was getting a CA-DC link >>>>>>> Overvoltage error. When talking to Midnite, their first response was to >>>>>>> make sure that there was only one N-G bond in the whole system. When I >>>>>>> mentioned that the solar is a separate service and thus there is a N-G >>>>>>> bond >>>>>>> in both the main panel and the inverter distribution panel, they said to >>>>>>> remove it from the inverter distribution panel. I want to make the >>>>>>> system >>>>>>> work right, but I also am hesitant to do something against how I have >>>>>>> understood the NEC to be for a long time. I am curious if you all have >>>>>>> thoughts on this or run into a similar situation. >>>>>>> >>>>>>> Cheers, >>>>>>> Dave >>>>>>> >>>>>>> -- >>>>>>> >>>>>>> [image: Logo] <https://www.sungineersolar.com/> >>>>>>> Dave Tedeyan, P.E. >>>>>>> Owner | Sungineer Solar >>>>>>> p: he | him | his >>>>>>> a: 1653 Slaterville Rd. >>>>>>> <https://www.google.com/maps/search/1653+Slaterville+Rd.+%C2%A0+%7C%C2%A0Ithaca,+NY+14850?entry=gmail&source=g> >>>>>>> >>>>>>> <https://www.google.com/maps/search/1653+Slaterville+Rd.+%C2%A0+%7C%C2%A0Ithaca,+NY+14850?entry=gmail&source=g>| >>>>>>> Ithaca, >>>>>>> NY 14850 >>>>>>> <https://www.google.com/maps/search/1653+Slaterville+Rd.+%C2%A0+%7C%C2%A0Ithaca,+NY+14850?entry=gmail&source=g> >>>>>>> w: www.sungineersolar.com <http://www.sungineersolar.com/> >>>>>>> c: (607) 270-0370 >>>>>>> _______________________________________________ >>>>>>> List sponsored by Redwood Alliance >>>>>>> >>>>>>> Pay optional member dues here: http://re-wrenches.org >>>>>>> >>>>>>> List Address: [email protected] >>>>>>> >>>>>>> Change listserver email address & settings: >>>>>>> http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org >>>>>>> >>>>>>> There are two list archives for searching. 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