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] > <mailto:[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] >>> <mailto:[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] >>> <mailto:[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: >>>> >>>> Improper system design >>>> >>>> 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] >>>> <mailto:[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] >>>>>> <mailto:[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] >>>>>> <mailto:[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] >>>>>>> <mailto:[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] >>>>>>>> <mailto:[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 >>>>>>>>> >>>>>>>>> -- >>>>>>>>> >>>>>>>>> <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 >>>>>>>>> <http://re-wrenches.org/> >>>>>>>>> >>>>>>>>> List Address: [email protected] >>>>>>>>> <mailto:[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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