Output Voltage is 265v

Can you confirm the version of the control board in the inverter under question?  (STAT page -> second line or so.)

And also can you report the firmware in the inverter? (OUT page -> Diagnostic -> top 2 lines.)

(Admittedly, this sounds like a known Rev. B board issue.)

<a contenteditable="false" data-ipshover="" data-ipshover-target="/profile/2-sid-genetry-solar/?do=hovercard" data-mentionid="2" href="/profile/2-sid-genetry-solar/" rel="">@Sid Genetry Solar

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Well, that answers that....

Have you adjusted/checked the Calibration settings?  A Rev. C board should be +/-5v (parts tolerances) at zero calibration, so I'm wondering if the software calibration adjustments aren't zero.

CFG -> System -> Calibrate Readings -> "AC Out" line -> is it zero?

Also keep in mind that if the inverter is connected to the grid, it will match the input voltage & sync to the input signal, even if it doesn't switch over.  (More often than not the AC input voltage is quite a bit higher than 240vAC.)  This is so it is always ready for a seamless transition.

if the inverter calibrations are at zero, and the AC Input IS connected to the grid...disconnect the grid, and the output voltage should drop close to 240v (assuming the AC Output voltage config is set to 240v).

If this is the case...please note that the inverter firmware counts on the configuration being correct.  If you adjust settings so the output is 240v when the input is 265v, let's just say that the ATS "seamless transition" won't be very seamless.  (Worst case, it could potentially damage the inverter.)

Bingo, looks like somehow the board has AC OUT calibrate settings to add 26v ? I'll set that to 0.

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@sid-genetry-solarThank you!

Well...that would do it!

FYI the calibration scale is an arbitrary number, so it's not necessarily "volts."  Calibration is largely a leftover from the Rev A.1 / B boards which used optoisolators to electrically isolate the AC feedback signal.  Well, those little boogers are anything but predictable in linear situations--so self-warming and ambient temperatures would change the voltage feedback significantly.  And that's not even mentioning different manufacturing batches!

I learned quick...Rev. C uses feedback transformers, which are extremely stable.

Are you using AC input on the inverter?  (Kinda guessing from your original message that you're relying on an external ATS switch?)

3 hours ago, Sid Genetry Solar said:

I learned quick...Rev. C uses feedback transformers, which are extremely stable.

Yay!

3 hours ago, Sid Genetry Solar said:

Are you using AC input on the inverter?  (Kinda guessing from your original message that you're relying on an external ATS switch?)

I use the input of the inverter to charge the battery during offpeak. 12am-3pm. I built an automatic transfer switch that does this automatically using contactors.  For some reason the inverter doesn't like it when it supplies itself AC, so I have another contactor that disconnects the AC input during peak. I'll send you a diagram if you're interested.

I sometimes use more than 6000w during offpeak, so I can't use the 6k inverter as an ATS. I do have two 240v of them 1 revb and 1 revc. Which way would suggest pair them?

I also have some questions about my particular setup.  Neutral bonding, and grounding. lol!  

1 minute ago, jphein said:

For some reason the inverter doesn't like it when it supplies itself AC,

Well, picture in your mind a dog that's finally caught it's tail and is running in circles...

...but the finish line is 100 meters directly ahead.  Doesn't work very well!

Basically, as you found out, the inverter does not like AC mains to be applied to the output--it's not designed for that.  It has no means of syncing up to AC connected to the output--meaning that if the inverter is out of phase with the line *poof* there go the FETs.  Such a "backfeed" can actually be worse than a dead short on the output (which FWIW the inverter is not likely to survive!)

If you wire the output to the input, the inverter will "see an AC signal", sync to it...and then try to transfer to it.  Well, when it connects the main transfer relay, it also shuts down the main FETs--which causes the AC to "disappear" (as the inverter's output is the AC source in this case).  In which case the inverter realizes that there's no AC, and it falls back to battery mode, generating an AC output--and the whole cycle starts over again.

Generally speaking, you will want to have the AC input and the AC output of the inverter connected to separate breaker panels.  Connecting both of them to the same panel is not a very safe system.

6 minutes ago, jphein said:

neutral bonding,

You probably saw all the warnings in the manuals for Rev. A.1 / B about neutral bonding/backfeed issues.  Again, I learned quick: Rev. C does not have this issue, as it has a 2-pole AC input relay that disconnects BOTH input lines.  With a Rev. C inverter, this is kinda a moot point.

7 minutes ago, jphein said:

and grounding

not my favorite topic, but you can ask 😉.

7 minutes ago, jphein said:

I do have two 240v of them 1 revb and 1 revc. Which way would suggest pair them?

Hmph.  Your usecase may require features that don't yet exist (but which are possible, and planned).  Any sort of paralleling kinda requires Rev. C...and code that I haven't had time to write yet.  I tried paralleling functionality with Rev. A.1 / B, but the lack of an input AC current sensor was a huge problem.  Adding insult to injury were those not-so-accurate AC voltage feedback optos.

2 hours ago, Sid Genetry Solar said:

Well, picture in your mind a dog that's finally caught it's tail and is running in circles...

...but the finish line is 100 meters directly ahead.  Doesn't work very well!

Iol, I i see!

2 hours ago, Sid Genetry Solar said:

Generally speaking, you will want to have the AC input and the AC output of the inverter connected to separate breaker panels.  Connecting both of them to the same panel is not a very safe system.

OK, I'll get another panel!

2 hours ago, Sid Genetry Solar said:

You probably saw all the warnings in the manuals for Rev. A.1 / B about neutral bonding/backfeed issues.  Again, I learned quick: Rev. C does not have this issue, as it has a 2-pole AC input relay that disconnects BOTH input lines.  With a Rev. C inverter, this is kinda a moot point.

When running the inverter on battery I don't have any neutral to ground bonding. My ground does go all the way back to the main panel where ground is bonded to neutral,  and there is a grounding rod.  The main panel is connected to the grid.  However the L1, L2, and Neutral of my sub panel are all disconnected from the main panel, and thus the grid when the inverter  is connected.   Is this safe? To have no neutral ground bonding? 

2 hours ago, Sid Genetry Solar said:

not my favorite topic, but you can ask 😉.

Should I have another grounding rod when I'm on battery, and not use the ground from the grid main panel? I also use solar to charge the battery on the DC side. The solar panels are grounded to the same ground all the way back to the main panel. 

2 hours ago, Sid Genetry Solar said:

Hmph.  Your usecase may require features that don't yet exist (but which are possible, and planned).  Any sort of paralleling kinda requires Rev. C...and code that I haven't had time to write yet.  I tried paralleling functionality with Rev. A.1 / B, but the lack of an input AC current sensor was a huge problem.  Adding insult to injury were those not-so-accurate AC voltage feedback optos.

Let me know when it's ready, and I'll buy another revC controller! =]

Or, maybe convert both to 120v input and use split sync? <a contenteditable="false" data-ipshover="" data-ipshover-target="/profile/2-sid-genetry-solar/?do=hovercard" data-mentionid="2" href="/profile/2-sid-genetry-solar/" rel="">@Sid Genetry Solar

My loads are pretty balanced. 

Also, what do you think the consequences are of running my house @ 276v for 2 months? My oven clock was always fast, that's for sure. 

With the Rev. C control board, it has the auto 120/240v input...but you would need to convert the entire inverter from split-phase to single-phase.  Yes, split-sync could be used--but it would halve your maximum charge power, as the current split-sync setup uses the AC Input on the "slave" inverter for a sync signal.

I'm not aware of any...most SMPS (switch mode power supply) devices have a wide voltage range input.  Oven clock running fast likely has to do with the AC output frequency of the inverter; you may want to trim the inverter's AC output frequency down to resolve this.

So the inverter's main input relay only disconnects L1 / L2, not Neutral.  (But I gather you aren't using the internal AC input relay on the inverter!)  There is no reason at all you can't have a common neutral from AC mains through to the subpanels...and said neutral would be ground bonded.  If your transfer switch disconnects all 3 legs, you could bypass the Neutral disconnect and utilize the grounded neutral from the mains panel.  Just as long as L1 / L2 are fully disconnected, you'll be fine.

IIRC... The industry maximum [30-min surge] voltage to residential households is 128v. At 136v (272v 2-leg) aka +8v, you're going to be just fine.
FYI, mean voltage at the substation is 130v. And you can plug in regular equipment at will inside them. No need to stress over +6 volts.

By the way, if you don't have one, i strongly recommend getting a type-2 surge arrester for your main panel. Most install like a standard gfci breaker. It will save your bacon one day when you have a much more significant voltage spike. 🙂