18 minutes ago, Youda said:

Input ADC yes

Output ADC yes

HVBUS ADC no

I doubt that there will be fixed voltage ratio of HVBUS to Output that is checked. IMHO, these inverters just measure the output and then loopback. Since the output voltage depends on the loads too, loopback and PWM duty cycle will be used to adjust voltage on the fly.

Shifting about 10V down should be feasible.

Thanks a lot - I have the same vision for AC input and output, as well as HVBUS does not affect when the AC output voltage is lower than the HVBUS

24 minutes ago, Youda said:

...

For the export of active power to happen, inverter increases its output voltage a few volts above the grid voltage, while keeping the phase and frequency locked. This forces the energy to flow back to the grid.

...

Yes, I have seen threads on this forum where this was worked out in great detail and appropriate conclusions were made.

Anyway, thank you very much for mentioning this point.

14 minutes ago, Youda said:

Just one note to add: the root cause of why there is no 220V on the grid during the day is that other people are drawing too much current from the grid and the power line to the utility transformer is too long and thin. This causes voltage drop due to line resistance.

The fact that ppl are using voltage stabilisers makes this even worse, as the stabiliser is just pulling even higher current from the line, in order to make a proper voltage (technically being auto-transformer with a servo).

I agree with you 100%.

This is exactly what I tell my friends who complain about the energy supply company, but at the same time do not want to limit their electricity consumption to improve the situation ☹️

18 minutes ago, Youda said:

The propper fix is:

• to improve quality of the cable between you and the transformer,

• or make it shorter,

• or getting your own powerline from the same transformer.

...but I am sure that none of the above are manageable...

This has already been done - I am literally 15 meters from the grid transformer, I laid short but thick cables to the power grid, I distributed the export so as to somehow balance the voltage on the phases of the power grid. But the power of the power grid transformer does not correspond to the all-season load.

It would be better not to torture my inverters, but to wait until the grid transformer burns out and the power supply company replaces it with a more powerful one 😈😈😈

Edited July 7, 2025Jul 7 by bobah1248

@bobah1248 BTW, is this service manual aplicable to your inverters?

Axpert MAX E 11K TWIN service manual 20220406.pdf

@Youda Yes, this service manual is aplicable

But my inverter is missing several minor modules:

• SCR Board

• PV EMI Board

• REMOTE & WIFI Board

• AC breaker

The inverter's appearance and controls look 100% the same. The "1.2. Basic topology introduction" diagram, cross wiring PCBs, fault and warning codes are same.

On 2025/07/07 at 1:02 PM, bobah1248 said:

It is possible that I am simply exaggerating and the firmware in my inverter does not care about the listed inconsistencies.

The AC input voltage does indeed feed into many of the inverter's calculations. I certainly don't like the idea of trying to force the invrerter to do things it was not designed to do, by fudging the measurement resistors or by other means. Inverter firmware is more complex than many people imagine.

49 minutes ago, Coulomb said:

Inverter firmware is more complex than many people imagine.

I agree.

When my inverters burned out, I thought a couple of times how I could implement the inverter control program myself.

But it seemed like a colossal amount of work that would take about six months.

55 minutes ago, Coulomb said:

I certainly don't like the idea of trying to force the invrerter to do things it was not designed to do, by fudging the measurement resistors or by other means.

In any case, before trying to cheat the firmware, I turned to this forum to understand what consequences could await me, in addition to understated readings and generation of undervoltage when working without a grid (according to my calculations, when setting 220V, the inverter in offline mode will produce almost 209V; and this is just the tip of the iceberg that i can see now).

I also thought that instead of constantly overvolting, I could temporarily connect resistors. This is like a kickstarter for hysteresis - inverters turn off export when the voltage is below 175V, and turn on again when the voltage is above 195V or so.

This would allow me to restore export when the voltage temporarily dropped below 175V, but then returned to 185V. And because of hysteresis, export does not resume.

Thus, I could push the inverter to resume export, fooling not the entire inverter, but only a part of it and for a very short time (connect a "patch" resistors for a few seconds)

Hmmm. What would happen if you keep grid relay forcibly closed during the drop under 175V?

• Maybe if will work.

• Maybe it will produce kind of "relay stuck error"

• Or, maybe it will burn....and you will finally have a reason to find and buy a better inverter ;)

Edited July 9, 2025Jul 9 by Youda

15 minutes ago, Youda said:

What would happen if you keep grid relay forcibly closed during the drop under 175V?

I am 90% sure that it is shorted for the following reasons:

1. the output voltage is equal to the input voltage to the inverter

2. the screen shows the "bypass" icon

The only difference is that the inverter pumps in as much solar energy as the household consumers need (according to its output ammeter). At the same time, the input ammeter shows fractions of an ampere, which means no export (and import, if there is enough solar energy)

In any case, forcing the relay to close is a very bad idea: it explodes IGBT transistors, burns IGBT drivers and even control transformers inside the inverter ☹️

Just checked my Infinisolar hybrid, where I can specify the min.grid voltage before the disconnect manually, and the lowest value that Infini accepts in that field is 175V too.

Based on that and since my Infini is from Voltronic too, I would say that all their machines use the same constants & limits for this....therefore, the constant 175 should be visible in the Axpert Max firmware on a couple of places:

• Either in a definition table, with all other limits, that are being referenced dynamically

• or as a true constant, embedded directly in the code-block containing the respective conditions for grid relay control.

Finding the decimal value 175 and checking whether it is on the place that makes sense should be feasible - what do you think @kuba.cz and @Coulomb ?

Well, I can imagine that there is another check that triggers something like "grid voltage too low error" once the grid voltage goes even more down. And the constant for the potential secondary check is yet unknown...but that can be diagnosed later.

@Youda In my inverter selial interface command QPIGS (Device general status parameters) has valid parameters:

Y	Solar feed to grid status (reserved feature)	0: normal 1: solar feed to grid
ZZ	Set country customized regulation (reserved feature)	00: India 01: Germany 02: South America
AAAA	Solar feed to grid power (reserved feature)	A is an Integer ranging from 0 to 9. The units is W.

I believe that it is under the ZZ group that all the settings for exporting to the power grid are hidden

Edited July 9, 2025Jul 9 by bobah1248

12 minutes ago, bobah1248 said:

I am 90% sure that it is shorted for the following reasons:

1. the output voltage is equal to the input voltage to the inverter

2. the screen shows the "bypass" icon

The only difference is that the inverter pumps in as much solar energy as the household consumers need (according to its output ammeter). At the same time, the input ammeter shows fractions of an ampere, which means no export (and import, if there is enough solar energy)

In any case, forcing the relay to close is a very bad idea: it explodes IGBT transistors, burns IGBT drivers and even control transformers inside the inverter ☹️

Of course! Let me be a bit more precise:

• It's clear that keeping grid relay closed all the times, especially before the startup, would blow-up everything.

• The idea is: let the inverter to phase itself to the grid and close the relay first. Then, keep that relay closed forcibly during those valleys of grid voltage drops.

I can imagine that the conditions for closing and opening grid relay are even more complicated and all the steps are being done in a predefined sequences, with check-ups before moving on. So, if the inverter detects a voltage drop, but is unable to open the relay, it will not proceed with de-syncing from the grid and changing it's own output voltage & frequency. But it will work for a second and then throw an error instead.

But you're right, it's a dangerous test and if inverters in your country are pricey and hard to find (based on the amount of work you've put into fixing blown one) then it does not makes sense to undertake such a risk.

2 minutes ago, bobah1248 said:

@Youda In my inverter selial interface command QPIGS (Device general status parameters) has valid parameters:

Y	Solar feed to grid status (reserved feature)	0: normal 1: solar feed to grid
ZZ	Set country customized regulation (reserved feature)	00: India 01: Germany 02: South America
AAAA	Solar feed to grid power (reserved feature)	A is an Integer ranging from 0 to 9. The units is W.

I believe that it is under the ZZ group that all the settings for exporting to the power grid are hidden

I believe the same, that is exactly how it generally works.

But there will be at least two places with limits:

• first is the selected table of grid codes and their parameters, here reported via ZZ parameter.

• second would be the minimum enforced by the firmware itself.

Reason: with my inverter, I can select grid code via GUI, and this changes the min voltage value. Apart from that, I can override min voltage value manually. But cannot go under 175V anyway. So, there's a secondary check.

BTW: all these checks work even if you talk to inverter via serial protocol. Once you sent command with values that are out of range it returns an error and the command is not accepted:

33 minutes ago, Youda said:

• The idea is: let the inverter to phase itself to the grid and close the relay first. Then, keep that relay closed forcibly during those valleys of grid voltage drops.

This can be checked in simpler and less dangerous ways.

For example, measure the voltage using AC voltmeter between the L terminals of the inverter input and output (then between N terminals) - if it is about a couple of volts or lower, then the bypass relay is closed.

Another way is to switch parameter 03 ("AC input voltage range") from APL mode (90-280VAC) to UPS mode (170-280VAC), then wait until the voltage in the network drops below 170V (this happens to me on one phase every day) and look at the bypass icons, input and output voltage, you can measure with a voltmeter as in the previous case.

Any way, I checked both of them and can say - if bypass icon present on inverters display, the grid relay and load relay are closed.

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31 minutes ago, bobah1248 said:

Another way is to switch parameter 03 ("AC input voltage range") from APL mode (90-280VAC) to UPS mode (170-280VAC), then wait until the voltage in the network drops below 170V (this happens to me on one phase every day) and look at the bypass icons, input and output voltage, you can measure with a voltmeter as in the previous case.

I assume that you have APL mode set, as mentioned in your very first post. So, the stop of exporting power to the grid is not being controlled by opening the relay, but by lowering the voltage produced by the inverter once the grid falls under 175V. If so, then fiddling with the relay has no point.🤔

32 minutes ago, Youda said:

If so, then fiddling with the relay has no point.🤔

I'm glad I got the point across. 😄

16 hours ago, Youda said:

Finding the decimal value 175 and checking whether it is on the place that makes sense should be feasible - what do you think @kuba.cz and @Coulomb ?

Not exactly 175V but I can see two limits related to grid voltage in 64.xx firmwares. The first one depends on setting 03. For APL, grid is considered "lost" at 90V and recovers at 100V. For UPS it's 180V/170V.

Then there are the following limits for exporting to grid which are set depending on the country:

	lower limit	upper limit
India	195.5V/200.5V	253V/248V
Germany/South America	184V/198V	264.5V/250V

These are hardcoded in the firmware and cannot be changed by any serial command. The only way to change them is to modify the firmware, which would only be possible if we had the original one for this inverter.

@kuba.cz Thank you very much!

What you wrote coincides with my observations (plus or minus the measurement error of the inverter itself)

My inverter says that the ZZ parameter is 01, i.e. Germany.

In other words, this is already the lowest possible level 😥