OomD

Makes sense, thanks!

Did you prioritise load over battery in your setup? If not try this. What do you timer settings look like? 

Bit difficult to guess without seeing the settings.
This is my guess:
If you add a lot of load suddenly the inverter will draw a bit of power(second or two) from the grid till it can ramp up the power from other sources. Similarly if you shut down a load suddenly then you might export a bit of power to the grid till it slows down the generation

Just to inform the non-technical guys as to what the actual problem is.
 
The AVR (Automatic Voltage Regulator) in a generator is a reactive thing. In other words, as the load on the generator changes the AVR adjusts things to try and keep the specified output (50Hz, 230V or so). You may hear the generator changing RPM's as you switch different loads on and off. When you have no load on the generator it becomes more difficult for the AVR to keep things steady. This is almost like a car engine running without a flywheel... it will work, but is much more erratic. So the load on the generator actually helps to stabilise it.
 
So, when you connect the generator as input to the Axpert, there is no real load on the generator (as the axpert has not switched the generator power to the output yet). So the voltage and frequency is a bit instable, and this is what the axpert complains about. Your grid power is very stable, on the other hand, and the axpert is made to work with a stable incoming grid supply.
 
The newest version of the axpert firmware basically just allows the incoming voltage to be a bit more unstable, so to speak, before it starts complaining about it. It allows for a greater variance of voltage and frequency.
 
One possible way of solving this, if you have no means of upgrading your axpert, is by connecting a load onto the generator, in addition to connecting it to your axpert input. This will help stabilise the generator output, and consequently the axpert sees a more stable input. As to what the load should be will really depend on the generator, but I'm guessing a load of about 100W should be enough (but don't quote me on this... never tried it!).
 
Hope this helps.

Solar Warehouse are selling the 4kW MPPT model under R10k right now.
https://www.inverter-warehouse.co.za/products/axpert-inverter-mks-5k-48v-4000w-mppt?utm_medium=cpc&utm_source=googlepla&variant=5189341839397&gclid=CjwKCAjw6djYBRB8EiwAoAF6oTfAysx8y6TrYqcLO5kM85GcEffEkLWl53dxCnk_6PbBpTry1hXJ8RoCQX8QAvD_BwE
I would suggest getting one of these units and installing it and then have the other unit repaired. If you have a problem again you will have a unit in reserve. I have a reserve unit that I bought off @Mike and it gives a lot of piece of mind while sitting in the garage doing nothing.

The low DC cutoff (setting 29), I thought, was the point at which the inverter will switch off (in the absence of grid power). The point at which it would return to grid (i.e.  start recharging the batteries) is setting 12.
 
Off course I might be misunderstanding the question.

@weber, thanks for your feedback. Yes, I thought the funny I found was related to the Axpert's own firmware, not your mod. I did notice that, as mentioned, going out of the setting and back in again allows further change.
Yes, sorry I meant Aut and not Def (Default). So, that would be the optimal value to use then.
You guys are to commended for your continued effort. I know it takes a lot of time away from more important things, just the fact that you're still doing it is awesome. If you ever start a donation page, which I think you should, I would be early in line to contribute.
The Aussie view feature, in particular, is brilliant!

@weber, thanks for your feedback. Yes, I thought the funny I found was related to the Axpert's own firmware, not your mod. I did notice that, as mentioned, going out of the setting and back in again allows further change.
Yes, sorry I meant Aut and not Def (Default). So, that would be the optimal value to use then.
You guys are to commended for your continued effort. I know it takes a lot of time away from more important things, just the fact that you're still doing it is awesome. If you ever start a donation page, which I think you should, I would be early in line to contribute.
The Aussie view feature, in particular, is brilliant!

Mockups of what will be on the main screen.
Screen 1
Battery SOC (State Of Charge, %), Volts, Amps, Units in(Kwh), Units out(Kwh), Run time, estimated remaining time, Load (Kw)
Solar panels Volts, Amps, Units in(Kwh), Load (Kw)
Grid Volts, Units in(Kwh)
House Load (Kw), Units used(Kwh)
Screen 2
Total volts, State Of Charge, Temperature
Inidividual battery voltages
Individual battery State Of Charge
Individual battery temperatures
 

Mockups of what will be on the main screen.
Screen 1
Battery SOC (State Of Charge, %), Volts, Amps, Units in(Kwh), Units out(Kwh), Run time, estimated remaining time, Load (Kw)
Solar panels Volts, Amps, Units in(Kwh), Load (Kw)
Grid Volts, Units in(Kwh)
House Load (Kw), Units used(Kwh)
Screen 2
Total volts, State Of Charge, Temperature
Inidividual battery voltages
Individual battery State Of Charge
Individual battery temperatures
 

Mockups of what will be on the main screen.
Screen 1
Battery SOC (State Of Charge, %), Volts, Amps, Units in(Kwh), Units out(Kwh), Run time, estimated remaining time, Load (Kw)
Solar panels Volts, Amps, Units in(Kwh), Load (Kw)
Grid Volts, Units in(Kwh)
House Load (Kw), Units used(Kwh)
Screen 2
Total volts, State Of Charge, Temperature
Inidividual battery voltages
Individual battery State Of Charge
Individual battery temperatures
 

Mockups of what will be on the main screen.
Screen 1
Battery SOC (State Of Charge, %), Volts, Amps, Units in(Kwh), Units out(Kwh), Run time, estimated remaining time, Load (Kw)
Solar panels Volts, Amps, Units in(Kwh), Load (Kw)
Grid Volts, Units in(Kwh)
House Load (Kw), Units used(Kwh)
Screen 2
Total volts, State Of Charge, Temperature
Inidividual battery voltages
Individual battery State Of Charge
Individual battery temperatures
 

Mockups of what will be on the main screen.
Screen 1
Battery SOC (State Of Charge, %), Volts, Amps, Units in(Kwh), Units out(Kwh), Run time, estimated remaining time, Load (Kw)
Solar panels Volts, Amps, Units in(Kwh), Load (Kw)
Grid Volts, Units in(Kwh)
House Load (Kw), Units used(Kwh)
Screen 2
Total volts, State Of Charge, Temperature
Inidividual battery voltages
Individual battery State Of Charge
Individual battery temperatures
 

Mockups of what will be on the main screen.
Screen 1
Battery SOC (State Of Charge, %), Volts, Amps, Units in(Kwh), Units out(Kwh), Run time, estimated remaining time, Load (Kw)
Solar panels Volts, Amps, Units in(Kwh), Load (Kw)
Grid Volts, Units in(Kwh)
House Load (Kw), Units used(Kwh)
Screen 2
Total volts, State Of Charge, Temperature
Inidividual battery voltages
Individual battery State Of Charge
Individual battery temperatures
 

Mockups of what will be on the main screen.
Screen 1
Battery SOC (State Of Charge, %), Volts, Amps, Units in(Kwh), Units out(Kwh), Run time, estimated remaining time, Load (Kw)
Solar panels Volts, Amps, Units in(Kwh), Load (Kw)
Grid Volts, Units in(Kwh)
House Load (Kw), Units used(Kwh)
Screen 2
Total volts, State Of Charge, Temperature
Inidividual battery voltages
Individual battery State Of Charge
Individual battery temperatures
 

Some progress. 
Writing firmware is a long slow process, especially if you can only spend evenings on it. Here's the control unit in it's box, with the LCD operational. I've completed various firmware modules by now (Real Time Clock, console interface, USB serial port, WiFi interface, LCD interface, etc). These are all the "building blocks" on top of which the main application will run. Should be starting the main application soon...

Well done, Weasel, you've spotted most of it.
This is a monitor and control system for my Solar installation, it will feature:
Monitoring each battery's voltage individually (string of 4). Monitor each battery's temperature (up to 16). Measure current into and out of the batteries. Measure current and voltage from PV's. Read grid voltage/Wh from the inverter. Integrate all this to determine Wh obtained form the sun, into batteries, used by the house, etc. Control the (Axpert) inverter to make optimum use of the batteries (not just based on voltage, but on SOC). Try and optimise usage of the PV panels. Display any 10 parameters (on the 7-seg LEDs) in real time - for viewing at a glance / from a distance. UI on the LCD for configuration, graphs (maybe), etc. Log to an SD card. Report via WiFi for remote access. Alarm indication with buzzer. Relay outputs to allow, for example, an aircon or geyser to use excess PV energy instead of wasting it once the batteries are full. Estimate remaining battery run time and display in real time. Integrate with the battery balancer (coming soon) Count battery cycles, monitor battery health over time to guess life expectancy. Etc. All this without having to keep your computer on.

Some progress. 
Writing firmware is a long slow process, especially if you can only spend evenings on it. Here's the control unit in it's box, with the LCD operational. I've completed various firmware modules by now (Real Time Clock, console interface, USB serial port, WiFi interface, LCD interface, etc). These are all the "building blocks" on top of which the main application will run. Should be starting the main application soon...

Some progress. 
Writing firmware is a long slow process, especially if you can only spend evenings on it. Here's the control unit in it's box, with the LCD operational. I've completed various firmware modules by now (Real Time Clock, console interface, USB serial port, WiFi interface, LCD interface, etc). These are all the "building blocks" on top of which the main application will run. Should be starting the main application soon...

Don't mix panels, get 300W ones.
It is easy to forget that current is drawn from a source, while voltage is "pushed" from the source. This means that the panels cannot "give" the MPPT more watts than what the MPPT wants... the MPPT will use as many wtts as it can get, up to it's own maximum. Why do I say this? Well, if your MPPT maxes out at 3KW of PV then it simply means it cannot use more than 3KW. You can put a 5KW collection of panels on, it will not damage the MPPT... the MPPT will simply only use up to 3KW and the other 2KW will be wasted.
In other words, use 300W panels, go up to 3.6KW or whatever, and let your MPPT use as much of it as it can.
This is the same as using very large capacity batteries instead of smaller ones... as long as the voltage is correct it does not increase the power you suddenly get. The batteres just last longer but your instantaneuous power remains the same.

Like edmundp says, indeed it is. I run my own software inside there instead of using Expressif's AT command mode, though, as it allows to unload lots of bloat from the main CPU.

Main PC board assembly is complete, sans the LCD. Now it's time to hunker down and get the firmware done.
 

Some progress... excuse the blurryness, the LEDs tend to flood the camera sensor so I used some tracing paper as a diffuser.
 

Main PC board assembly is complete, sans the LCD. Now it's time to hunker down and get the firmware done.
 

Main PC board assembly is complete, sans the LCD. Now it's time to hunker down and get the firmware done.