2 x MPP PIP Max 2x11kw output voltage issue

[irmscher001]

I have 2 x 11 kw off grid inverters installed in parallel in UK, with 6 Pylontech US5000. These are single phase, and initially were setup without PV, and monitored using Solar Assistant. They were setup to run at 230v single phase, and were running just fine charging at night and discharging in daytime. Overall, I rate the inverters highly to date, they've been a dream in fact, no big issues at all, the system's a beast.

Having started up 4 PV strings (total 10.3Kw), I have noticed that the inverters have changed output voltage to 220v now, instead of 230v as desired.

I have tried changing various things on inverters, but whenever I change the output voltage to 230v it defaults back to 220v.

Anyone have any ideas? What is changing this back to 220v, is this a Solar Assistant setting issue or an inverter issue? I have not shut down the system, It is running in Solar/battery/Grid priority.

Anyone with a PIP Max and Solar Assistant that can help please?

 

[#40Fan]

Are you changing the expected input voltage as well?

 

[irmscher001]

Are you changing the expected input voltage as well?

As far as I know I never changed that. Solar assistant doesn't allow it. I will check that on the actual inverter.

 

[stik]

i have exactly the same problem, it's something to do with the inverters, not SA (i'm not running that). in individual mode they'll accept an output change, but as soon as i parallel them up again they go back to 220v. after a few attempts (like 5 or so) i can usually get them to remember the correct setting for a few weeks. i've just learned to live with it now, tbh

 

[ChrisG-UK]

Hi Irmscher001,

I've just bought 2 x MPP Max 11kw inverters and 10.44kw of PV. 30kw of batteries arrives in 6 weeks. Looks like my setup is almost the same as yours.

I think I may have found something that could explain it? On page 40 of the tiny manual you get with the inverters there is a section at the bottom of the page that says 'Power Limitation'. It says "When battery voltage is lower than 55vdc, output power will be derated. ............ The minimum AC output voltage is 220v."

A 16S lifepo4 battery has for most of its SOC a voltage of 51.2v (3.2v per cell). So, could it be that when fully charged and the battery voltage is over 55v (3.4375v per cell) even up to 56v, you can set the inverter to 240v and it's happy and outputs 240vAC. However, as soon as the battery discharges down to its normal operating range voltage of 51.2v then the inverter sees this drop of 3.8v and derates the output down to 220v.

Looking at the graph shown, if your selected rated power is 240v at 55vdc on the battery, the graph shows that at 42v the rated power output would be the rated output power x 0.725 which is 174volts AC. The difference in output is 66vAC. The difference in battery voltage as per graph is 13vDC. So, the AC voltage falls by 5.08vAC for every 1vDC the battery voltage falls. If we apply this to the 3.8vDC drop we get a drop of 19.3vAC. I reckon that's the value that the inverter uses to derate it's output? 240vAC minus 19.3vAC gives you 220.7vAC.

If you set your output voltage to 230vAC it will still go to 220vAC as that is what the minimum derating level is. It won't go lower.

I'll have to see how I get on when my system is installed but that's a couple of months away. Maybe query this with MPP?

I guess this doesn't explain why your system worked okay when you didn't have PV connected though? Maybe it has something to do with it?

If you get anywhere with MPP let us know.

 

[stik]

I've asked MPP a couple of times now and they've been pretty unhelpful. I'm certain this is a bug in the firmware on the inverters that only affects them in parallel mode. I've got the 8kw version (which i'm 90% certain is identical to the 11kw, they're just pushing the limits hence the need for a de-rating curve as the battery voltage drops and the current goes up) Sometimes the setting sticks, sometimes it doesn't