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

 

[irmscher001]

Hi #40Fan, stik, ChrisG-UK...

First of all please accept my sincere apologies for my delay in not being on this forum. We had a relative terminally sick, and pass away. That stole my complete attention through a rough period. The solar system was the last of my worries.

I have just returned to this problem, yes, 10 months later, still not fixed.

After my initial message in 2023, I tried restarting the inverters at 240V and essentially wrecked one of the inverters that promptly failed. I think during the restart the parallel function failed. I recall it clicking loudly, an alarm, and then all parallel functions were missing in menus, and voltage settings for charge etc were blocked. The inverters damaged. I have no clue why it happened.

So an update. Last year at the time I tried dealing with MPPSolar. They wanted me to strip down and disassemble the unit myself. That just wasn't possible, due to events and my own skills that haven't done anything to that extent thus far. The property has been running on the single 11kw Max inverter ever since quite happily. I cannot fully blame MPP Solar as I haven't been in a position to provide resistance values etc, but equally I cannot say they were at all easy to deal with. They would not at the time just take the inverter back. Now in 2024 today, I can send it back for repair, but ultimately at likely massive own air postage to Taiwan. I will have to try dealing with them again.

ChrisG:
I don't think it is this. The inverter tends to limit maximum power but not voltage output. Essentially power overload occurs earlier the lower the voltage. In essence running Pylontech 15 cell typical battery voltages on discharge under load can be in the range 47.8 - 51.1 Volts thereabouts, and from experience maximum inverter capability is somewhere between 9-10 Kw. This is as you spotted the reduced voltage. This was a nasty surprise after buying the units, but ultimately it's not too bad, it's still powerful. With 2 units that's a full 18-20 Kw power capability which is still massive.

The issue I have now is, I have 2 PV strings (6.3kw) from rear roof on my single working inverter. The broken 2nd inverter means my front solar panels (4.2kw) are out of action. I'm down to keeping power output at or under around 8kw to not trip the inverter inadvertently. I can run the house on that, but the moment I want to suck power out to the EV charger and god forbid water heaters, it exceeds running the house and all of that at the same time. This was the reason for doing parallel big system as well as the redundancy of having two inverters.

It would be good to get in touch directly with others running these exact units be it 8kw or 11kw, for mutual support and troubleshooting. I will try sending you a direct message, but anyone with these inverters willing to join us please let me know.

 

[irmscher001]

Should anyone have Voltronic or same as MPP Solar PIP Max 11kw / 8Kw, please feel free to connect with other owners both here, and also (if I am okay to share a WhatsApp group):

MPP Solar PIP MAX Inverter Group

WhatsApp Group Invite

chat.whatsapp.com

I've done this as a way to connect owners of the same inverters to help each other.

Mods, I hope this is okay, this is just a way to connect owners of same inverter and is not an online forum, or for any other purpose.

 

[stik]

Sorry to hear about your relative

So when i first set my pair of inverters up they failed to go into parallel mode, or maybe i failed to follow the cryptic instructions properly. Either way there was a very loud hum for a second then something exploded and filled the garage with smoke! MPP accepted it was a fault and offered to send me a new main board for the one that exploded as a warranty claim, although they wanted me to pay the shipping which was about £90 i think. They also wanted me to open it up, and do the replacement when it arrived. I'm a relatively experienced hobbyist EE so this was fine for me, but i think with some care and attention anybody could do it. It takes quite a long time, there's a lot of screws and connectors etc, and everything's quite big and heavy. clear a well lit work area, take it slow, label everything as you go, maybe even video the disassembly so you can refer back.

Anyhow the thing i learned from this experience was do not connect the AC outputs together, make sure you have independent breakers on each one (this is a good idea anyhow) and open them before you turn the inverters on. get them up and running, make sure they're showing HS and SL on their displays and that they're showing the same output voltage, then you can close both breakers at the same time.

I wonder what's died in yours - i think this family of inverters used to have parallel operation enabled by a separate plug-in module, that's built inside as standard now. it's been a while since i've been inside mine but as far as i can remember it's still a separate board. it's got the parallel comms and current sharing connectors on, and is pretty simple i think, so maybe if yours won't go into parallel mode it's something to do with that?

Roughly where in the UK are you? I'm near Grantham. Happy to lend tools/assistance one weekend if you happen to be somewhere relatively nearby

 

[irmscher001]

Hi Stik. That's useful to know. Yes maybe it is something similar. I'm in West Midlands so a long way away, but moral support and a video call might suffice when the time comes to strip it down.

Interesting what you say about the parallel cards, that brings questions. Mine had them built in. The master inverter continued to work. They were put into Master & Slave before turning inverter on. I had a similar thing happen but wasn't brave enough to leave them running for more than a few seconds after not liking what I was hearing and seeing.

Do you recall afterwards having any 'high bus voltage' warning codes, and not being able to select parallel mode in menus, and also not being able to change charge voltages. Does this sound familiar? What happened to your parallel card, even if built in, is it on the main board you changed or separate?

It does sound like mine did similar to yours.

We need better instructions for starting up these inverters, but your comments are helpful in terms of opening the AC output breakers during the process, if that's what you suggest.