Just added 2nd Growatt in parallel single phase...

[DesertDude]

Greetings everyone...
Yeah, I'm a newbie... well, sort of...
I've been running solar for about 9 years now, the first 8 years or so on AGM until recently when I built an entirely new system with LiFePo4 batteries on a 24 volt system.
Things were working wonderfully with 2 LifePower4 SigSolar 24V batteries and a single Growatt 24V 3000W inverter. It was a rough beginning until I finally figured out how to set the Growatt to Lithium and have it work correctly. It's run all summer without a care in the world and I couldn't have been happier.
Then, a couple of days ago I tried adding a 2nd Growatt in parallel single phase and it all kinda went south on me. Everything actually worked fine in parallel mode except it no longer would run in Growatt menu #5 lithium setting... I had to go back to AGM or USE settings. It started with the ominous 4 & 20 error codes again as it did in the beginning before I figured it out.

So I guess my question is... Is there a way to set this up so that 2 Growatts in parallel will run in "lithium" mode???

I'm thinking the 2nd Growatt needs a cable from the BMS output to connect somewhere, but where? I'm guessing the 2nd unit needs a BMS input, henceforth the error codes. I tried every combination I could think of connecting to the batteries but no luck. I've yet to try this (since I've now disconnected the 2nd Growatt), but can I run that BMS cable to the 1st Growatt RS485 port that's still vacant?

I'm at a loss here, and things are getting desperate cuz everything is now going haywire and the batteries are acting really strange with faults, etc.
And just FYI, I'm a retired senior living completely off-grid and I so much need my electricity to survive out here.

Thanks so much for anyone who has read this far and might be able to help.

 

[BentleyJ]

Many have found closed loop BMS communication, especially with multiple inverters, to be nothing but problematic. In the short term there is nothing wrong with USE and just setting voltage values for charge and discharge. The key is keeping the batteries within the voltage limits of the BMS so you don't get High and Low protection cut outs.
Charging should be set at 28.0V (3.5V per cell) and the inverter should stop discharging at 24V (3.0V). These are conservative initial values and can be adjusted accordingly if needed.
One you get reliability restored with proper USE you can experiment with Lithium settings and if they don't work as expected you can revert back to known, good USE settings.

 

[DesertDude]

I can't thank you enough for taking the time to answer and give me a heads up on this... it is truly appreciated.
I had, or still have, a strong feeling your suggestion is the route I'm gonna have to take. In the beginning, before I got the system to work in Lithium mode I fought terribly in getting the right (or correct) voltages set, and it often would end up with cells going over the recommended range, of that makes any sense.

But today or tomorrow I'll reconnect the 2nd Growatt, set the battery type to "USE" and hopefully find the right values for charging and take it from there. I'm a pretty intelligent dude, but I'm baffled at why I can't figure all of this out!!

Anyway, I again thank you so very much. Have a really good one!

 

[DesertDude]

Well, gotta say I am now completely and totally baffled. I mean I'm utterly confused as to what just happened, or maybe that I just do not understand why this happened as it did.

I decided to go ahead and go out and re-connect the 2nd Growatt back into the system rather than wait any further. So I did just that, and powered everything up, and expected the alarms to go off with the ol' #4 & #20 errors generated by the Lithium setting in menu #5. I was all set to switch to "USE" and take it from there. Lo and behold no alarms!!! I was shocked (not literally - ha, ha) to see that everything was now working in "LI" mode. I mean... Huh??? Why all of a sudden did it decide to work? Not a question for anyone to answer... just a rhetorical statement.

Well, I'm just thankful and so pleased with this, but I'm the kinda dude that wants to know the 'why' things happen. Yet, I'll sit back and hope and pray that things continue as they are. I'm still however on pins and needles in that after all of this my SOC is way down... in the 50% range and it seems the batteries are not being charged whatsoever at the moment, though I can only assume the cloud cover is not allowing enough energy to charge. Oh well, such is life...

Thanks again.....

 

[DesertDude]

Yeah, I'm back... but this time out of concern of what I just discovered and think it important to ask.
Hopefully someone will read this far and maybe shed some light on this.

I fired up the app on my laptop - BMS Test - to check things out and it's showing one battery at a SOC of 63% and the other at 58%.
Both Growatt displays are showing a SOC of 58%.
I don't know which is right, or if it even matters. However, if the batteries are indeed at different states of charge, is that a big deal? Somewhere along the line I think I remember they should be identical.

Oh geez, as I'm typing this I just lost power. Oh! Now it just came back on... but yet I fear something is not quite right. Gotta go check on things... be right back.
Hmmmm... everything looked normal, but it brings the stress level up a bit.

Anyway, should I be concerned that the batteries are so far apart, and do I need to do something here and now... or will it self correct in a day or so???

Thanks!