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Question about connecting 2 inverters to 1 battery bank

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aussiesam

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I checked on this forum before buying and was told that connecting 2 inverters to 1 battery bank would work fine. So I went ahead and purchased a second inverter, I now own the EG4 3000EHV and the EG4 6000XP and was hoping to connect them both to a battery bank consisting of 5 EG4 LL batteries. Before I made the connection I called Signature Solar to ask some technical questions, this is when I was told by their support that connecting the 2 inverters to the same battery bank would cause issues when one inverter is charging and the other would be discharging. I was basically told not to do it. This is very frustrating because I had asked before purchasing these systems and was told that they could share the same battery bank. So before I make a permanent decision I just wanted to ask the experts + @EG4TechSolutionsTeam & @FilterGuy for a second opinion . Could you please confirm/deny that what I was told is accurate? Would this setup cause issues as I was told by Signature Solar or could they work with the same battery bank? (Each inverter would have its own panel, they would only be sharing the battery bank).

Your feedback would be greatly appreciated.
 
Open loop or closed loop?

I doubt both of your inverters, two different models, can talk closed loop with the battery. So they can't both know what SoC is.

People often connect multiple inverters of same model in parallel (or series to make 120/240V split-phase from 120V single phase), but in that case the inverters have a synchronizing cable between them.

If I made two inverters that didn't know anything about each other share a battery, I would install a shunt and let both sense it, so they know about each other's charge and discharge. (typically with inverters configured for lead-acid battery even if it was actually lithium.)

I might have one inverter closed-loop with lithium BMS while the other inverter thought it was AGM battery and connected to a shunt. I am contemplating that for an unusual system.
 
I suspect they would tell you that if both were trying to do comms to the battery pack.
 
I'm kinda surprised that they were against it.
They are usually only against things that involve purchases from someone else.
But everything you listed is EG4.
 
It can work, but there are a few things to keep in mind.

* If both inverters are running full bore, will the batteries be overloaded. (This should not be an issue for your set-up. You have a total of 9KW so the inverters will only draw 9000/51.2 = 176A. Your 5 LL batteries should handle that just fine.

* If both inverters are charging, can you exceed .5C on the batteries. I would have to look up what the inverters can do, but the 5 batteries can take 250A so you should be able to set things up to work within the .5 (250A limit).

* You can not have both inverters set up with closed loop.

* Both inverters set up for open loop should work fine.

* You could have one of the inverters set up with closed loop and the other with open loop. It should work OK, but I could imagine a few oddities.
(I would try this out with the closed loop on the 6K.)
 
How are you intending to connect the outputs of the two inverters? Because they are different inverters they cannot be paralleled.
 
Hedges said:
Open loop or closed loop?
Click to expand...
The original idea was to have the 6000XP running closed loop and the 3000EHV open loop using perhaps a lower voltage range. I wanted both inverters to charge the battery bank using only solar.

FilterGuy said:
It can work, but there are a few things to keep in mind.

* If both inverters are running full bore, will the batteries be overloaded. (This should not be an issue for your set-up. You have a total of 9KW so the inverters will only draw 9000/51.2 = 176A. Your 5 LL batteries should handle that just fine.
Click to expand...
If I would only use the 6000XP, I could potentially hit the 3000watt limit on one string based on how I would have to balance the loads in the house, adding the 3000EHV I would never exceed 50%, 90% of the time I would be under 2000 watts total. My other reason for doing this is because I actually have 50hz and 60hz equipment and using two inverters would allow me to generate both frequencies.

FilterGuy said:
* If both inverters are charging, can you exceed .5C on the batteries. I would have to look up what the inverters can do, but the 5 batteries can take 250A so you should be able to set things up to work within the .5 (250A limit).
Click to expand...
The 3000EHV can charge up to 80A, the 6000 can do up to 125A
 
The only oddity I've run into so far is what I'm referring to as micro-cycling. Since this time of year I'm using more than I'm producing AIO-B (no comms) is putting energy in (no AC connections yet) until it rises to 1% above my set min charge level. At that point AIO-A starts pulling all its power from the battery until it draws it back down to the min level, at which point it goes back to passing through the grid. It can do this 10+ times a day. Finally now it's getting enough sun that I'm making enough power that it's more than I'm using in the middle of the day so I'm getting some charge in the battery. Today is supposed to be another sunny day so we'll see what it does today.

20 kW of panels on a 4/12 pitch roof into A, 2 kW at 60° into B so far. 60 kWh battery bank.
 
FilterGuy said:
* You can not have both inverters set up with closed loop.

* Both inverters set up for open loop should work fine.

* You could have one of the inverters set up with closed loop and the other with open loop. It should work OK, but I could imagine a few oddities.
(I would try this out with the closed loop on the 6K.)
Click to expand...

With one or both open-loop, are those set for VRLA?
Do they try to track SoC? Will they do something undesired (like shut down thinking it is low SoC) due charge/discharge current from other inverter they are unaware of?
Or do they just go off voltage limits so everything should work fine?

It appears to disconnect based on low SoC: "45 Low DC cutoff SOC Default Default 20%, 5%~30% Settable"

My Sunny Island require a shunt to track DC connected devices. It doesn't appear 3000EHV AIO supports a shunt.
 
Hedges said:
My Sunny Island require a shunt to track DC connected devices.
Click to expand...
In the Lithium instructions SMA tell you not to use a shunt, I do and the SI continues to export the shunt flow data so I can monitor Kwh in vs out on my data logger but the SI no longer uses the shunt data for SOC calcs and only uses the BMS reported SOC.
 
I got the same issue and just talked to SS. I was just told today not to share the same battery bank but before setting everything up I was told that it was ok to connect two AIO to one battery bank. So I'd like to hear what options and/or settings can be used when sharing a battery bank. Or must I totally separate the 2 systems?

My setup:
18KPV grid tied and with CLP with close loop comm to 6 rack mount batteries (30KWh). One II-S and 5 Lifepower 4 V1 batteries.
Second inverter is the 6500EX and sharing the battery bank and suppling different loads is setup with USE battery bank voltage settings. I set Bulk to 55.2V and Float to 53.6V so that the 18kpv controls the charging and the 6500EX does not override the 18kpv. When the batteries are low the 6500 ramps up and helps charge the batteries. The 18 has 9,970 watts PV and the 6500 has 1,800 watts of PV. Both well below the limits.

Following the thread for advise.
tsp
 
SoTxUser said:
I got the same issue and just talked to SS. I was just told today not to share the same battery bank but before setting everything up I was told that it was ok to connect two AIO to one battery bank. So I'd like to hear what options and/or settings can be used when sharing a battery bank. Or must I totally separate the 2 systems?

My setup:
18KPV grid tied and with CLP with close loop comm to 6 rack mount batteries (30KWh). One II-S and 5 Lifepower 4 V1 batteries.
Second inverter is the 6500EX and sharing the battery bank and suppling different loads is setup with USE battery bank voltage settings. I set Bulk to 55.2V and Float to 53.6V so that the 18kpv controls the charging and the 6500EX does not override the 18kpv. When the batteries are low the 6500 ramps up and helps charge the batteries. The 18 has 9,970 watts PV and the 6500 has 1,800 watts of PV. Both well below the limits.

Following the thread for advise.
tsp
Click to expand...
Sounds exactly like my situation which is why I wanted a reply from EG4 so I reached out to them but they have not responded (yet).. Talked to someone again today at SS who gave a very strange explination claiming that if one inverter was in open loop... Hear this one: "the inverter could misreport the state of charge to the battery bms".. He said your battery could then be sitting at 56V yet report that its only 70% charged..

I've run eg4 batteries in open and closed loop and have never had an issue with the BMS, because when in open loop you would use voltage as an indicator of SOC. I've also never heard of an inverter reporting to a battery what its SOC should be, thought it worked the other way around..
 
EG4 reply :

"We apologize for any confusion and inconvenience this may have caused. Unfortunately, these inverters cannot share the same battery bank, as it will cause issues, as explained by Signature Solar.

A possible solution would be to have the inverters separate, assigning three batteries to each. However, these two inverters cannot be paralleled together or connected to the same battery bank."
 
aussiesam said:
EG4 reply :

"We apologize for any confusion and inconvenience this may have caused. Unfortunately, these inverters cannot share the same battery bank, as it will cause issues, as explained by Signature Solar.

A possible solution would be to have the inverters separate, assigning three batteries to each. However, these two inverters cannot be paralleled together or connected to the same battery bank."
Click to expand...
Just to clarify... I know that 1) the inverters cannot be paralleled (it's impossible in my case), 2) the inverters cannot share the same load (kind of the same thing) but is EG4 saying that they cannot be connected to the same battery when everything else is independent except for the battery bank?

tsp
PS: If so, in my case, I'd rather not use the 6500 unless I get some cheap batteries for it... like the E-W batteries if they're still $800. I "think" they communicate with the EG4 6500EX.
 
Thy problem is that you cannot have the inverters feeding the same load center. If thy went to 2 different banks it should work out just fine. Yes 1 inverter could be charging and the other 1 could be discharging. It would be better if they were the same and paired together. I have 2 inverters on the same battery bank and thy work paired together and separately.
 
aussiesam said:
EG4 reply :

"We apologize for any confusion and inconvenience this may have caused. Unfortunately, these inverters cannot share the same battery bank, as it will cause issues, as explained by Signature Solar.

A possible solution would be to have the inverters separate, assigning three batteries to each. However, these two inverters cannot be paralleled together or connected to the same battery bank."
Click to expand...
What a giant pile of BS. lol
 
wpns said:
Just brainstorming: Could one inverter be talking CAN and the other one RS485/Modbus in order for both inverters to be doing closed loop with the same battery bank?
Click to expand...
No. Unfortunately that would not work.
 
We were doing something similar before we got our third Deye inverter.

Four of our five packs were talking closed-loop to the two parallel Deye units.
The fifth pack (which wasn't talking to the other four, only DC connected) talked closed-loop to our Sofar hybrid.

All packs have Seplos V3 BMS's.

It worked fine and the Sofar got reasonably matching SOC for the bank compared with the Deye units.
 
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