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48v LL Battery cluster overloading charge amps modbus register

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SomeJ
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I have 36x 48v LL batteries clustered with closed loop communications to a Schneider Insight Facility device.

There is a mix of v1, v2, and S versions in the cluster.  Currently a v2 unit is acting as the cluster master and handles the communications with the Insight Facility device.

What I am seeing is when the charge amps into the cluster goes above ~328amps the modbus register overloads and loops around to a negative number.  I found some old modbus docs and the info there supports what I am seeing.

image

 

How this is presenting its self to the Insight/Conext system is when the register rolls over to negative the system then thinks the battery cluster is now discharging instead of charging.  While this is not a problem in general functionality, it does create issues with proper energy charge/discharge/use tracking/stats.

 

An example of what I am seeing.  Say the battery cluster is charging at 350amps.  The cluster master then reports to Insight Facility that it is actually discharging at -305.35amps.  How did we get to this number... 350amps - 327.67amps + -327.67amps = -305.35amps Layman terms.... (Actual charge amps) - (register max pos value) = (rolled over amps).  (rolled over amps) + (register max neg value) = (amps displayed by master BMS)  I suspect this same issue would happen if the combined discharge amps went below -327.67amps, the reported amp "draw" would wrap around into a pos number and the Insight Facility would then report the batteries as charging instead of discharging (I don't have enough inverters installed to be able to test that theory though) .

I do not know what the current firmware version is that I am running on the batteries, but I do know they all have the same version on them.  I added some LL-s units to the cluster earlier this year and had to downgrade their firmware to get them to talk properly with the rest of the cluster.  I could try using a LL-s unit as the master, but the problem will still be there if the modbus register is still a 16bit signed integer.  Same with upgrading firmware, I can give it a try, but unless an engineer verifies the modbus register size has been increased, then the issue will persist.

So I guess the question is... Has anyone found a real way around this issue while maintaining full closed loop coms with the battery cluster and Insight Facility?  And is EG4 aware of this issue?  This probably was not as big of an issue with the old 16 battery limit, but now that they support up to 64 batteries in a cluster, logically it would take more amps to fully charge the cluster if it is being exercised daily.

 

Thanks!

J

 

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SomeJ
Posts: 7
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(@somej)
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I can't find a way to edit the original post while it is in a pending state, but one solution that EG4 could employ without increasing the register size, would be in change the unit of measure from 10mA to 100mA.  This would then allow for a reading of up to 3,276.7amps.  Im not sure if that would break any kind of unit standard being used by the closed loop communications.  I do know that the Insight Facility unit only displays amps to 1 decimal point, so having a 2 decimal point granularity is overkill/ignored by this particular platform.

 

J

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SomeJ
Posts: 7
Topic starter
(@somej)
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Joined: 3 months ago

Here is a graph from yesterday showing how this effects the tracking of data.  That sudden big drop in the amps is when the register overflowed and wrapped around to a negative number.  When that happens the system begins counting those amps as discharge / load, so the longer it goes on the more inaccurate the data for that day will be.

image
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SomeJ
Posts: 7
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(@somej)
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Joined: 3 months ago

Since it's been 2 weeks with no response from EG4... I figured I'd give a bit more info to show that this is NOT a problem with the Insight Facility device.

The register I am reading from the facility devise its self is #515 which is a 32bit signed integer, so the storage space is more than enough for the numbers we are talking about.  The only logical conclusion I can come up with is the BMS of the LL batteries is reporting the wrong amps when using modbus with such a high total amp draw or charge, especially given that such a small storage space was given to that register.

Insight Facility document showing the info for the register I am pulling and what is being used by the facility unit its self for graphing.

image

Registers 519, 521, 523, and 525 all use the info from 515.  So if the amps provided by the LL's BMS is wrong, then 4 other register values are directly effected, on top of the tracking/stats registers as they are going to be summing the battery charge and invert power over time.

To further add, when looking at the BMS data reported to the facility device through the web interface, the BMS is reporting that it could handle 3600 discharge amps or 1800 charge amps, which is accurate for the number of batteries installed in this cluster, however the BMS is not able to report a real time amperage number even remotely close to those maximums.

image

 

J

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