What is a good LBCO to avoid the inverter driving the bank under 2.5v sustained?

[hwy17]

My system currently lacks any means for the Orion BMS to communicate a shutdown request to the Schneider XW+. The Orion can call for 2.2kW grid input when it reaches a set low SOC, but it's possible our load could inadvertently outpace the 2.2kW and keep draining the battery bank.

Long term I have two possible solutions:

- Double the 2.2kW to 4.4kW so that load outpacing the backstop input is ruled out.

- Enable canbus comms between the Orion and the Schneider so that it can communicate a shutdown request.

In the meantime my low battery failure modes are:

1. Inverter observes LBCO by the voltage at it's terminals and shuts itself down (preferable)

2. Orion observes sustained cell <2.5v or pack <40v and opens it's contactors under load (not preferable)

What LBCO voltage would be most likely to achieve result #1 before #2, but with the least likelihood of an early "false alarm" LBCO event?

46v, 44v, 42v, 41v?

 

[sunshine_eggo]

First, enable canbus. It's awesome. My Batrium tells my stuff what to do.

It may take some trial and error on your part, but a voltage based cut-off can be impacted by load triggering premature cut-off. HOwever, do you really care if cut-off happens at 5% or 10% or some exact value, or are you okay with, "this battery is close to empty."

I would start with 44V and see how that serves.

 

[hwy17]

First, enable canbus. It's awesome.

It sounds hard though! All I've got is a few crumbs of a lead on some canbus messages that might shutdown the inverter. Definitely not any full support for SOC communication or anything like that.

Thanks I will try 44. I'm fine with the first discovery being an early LBCO rather than a late one and contactors opening.

 

[toms]

With my LiFePO4 that doesn’t have inverter comms I set my BMS cell LVD to 3.0V, and my inverter LBCO to 50.0V

This seems very conservative, but I regularly run that system to inverter shutdown and get over 80% of battery capacity, so I see no reason to stretch the cells any further.