Hi Bill,
Note, I'm not using the latest firmware.
What will happen to your system if your house 24V battery cuts out? Does this just serve the inverter? I think the answer will help with your recommended settings.
I also set SOC @ 0%. But within settings, you also set cell - level LVD. So there is redundancy. So, I disabled SOC cut-off by moving to 0% not wanting to confuse my cutoff point.
In the end, you want your loads (or charging) to stop before the battery BMS has to interrupt. So, your inverter probably has LV cutoff setting. Set this above where your battery BMS cuts out. And if you have non-inverter loads also, you could probably enable the Chargery alarm to sound at some LV threshold before the BMS cuts off.
Think of the BMS as last resort to protect the battery. So ensure your settings protect the battery, but don't think they have to do more or build in a lot of cushion.
I also had initial issues with the voltage differential getting as high as 200mV, before my battery balanced. After one or two charge cycles the balance feature resolved, so I no longer have voltage differential issues. Now, always less than 25mV, usually less than 15mV. I moved my cell-level balance to >3.35V and during storage, charge and discharge. It is now top-balanced, if that term isn't obvious. On an average night, I'm only using 30% of the capacity, so this top balance will suit my application great.
On the charge side setup, I have my Magnum SCC setup to CC/CV and charge @ 13.8V for 6 minutes in the absorb phase. This corresponded to cell voltages around 3.36V. And 95% SOC from one of the detailed voltage / SOC charts posted on the forum. Again, I prefer to have the charging cutoff than BMS "save" the battery. So, my cell-level voltage maximum is higher in the BMS than the charger.
Hope that helps.
Doug
Testing for Low Cell Volt Disconnect via using my "Empty Cell Voltage" setting did not work for me. See my info. below
Hi Doug: Thanks for feedback.
Re Your : What will happen to your system if your house 24V battery cuts out?
I have two MPP LV2424 All In Ones I will eventually wire up for 240vac split phase. I have yet to configure my exact cut outs, but have decided Not to use the Battery Cut Out method. My currently favorite option: I was going to wire the Discharge relay control from my Chargery BMS8T to an SSR to turn off my All In One units if the BMS had a discharge side trigger. That would protect my LiFePO4s from death by low cell voltage which I believe is the biggest LiFePO4 early kill a cell risk. I would be using Will P's SSR Youtube lesson method for that method. I would then likely wire the BMS's Charge side relay control to another SSR that would turn off my All In One's Charger by cutting off my Solar Panel Input (up to 30 amps) if my BMS triggered for a charge related fault.
I had consider other options. I was considering configuring the Chargery's discharge side relay control to turn off the All In One's Inverter (as mine does not have a separate switch for only that function) by using another SSR to disconnect my 120 vac output from my All In One units. The drawback to that method is it would would still leave my inverter and full unit with stand by idle draw on battery. While that configuration has the advantage to recover from a empty cell volt fault trigger without attention by leaving my All In One's MPPT solar charger in tact, ... the Idle consumption of my All In Ones could potentially kill a low battery cell if no one was there to attend the heads up.
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Re Your : I also set SOC @ 0%. But within settings, you also set cell - level LVD. So there is redundancy. So, I disabled SOC cut-off by moving to 0% not wanting to confuse my cutoff point.
My default for Low SOC cut off was set at 20%. I just tested that Low SOC cut off by configuring that specific setting up high to test BMS relay control with a SSR with led light. Yes, it turns off whatever you might connect to a relay (would turn off my whole All In One). If that is the case,
I like idea of keeping that SOC cut off setting. I will likely test my BMS to see just what voltage it cuts off at what % I set it to. I might want shift that setting to 10% after seeing what battery voltage that translates to. Disabling the SOC cut off does not make sense to me.
The only setting I could find in my Chargery BMS8T V 4.0 that resembles a Low Volt Disconnect is labeled "Empty Cell Voltage". I recently upped that setting from 2.5 volt (default for LiFe) to above my current lowest cell voltage (I set it at 3.61v when my lowest cell volt showed as 3.48v), & It Did Not yet trip my connected SSR led light to OFF.
!!! Heads Up: My Testing for Low Cell Volt Disconnect via using my "Empty Cell Volt" did not do the job for protecting my LiFePO4s from low cell voltage !!! I also do not see any other setting that might be used to protect from low cell voltage (which I believe is the biggest danger to LiFePO4s). I will leave my test in tact for awhile as the battery further drains to see if I can get a low cell volts reading to ever release my connected SRR relay. I wonder if that setting only works at lower voltage than I set if for ??? Currently, I am alarmed by what I just found out via testing what this BMS can do (part of my hands on learning program).
IMO: I have a faulty Chargery BMS8T, or a V 4.0 firmware update that needs a further update. Maybe someone here, or at Chargery has an explanation? I hope this is food for discussion.
IMO: Those with the Chargery BMS8T (especially V 4.0) might want to test to see if you have low cell volt protection.
Doug: Maybe setting your Low SOC cutoff to 0% still allows it to work. I would think setting it at 1% or more would be better. I personally want that redundancy, but it only work related to full battery SOC. ... I wonder if anyone else has the problem of no low cell volt protection I just figured out this morning. ?? Low Cell Voltage Protection is the main reason I purchased this BMS!
I do not see any other setting to test for that. I tested the "Cell Empty Voltage" setting on my Chargery , and it did NOT work (in my test). What are you Best Fix It Ideas, or better Test Ideas for that ???
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Doug: Re Your: I also had initial issues with the voltage differential getting as high as 200mV, before my battery balanced.... Now, always less than 25mV, usually less than 15mV. I moved my cell-level balance to >3.35V and during storage, charge and discharge.
I just shifted my Balance Start Voltage from default 3.2v to 3.3v ; ... and changed my Stop Diff setting from default of 30 mV to 20 mV. ... Plus favor turning ON Balance for all three: In Charge, Discharge, and in Storage (mode). I kind of liked your ideas on that (while I might go back to default and see if that is less draw down of battery which I noticed before even connecting my battery to my All In One units).
Re Your : ... you want your loads (or charging) to stop before the battery BMS has to interrupt. So, your inverter probably has LV cutoff setting. Set this above where your battery BMS cuts out.
YES, ... I got that idea down early. & Re Your: Think of the BMS as last resort to protect the battery. ... IMO: Absolutely Yes: Use a good BMS as a back up for protecting your kind of big $ LiFePO4 Investment.
Thanks Doug. Any other feedback, info., and/or opinions welcome. :+)