Batteries mysteriously drained down to ZERO...

[openplanet]

LiFePO4 400Ah bank.  Two Classics.  Both had been set to OFF in the morning because I didn't want to risk overcharging and would be away for the day (haven't automated that yet). Got home at night.  SOC 59%.  Set the Classics to ON in case I forgot to in the morning.  At 7 am everything died, battery bank was at ZERO.  (Normal overnight drop is in the 10% range.) No new or unusual loads had been on overnight.  No smell of smoked or melted wire insulation.  Absolutely the ONLY thing I can think of is that there was something about turning the Classics back ON at night (about 10 pm) that...what?  Grasping at straws, one of which is this trusty forum!
Thanks as always for any ideas.

[ClassicCrazy]

I had something like that happen with my Calb LiFePO4 batteries. I thought I had quite a bit of energy in them , shut off the solar since it was cold but left the Classic on and it had drained them down to shutdown .  That is why I realized a separate low voltage cut off needs to be on lithium batteries . At the time I got those BMS were not plentiful and very expensive so I tried to do without.

Larry

[mike90045]

I just don't see a charge controller being able to drain a partially charged battery bank overnight.  Something else must be going on. 

Maybe an internal LVD activated and you have to reset that first.

[boB]

First thing we need to know is your battery bank voltage.

Taking things at worse case, 12V system, 400 AH would be 12V X 400 = 4800 watt-hours energy storage.

Let's say the two Classics were drawing 10 watts while off for 24 hours.   

That would be 240 watt hours.

What does your ammeter say as far as current draw ?

[Steve_S]

What about the LFP Pack, are they DIY or Commercial / Retail ?
Common Port or Separate port BMS ?
What information can you provide about the BMS.  Typically they have Low & High Voltage cutoff as well as Temp cutoff(most do High Temp but not all, if they do Low Temp and if you hit 32F/0C they won't charge for safety reasons).  You need to program your classics for the Low Voltage cutoff point and set your profile for the LFP packs, adjust your inverter as well.   

[ClassicCrazy]

What about the LFP Pack, are they DIY or Commercial / Retail ?
Common Port or Separate port BMS ?
What information can you provide about the BMS.  Typically they have Low & High Voltage cutoff as well as Temp cutoff(most do High Temp but not all, if they do Low Temp and if you hit 32F/0C they won't charge for safety reasons).  You need to program your classics for the Low Voltage cutoff point and set your profile for the LFP packs, adjust your inverter as well.

The thing is that there really isn't a low voltage cutoff for the Classic . You can program high and low voltage cutoff for the charging but nothing is there to turn off the Classic itself.  In my case - it was not over night but over a period of time and I didn't think about the no load draw of the Classic and had no other BMS of low voltage battery cutoff.

Larry

[openplanet]

boB--Sorry, should have mentioned it's a 48v (nominal) bank.  Normal night time draw is around 2.5 Amps or 150 ish Watts.  So basically impossible that normal draw overnight could take the bank from 59% SOC to Zero.

[ClassicCrazy]

boB--Sorry, should have mentioned it's a 48v (nominal) bank.  Normal night time draw is around 2.5 Amps or 150 ish Watts.  So basically impossible that normal draw overnight could take the bank from 59% SOC to Zero.

What amp hour capacity do you have your SOC set for ?

Larry

[openplanet]

Larry--If you mean what battery Ah value have I configured the Classics with...400.
What's so puzzling about this event is that it did NOT happen after any configuration change, hardware or software.  Big concern though, as you can imagine.

[ClassicCrazy]

Larry--If you mean what battery Ah value have I configured the Classics with...400.
What's so puzzling about this event is that it did NOT happen after any configuration change, hardware or software.  Big concern though, as you can imagine.

So your battery bank went to zero volts ?
It must have been that your batteries were not really all the way charged for some reason .
How are you terminating the absorb charge on them ?

Larry

[Steve_S]

have you considered the possibility of a Bad Cell in the battery or failed BMS if you have one ?
Depending on your battery, If it's like a BattleBorn and encased or open unmanaged without BMS etc...   

[estragon]

I'm curious:
Where did the 59% SOC number come from?
When was the last time the SOC would have been reset, and how (end-amps/wbjr, absorb timer)?

What I'm thinking is if it's been a long time since 100%, the actual PSOC got walked down by loads more than captured by SOC metering.  With a pretty flat LFP voltage curve over useable SOC, it would be easier to miss than with LA.