Procedure if the SBMS switches off due to Low Battery?

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Barry Timm

Jun 7, 2021, 10:51:22 AM (5 days ago) Jun 7
to electrodacus
The other morning I realized that I'd left some high consumer devices on in my RV and my 7.8kwh LFP was down to 35% SOC. It occurred to me that I did not understand what to do if the SBMS gets to the low battery protection switch off threshold.

How do I get the BMS to accept solar charging when it has switched everything off?


Oberon Robinson

Jun 7, 2021, 1:04:56 PM (5 days ago) Jun 7
to electrodacus
Barry, the low-voltage disconnect is separate from the high-voltage disconnect.  If your battery gets drained, you will have a LVD condition, but charge sources will not be disconnected.  So it will still charge from solar, and as soon as your battery charge level rises above the LVD threshold, your devices will be able to run again too.

Dacian Todea

Jun 7, 2021, 2:01:14 PM (5 days ago) Jun 7
to electrodacus

As Oberon already replayed the Loads are separate from charge sources so if any cell gets below 2.8V then all loads will be disconnected but charge sources are still connected so if there is solar or other charge source available cells will be charged. But if for some reason a cell drops below 2.5V (should not happen if all loads are disconnected at 2.8V) then charge will also be disabled and you will need to manually slowly charge that cell or cells that dropped below 2.5V to re-enable charging.
But if cell is below 1V it is possible it may even went negative and then is not a good idea to for charging as cell may have been damaged.
But if all is installed correctly Loads will be turned off at 2.8V (likely voltage will recover to 2.9 or 3V after load is turned OFF) then battery can easily wait in this state for next day when there will be solar available and battery will be charged then loads will be re-enabled.

Barry Timm

Jun 10, 2021, 3:19:09 PM (2 days ago) Jun 10
to electrodacus
Many thanks guys. 
I must have been confused with an earlier discussion regarding the 2.5v threshold, as I was under the impression that once the Low voltage threshold was reached and loads were cut, the entire SBMS was effectively switched off. I recall a lot of discussion about why the SBMS was not programmed to allow charging in that situation. 

Thanks for the clarification. This is a relief as I have left my standalone regulated power supply device in Yuma, while w head North for the summer.

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