Why is my SBMS0 not Balancing?

73 views
Skip to first unread message

Soggy Paws

unread,
Jun 5, 2021, 2:38:30 AM (7 days ago) Jun 5
to electrodacus
12v LiFePO4 system, installed and operational now for several months.  It was balancing as expected according to our settings.  Suddenly it seems to not be balancing, even with a high delta, current flowing, etc.  We have obviously done something but I'm not sure what.
I know the basic requirements for balancing are:
- At least 300mA charge current
- Cell voltages (all??, or only one?) above the Cell Balance min
- Cell voltage deviation above the Cell Balance min dV
We had all those boxes checked, yet no balancing was going on.
Here are a couple of guesses:
1. We've been talking about changing our balancing settings (changing the delta, and the beginning balancing voltage).  We MAY have gone in and changed the settings and saved parameter settings, but NOT actually powered off/powered on the SBMS0.  
Q: Would that cause it to stop balancing altogether, or still balance at the old settings? (We  can't remember if we actually did change the settings or just talked about it, but I know we have not powered of/on the SBMS0)
2. Heat related?  All the screen shots I have of balancing near charge termination, the SBMS0 temperature was around 73-75 F. (22-24C).  It summertime now and we are off the dock with no air conditioning.  The SBMS0 FET Temperature today was 81F (27C). Could there be a protection setting that shuts down balancing when the temp gets too high?
20210605_142908.jpg
Not Balancing Screenshot_20210605-114707_VNC Viewer.jpg
I searched for an old thread about balancing but didn't find one--lots of discussions about balancing buried in other discussions, so I thought I'd start a thread that just addresses this one question.
Thanks, Sherry

Dacian Todea

unread,
Jun 5, 2021, 1:39:16 PM (7 days ago) Jun 5
to electrodacus
Sherry,

If you changed anything in parameter settings and saved but did not power cycle then the old settings are still active. For safety reason there are two separate memories an non volatile EEPROM where settings are saved and a working RAM memory that is loaded with all the EEPROM content at power ON and it will only work based on the RAM memory content.  So if anyone by mistake changes the content of EEPROM by saving new settings they will not take effect until a power cycle is performed.
But looking at your photos the problem seems to be that current is negative meaning discharge so either you connected the battery current shunt wires with reverse polarity ADC1p will need on the Battery+ side of the battery or during last power up you had a current going through the shunt so zero offset calibration was wrongly done.
Both photos show a Load current tho shows cell voltage increasing so it is one of the two problems mentioned above.

Soggy Paws

unread,
Jun 5, 2021, 8:37:41 PM (7 days ago) Jun 5
to electrodacus
Hi Dacian, sorry I should have annotated my screen shot.  In that picture, we had 43 Amps coming from the Solar array (measured via Shunt, and confirmed from MPPT controller) and 38 actually going into the battery (measured via shunt).  The -10Ah is the estimated remaining Ah we need to charge to get to 100% (I reset this value every day when the SBMS0 says we are at 100%, and then keep a running total from the Battery number).
This has been working (balancing, etc as expected, current flows approximately correct) without messing with any wires or any changes, except changing the Parameter Settings as explained in my first email, but not restarting the SBMS0.
We will cycle power this afternoon after charge completion and see if that fixes it.  
I just wanted to make sure I understood whether NOT cycling power after making a parameter change would stop balancing.  Or if there was a high temp limit based on the SBMS0 FET Temp.

One final question:  Does your logic require ALL cells to be above the Cell Balance min value, or only just one, before balancing start?  I think we previously had the Cell Balance min set to 3.4, and in this case, only one cell is above that limit.  That might explain it.


Not Balancing Screenshot_20210605-114707_VNC Viewer annotated.jpg

Dacian Todea

unread,
Jun 6, 2021, 2:28:33 PM (6 days ago) Jun 6
to electrodacus
Sherry,

I did not properly looked at your photo and just assumed the web photo was just took immediately after the photo of the SBMS screen thus I only looked at the voltage graph and the -10.3Ah I seen as -10.3A that was super close of the -9.463A I saw on the SBMS screen.
Yes all cells need to be above cell balance minimum limit in order for the cell balancing to be activated. I think the default I set is 3.2V so if you changed that to 3.4V then in this case you show the cell balancing will not be active as only one cell is above 3.4V
 

Jim Fowler

unread,
Jun 7, 2021, 12:29:23 AM (6 days ago) Jun 7
to electrodacus
I've experienced the same issue with my SBMS0. I have to periodically power it off and back on to get it to start balancing again. It's actually rather annoying and has made me consider switching to a different BMS. Especially since I have to rest the date and time every time it has to be powered off. Haven't been able to narrow down yet what causes it. Sometimes it will go days and still balance fine, sometimes it will stop balancing the same day it was reset.

Dacian Todea

unread,
Jun 7, 2021, 2:42:20 AM (5 days ago) Jun 7
to electrodacus
Jim,

Please send a photo of the first monitoring screen when it is not doing cell balancing and I will let you know why that is happening.
For cell balancing to be performed there needs to be a minimum of 300mA of battery charge current and a cell delta higher than 11mV assuming you did not changed any of the advanced parameter settings and just used the default.

Reply all
Reply to author
Forward
0 new messages