SBMS0, Setting max SOC

[Torben Dahl-Nielsen]

In section 8 of the manual is says:

'The max SOC limit is in this example set at 70% and what will happen is that every new day the battery will first be fully charged 100% SOC but then the next charge cycles for the same day will only start at 67% and end at 70% so it will stay around 70% SOC and cycle there with a 3% SOC hysteresis '.

Section 8 is however on '

[Torben Dahl-Nielsen]

Sorry, hit wrong key...

Section 8 is however on 'Dual PV array functionality and SOC charge limiting', and I am not using Dual PV.

Is it in general possible to set SBMS0 up to have SOC staying on some level like 80% or even 50% - and thus avoiding to go towards 100% SOC in the beginning of the day. I have read, that over long periods, when no mentionable load is on, this is good for the batteries.

(Maybe very obvious to understand from the manual, but I am in doubt).

Best,

Torben

[Torben Dahl-Nielsen]

After studying the manual again, I assume the answer for my wish could be:

• Use an available available extra EXTIO - say EXTIO 5.
• Set the this EXTIO 5 to 'Type 3 High SOC Alarm' and set its SOC to 80%
• Connect wire as:
  • Battery+ to resistor
  • resistor to EXTIO 5+
  • EXTIO 5- to EXTIO 4+
  • EXTIO 4- to charger remote control+
  • charger remote control- to battery- (if relevant) 

where EXTIO 4 is set to type 1, the default.

Now I assume, that EXTIO 5 is open, when SOC is below the 80% treshold. And the result should be, that the charger is charging, when voltage is below 'end of charge' (leaving EXTIO 4 open) and SOC also is below 80% (leaving EXTIO 5 open).

Anybody has an opinion, if this would work?

[B0bD]

I think a lot of the discussion about not charging to 100% refers to 100% = 3.65 volts.

The default on the SBSMO is 3.55, and this can be set lower if you wish.

Since the SBSMO stops the  charging at the set voltage, without any "absorb" at that voltage, the potential issues with constant charging to 3.65 are largely avoided.

In my system, the battery only spends very little time at 3.55.  on charge, it takes 5 minutes to go from 3.45 to 3.55; once charge stops, it takes only a couple of minutes to drop to 3.45, and it continues dropping to a steady state.

I have it set so that charging resumes at 90%; then during the day it cycles between 90 and 87%.

Just an opinion, but are you sure that the complications you describe are really needed?

[Jhon]

First of all, you might get the battery to last more then 10 years but the way things are going, we will most likely be replacing the cells before the end of their life anyway.

Would it not be better to turn of all charging and discharging if you are not using the batteries by simply unplugging the ribbon cable?  However if you are talking about a periodically used cottage, running security camera's and want to use the batteries to power those and send data back, you would be better off to use a raspberry pi, or similar  setup to monitor the temperature, the data from the SBMS0, etc and make some "intelligent" decisions for when you are not there to make them.   I think there are just too many possible scenarios we can imagine for the SBMS0 to accommodate.  Which is half the fun, we get to do some thinking for ourselves like you are doing now.

You can play with things, but from what I understand, changing the advanced settings needs some changes in other places as well that are not documented.  (I could be wrong)  I trust Dacian, he has shown time and time again he really knows his stuff, so I don't mess with the defaults.  (I will be adding a raspberry pi myself though)

[Torben Dahl-Nielsen]

Hi B0bD and Jhon, Thanks for feedback, I appreciate.

B0Bd: 

Agree that 3.55 isn't pushing things to the limit, but still some out there think staying closer to the middle is healthier, and I am reluctant to lover this voltage, since Dacian states, that you might need to adjust other advanced settings accordingly.

You write: 'I have it set so that charging resumes at 90%'. Wonder there you specify this? In the manuals section 8 the upper right picture shows the setup of 'DMPPT Settings', where Dacian has 70% while the text also talks about having the SOC around 70% during the day. I assume this is the place, even if no DMPPT is involved?

On the other hand the max charge current of 10A in the line above can have no effect without an DMPPT - since SBMS0 can only turn of and on external chargers....

One last thing I am in doubt about is the SOC functionality. In  section 11.5 Dacian writes: ' In this menu you can see the 16pin connector pinout and you can set the 4 EXT IO pins as one of the 5 types including the possibility to change state when battery SOC is above or below a user defined SOC'. I only find descriptions of the 5 types elsewhere on the internet (not in Dacians manual). But still in doubt for type 3: Is this to allow specification of a percentage in the line below. And will this have effect, that when battery voltage is below the specification the EXTIO is closed, while it is opened, if the battery voltage exceeds the specification? (or maybe the other way around, I guess one way to find out, is to measure the EXTIO open/close state while the percentage parameter is being changed).

[B0bD]

ON the DMPPT screen, the first line - Max PVOUT current, is used if you have two arrays. The SBMSO uses that setting to decide whether to turn on one array or both, to keep the current within a maximum charging limit.  It only works if you have PV1 and PV2 connected and have a means of separately turning them on.

The next line - Max SOC - is the setting that SBMSO uses to control the second and subsequent charges of the day.  The first charge will be to 100% (3.55 volts at the default setting.  Then, once teh battery gets drawn  down to the Max SOC setpoint minus 3%, charging will resume and charge until the setpoint is reached..  I set mine at 95%; after the first charge of the day it then cycles between 92% and 95%.  Works great.

As far as the discussions about battery life and SOC, no dpubt if you don't use them much they will last longer.  The specification for most of the 280AH LFP batteries states 3000 cycles; cycling 100%. For me, that provides more than two decades of life, so I quit worrying about it, especially when charging to 3.55 volts without absorb is already conservative.

[B0bD]

Here is a plot showing the behaviour I described, with the Max SOC set at 95%.

The graph starts a couple minutes after reaching 3.55 volts, at which point the SOC is set to 100%, and the charging is stopped.

Then, as the SOC drops to 92% after a couple of hours, charging starts, and is on until the SOC hits 95%.  During that charging, the average cell voltage only hit 3.36 volts.

[Torben Dahl-Nielsen]

Yes B0bD, maybe I worry to much for no reason. My Idea was, that when I buy much capacity (24 310Ah cells) there is not much reason for pushing towards the upper edge, I will be able to manage without sun for weeks in any case. And in periods where the boat is left unused with hardly any load is will stay close to the 3.55V all the time - for months. Probably no problem.

Another down to earth thing. On electrodacus.com it says today 2 October:

     Out of stock.
     Orders can be made again starting in October.
     For any questions use the forum: Electrodacus Forum

And I don't know how to order (for Europe) 

lørdag den 2. oktober 2021 kl. 00.26.21 UTC+2 skrev B0bD:

Here is a plot showing the behaviour I described, with the Max SOC set at 95%.

The graph starts a couple minutes after reaching 3.55 volts, at which point the SOC is set to 100%, and the charging is stopped.

Then, as the SOC drops to 92% after a couple of hours, charging starts, and is on until the SOC hits 95%.  During that charging, the average cell voltage only hit 3.36 volts.

On Friday, October 1, 2021 at 1:51:04 p.m. UTC-4 B0bD wrote:

ON the DMPPT screen, the first line - Max PVOUT current, is used if you have two arrays. The SBMSO uses that setting to decide whether to turn on one array or both, to keep the current within a maximum charging limit.  It only works if you have PV1 and PV2 connected and have a means of separately turning them on.

The next line - Max SOC - is the setting that SBMSO uses to control the second and subsequent charges of the day.  The first charge will be to 100% (3.55 volts at the default setting.  Then, once teh battery gets drawn  down to the Max SOC setpoint minus 3%, charging will resume and charge until the setpoint is reached..  I set mine at 95%; after the first charge of the day it then cycles between 92% and 95%.  Works great.

As far as the discussions about battery life and SOC, no dpubt if you don't use them much they will last longer.  The specification for most of the 280AH LFP batteries states 3000 cycles; cycling 100%. For me, that provides more than two decades of life, so I quit worrying about it, especially when charging to 3.55 volts without absorb is already conservative.

[B0bD]

Actually, if your installation is more or less unused for a while, each day the battery will be charged up to 3.55 volts, but it will only stay there for a little while before settling down to mare like 3.3-3.4, where it will stay until the next morning when charging will resume.  I think you will find that while the peak of 3.55 is reached each day, the daily average will be very close to the resting voltage.

This assumes that you are stopping the charge as soon as 3.55 is reached.

What is your charging setup?

As far as contacting Electrodacus, just start a new thread with your specific question.

[Dacian Todea]

Sorry, It was a busy period and was not able to answer.

The few seconds the battery gets to 3.55V each day is needed to calibrate for 100% SOC else SOC will become incorrect.

Charging to 3.55V even multiple times per day will not influence the battery life in any significant way. My current A123 system battery is already over 4 years old and is used with SBMS120 that can not limit charging as the SBMS0 to a lower SOC after first charge so it will charge to 3.55V multiple times each day and based on current degradation battery should be good for about 15 years. Most of the degradation is due to calendar aging and smaller amount due to cycling and the calendar degradation is mostly influenced by battery temperature.

NMC and LiCoO2 are a very different sorry and there charge voltage will have a large influence in battery degradation that is why my default for those batteries is 4V instead of 4.2V and 4V means battery is only charged to about 80%.

With LiFePO4 things are very different and voltage is no indication of the SOC so charge needs to be done to at least 3.55V to make sure battery is full and so to know what the actual battery SOC is.

If you see a LiCoO2 at 4V resting voltage you know that battery is at around 70 to 80% but if you see a LiFePO4 at say 3.3V the battery can be 99% SOC or it can be 60% SOC you will have no idea based just on voltage.