SOC % at 100% while Cell Volt only at 3.4volt - Need Help.

[Gilbert]

Finally received my 8x of Lifepo4 310Ah cells, 2P4S to 12v @ 620Ah, 

I kept the original provided ribbon length, and used Cat6 for Shunt & temp sensor.  All connections are clamped tight, then soldered.  

I am temporary setting up the minimum to test the Lifepo4 Cells, so only the inverter/charger, I attached my full system schematic incase you need it.  

The Issue I am having right now is the SBMS reads 13.39v and SOC already at 100%.

It doesn't make sense to me.  I read the beginner guide, user manual, and searching here for answers but no luck.  I attached few pictures of my wiring, SBMS settings, and a 30sec timelapse showing the SOC goes to 100% + few minutes before I manually stopped the charger. (worried it may damage the cells)

While charging (when SOC reached 100%), the battery voltage is only at 13.48-13.50v (cells voltage 3.37v-3.40v).   After I stopped the charger, the SOC immediately drop to 99% and battery voltage is 13.27volt (cell voltage 3.315-3.32v)

I did used an external voltmeter, to measure the battery, and it reads the same voltage.

As you can see from the pictures, I looked into (and if needed adjusted) the parameter settings, and ADC for the Shunt (both shunts are 50mv/500A) so I set the ADC to 0.1000mOhm

I set my charger to charger up to 14v, but from what I am reading on the SBMS, I worried so I stopped the charging once SOC reached 100% + few minutes.

As I mentioned above, I am temporary setting up the minimum to test the Lifepo4 Cells Capacity, but I think the incorrect reading I am getting now isn't related to the cells, but the SBMS.

Any help will be appreciated.  is the SBMS defective?   or any settings I made causing this issue?  

[Gilbert]

Here is the 30sec timelapse video I mentioned in previous msg, shows the SBMS when the battery charges to 100% with voltage at around  13.48-13.50volt.

[Plamen]

Gilbert,

I have SBMS120 so i might be wrong. The SBMS0is ok you just need to calibrete your shunts. You've set the value in the settings but still they may vary from whats labeled on them.

I don't know what stat 00780 means, but noticed that your charging and loads are off, at least SBMS0 thinks they are. That means yot charger is not controlled by SBMS or its not connected/configured properly.

Whatever the reason you should fix it first, no matter that it's a temporary/test setup.

In Your schematic if it's not one of those smart control alternators you'll burn it if connected so.

You need a DC-DC charger.

[Gilbert]

Thanks for your input!

May I ask how to calibrate my shunts?

Originally, I didn't adjust the Shunts setting at all until around SOC 95% charged, it was something like 0.7mohm (if I remember correctly, whatever the default that came with)   Then I did the math of 50mv/500A = 0.1000mOhm, and adjusted the Shunt Value in the ADC setting.  but the SOC % stated at 95% (that was this morning)  I was thinking if adjusting the mOhm helps, then 0.7 to 0.1 should be a huge difference, but not even 1% of SOC changed.   Is there another way to calibrate my Shunts?  

Thank you!

[Plamen]

That's Dacian post on same subject:

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If you want accuracy you will need to calibrate both shunts starting with the battery one.  To do so you need to have a two fixed current limits say a 10A as that is probably the max your multi meter can measure and 1A as the low value.

So say the SBMS self consumption is 0.8W (WiFi ON) battery voltage 26V then 0.8W / 26V = 0.030A so your battery current shunt will indicate -0.030A probably will fluctuate 2 to 3 bit so depending on current shunt each bit is 9mA or 6mA

Then when you add 1A exactly as load you should read -1.030A and with 10A you will read 10.030A if not then you need to modify the current shunt value to match this measurement Say you use the 150A current shunt your default value will be 0.5000mOhm so if you read say less than 10A when you know for sure you have exactly 10A trough the shunt say you read 9.900A that will be 1% error then you can just change the resistance live probably 0.4950 in this example will provide you with the correct reading.

Once that battery current shunt is calibrated you will calibrate the PV shunt based on the battery shunt that is now calibrated so say you have the 100A current shunt there so 0.7500 by default and say this time you have 10A or even 20A coming from PV panels not important what current value you get just disconnect all loads and just have the PV current that way the current trough the PV shunt will be exactly equal with current

trough battery shunt and then adjust the PV shunt value until PV current matches battery current exactly then you will have no discrepancy between the current shunts as they re both properly calibrated.

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Once again, connect your charger so SBMS controls it or you'll get distracted and overcharge your cells. 

After it's done test it to see it's actually working. Then leave SBMS0 do it's job. When connected first time soc starts from 50% as there is no way SBMS to know where your battery is. So it might get to 100% and still be at 60% real or jump fom 55% to 100% in one sec.  After the first charge (any cell gets to 3,55v) the soc is set to 100% and from there should be ok. If you didn't let the SBMS to complete at least one charge soc will not be correct and there is chance your settings are correct. Just let SBMS do it job.

[Gilbert]

Thank you!!  Really appreciated your details.  Help me understand alot more!

I also just realized I never power cycle (reboot) my SBMS0 since I started it.  (which maybe that is why my Stat was 00780)

I just reboot it

- disconnected my PV+ from the PV Shunt

- then remove the 12pins battery sensing cable

- waited about 30sec-60sec

- Reconnect the PV+, then the 12pins ribbon.  

Now the SBMS is reading only 50% at 13.2v, and Stat is 20480 (at least something looks different now)

I will do what you said, and charge it fully, so the SBMS will know what is 100%.  

Then I will fully discharge the Lifepo4 battery, so I can test it's capacity, as they should be 620Ah.

Will report back for any updates!

Thank you again!!

[Plamen]

Yes 20480 is what my SBMS120 have when normally operate.

[Gilbert]

Thanks Plamen! 

Really appreciated.   I just started charging my Battery again, to full.   Will see how it goes.

I do have another questions and figured I start a new post since it is a new questions, hopefully my setup/SBMS is operating normally as well.

Thanks and have a great weekend Plamen!