SOC wont reset to 100%

[green moon]

Gidday,

I have never managed to get my SOC to go to 100% even when the SBMS0 reaches the End Of Charge voltage and the EOC lights up on the screen.

Id let my battery run down a bit and now fully charging to my end of charge voltage.

What else must I set or change in the SBMS0 to reset the SOC which never gets above 56%

I charge my batteries only to 13.85V and have the EOC set at 3.45V

Thanks

[Dacian Todea]

The default settings for SBMS0 are to stop charging at 3.55V that is when battery will be fully charged and SOC reset to 100%

I guess you modified the advanced parameter settings as default as EOC is set just 2mV lower at 3.53V

You will not be sure that battery is fully charged at 3.45V it may be nowhere near close to fully charged depending on battery and charge rate.

I will suggest leaving the default settings for best performance. You can check my battery capacity degradation after 3 years of full time heavy use with those default settings and you will see that I had less than 5% degradation over the 3 year period most of that is not related to cycling (even if there is heavy cycling ) but is mostly related to calendar aging.

What is your charge source ? Hope the SBMS0 has access to turn that ON/OFF else it can not protect your battery from overcharge.

[Marinepower]

Searching through the forum here trying to determine why my SOC will not reset to 100%. I think I may have found part of my answer here in this old thread.

Like the OP, I changed my end-of-charge to 4.2v as I'm doing some bench top testing of a new 280ah lifepo4 bank and charging with a 4amp bench top power supply.   At a 4amp slow rate of charge, it is very full when the 1st   cell reaches 4.2v shoots up alarmingly thereafter.  My cells are the EVE 280 cells that seem to be everywhere these days. On a side note - after a top balance, they seem to be very consistent in voltage btw, all the way into the knees.  

Dacian, could you clarify your above response.? If the end-of-charge being activated does not reset the SOC to 100% then what is the trigger?  Is it being within 0.2v of the "Over Voltage" limit set in the advanced parameter menu? Other?

Is there a way to fool the system to get it to reset to 100%?

[Dacian Todea]

Marinepower,

Please use the default settings for type 1 battery. 4.2V will just damage your LiFePO4 battery the 4.2V limit is for other type of chemistries like NMC or LiCoO2

Is a bit unclear what you are asking and your values are way out of spec so please set the battery type 1 (even if is already selected as by selecting again will load the default values) then set the number of cells you have in series likely 4 or 8 and capacity then save the settings and power cycle the SBMS for the settings to take effect.

[Marinepower]

Sorry that was a typo.  I meant 3.42v.  Ie, i have set in the advanced parameters menu the end-of-charge voltage to 3.42v (as oppose to the default 3.53v).  I have also set the number of cells to 4 and to type 1 (LFP) - and followed all other instructions.

I think mine is the same question as Green Moon the OP.  

What in the SBMS logic causes the SOC to reset to 100%?  I have reached EOC ("end-of-charge") and that function was illuminate on the 3rd page of the monitoring menu.  But the SOC has not reset to 100% (it shows instead 70%).  In the SBMS manual page 21 says " After the first full charge (on battery type 1 when when highest cell gets to 3.53v and EOC flag will be set the  battery SOC will jump to 100%) from that point SOC will represent the real value."

If the SOC software is not compatible with altering the EOC value in the advance menu, is there a work around to manually change the SOC to 100%.

[Dacian Todea]

The End of Charge will not reset the SOC to 100% and also will not stop the charging that will be done by the Overvoltage parameter that is by default set at 3.55V

3.4 or 3.42V is just to low to be sure you got a full charge and battery may only be at 70 or 80% and you will not be able to be sure that is fully charged unless you are at least at the 3.55V level that I set.

The EOC will be set without any delay so even if you have the EOC limit for a few ms or maybe because of cell balancing so that is not a reliable flag to use for SOC calibration the Overvoltage on the other hand has a default 6 seconds so the voltage of any cell needs to be above 3.55V for 6 seconds consecutive so it will not be influenced by cell balancing (that is only ON for 3 seconds at a time) and also will not not influenced by so high charge sourges like it may be the case when charging with a not so filtered AC charger.

I shown this many time so you may have seen it before but the 3.4V is just to close to where the cells will be for a long time within mV from that so very easy to exceed plus EOC has no time delay. Most other BMS will use the manufacturer 3.65V limit (if they are well designed) and the bad ones 3.9 to 4V to allow absorption and float and not disconnect the battery and that will be detrimental.

The most conservative setting I can make is 3.55V and guarantee that battery is full or very close maybe 3.5V for very good batteries and low charge rate but to be sure for most cases I selected the 3.55V and any other lower value like 3.45V will create problems like setting the SOC to 100% and stopping charging while battery is nowhere close to full may be as bad as 70% in reality and then when you get to 30% SOC and you think you have still a third of the capacity you realize the battery is empty.

[Marinepower]

Thank you Dacian for your reply.

I have not had a chance to re-test the system yet but what you say makes sense.  The "Over-voltage" value and not the "End of Charge" value dictates both when the type 1 I/O opens ( and stops charging ) and this also resets the SOC to 100%.  

I am just doing some preliminary kitchen-table top-balance, capacity and system testing and design of the bank right now before it get installed on the boat.  Tomorrow I will try to charge again to full and reset the SOC to 100%.I manually ended the charge for the first charge cycle, as I noticed EOC had been reached on the SBMS but the charge relay did not trip. 

I did a top balance a few days ago in stages (3.42, 3.55, 3.62) and observed there was maybe 5 amp hours btw 3.42 to 3.62 at the low rate of charge my bench top power supply can provide.   Hence why I started at this lower EOC charge value.   When the system gets installed on the boat, I will revert to SBMS default values, as that will be a much higher rate of charge.

[Doug Wierenga]

Hi,

Did you get your SOC to reset to 100%?  If so, did you end up adjusting the Over-voltage setting to something other than 3.55V?

For an hour, during absorb, my battery was at 14.0V w/ 20mV to 30mV cell differential.  I figured this close enough to 100% (I prefer more conservative approach to charging.). But, my SOC didn't reset to 100%.  I planned to tune the parameters just slightly so it triggers 100% SOC.

Thank you,

Doug

[Dacian Todea]

Doug,

It is a bad idea to absorb of float charge a lithium battery (any type of Lithium including LiFePO4).

Is better (more conservative) for battery to get fast to 3.55V then stop charging.

So set your charge absorb voltage to 14.4V or above so that it never gets to absorb just bulk charge as the SBMS0 will stop the charger (assuming charger remote ON/OFF is connected to SBMS).