Battery will not go over 57.35V

[MrSwede]

Hi,
Is it a physical limitation (degradation) of my cells when they will not charge to more then 57,35V?
The BMS (Seplos 10E) is just in a warning state (single cell and total voltage) so it should just limit charging to 10A, but the battery has been sitting on 57.30-35V for over 2 hours now, not accepting any current.
I have protection limits on 3,65V/cell and 57.6V/total. The balancer is keeping the diffvoltage to 1-3mV. DVCC is set to 57.6V.

What am i missing?

 

[Steve_S]

57.35 is TOO HIGH @ 3.58V at cell point, that is 0.180 Volts over the Working Voltage Range.
Change your charging profile to work within the Working Voltage Range of LFP.

Bulk/Absorb @ 55.2V (3.450 Volts per cell). Set ABSORB to run a Max of 1 Hour. EndAmps/TailCurrent switches it to Float.
FLOAT @ 55.1V (3.443 Volts per cell))
EndAmps/Tail Current for a 300AH Battery = 15A
-- This is calculated from ONE Battery Pack (largest AH) as follows: 100AH x 0.05 = 5A, or 300AH X 0.05 = 15A.
If there is Active Balancing, start @ 3.420 Volts with an allowable Delta of 0.010

NOTE: LOW VOLT DISCONNECT should be no lower than 2.700 Volts per cell to prevent "bricking" BMS and allowing it to take charge when charge applied. The last thing you want is to have the cells go below 2.500 Volts.

This will prevent a High Volt Disconnect on cells, sleep them within the Working Voltage Range (their happiest place) and keeps cell stress minimal.
See attached chart.

 

[SeaGal]

What am i missing?

Apart from @Steve_S very good points (as always)...

It would appear the BMS is doing exactly what you configured it to do - that is limit the voltage to 57.6V. When a charge current is flowing the voltage of your battery pack will rise; partially due to the cell voltages and partly due to the current flowing and the total cell and bus bar resistance. Once 57.6V is reached (give or take the BMS's voltage measurement accuracy), it will disconnect and the voltage will slump a bit. Looks quite normal to me.

 

[MrSwede]

This BMS does not allow float, it just have a target voltage (which i have set to 56V normally).
Today i just wanted to topbalance my packs.
I have now manually reverted to 56V again.
I have set my balancer to start balance at 3.45V/cell and stop at 3.4V/cell. I cycle my batteries daily, and recharge them to 100% daily aswell.

 

[MrSwede]

Apart from @Steve_S very good points (as always)...

It would appear the BMS is doing exactly what you configured it to do - that is limit the voltage to 57.6V. When a charge current is flowing the voltage of your battery pack will rise; partially due to the cell voltages and partly due to the current flowing and the total cell and bus bar resistance. Once 57.6V is reached (give or take the BMS's voltage measurement accuracy), it will disconnect and the voltage will slump a bit. Looks quite normal to me.

But shouldn't the BMS make a notice that it has disconnected then?
It never showed higher voltage then 57,35V even when there was current flowing to the battery.

 

[upnorthandpersonal]

This BMS does not allow float, it just have a target voltage (which i have set to 56V normally).

Float and target voltage are configured on your charge controller, not the BMS. The BMS makes sure you don't go over your protection values.

 

[MrSwede]

Float and target voltage are configured on your charge controller, not the BMS. The BMS makes sure you don't go over your protection values.

No, my Battery is CAN-bus connected to my Victron GX. It overrides the (bulk/absorption/float) settings on my inverter/charger.
So i can only set a target voltage and when that is reached, it will continue to deliver that voltage.

 

[upnorthandpersonal]

Ah, right - comms BMS. There's quite a few issues with those still when trying to get ideal parameters set. I'll see if I find time to check the Seplos in more detail. I know Andy from Off Grid Garage tested that one at some point - maybe you can find that video and see if it's useful to your situation.

 

[Quattrohead]

The BMS is doing exactly what it is supposed to do, their default settings are not ideal but it sure as hell saved your batteries.
Your cells are perfectly balanced, go out and enjoy your life and let the BMS do its job.

 

[MrSwede]

The BMS is doing exactly what it is supposed to do, their default settings are not ideal but it sure as hell saved your batteries.
Your cells are perfectly balanced, go out and enjoy your life and let the BMS do its job.

The BMS is not at default, and it didn't save my batteries. You make it sound so dramatic.
I had control of the situation in multiple layer/steps.

I still wonder why it didn't charged more, could it be a calibration issue, and the BMS thinks it's at 100% therfere doesn't allow more charge even if there is room for more?
I'd believed that it should apply chargecurrent until a protectionlimit were reached and then disconnects.

 

[Steve_S]

Understand that charging past 3.450 volts per cell is OVER the actually working voltage.
LFP like all chemistries has 2 Voltage Curves. 1 is the Allowable Range which is where the cells are not damaged or harmed. This range is from 2.500 to 3.650. The "Working Range" which is the very flat voltage curve is what actually delivers the Rated Cell AH, this range is from 3.000 (0% SOC) to 3.400 (100% SOC) with the obvious Nominal Voltage being 3.200 Volts per cell.

The most common "SAFE RANGE" people use is from 2.800 to 3.450, with a conservative Low Volt disconnect set to 2.700 with Battery BMS Poweroff set to 2.600, so as to never leave cells too low causing the BMS to brick itself.

Please appreciate that when a Battery Company (EVE, CATL, BYD etc) test LFP cells for Capacity + Matching & Batching, they are testing only the WORKING RANGE and validating that the Working Range can actually deliver the rated AH within spec, which includes IR thresholds. Those that do not qualify are graded B-Grade, those that "fail" tests on any point, be it Voltage &/OR IR specs are classed as BULK and goto Grey Market brokers. cells that even fail that point, go into Recycle process and never see the light of day.

In essence, you are attempting to put 1.1 Litres into a 1 Litre container and the BMS is not allowing for that.

Andy @ Andy's Garage has tackled Seplos BMS' and even did a bit of hand to hand combat with them. His information is generally ok and he has realized over the past couple of years to stay moderately conservative & within chemistry parameters for a happy & successful battery system. Here is alink to his Seplos Related Videos.

https://www.youtube.com/results?search_query=andy+seplos

 

[MrSwede]

Understand that charging past 3.450 volts per cell is OVER the actually working voltage.
LFP like all chemistries has 2 Voltage Curves. 1 is the Allowable Range which is where the cells are not damaged or harmed. This range is from 2.500 to 3.650. The "Working Range" which is the very flat voltage curve is what actually delivers the Rated Cell AH, this range is from 3.000 (0% SOC) to 3.400 (100% SOC) with the obvious Nominal Voltage being 3.200 Volts per cell.

The most common "SAFE RANGE" people use is from 2.800 to 3.450, with a conservative Low Volt disconnect set to 2.700 with Battery BMS Poweroff set to 2.600, so as to never leave cells too low causing the BMS to brick itself.

Please appreciate that when a Battery Company (EVE, CATL, BYD etc) test LFP cells for Capacity + Matching & Batching, they are testing only the WORKING RANGE and validating that the Working Range can actually deliver the rated AH within spec, which includes IR thresholds. Those that do not qualify are graded B-Grade, those that "fail" tests on any point, be it Voltage &/OR IR specs are classed as BULK and goto Grey Market brokers. cells that even fail that point, go into Recycle process and never see the light of day.

In essence, you are attempting to put 1.1 Litres into a 1 Litre container and the BMS is not allowing for that.

Andy @ Andy's Garage has tackled Seplos BMS' and even did a bit of hand to hand combat with them. His information is generally ok and he has realized over the past couple of years to stay moderately conservative & within chemistry parameters for a happy & successful battery system. Here is alink to his Seplos Related Videos.

https://www.youtube.com/results?search_query=andy+seplos

Thank you for your detailed answers, very nice.
Ok, so i need to alter my limits a bit, thank you.
Since i can't use absorbation and float, should i topcharge my batteries once in a while, or i don't need to thi9nk about it once they have been balanced?

 

[Steve_S]

With the info you provided previously, your cells are actually very well balanced and there is no need to Top Balance these again.
The terminology between companies varies a bit... Lack of Globally Standardised terminology that everyone accepts.

BULK = Constant Current - Constant Voltage. This also applies to ABSORB which is intended as the final charge for a fixed timed limit OR until EndAmps/Tailcurrent is reached at which point that transfers to FLOAT mode. Sometimes ABSORB is called BOOST.

Float Mode is Constant Voltage - Variable Current to accommodate the increasing Internal Resistance which reduces the Amps being taken by the battery.

BMS Quirks, they ALL have them and Seplos is No Exception. Many BMS' (Seplos is one) will not register 100% full UNLESS one or more cells reach High Volt Disconnect. This is a FLAW which most are working on addressing now. These values should be programmable due to the various use cases... As far as I know, only 3 brands have that ability at present. Other BMS' require 3 to 4 full cycles to "Learn" what the implied SOC's are.

Essentially, LFP requires CC-CV to get to 95% SOC, then it takes CC-VC to finish that last 5% to top-off & balance out internally.