Charging to 100% with Seplos BMS

[cajocars]

I have a Seplos BMS 100A, new version 10E

This bms considers 100% when the single cell overvoltage protection or the total voltage overvoltage protection is triggered

I have these set to 3.5V and 56V respectively

Today I started charging when I was at 80% at 50A; after 1 hour the voltage was 55V and rapidly increasing, it would have reached 56V in a matter of minutes; the SoC had been stuck at 98.2% for a while

So I dropped the current 9A (the bms has a set voltage called ‘overvoltage alarm’ that does the same when a certain voltage is hit, but I did this through the inverter)

As soon as I dropped the current, the voltage dropped from 55V to 53.8V and after 2 hours it was still at 54.5V, which is lower than what it was 2 hours before when the current was 50A


So I can hit 100% (overvoltage protection) by charging at 50A, but charging at lower amperage (9A) seems to never get me there

It would seem beneficial to charge at a lower rate when close to 100%, but it just seems to never reach 100% because the voltage doesn’t increase

 

[kundip]

This may help if you have not solved already:

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&cad=rja&uact=8&ved=2ahUKEwiKyo7olaP-AhWlRmwGHRlhAq8QtwJ6BAgKEAI&url=https%3A%2F%2Fwww.youtube.com%2Fwatch%3Fv%3DuuB3qwjh994&usg=AOvVaw3CzzlrZYpyFuAxagg_kmW3

 

[Lt.Dan]

Can't go off of voltage to estimate state of charge. Especially with high charge/discharge currents.

If you put 10a in it for hours, and it only got up to 54.5v, that's just above 3.4v per cell, and it's getting close, but not quite there. The extra amperage at 50a is giving false readings because of the high current. You can't use voltage as an estimate of state of charge until the constant current portion of the charge cycle is complete, and the constant voltage cycle drops the current under 5a or so.

 

[SeaGal]

Apologies if my reply is already covered in the YouTube link above but not sure I can handle 59 minutes of Andy, good as he is

This bms considers 100% when the single cell overvoltage protection or the total voltage overvoltage protection is triggered

That doesn't sound right - are you sure? The BMS should firstly keep track of current in and out to work out the SOC, but if that has drifted, there is usually (at least with my JBD BMS) a cell voltage that the BMS will consider as being 100%. BUT that is not the same as the cell overvoltage protection. You wouldn't want the BMS to repeatedly charge up to the overvoltage protection value - that should be a fail-safe if something else has gone wrong.

Today I started charging when I was at 80% at 50A; after 1 hour the voltage was 55V and rapidly increasing, it would have reached 56V in a matter of minutes; the SoC had been stuck at 98.2% for a while

I would have expected any decent BMS -> inverter comms system to reduce the charge to the batteries as the SOC goes above (say) 90, then 95% etc. Not to keep a charge rate of 50A when it thinks the pack is over 98% SOC.

 

[Void]

Hi Everyone, just want to find out something, I am totally new to this so please excuse if its a "stupid" question.

My batteries (2x 100ah 5Kw) charges to 100% SOC fine with 56.4v as soon as it reached 100% it discharges with 5-6amps without any load from the batteries till it reaches 53.2v and charges back up to 100%, I understand the micro cycling of seplos, but is 5-6 amps not a bit much of a discharge? The issue for me is that its doing this about 3-4 times a day, will this in the long run damage / shorten the life of the batteries?

 

[SeaGal]

as soon as it reached 100% it discharges with 5-6amps without any load from the batteries

What is discharging the batteries and how are you measuring this 5 to 6 amps?

 

[Void]

What is discharging the batteries and how are you measuring this 5 to 6 amps?

I really dont know what is causing the discharge, there is enough PV power & the grid is on, it discharges to about 98% and then the process restarts, I am watching the batteries VIA the battery monitoring software, can also see on the inverters once SOC is 100% there is a 400w - 500 w discharge

 

[Void]

Hi Everyone, just want to find out something, I am totally new to this so please excuse if its a "stupid" question.

My batteries (2x 100ah 5Kw) charges to 100% SOC fine with 56.4v as soon as it reached 100% it discharges with 5-6amps without any load from the batteries till it reaches 53.2v and charges back up to 100%, I understand the micro cycling of seplos, but is 5-6 amps not a bit much of a discharge? The issue for me is that its doing this about 3-4 times a day, will this in the long run damage / shorten the life of the batteries?

So my son just confessed last night he when to the calibrate section and clicked on the option that says calibrate voltage. Can this maybe cause the issue? I know the manual says not to do anything under that section. Is there a way to undo this?

 

[LydMekk]

Spank the "kid". That way he learn never to do it again... ^^

 

[Void]

Spank the "kid". That way he learn never to do it again... ^^

Already did, just too bad it wont undo this

 

[oglark]

What is discharging the batteries and how are you measuring this 5 to 6 amps?

I think he means the battery voltage settles after the charging current is removed. Anyway that is normal. It should settles somewhere to 3.3 to 3.4 V per cell.

‘Normal’ LiFePO4 post-charge settling?

I’ve built a first 90Ah 8S battery and am planning on building a 280Ah 8S battery soon. The 90Ah is my first battery build and I’m trying to characterize the battery to figure out if it is behaving normally or not. I’m charging with a 10A 28.6V LiFePO4 Charger that gets the battery up to...

diysolarforum.com

 

[Milky_pete]

So my son just confessed last night he when to the calibrate section and clicked on the option that says calibrate voltage. Can this maybe cause the issue? I know the manual says not to do anything under that section. Is there a way to undo this?

Did you ever figure this one out? I pressed this button too and I'm wishing I hadn't... I'm not sure if the voltages shown in BMS-Studio are correct any more