High cell voltage disconnect issue

[MarkUK]

Hi guys, first post so go easy on me

OK, just installed 2 new 120ah Sterling (parallel connected) Lithium batteries and charging via a Victron Smart Phoenix 50 amp charger on its dedicated Lithium setting. Its bulk CV is 14.2v but as its talking to my Victron BMV 712 smart via Bluetooth network its seeing around 14.28v on the BMV monitor.

The problem is the batteries BMS trips on high cell voltage (circa 3.7v) when it gets full. This seems a bit harsh on the charger. I'm worried this sudden disconnect may damage my charger?

As I'm new to Lithium use, is this the way the batteries charge, IE I'm used to seeing with FLA the battery charger going to absorb mode then float etc, never just hard tripped like the BMS is doing currently. It just seems a bit harsh. I do know there is no float setting for Lithiums.

Should I lower the CV a bit? I have that option. Do you think it will stop the BMS hidh cell voltage trip?

Thanks a lot guys

 

[DJSmiley]

14.2V is fine. You can lower it to 14V, but that's more hiding the issue than fixing it.
But still, 14V works about as fine, only a slightly longer charging time, but that's not really an issue since that only applies to the last few %. You will gain some more cycles so it does have some benefits. That's eg also the reason why Victron uses 14.2V, while some other chargers do 14.4 or even 14.6. Victron has some more conservative settings. Some do prefer even lower voltages to gain more lifetime out of the cells.

Normally, with 14.2V, that's 3.55V / cell.

That shouldn't trigger OVP at 3.65V. Hoever, if the cells aren't in balance the voltage between the cells might vary, causing 1 cell to trip the BMS.
You're pushing 50A. At high amps, voltage drift will be a little more on the top end. But with 2 batteries, it's 25A for each 120Ah battery. I won't call that high charge which could explain the drift.

Can you check how the cell voltages are on the pack? If there are any cells with a big deviation in a single pack that might indicate some issues with the battery. It's unlikely this occurs at both batteries. Usually, a decent balanced pack should have all cells pretty close.

 

[MarkUK]

Hi DJ

Thanks for your reply

I see what you mean with regards to higher CC results in slightly higher out of balance.
I turned the CC down to 25 amps and the balance diff was only around 0.002v

It's always cell 3 on both BMS that seems to run away at the final stage of charging.

I'm more worried about the charger being damaged during the disconnect. What do you think?
The BMS still allows discharge which means all my essential loads are still online.

Thanks

 

[fega72]

The charge disconnect will not damage the charger.

 

[Steve_S]

LFP Nominal Voltage is 3.200 Volts per cell.
Working Voltage Curve is 3.000-3.400.
Allowable Full Voltage Range is 2.500-3.650
From 2.500-3.000 and 3.500-3.650 only represent's about 5% of "Gross Capacity" as these are "The Charge Cliffs" of the voltage curve.
Please download: https://diysolarforum.com/resources/general-lifepo4-lfp-voltage-to-soc-charts-tables-12-24-48v.109/

LFP likes Constant Current (Amps) up to 0.5C Rate Max until cells reach 85-90% full, then Constant Voltage / Variable Current to finish to 100% SOC.
12V/120AH Battery by default should be able to deliver 120A for 1 Hour (1.0C-Rate), it should be able to take 60A Charge (0.5 C-Rate) for two hours.

! WARNING !
You Mentioned Sterling Lithium and said you put the Charger on "Lithium" NOT ALL LITHIUM IS THE SAME ! It is Very Different and VERY Specific. Settings CANNOT be intermixed - you could cause a Catastrophy Quickly ! Please provide a Link to the Batteries you have so we are all talking about the same thing !

 

[Steve_S]

SOURCE: https://diysolarforum.com/resources/luyuan-tech-basic-lifepo4-guide.151/

 

[MarkUK]

Hey Steve, thanks for the detailed help, much appreciated

Here's the link to the Sterling batteries

Lithium Batteries 12V Leisure Battery (5 Year Warranty)

AL series LiFePO4 - Lithium Iron Phosphate batteries. Spec list Charge Discharge Part No Ah Capacity Charge V Current (A) (max) Current (A) (max) Bluetooth Series limit Dimensions (cm) LWH Weight (Kg) Battery Terminal AL1220 20Ah <14.4V 20A 40A no 48V 19 x 7.7 x 18.7 2 M5 5mm AL1260 60Ah <14.4V...

sterling-power.com

According to the spec sheet supplied, they should be charged between 14.4v and 14.6v. My Victron Phoenix default Lithium CV is 14.2v so I thought that setting is fairly conservative, yet the BMS cell high volt is still tripping out when it reaches 3.7v

 

[DJSmiley]

14.4-14.6V is 3.6-3.65V/cell.

That basicly leaves no marging for any cell balance, thus the BMS will trip frequently. Defenitely not an ideal situation. 14.2V is much better, and as said I prefer even lower.
Appearently your cells shift at the high end with a high charge rate. So either charge with lower amps or lower the max voltage. I would suggest the last.

 

[Steve_S]

First Sign of a CRAPPY COMPANY is they tell you to charge LFP to Max Allowable Voltage ! That is so much BS I could get very violent with shmucks who suggest such nonsense. That is Hopium being sold and has nothing to do with reality.

BattleBorn for example uses A+ Cells, their 100AH Packs are actually higher AH cells and derated to the spec. Even they will not take 3.650Vpc ! without trips. Now patly that is because people try to push Max Amps to Max Voltage and that never ends well...

For example, the MATH.
For a 12V System the formula is, 3.200 (Nominal Voltage) X 4 cells (std for 12V) X Cell AH Rating. 12.8V x 100AH = 1,2080Wh or 1.2kWh
SOME companies will do this... 3.650 X 4 for 14.6V X 100AH = 1,460Wh or 1.46kWh a few Notorious companies do & did that. INSTANT RUN AWAY !

Bulk Absord to 14.0 Volts then Float @ 13.8 (3.450Vpc) which is top of working voltage range and that will saturate the cells with CV. I'm typically in float by noon and then the solar only runs things till it can't generate enough, then the batteries run things.

EndAmps/Tail Current = 0.05C Rating of battery. for the 12V/100AH = 5A (100AH X 0.05)

Again, above 3.500 and below 2.900 represent 3-5% of Total Gross Capacity.

 

[MarkUK]

Thanks DJ/Steve

I can't get Battleborns over here so I went with Sterling as they seem top of the tree stuff for us. I see they are sold in the US too.

I'll lower the Victron CV to 14v and see how that goes.

Thanks again guys

 

[John Frum]

Hi guys, first post so go easy on me

Do you mean not to descend upon you like a pack of hyenas with a bone marrow jones?
Or... just not to get excessively technical?

Personally I prefer hyenas to charity muggers.

 

[MarkUK]

Ha, tech I like, was more the pack of hyenas

 

[MarkUK]

First Sign of a CRAPPY COMPANY is they tell you to charge LFP to Max Allowable Voltage ! That is so much BS I could get very violent with shmucks who suggest such nonsense. That is Hopium being sold and has nothing to do with reality.

BattleBorn for example uses A+ Cells, their 100AH Packs are actually higher AH cells and derated to the spec. Even they will not take 3.650Vpc ! without trips. Now patly that is because people try to push Max Amps to Max Voltage and that never ends well...

For example, the MATH.
For a 12V System the formula is, 3.200 (Nominal Voltage) X 4 cells (std for 12V) X Cell AH Rating. 12.8V x 100AH = 1,2080Wh or 1.2kWh
SOME companies will do this... 3.650 X 4 for 14.6V X 100AH = 1,460Wh or 1.46kWh a few Notorious companies do & did that. INSTANT RUN AWAY !

Bulk Absord to 14.0 Volts then Float @ 13.8 (3.450Vpc) which is top of working voltage range and that will saturate the cells with CV. I'm typically in float by noon and then the solar only runs things till it can't generate enough, then the batteries run things.

EndAmps/Tail Current = 0.05C Rating of battery. for the 12V/100AH = 5A (100AH X 0.05)

Again, above 3.500 and below 2.900 represent 3-5% of Total Gross Capacity.

Cool, set the CV at 14.0v now and tail current at 6A (120AH battery).
Quick question, tail current is set for just 1 battery in the bank isn't it? I've got 2 in parallel (240AH). I don't need to double the tail current to 12A do I?

It's all on charge now, will let you know how it goes

 

[mikefitz]

The problem is the batteries BMS trips on high cell voltage (circa 3.7v) when it gets full.

This is not uncommon with the lithium batteries from Sterling. The batteries are put together without correct top balancing, this results in the BMS cutting off charge with a cell over volts well before even a modest charge voltage.
Try and determine the actual charge voltage at which the cell goes over volts. If its less than 13.85 volts return the battery for a replacement. The batteries may be the smart versions with the Daly BMS so you should be able to see how far the cells are out of balance and the pack voltage when the BMS detected over volts.
If you have the smart BMS check that charge and discharge currents are being reported correctly and that the SOC is operating correctly.
I am in contact with a number of users with Sterling batteries that are having issues either with charging or the incorrect reporting of the BMS. I have spoken with Sterling technical who are aware of these issues and will replace the battery free of charge.
I would test your batteries independently to establish if one or both fail to meet acceptable performance.
These batteries seem to have no quality control and its down to luck getting a battery that performs well.

Mike

 

[MarkUK]

Hi Mike

Both batteries are brand new, less than a week old and you are spot on, the SOC readings on both are wildly out as the BMS does not register any current out below 5A!
Sterling technical support UK have been very helpful but have not offered replacements. I don't really use the Daly app much for SOC as I have a Victron BMV 712 smart.
Do I need them replaced? The price point is good considering the Victrons are near double the price.
I'll be happy if they just get a full charge and work well.
What do you think?
Thanks

 

[Steve_S]

Cool, set the CV at 14.0v now and tail current at 6A (120AH battery).
Quick question, tail current is set for just 1 battery in the bank isn't it? I've got 2 in parallel (240AH). I don't need to double the tail current to 12A do I?

It's all on charge now, will let you know how it goes

Actually the tail-current / endamps is set by the highest AH Pack in the bank, not collectively. It will be the last to attain "full" as such. Victron and others use this as a guide.

As Mikefitz suggests, get them swapped !

 

[mikefitz]

I'll be happy if they just get a full charge and work well.
What do you think?

The lowest practical charge voltage you can use that gives a reasonable charge time is slightly over 13.8 volts. However this may not allow the balancing to operate long enough to have any effect on small imbalances.
Sterling have sold you a battery that is stated to charge at normal charger voltages that it clearly does not.
If ether battery reaches high cell cut off at a 14 volts charge I suggest you return the battery.
Do not be surprised if the replacement/s also have issues.

Alternative low cost batteries available in the UK from,

Roamer - Premium LiFePO4 Leisure Batteries for off grid

For continuous power for non-stop adventures, say hello to Roamer – the next generation in SMART 12v and 24V LiFePO4 leisure batteries for campervans, boats and off grid life. Equal parts power, intelligence and reliability - managed with a smartphone app that puts the power in your hands. 10...

roamerbatteries.com

The under seat battery looks useful for a van conversion,

12V 230Ah Seatbase Lithium Battery — Roamer Lithium Batteries

The Seatbase LiFePO4 fits perfectly under a campervan swivel seat. With premium compact cells providing 230Ah of useable capacity and a high power BMS...

roamerbatteries.com

Product Selection Super Series

Select you lithium motorhome leisure battery or your camper, caravane, marine and boat LiFePo battery

www.ksenergy.co.uk

Roamer Batteries use prismatic cells, KS energy use multiple cylindrical cells ( like Battleborn)

The smart versions from both sellers do not use Daly BMS so you dont get the Daly issues.

Be aware that these sellers import from China, are small companies and are at the mercy of their supplier as to quality.
Again its possible that batteries from these sellers may have unbalanced cell/cell groups and suffer high cell BMS disable at low charge voltages. Both companies will offer replacements if this occurs.

My take on a battery where there is cell imbalance with one cell causing BMS charge shutdown is that this cell, the weakest cell, is suffering more stress than the others, and may thus reduce the service life of the battery.

Mike

 

[MarkUK]

Thanks Mike, you've been very helpful, nice one

 

[Joe beer]

Hi. I have 2 of these batteries on an install. One bought 6 months ago and one reciently.

Been having a few issues with the older one. It seems to have a Ballance problem . One cell seems to go over voltage and disconnects the charge relay very easily when charging normally (victron charge controller is set to 14.2v and it disconnects well below this when cell 2 spikes up to 3.75v ). The cell spikes so quickly that I don't think the Ballancer ever kicks in properly so this problem may get worse and certainly won't go away.

Power reciently switched off due to low voltage. (Low voltage disconnect on victron battery protect set to 12.0v ) but looking at the victron bmv712 data it disconnected at only 94ah discharge. Well short of the 108ah I should have got at this LVD setting (90% of 120ah capacity) It seems like the battery is not getting it's full charge due to the high cell voltage disconnect problem.

I have now added an additional identical 120 sterling battery in parallel to increase the capacity and hopefully avoid more LVD issues on dull days.

I looked at the Daly BMS app data while installing it and noticed that some of the settings were different on the 2 batteries. Settings were different on both the "active Ballance " screen and "protection parameters" screen"

Can someone with these batteries please post screen shots of the "active Ballance" and "protection parameters" screens on smart BMS ap and also include if your batteries are performing well with these settings.

Have read in a few places now that there are quality control issues with initial Ballance and with Daly settings but have not found what the settings should be .

Cant work out how to post my screenshots here.