Top balancing server rack batteries

[nelsonjrgomes]

Hello,

I've bought 2 x 100 Ah 48V server rack batteries from an Aliexpress seller, to pair with my Growatt SPH Hybrid Inverter. The batteries BMS communicates with my inverter. They are connected in parallel (not yet through a positive and negative bus bar, but that is going to be done in the next few days)

The batteries are working (I have them for about one month), but they are unballanced - when charging, near the top, there are cells whose voltage exceeds 3.7 and the BMS enters safe mode (or whatever is called) - and tries to balance the cells, only resuming normal function when every cell is under 3,4 volts. Unfortunately, I can't define, in my inverter, a max SOC percentage to try and avoid triggering OV protection - the inverter will always try to charge them to 100%, as long as I have excess production in pv.

I've read over here, in the forum, that I have two options - disassemble each battery, top balance cells individually and then reassemble (the hard way); or try to charge slowly each battery, and wait that the BMS with it's internal (passive) balance manages to do what is intended - top balance each battery.

I was thinking in charging each battery, through inverter, to about 95 or 97%, and then, as I don't have a battery charger (besides my hybrid inverter), I was thinking about buying a lab power supply that manages 60 v 5 A to charge the battery slowly (like 3 amps, 56 volts total).

Does this make sense - using the lab power supply to charge the battery? This way, if it doesn't solve the problem, I could use that same lab power supply to individually top balance the batteries.

Thanks in advance,

Nelson


- can I use it to charge the battery to

 

[timselectric]

Solid plan

 

[42OhmsPA]

If you disconnect your battery communication, can you set a user mode and limit charge voltage?

 

[nelsonjrgomes]

If you disconnect your battery communication, can you set a user mode and limit charge voltage?

Unfortunately no. If the batteries are lead acid, I can input those values. As soon as I select lifepo4, I have no control in charge voltage - I can only define the minimum soc percentage...

 

[Darren67-72]

You can use the FLA (flooded) setting. All chargers are basically the same. It's all in the settings. Good luck, have fun!!!

 

[meetyg]

You can use the FLA (flooded) setting. All chargers are basically the same. It's all in the settings. Good luck, have fun!!!

Not always!
Some chargers do Equalization for LA batteries, which is something you don't want on Lifepo4!

To the OP: Check if you have a "USE" or user-defined battery type option in the inverter.
If so, you can choose that and set appropriate voltage settings.

As for top balancing, yes, charging slowly with a power supply might help.

 

[nelsonjrgomes]

To the OP: Check if you have a "USE" or user-defined battery type option in the inverter.
If so, you can choose that and set appropriate voltage settings.

No, I have no such options - from what I'm reading, in Growatt SPF series there are other options, as it's an off-grid inverter; my inverter, since is hybrid, only have the option to connect lithium battery if there is a BMS capable of communicate with the inverter, and in this case, the inverter doesn't allow for any tweaks, beside defining the min soc percentage (and different priority modes, as grid first, battery first).

I already have a 60v 5a lab power supply on it's way, and we'll see if I manage to top balance the batteries this way. If this doesn't help, I'l disassemble and do it cell by cell.

Thanks,

 

[Just John]

I've read over here, in the forum, that I have two options - disassemble each battery, top balance cells individually and then reassemble (the hard way); or try to charge slowly each battery, and wait that the BMS with it's internal (passive) balance manages to do what is intended - top balance each battery.

I was thinking in charging each battery, through inverter, to about 95 or 97%, and then, as I don't have a battery charger (besides my hybrid inverter), I was thinking about buying a lab power supply that manages 60 v 5 A to charge the battery slowly (like 3 amps, 56 volts total).

Provided you can obtain access to the busbars, you can charge individual cells to "full" without disassembly.
You would of course need the bench supply to do this.

 

[nelsonjrgomes]

Thank you for your input. I haven´t had the time to top balance the cells yet, but I believe there is a easy access to the busbars - some screws hold the top lid for the rack battery, and from there, I probably can see the individual cells and their busbars. For what I've read, there is the possibility to charge each cell without disassembling the whole package, and it's probably the route I'll take (just have to find the time to do so).

 

[Just John]

Thank you for your input. I haven´t had the time to top balance the cells yet, but I believe there is a easy access to the busbars - some screws hold the top lid for the rack battery, and from there, I probably can see the individual cells and their busbars. For what I've read, there is the possibility to charge each cell without disassembling the whole package, and it's probably the route I'll take (just have to find the time to do so).

That is certainly what I would do. Search the resources section here for "top balance " and you will find some well written docs on how and why.

 

[jpimlott]

You should be able to put it in user2 battery type without com cable and set any voltage you want

From the manual
AGM (default) Flooded Lithium (only suitable when communicated with BMS) User-Defined If “User-Defined” is selected, battery charge voltage and low DC cut-off voltage can be set up in program 19, 20 and 21.

User-Defined 2（suitable when lithium battery without BMS communication） If “User-Defined 2” is selected, battery charge voltage and low DC cut-off voltage can be set up in program 19, 20 and 21. It is recommended to set to the same voltage in program 19 and 20(full charging voltage point of lithium battery). The inverter will stop charging when the battery voltage reaches this setting.

I have the LVM 24 volt model and it works that way. Same settings numbers too.
I use solar assistant to control, log, and monitor the system.

 

[nelsonjrgomes]

Thank you for your input. However, SPH does not have those settings - I believe those are only for SPF inverters. I can only set lead acid or lithium, and it I choose the later, I have no control over the charging (well, I can set different priorities and define a minimum soc, but no more than that).

 

[NinjaDeathMonk]

I was thinking in charging each battery, through inverter, to about 95 or 97%, and then, as I don't have a battery charger (besides my hybrid inverter), I was thinking about buying a lab power supply that manages 60 v 5 A to charge the battery slowly (like 3 amps, 56 volts total).

Hey, @nelsonjrgomes, I was wondering if this worked out for you. I got some brand new EG4-LifePower4 Lithium Battery 48V 100AH. One of them gave me an 87.50 Ah on the first capacity test. I have cycled it a bit to no avail. Cell #9 keeps triggering the low voltage disconnect. But the only charger I had is not adjustable and charges at 25 amps. So I got a lab power supply like yours. Did 56v & 3a work out for you? I only see the cells balance when it is fully charged and the BMS cuts of any charging. How long did you keep the lab power supply running? Maybe @SignatureSolarJames has some tips?

Also, as I was writing this, I stumbled unto a thread about a newer firmware 3.26. I've got 3.10 on my batteries. I suppose I should update that before the top balance.

Thank you for your time.

edit: fixed a word