UK Using 3 Fogstar 5.12kWh Energy Server Rack Batteries, cant keep them in sync

[Oldman2]

I have a Solis RAI-3K-48ES-5G AC Coupled Inverter and 3 Fogstar 5.12kWh rack batteries, the Pace BMS in these is set to mimic Pylontec as Fogstar isnt on the Solis list and that seems to be working out just fine.
My problem is 2 of the rack batteries will charge and discharge in sync with each other in percentage terms read from either the batteries screen or from the BMS via PbmsTools V2.5FN. The current discharge and charge remain pretty close to the same on these 2 batteries too when viewed via PbmsTols.
Battery 3 though seems to have a mind of its own, generally lagging behind the other 2 by up to 5% in charging and not taking the same charge current as the other 2.
Even if I charge all 3 together to 100% via solar during the day, by next morning they will be 71%, 71% & 67% As you can see B1 & 2 are still in sync 12hrs later but B3 is way off at 67%.

The 3 batteries are in parallel with pos/neg supply cables to opposite ends as in photo. I have tried various other combinations starting with red to battery 3 and black to battery 1, both supply leads to battery 2 and also both to battery 3 with pretty much the same results. Battery 3 always goes out of sync with the other 2 remaining in sync.
This lead me to the conclusion that B3 had a problem so I swopped it for another battery, within 24hrs the replacement B3 is again out of sync.
I tried a constant 39A charge from the Solis.
B1 registered 12.01A 54.10v 70% on PbmsTools
B2 registered 11.64A 54.08v 69%
B3 registered 15.16A 54.03v 71%

Why would B3 get the lions share of charge current? I thought they should be balanced at around 13A each.
So does anyone have any ideas as to how I get the 3 batteries to act as one or close to same?
Anyone here also using multiple Fogstar 5.12kWh server rack batteries? Your experiences may help.

 

[houseofancients]

Move either you positive ( red) or negative ( black) to the other end of your battery stack..
Make sure they are connected at the most positive and most negative end of your battery

 

[Oldman2]

Move either you positive ( red) or negative ( black) to the other end of your battery stack..
Make sure they are connected at the most positive and most negative end of your battery

Already tried all combinations of cables as stated in the paragraph under the photo, as per the photo and with red lead to bat3 and black to bat1. Same results, but thanks for the reply.

 

[SeaGal]

Move either you positive ( red) or negative ( black) to the other end of your battery stack..
Make sure they are connected at the most positive and most negative end of your battery

It already looks correct that in the pic?

 

[SeaGal]

Could the differences just be the (in)accuracy of the BMSs? I would expect the voltages (but not necessarily the currents) to be the same if they are connect in parallel. What do the voltages show if the batteries are connected together, but disconnected from the Solis?

And on an unrelated note, is that a valid orientation for the battery packs? I would have expected they should be mounted on each other vertically, so that the prismatics are vertical inside.

 

[houseofancients]

Already tried all combinations of cables as stated in the paragraph under the photo, as per the photo and with red lead to bat3 and black to bat1. Same results, but thanks for the reply.

Hmm , missed that cable from 3 to inverter, thought it was going to batt 2 ( didn't have glasses on )

When you batteries are hooked up correct ( which they seem), it could very well be they are at different SOC'S , and thus have different resistances.

One way to make sure they are at the same SOC, is to set your Solis to volt ( AGM), and adjust the voltages.
Use 56,8 for absorb and 55,7 for float.
This will allow them to get to the same SOC ( in sync) , and thus charge and discharge more even.
This should not be permanently setting, but rather a few days !

 

[Oldman2]

When you batteries are hooked up correct ( which they seem), it could very well be they are at different SOC'S , and thus have different resistances.

One way to make sure they are at the same SOC, is to set your Solis to volt ( AGM), and adjust the voltages.
Use 56,8 for absorb and 55,7 for float.
This will allow them to get to the same SOC ( in sync) , and thus charge and discharge more even.
This should not be permanently setting, but rather a few days !

Wouldn't all 3 batteries at 100% charge for 4 or more hours yesterday for instance while my PV exported its excess get the in sync same SOC result? Not sure I can set up my Solis easily to do what you suggest.

 

[MisterB1959]

have you asked Fogstar themselves, Im sure Becs or Ben will be able to help

 

[Oldman2]

Could the differences just be the (in)accuracy of the BMSs? I would expect the voltages (but not necessarily the currents) to be the same if they are connect in parallel. What do the voltages show if the batteries are connected together, but disconnected from the Solis?

And on an unrelated note, is that a valid orientation for the battery packs? I would have expected they should be mounted on each other vertically, so that the prismatics are vertical inside.

I will try isolating the batteries to see what the voltages are, I do read and record the voltages and % several times daily but not with the Solis disconnected. As to the orientation of the cells, Ive been in conversation with Ben at Fogstar since I got my first battery in May and he's not said anything about always using them laid flat, I'm not aware its a condition of use?

 

[Oldman2]

have you asked Fogstar themselves, Im sure Becs or Ben will be able to help

Yes Ive worn @Ben@Fogstar out it seems, we have a very long email history on all things related to these batteries. He it seems, has no advice to offer.

 

[houseofancients]

Wouldn't all 3 batteries at 100% charge for 4 or more hours yesterday for instance while my PV exported its excess get the in sync same SOC result? Not sure I can set up my Solis easily to do what you suggest.

SOC is a BMS calculated value..
So unless all cells are in balance, and all batteries are in balance, SOC isn't a good value to go on.

Off-grid garage will give you good explaintion on how this BMS works ( jakiper also uses the PACEbms)

 

[Steve Fractals]

Could the differences just be the (in)accuracy of the BMSs? I would expect the voltages (but not necessarily the currents) to be the same if they are connect in parallel. What do the voltages show if the batteries are connected together, but disconnected from the Solis?

And on an unrelated note, is that a valid orientation for the battery packs? I would have expected they should be mounted on each other vertically, so that the prismatics are vertical inside.

Don't think orientation matters for LifePo4 battery banks. From my reading they can be mounted any way that fits in with where you want them providing connecting wires all equal.

 

[DIYrich]

Does your BMS show the individual cell voltages? If so, are they in balance when fully charged?

If not, have you balanced the battery? Held it at full charge, with max charging voltage, for a few hours?

Can you run on 2 batteries? Try running battery 3 with one of the others.

 

[Quattrohead]

Does PbmsTools allow you to see all the cell voltages, temperature etc ?
There may be calibration adjustments and you can reset the SOC like you can with the JBD BMS tools for their BMS.
The difference you are seeing is not drastic, I would just keep an eye on it.

 

[Oldman2]

Does your BMS show the individual cell voltages? If so, are they in balance when fully charged?

If not, have you balanced the battery? Held it at full charge, with max charging voltage, for a few hours?

Can you run on 2 batteries? Try running battery 3 with one of the others.

Yes my BMS shows all cell voltages as in this example below.


I can run on any number of batteries as they have breakers fitted so I can isolate any while still keeping the others connected to the inverter.
Ive not tried to balance any of the batteries, once the pack voltage reaches 100% the current drops to zero so any balancing that was being done by the bms stops. I've not seen any voltage differences in more than double figure mV recently that I recall.
Yes @Quattrohead I do have full control of the bms & could adjust the SOC but its maybe a dark art with no reset to go back to start position.

I will try running on b1 & b3 only and see what happens. I did wonder if there is some error that creeps in when odd numbers of BMS/batteries are connected....shows I'm overthinking it doesnt it!

​

 

[Quattrohead]

Can you see all 3 batteries in the multi monitoring tab ?
Then you can compare. What is the balance start voltage set to ?
If all 3 sets are close you could set the out-liner to the same SOC and see how she goes.
It's not a critical setting, more informational than "real"

 

[Oldman2]

Can you see all 3 batteries in the multi monitoring tab ?
Then you can compare. What is the balance start voltage set to ?
If all 3 sets are close you could set the out-liner to the same SOC and see how she goes.
It's not a critical setting, more informational than "real"

I don't see all batteries in multi monitor, but I can select each via the 1-15 buttons. The balance threshold is set as delivered to 3.50v with balance Vcell at 30mV. By altering the SOC do you mean the remaining capacity mAH in sys config? What would you consider "close" ? I've had them be 5% different after a few days, that's a 5000mAH adjustment which I would consider as a lot.
Rain stopped play for today, PV is down to 60watts and the 2 batteries currently in use are discharging into the house load.

 

[DIYrich]

Ive not tried to balance any of the batteries, once the pack voltage reaches 100% the current drops to zero so any balancing that was being done by the bms stops. I've not seen any voltage differences in more than double figure mV recently that I recall.

​

in more than double figure mV recently that I recall.

What do you recall? My cells are balanced to within 0.005v.

Charge at 58v.
Start balance at 3.40v
continue charging until voltage difference (high to low cells) is less than 0.010.

 

[Quattrohead]

Balance threshold is too high, try 3.4v and I personally go with 15mv differential.
Seems like you may have a cell in that 1 battery that is not so great and it limits the charge that battery can absorb.

 

[houseofancients]

Balance threshold is too high, try 3.4v and I personally go with 15mv differential.
Seems like you may have a cell in that 1 battery that is not so great and it limits the charge that battery can absorb.

Which is why I told him early on to charge at 56,8 and float high too, to give the passive balancer a chance..

Btw also linked the Andy video so OP at least understands the BMS he's working with, and may pick up on a setting or 2