How to top balance Coolithium LiFePo4 batteries with Growatt SPF5000 ES?

[ventura]

I have 3 Coolithium 48V 200Ah (15S) batteries. I have BMS communication set up wit Growatt SPF5000ES. The charge voltage is set to 53.2V by default by the BMS (?) and I cannot change it in the inverter's interface. I guess it is controlled by the BMS. 53.2V is 3.546...V per cell.

1. First question I have: is this normal that the BMS is configured so it is ordering the inverter to charge with a bit less than 3.6V per cell?
2. My second question is, how do I top balance this? Should I just switch from BMS to user defined mode on the inverter and manually set the Charge voltage to 54.75V (3.65V per cell) or 54V (3.6V per cell). Is this the normal way?

I attached an image of the sticker on the side of one of the batteries.
Thanks for the answers in advance.

 

[GXMnow]

It's impossible to know what the BMS is doing without knowing the code. It is possible it has seen the imbalance, and it knows that going any higher with the voltage could cause one cells o go above 3.65 volts. Or it was just manually set there are the factory because they know it could drift far enough out of balance over time to be an issue to go higher. Either way, the BMS is trying to avoid a cell over voltage from happening.

No mate how well you try to top balance a pack, it is very difficult to get all of the cells to top up to 3.6 volts at the same time. The 53.2 volt setting is probably fine. Going over 3.54 volts per cell should be well into where the BMS triggers the balancing function. And that voltage is also well over 95% SoC on LFP cells, so you are not really losing any capacity. It is just allowing a bit of balance margin. 3.54 per cell is actually higher than most people go for daily cycles on LFP cells. Andy at Off Grid Garage recommends 3.45 volts per cell and has been doing that for years.

As for top balancing, the BMS needs time at over 3.45 volts per cell. How low can you set the charge current? You may have to disable the BMS comm. to override the settings. Leave the voltage at 53.2, but lower the current as far as you can and set it for the longest absorb you can. Holding the voltage there but at a low current will allow the BMS to bleed off some voltage from any high cells so they can balance. Even at just 2 amps of charge current, the 120 milliamps of balance current on my Daly BMS units can't stop a cell from still charging into it's over voltage protection limit. But as long as the balance is good enough for it to drop to absorb mode without a cell hitting over volt, the current should taper down enough for it to start working. If you watch Andy's channel, he has has several which talk about how the better balanced and matched packs can charge closer to the full 3.65 volts per cell. One company he tested even had the batteries graded and the lower grade cheaper units have a lower max charge voltage to allow for the cells to not stay balanced as well.

The BMS should never be the device that turns things off. It is a safety device to minimize damage when things go wrong. If the battery goes out of balance, the charger should slow down and stop the charge sooner so the BMS has a chance to balance it back up.

 

[ventura]

It's impossible to know what the BMS is doing without knowing the code. It is possible it has seen the imbalance, and it knows that going any higher with the voltage could cause one cells o go above 3.65 volts. Or it was just manually set there are the factory because they know it could drift far enough out of balance over time to be an issue to go higher. Either way, the BMS is trying to avoid a cell over voltage from happening.

No mate how well you try to top balance a pack, it is very difficult to get all of the cells to top up to 3.6 volts at the same time. The 53.2 volt setting is probably fine. Going over 3.54 volts per cell should be well into where the BMS triggers the balancing function. And that voltage is also well over 95% SoC on LFP cells, so you are not really losing any capacity. It is just allowing a bit of balance margin. 3.54 per cell is actually higher than most people go for daily cycles on LFP cells. Andy at Off Grid Garage recommends 3.45 volts per cell and has been doing that for years.

As for top balancing, the BMS needs time at over 3.45 volts per cell. How low can you set the charge current? You may have to disable the BMS comm. to override the settings. Leave the voltage at 53.2, but lower the current as far as you can and set it for the longest absorb you can. Holding the voltage there but at a low current will allow the BMS to bleed off some voltage from any high cells so they can balance. Even at just 2 amps of charge current, the 120 milliamps of balance current on my Daly BMS units can't stop a cell from still charging into it's over voltage protection limit. But as long as the balance is good enough for it to drop to absorb mode without a cell hitting over volt, the current should taper down enough for it to start working. If you watch Andy's channel, he has has several which talk about how the better balanced and matched packs can charge closer to the full 3.65 volts per cell. One company he tested even had the batteries graded and the lower grade cheaper units have a lower max charge voltage to allow for the cells to not stay balanced as well.

The BMS should never be the device that turns things off. It is a safety device to minimize damage when things go wrong. If the battery goes out of balance, the charger should slow down and stop the charge sooner so the BMS has a chance to balance it back up.

Wow! So much more than I could ask for! Thank you for the knowledge and your time for writing this up.

I will do thing as per your suggestions and will set things up so I have the batteries almost fully charged, then I will set the inverter to manual mode and bypass grid power so battery is not used for discharge. I will also limit charge current to 2 amps and leave voltage at 53.2. Ill let this be for a while. I just have to wait for some sunny days that are rare nowadays

Thank you again for your extremely useful writeup.

 

[tabascoz]

Hi there,

Sharing my experiences with SFP 5000ES and DIY Eve 280ah 16S / DalyBMS 200a + 5A active balance module.

I built everything in November and had the inverter set to USR2 battery type, set float and charge power to 58.4, in Dalybms set soft and hard upper cell voltage limit to 3.60V and 3.65V;

By the end of November , taking advantage of rainy days, i did some top balance over the course of two days.



The cell graph above showed that Dalybms and Growatt were in good terms and cutting off charge when any packs reached 3.6 and balancing were doing its thing and bringing bottom cells to catch up. (of course all this process were closely watched by me)

Recently i was able to get Daly to talk to Growatt over RS486 and have them operating perfectly. I still can set float/target voltages and kept them at 58.4, but now Gorwatt stops charging when SOC is in 95%, i am unsure if there's something i should do to go to 100% but decided to let it be this way as it seems a good idea to not keep topping the batteries. it could also be because i was not able to get anywhere close to 70% with my current solar production and home demand in winter. I am planning to double solar panels soon and will see if Growatt charges them at 100% with solar production and if it worth it to doing so or not.

But with this 95% apparent limit it also came with a bad consequence that it is way harder to balance batteries, as they all keep around 3.45 zone, but (thanks to GXMnow) I watched Andy's videos and shouldn't be a problem to keep it this way.