EG4 BMS soc accuracy issues

[thismainething]

I was wondering if anyone else is running into issues with the BMS regularly showing incorrect SOC. When charging, the SOC will reach around 85% to 95% then jump all the way to 100%. When the inverter enters bypass mode the BMS will show the SOC dropping from 23% to 16% in just 8 hours. That's 700 watt hours going missing.

Set up is two 100ah 48v batteries. One is EG4 the other is eco worthy. I experienced the exact same issue using just EG4 batteries.



Thanks

 

[42OhmsPA]

Sounds like out of balance cells to me.

 

[EG4TechSolutionsTeam]

I was wondering if anyone else is running into issues with the BMS regularly showing incorrect SOC. When charging, the SOC will reach around 85% to 95% then jump all the way to 100%. When the inverter enters bypass mode the BMS will show the SOC dropping from 23% to 16% in just 8 hours. That's 700 watt hours going missing.

Set up is two 100ah 48v batteries. One is EG4 the other is eco worthy. I experienced the exact same issue using just EG4 batteries.



Thanks

Change the inverter to lead acid mode and set the bulk charge to 56.2. This will help balance out the battery cells. Are you discharging batteries to 20% and charging back to 100% regularly or at least a few times a month?

 

[marionw]

Setting the Bulk Charge Voltage to 56.2 = 3.5125 volts per cell which at first glance looks good. However, if you have one or more "runner" cells, cells that charge much faster than others, and those cells reach Cell Over Voltage Protection thus shutting down the entire charge for the battery (BMS protection) then you still will not get cell balancing. All that will happen at this point is that the balance circuit will place a balance resistor across the cells that exceed the balance threshold voltage and the cells will be bled down as the balance resistor acts a a small load on the cell.
Trying to manage the charge voltage to prevent the runner cell from reaching cell OVP is possible but I have found that more often than not there will not be enough charge current to get those stubborn low cells to charge.

Draining the battery to 20% SOC might be a good idea however if the battery has never been fully charged where the BMS reset/calibrated SOC then trying to reach a BMS reported 20% SOC is only a guess. Better yet discharge the battery to where most cells are around 3.25vdc which is in the lower "knee" of the discharge curve.

Then charge the battery using a low charge current of 10 amps or less which might allow all cells to charge while maintaining a low cell differential voltage. Slowly increase the charge voltage to maintain charge current of around 10 amps until all cells approach 3.40vdc. At this point if cell differential voltage is low (for me that is 50mv or less) maintain charge current. If there is a significant cell voltage differential reduce charge current to around 5 amps and hopefully all cells will charge together.

There is no "magic" way to do this short of opening the battery and using an Active Balancer or a variable benchtop power supply to individually charge the lower cells. Personally I would go with an Active Balance as you can get a 4 amp Enerkey for around $58.00 and you might spend this much for a power supply. I have two Enerkey active balancers where I cut off the ring terminals from the balance leads and added small alligator clamps/clips (ones that do not expose the ends of the jaws)

In addition, if possible, download the appropriate software tool for your batteries from the EG4 website and use the software to monitor the battery during the charge