Cell Balancing power

More balancing power matters! This is seen by the battery technician as the length of time that the battery will take to level the state of charge.

Scenario

When a battery pack is initially assembled together, each cells can be at completed different states of charge. This presents itself as a problem that has two methods to solve the problem

1. manually pre-balance the cells before assembly at the factory

2. expect that the BMS automatically resolve the problem

For large capacity cells this is only achievable when there is plenty of balancing power to remove or relocate the energy from one cell to another. For example a 14kWh battery at 52v nominal battery has 270Ah cells.

Using the example chart below if the cells were paired together we can see that cell #5 and #6 that have approximately 200Ah difference to resolve. When the battery is trickle charged at 1.3A and the cell balancing clamps the cell voltage to be held at the existing SoC the cell monitor will need to run continuously at 5W of bypass heat. This will take 1 week (160 hours). If attempted with a smaller balancing rate of 30mA this is 0.72Ah/day compared to the LongMons at 28.8Ah/day which is 40 times slower so in theory would take 40 weeks.

Prior to balancing when first assembling various cells

 Post balancing