Other Parts Discussed in Thread: BQ78350, BQ76940,
Hi all,
We use a BQ78350-R1 in conjunction with BQ76940 AFE in a 14 cell LiFePO4 pack. On the other side this BQ78350 is in communication with our TMS320 MCU. The BMS balancing algorithm running on the BQ78350-R1 is a black box to us.
Due to the layout of cells in our application, they are bunched together in 2 packs of 7 cells, which in turn are separated by 2' of 10 gauge cable (approx resistance of this cable is 2mΩ). I am worried that because of the difference in resistances between cells, and because cell balancing does occur during charging (~10-20A in our application) that this could drive cells adjacent to the joining cable out of balance. Essentially, cell 8 in our pack will at 20A of charging current appear to be 2*20 = 40mV higher than it is in reality. And so I have three questions:
1: Can we set an upper limit on the charge current at which balancing will occur?
2: We have previous experience with an off-the-shelf BMS which allows the user to add what it's manufacturer refers to as "Busbar Compensation". Essentially, we could pre-configure the inter-cell resistances and subtract the product of this times the charge current to reveal the true cell voltage and accurately calculate each cell's internal resistance. Is a comparable feature available on the BQ78350-R1?
3: Am I being overly cautious here, is this small resistance worth being concerned about - will that 40mV be lost in the noise? We have not had the time to put a large number of cycles through our packs, I am more concerned about the longer-term effects of this.
Thanks guys!
Steve