Our customer is experiencing field failures as described below. Please advise asap as these are critical problems:
Issue 1. SCD flag remaining ON after discharge current goes to zero.
We are seeing a number of batteries with the following situation: When the battery is attempted to be recharged from a partial-charge condition (20-30% RSOC), the pack will charge for a period of time and will then throw a charger fault. Our charger reads the battery state from the SMBus and determines the condition to subject the battery to. At any rate, what happens is that the battery will not accept charging current for some reason. Upon removal, the battery is read by the bqEv software and what shows up is a red SCD flag in the Safety Status bar. When the battery is returned to the charger, it then resumes normal charging and charges to 100% RSOC, but the SCD flag seems to be still set (even after a period of time when the battery is left idle). Note that the average current has dropped to zero and has remained so for a length of time greater than the Current Recovery Time, so according to the data sheet the SCD flag should have cleared. Also note that this condition is observed at our customer’s warehouse. When the batteries are packaged up and sent back to our engineering site, the flag is no longer set. What gives?
Issue 2. Battery internal fuses blowing.
In this situation, we are seeing a number of batteries returned with the fuse in the pack (schematic similar to the Eval board but without the ZVCHG or the secondary fusing protection) being blown. The concern is that the physical fuse is supposed to be the final protection after all the software shutdowns are exhausted. We have seen the short circuit operate correctly on a single short, but when the short is sustained and the pack attempts to recover with the short still present, the fuse will blow after a number of retries. The question is what actually occurs during an attempted restart, and how can we keep whatever is happening from reoccurring ( possibly the old power supply designer trick of slowing down the turn-on and speeding up the turn-off of the DSG FET in order to minimize inrush current). Again, any help here?
