It was a good thing to follow closely through the first charging of the traction battery pack. When the first cell voltages reached the balancing threshold I started to be worried of the CBMs possible overheating as I had only tested the CBMs in free air in a vertical orientation with a very small charging current. I consentrated for a while into other things and when I checked the charging situation again about 20 of the 24 CBMs were active and the whole enclosure was clearly too hot to survive. I stopped the charging but it was too late. The heat shrink tube used as insulation between the CBMs melted resulting in a short between two CBMs. Smoke started to rise and I started to remove the fuses to disconnect the batteries from the smoking CBMs. Finally all 24 fuses were removed and no flames were seen. The molten heat shrink tubing and smoked CBMs are shown in the first picture. This was a good reminder for me about how easy it is to underrate cooling.
Luckily the PCM board was not harmed. As seen in the picture the CBMs were removed from the enclosure dropping the balancing current to just 60 mA provided by the PCM board only. While charging the battery pack with 10A the charging was now stopped into a cell over voltage as one of the cells reached a voltage of 3,9V. Some other cells were clearly not yet full so I made a manual balancing for the battery pack by sinking current from the fully charged cells and charging the ones with lower state of charge. After a while of manual balancing I got the cells balanced enough to make the charger to stop charging normally; the charging voltage was about 87,6V and the charging current was reduced into about 1A.
Now the first traction battery charging cycle is done. I am curious to see if 60mA top balancing current is enough to keep the cells balanced. Anyway I am so far very pleased with the PCM board!
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