sunnuntai 28. lokakuuta 2012

The cell that keeps giving

Jack has been testing the new CA-series cells from CALB and they just keep giving. In addition to improved cold resistance and a flatter charge/discharge curve, or perhaps thanks to it, the cells seem to be able to take 3C charge with no sweat at all. That means 120 amps into a 40 Ah cell. And not just take some charge, but take over 90% of capacity in 20 minutes. To me that means you could just forget about the usual CC/CV charging, do the fastest CC (Constant Current) you can muster and quit when you reach about 3.55 volts per cell. The cell doesn't even really warm up. Not at least until you try to push that last 3% with an additional CV (Constant Voltage) phase that now seems quite unnecessary with these cells.

On the subject of BMS I'm inclined to not even consider Top Balancing as an option to anyone anymore. Not only does a cell level BMS unbalance your pack it also seems that baking your cells at an artificial top voltage does not lead to a full charge, but instead could even damage the cell. Whatever cell drift or age induced unbalancing they claim is most likely caused by the BMS itself. In other words the very same system they claim you need to combat these issues is the root cause of them. I have also asked proponents of BMS or active live cell balancing to present numbers to back their claims on the superiority of BMS in charging or cell lifetime balance issues, but NONE have given ANY. In my book that just about sums it up. Safety wise I believe a BMS will cause more problems than it will solve.

2 kommenttia:

  1. Just watched the latest episode and I have to agree, amazing result at 3C charge rate with the CALB CA cells. Fast charging is probably better for the cell life. I have a feeling that even 4 or 5C would be fine too. They even hinted charging below 0C is ok, hopefully that is covered later.

    Are you planning to order new CA cells or reuse your SE cells?

    1. I will initially test the car with the SE40AHA cells and AXE7245 controller from the kWsaki motorcycle. That should give me an idea if the 25 cell pack has enough voltage and if a controller like the AXE7245 which can do 200 amps continous and 450 peak is adequate. Note that my motors are rated for 72 VDC. Going to higher voltage means not only more cells, but also a bigger charger and a pricier controller. I just got the combustion engine out of the Xsara and should write a little post about that.