Re: Is US Ready for EV's ?

Eric Johnson

While it is true that EV batteries can overheat and catch fire, the bigger problem is damage to the main battery pack caused by individual cells that are not well matched with other cells in the pack.  Individual cells have to be connected in series to achieve the voltage required to operate the EV power supply to the drive motor.  If an individual cell does not hold enough charge to match up with the other cells, it will become depleted before the others, and at that point, it will be subjected to reverse polarity during the discharge cycle.  When the battery pack is set up to be recharged, this individual cell will overheat, and that can lead to a fire.  If the temperature sensor system is working, the charge cycle will automatically shut down.  But now the owner is left with a main battery that is 98% OK, and 2% defective.  Time for a new battery. To avoid this scenario,  some EV owners are being asked to never discharge below 30% of capacity, and to never charge above 85% of maximum capacity. 

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