Yes. The protection circuit that disables cells uses a special resistor that changes how resistive it is based on temperature (a thermistor), to determine what the temperature of the cell is. If it detects that the cell is heating up, it is SUPPOSED to disable the cell, to prevent it from exploding in a blaze of fiery glory.
In a nutshell, this is how a lithium ion battery's charger works:
1) There is a small microcontroller with a small eeprom baked in, that controls the charging process, and contains the "Fuel gauge."
a) This eeprom has a baked in "design capacity" value written in it, that lets the computer know how many mAh the battery is, so it can better estimate time on battery, in addition to the value stored in the fuel gauge register.
b) The fuel gauge register is a small sram backed by the battery. It keeps track of the time on, and off the charger, and gets updated by the battery's microcontroller. The microcontroller uses the "design capacity" value to determine the upper bounding condition for when it thinks the battery is full. (It wont charge beyond design capacity unless the charge logic is seriously screwed up.) This is resettable by the micro controller, and there is secret black magic to get it to set it to 100% to account for 'drift'.
c) The microcontroller monitors the health of each cell cluster in the pack using the voltage of the cell cluster, the resistance of the cell cluster, and the temperature reading read by a thermistor stuck to the side of every cell cluster. Using some likely industry proprietary weighting algorithm, it stops charging, or disables cells if they act goofy. It sets a flag in the sram to disable further charging of disabled cells. Removing the cells from the microcontroller completely will blank the sram, which is why rebuilding the pack with new cells is possible.
C1) If the voltage dips below 3v, the controller believes the cell has experienced catastrophic cathode degredation, and wont charge the cell cluster. This is problematic, as healthy cells can self-discharge below this threshold when they are stored at 10% charge or lower for several weeks. There are special chargers to revive such batteries, but danger will robinson! The logic disables such cells for important reasons, so dont use such chargers unless you KNOW that pack has healthy cells in it that are just self-discharged.
C2) If the temperature exceeds the preset safety limit, the cell will be permanently disabled. (or until the controller loses all power..)
C3) If the voltage returned from the cell cluster reads 4.5V or higher, the controller thinks the cell cluster is fully charged, and wont supply additional charge voltage to that cell cluster. This is to avoid lithium dendrite formation between the anode and cathode, as such dendrites will internally short-circuit the battery, causing exploding self-destruct of the battery.
Author
Topic: The Generic Computer Advice Thread (Read 573664 times)