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Rechargeable Li-ion batteries usually have three terminals. I think one must let electrons in and one must let electrons out, so is the third terminal allowing some other type of particle to nip around?
Quote from: Geezer on 31/08/2011 18:29:44Rechargeable Li-ion batteries usually have three terminals. I think one must let electrons in and one must let electrons out, so is the third terminal allowing some other type of particle to nip around?It's a thermistor terminal to monitor the temperature of the battery. You don't want your electrons nipping about too energetically do you.
On basic batteries this is a connection to a thermistor, used to prevent overcharging the cell, by allowing the rise in temperature to be accurately measured, as the voltage of the cell is dependent on temperature.
Because that's not the only thing it depends on.
BTW, nickel-cadmium rechargeable batteries can get pretty toasty too, but I don't think they have T terminals.
Lithium cells have a terminal voltage dependent on charge state and temperature. If the cell is too hot or too cold it will not charge properly. If charged to a point over 100% of capacity it will heat up, and generates gas that causes the cell to swell up, and eventually burst. The problem with these cells is the gas generated is flammable, and the materials that make the cell are both flammable and react with moisture. Thus you get the all too common laptop flaming battery.
And time, they commonly measure rate of change of temperature as an indicator of the state of the battery.