Does anyone know what the 3rd pin on a cordless dril lithium ion battery pack does?

[Triode]

(edit, it appears to be a 10k thermistor)

Does anyone know what the 3rd pin on a cordless dril lithium ion battery pack does? It is labeled D on a Kobalt Drill.

I know that if you jumper the battery to just + and -, the drill will not work. If you connect it to a power supply that supplies the same voltage, 24V in this case, it also doesn't work. Jumper it to the 3rd pin on the battery (with + and - also connected properly) and it starts working, disconnect the 3rd pin and the drill still works for 2-3 seconds then stops again.

I've also found that the 3rd pin on the battery reads 0V against the - pin.

I haven't tried just jumpering it to ground. I don't know what it does and don't want to destroy the drill electronics.

Is it just a themister? I've noticed some other brands have this pin on the charger but not the drill. It would make sense that maybe some only worry about overheat on charging. But if it is a thermistor I guess kobalt decided to watch out for it on usage as well.

 

[Nigel Goodwin]

It depends entirely on the individual design, but it's usually just a temperature sensor used during charging - not normally used at all during use.

 

[Triode]

Yeah, it seems odd. But apparently in a Kobalt brushless 24V tools it is used for the tool too. I've been able to confirm by putting in a 10k regular resistor, which corresponds to 25ºc, and it runs, and if I use one that would represent a high temperature it turns off.

 

[dr pepper]

One I pulled apart had some kind of logic device connected to a smaller pin, I think it would have been some kind of electronic fuel gauge.
I wouldnt be surprised these days that theres some kind of logic in some drills that decides the battery life is over and it will no longer work with that battery.