Laptop batteries ... are they usually protected?

[Dr. Tweedbucket]

.... or do they just have really good chargers?

I usually leave mine plugged in all the time ( maybe I shouldn't do that )... but they seem fine with it. The other bad thing is sometimes if I let them sit, the batteries run down dead as a door nail. That's probably another bad thing to do.

Thoughts?

 

[markr6]

I don't think the individual cells are ever protected. But there is a separate protection circuit to prevent/reduce accidents.

Some laptops have a battery saver feature that you can enable/disable which charges the battery pack to only 80% max or something like that.

 

[127.0.0.1]

no

laptop packs use unprotected cells


but

each cell has detection wired to it, and the controller does run
the protection for each cell and the pack as a whole, so if one cell
goes wonky, the whole pack is unusable as it's charge circuit is shut down

it is this exact reason why so many counterfiet cells exist on fleabay. MANY thrown out laptop packs
have a lot of good cells, these are taken out, tested, rewrapped and resold as new. the ones that are
so dead they are the cause of the pack shutdown, those are tossed, or rewrapped by the really shady counterfeiters

I can get a box of 20 dead laptop packs for 1 dollar, and get 80 somewhat ususable 18650's from them,
rewrap them and slap on my own protection chip, and sell for 3-5 bucks a pop.....big money in being a sleazeball

 

[HKJ]

.... or do they just have really good chargers?

I usually leave mine plugged in all the time ( maybe I shouldn't do that )... but they seem fine with it. The other bad thing is sometimes if I let them sit, the batteries run down dead as a door nail. That's probably another bad thing to do.

Laptop battery packs have protection that is way superior to the small protection pcb we see on single cells. The single cells do not have protection, it is a common protection for the pack.

 

[Dr. Tweedbucket]

no

laptop packs use unprotected cells


but

each cell has detection wired to it, and the controller does run
the protection for each cell and the pack as a whole, so if one cell
goes wonky, the whole pack is unusable as it's charge circuit is shut down

it is this exact reason why so many counterfiet cells exist on fleabay. MANY thrown out laptop packs
have a lot of good cells, these are taken out, tested, rewrapped and resold as new. the ones that are
so dead they are the cause of the pack shutdown, those are tossed, or rewrapped by the really shady counterfeiters

I can get a box of 20 dead laptop packs for 1 dollar, and get 80 somewhat ususable 18650's from them,
rewrap them and slap on my own protection chip, and sell for 3-5 bucks a pop.....big money in being a sleazeball

Wow, that's interesting, I never thought of doing that, but sounds like good way to snag spare batteries.

Part of the reason I asked is I had a laptop who's battery got really pretty warm while charging. It was on the edge of being hot and I got a bit concerned and unplugged it. The next time I plugged it in, I monitored it and it seems to be ok then. Since then I haven't trusted charging them un attended.

 

[nitedrive]

Sorry this is a bit old but since I used to do work like this, yes, all Li-Ion laptop batteries are protected at the pack level. A typical setup from about a decade back (and they are likely the same today) will monitor each cell's voltage individually. Note that if the cells are wired in parallel (typical in say a 6 or 9 cell 18650 setup) then the voltages of the pair are measured. If any cell exceeds a threshold voltage the input to the pack is shut down so it can't continue to charge. This is done by switching off a pair of FETs that allow current in or out of the battery.

This same circuit also protects from under voltage and over current. The under voltage protection again checks the cell voltages and would typically shut down the pack. There are two types of over current protection. The first is a mild over current condition. Say drawing 50% more current than the battery is rated for. In this case the safety circuit measures current through a sense resistor and will shut things down when the voltage across the sense resistor is too high. However, in the case of a hard short this can take too long. A hard short will actually cause the cell voltage to seriously drop. That serious cell voltage drop in turn drops the voltage of the signal that controls the switching FETs. Thus those FETs turn off and the current flow is stopped. With the current flow stopped the cell voltage will recover but the safety circuit will not reset until the short has been removed.

Finally there is a last ditch safety circuit that is independent of the one above. It protects against over charge as well as over temp. This circuit again measures the cell voltage. It has a higher threshold than the one above. If the voltage gets high enough to trigger it or if the battery temperature rises too high it will trigger a thermal fuse. That fuse is non-resetable. Once blown the battery is dead. Of course the only time it should ever be used is if the primary safety circuit, a circuit which should protect the battery from any over charge or discharge situation, fails. In that case the manufacture doesn't want the battery to be used ever again.