Re: Laptop Battery Problem


"budgie" <me@xxxxxxxxxxx> wrote in message
news:pf7p42pokck4g7oge82d97eufk76m2ggoa@xxxxxxxxxx
On Mon, 24 Apr 2006 09:04:16 +0100, "The Electric Fan Club"
<ian.shorrocks@xxxxxxxxxxxxxxxxxxxxxxxx> wrote:

This sounds exactly like a dead battery. The charging circuit has
detected
that the battery is discharged below the minimum limit and has (correctly)
refused to charge the battery. There is no method of recovering the
battery
and indeed, it is extremely dangerous to try.

Don't know where you get that extremely dangerous stuff from.


When a cell is discharged below 3.0 volts (2.5 volts for some early cells),
the cell chemistry deposits copper on the internal structure of the cell.
If a cell is charged in such a condition, the copper will shunt the cell and
pass an unwanted discharge current. It also bypasses the PTC element in the
cell, if there is any (the cell's in-built protection). This discharge
current, if large enough can cause the cell chemistry to then liberate
oxygen gas. As soon as the highly flammable electrolyte and the oxygen find
themselves in the same place (along with any lithium that has been liberated
during use), the cell ruptures, shooting out quite a large flame, igniting
anything near it. We've tried it, so we know, bu then we have blown up
Ni-Cd batteries albeit deliberately.

There are published schemes for recovering Li-ion cells that have been
allowed to reach this condition for short periods of time but the very
thinly plated out copper reduces the cell's capacity (having been removed
from the chemistry) and increases the cell's self discharge rate. These
schemes recommend (or in some cases, *should* recommend but don't) that they
are carried out in a fire proof area.

Lithium-ion cells are extremely dangerous items if abused in any way. Used
properly with correctly designed charging circuits, there is little danger.
No charger that I know of will bring an over discharged battery back into
the minimum charge zone and indeed should not do so. Having said that, it
may be that you are aware of a specific charger that leaks enough current to
do so. If so it is either a badly designed charger, or specifically
intended to perform the recovery outlined in the last paragraph.

Bare Lithium-ion Polymer cells are a particular fire risk, because if
anything penetrates the thin heat shrink sleeve, the cell will burn.

It is interesting to note, that we have recently received some Lithium-ion
Polymer cell samples that are claimed to be able to sustain quite heavy
discharge rates (like in about 10 to 15 minutes) without damage. The claim
may be true as they haven't exploded - yet. The jury is still out on the
number of cycles.


.

Relevant Pages

  • Re: Laptop Battery Problem
    ... When a cell is discharged below 3.0 volts, ... pass an unwanted discharge current. ... and our charger designs were based on a more conservative 3v0 low voltage ... This aligned well with the majority of available pack protection chips. ...
    (comp.sys.laptops)
  • Re: NIMH issues
    ... Depends on the design of the charger. ... "bump" in the voltage when they are full after which the voltage actually ... voltage of the battery because batteries "recover" when the load is removed. ... A NiMH cell is generally considered empty ...
    (sci.electronics.misc)
  • Re: Extending the Life of a Rechargable Battery
    ... I heard the battery will go bad faster if you partially charge, discharge more frequently. ... NiCds and NiMH batteries can be fully discharged, but not below 0V on any cell. ...
    (sci.electronics.design)
  • Re: AA and AAA battery charger problems?
    ... The next most discussed charger appears to be the La Crosse BC-900. ... the circuit, by removing the battery and then connecting it again, to let ... cells in the middle of a 6-7 cell stack has reversed polarity. ... still near my vehicle and a much-needed cell has reversed voltage I use a small ...
    (rec.photo.digital)
  • Re: Extending the Life of a Rechargable Battery
    ... I heard the battery will go bad faster if you partially charge, discharge more frequently. ... NiCds and NiMH batteries can be fully discharged, but not below 0V on any cell. ...
    (sci.electronics.design)