Laptop Battery Problem

On Mon, 24 Apr 2006 14:27:49 +0100, "The Electric Fan Club"
<ian.shorrocks@baeMY_CLOTHESsystems.com> wrote:

>
>"budgie" <me@privacy.net> wrote in message
>newsf7p42pokck4g7oge82d97eufk76m2ggoa@4ax.com.. .
>> On Mon, 24 Apr 2006 09:04:16 +0100, "The Electric Fan Club"
>> <ian.shorrocks@baeMY_CLOTHESsystems.com> 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.

You must be referring to extremely early (Lithium) cells,. The "standard" 18650
cells we worked with had a factory recommended "user-no-go-below" voltage of
2v5, and our charger designs were based on a more conservative 3v0 low voltage
cutoff. This aligned well with the majority of available pack protection chips.
There is also limited capacity delivered at those lower voltages, as the
terminal-voltage-vs-time curve droops (under constant current) below about 3v3.


>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.

Completely agree with that, although there are authenticated cases of
spontaneous conflagration in cellphones. User abuse has been ruled out in most,
but abuse by a feral phone has not.

>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.

We may be discussing apples and oranges. You use the term "over-discharged".
I am referring to a cell/pack that has been locked out by going under-voltage,
meaning under that low voltage cutoff point. In the case of the cells we used,
3v0 was the cutoff point for the pack electronics while 2v5 was the
manufacturer's recommended low voltage shutoff, below which was the onset of
deleterious and non-reversible changes.

Once a cell/pack went hit that 3v0 threshold, the PPM went high impedance and
limited further discharge to uA or nA. On test, packs that reached 3v0/cell
were still about 2v95 when we gave up monitoring their condition several months
later, so within that half volt range there was every opportunity to recover the
cells back into normal operation.

The PPM provided a high - but sensible - impedance to charging when in the UVLO
state. Remember that UVLO is a protective state to prevent further discharge -
it is NOT intended to be a terminal state. Chargers that normally operate on a
current-limited constant-voltage will simply present their (say) 4v2 potential
to the pack, usually through their own *additional* limiting impedance as they
do for below-safe-temp cells, to provide a trickle charge. With the low rate of
self-discharge, this trickle will progressively bring an UVLO-ed pack back into
the non-locked-out state and normal recharge will commence.

This is not (IMO) a *special* or *trick* charger behaviour. In service, packs
are going to be discharged until either the load appliance (typically in
single-cell loads such as cellphones) or the pack electronics decides the low
voltage threshold has been reached and UVLO occurs. If the charger wan't able
to recover these packs they would be single use items, not rechargeables.


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

I find that particularly "interesting". The manufacturers of the cells we used
had a nail penetration test, whereby a cell at nominal voltage (3v6 usually) had
to survive a complete transverse penetration by a steel nail without explosion
or fire. And no, we haven't felt enticed to reproduce these results!


>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.

That's really about tradeoffs in the construction and the chemistry. I wouldn't
expect to see 200 cycles from them.

"budgie" <me@privacy.net> wrote in message
news:n30r42p7s3gp8e2bev8h6vvt2lh4vjsq04@4ax.com...
> On Mon, 24 Apr 2006 14:27:49 +0100, "The Electric Fan Club"
> <ian.shorrocks@baeMY_CLOTHESsystems.com> wrote:
>
>>
>>"budgie" <me@privacy.net> wrote in message
>>newsf7p42pokck4g7oge82d97eufk76m2ggoa@4ax.com. ..
>>> On Mon, 24 Apr 2006 09:04:16 +0100, "The Electric Fan Club"
>>> <ian.shorrocks@baeMY_CLOTHESsystems.com> 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.
>
> You must be referring to extremely early (Lithium) cells,. The "standard"
> 18650
> cells we worked with had a factory recommended "user-no-go-below" voltage
> of
> 2v5, and our charger designs were based on a more conservative 3v0 low
> voltage
> cutoff. This aligned well with the majority of available pack protection
> chips.
> There is also limited capacity delivered at those lower voltages, as the
> terminal-voltage-vs-time curve droops (under constant current) below about
> 3v3.
>

No I am refering to current technology cells. The 2.5v lower limit applies
to early technology cells that used carbon anodes. There is still current
production that uses this early technology. Your cells sound like these.
>
>>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.
>
> Completely agree with that, although there are authenticated cases of
> spontaneous conflagration in cellphones. User abuse has been ruled out in
> most,
> but abuse by a feral phone has not.
>
>>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.
>
> We may be discussing apples and oranges. You use the term
> "over-discharged".
> I am referring to a cell/pack that has been locked out by going
> under-voltage,
> meaning under that low voltage cutoff point. In the case of the cells we
> used,
> 3v0 was the cutoff point for the pack electronics while 2v5 was the
> manufacturer's recommended low voltage shutoff, below which was the onset
> of
> deleterious and non-reversible changes.
>

The 3.0 volt cutoff point may be designed so that cells can be used from
more than one source without having to have 2 versions of the management
circuitry. In this case 'overdischarged cells that are below 3.0 volts but
above the chemistry minimum of 2.5 volts can obviously be charged without
danger.

> Once a cell/pack went hit that 3v0 threshold, the PPM went high impedance
> and
> limited further discharge to uA or nA. On test, packs that reached
> 3v0/cell
> were still about 2v95 when we gave up monitoring their condition several
> months
> later, so within that half volt range there was every opportunity to
> recover the
> cells back into normal operation.
>



> The PPM provided a high - but sensible - impedance to charging when in the
> UVLO
> state. Remember that UVLO is a protective state to prevent further
> discharge -
> it is NOT intended to be a terminal state. Chargers that normally operate
> on a
> current-limited constant-voltage will simply present their (say) 4v2
> potential
> to the pack, usually through their own *additional* limiting impedance as
> they
> do for below-safe-temp cells, to provide a trickle charge. With the low
> rate of
> self-discharge, this trickle will progressively bring an UVLO-ed pack back
> into
> the non-locked-out state and normal recharge will commence.
>
>
> This is not (IMO) a *special* or *trick* charger behaviour. In service,
> packs
> are going to be discharged until either the load appliance (typically in
> single-cell loads such as cellphones) or the pack electronics decides the
> low
> voltage threshold has been reached and UVLO occurs. If the charger wan't
> able
> to recover these packs they would be single use items, not rechargeables.
>


I stand by my statement that: chargers should make no attempt to charge any
cell that is below its minimum voltage. This should be independant of the
circuitry on the cell pack. The charge monitor on the cell pack should cut
out at the minimum voltage (unless that functionality is built into the
appliance), but it should not prevent charging as charging from the minimum
voltage is perfectly OK. I would regard any cell pack that refused to allow
you to charge it once the minumum voltage had been reached as badly designed
(effectively a primary cell as you state). The refusal to charge from below
this point should be a function of the charger *not* the cell pack (though
IMHO there would be no disadvantage in a belt and braces approach).

>
>>Bare Lithium-ion Polymer cells are a particular fire risk, because if
>>anything penetrates the thin heat shrink sleeve, the cell will burn.
>
> I find that particularly "interesting". The manufacturers of the cells we
> used
> had a nail penetration test, whereby a cell at nominal voltage (3v6
> usually) had
> to survive a complete transverse penetration by a steel nail without
> explosion
> or fire. And no, we haven't felt enticed to reproduce these results!
>

Owners of iPods and their derivatives have repeated the demonstration on
many occasions - usually destroying the iPod and a sizeable area of floor in
the process (many photographs have even turned up on numerous blog sites).
These devices use Lithium-ion polymer cells which are supposed to reduce the
hazard because they (allegedly) lock the flammable electrolyte in the
polymer. However, they still seem to burn, especially well if over-charged
or recharged from over-discharge.. We have to check these things out as we
are in the aerospace business and there are considerable liability issues
with our products. Generally once you enclose the cell is something
substantial, it ceases to be a problem, though this does not solve the
problem of diyers who are unaware of the dangers.

>
>>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.
>
> That's really about tradeoffs in the construction and the chemistry. I
> wouldn't
> expect to see 200 cycles from them.

The manufacturer claims 500, but we will make our own minds up once we get
that far.

On Tue, 25 Apr 2006 08:01:11 +0100, "The Electric Fan Club"
<ian.shorrocks@baeMY_CLOTHESsystems.com> wrote:

>
>"budgie" <me@privacy.net> wrote in message
>news:n30r42p7s3gp8e2bev8h6vvt2lh4vjsq04@4ax.com.. .
>> On Mon, 24 Apr 2006 14:27:49 +0100, "The Electric Fan Club"
>> <ian.shorrocks@baeMY_CLOTHESsystems.com> wrote:

(snip)

>>>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.
>>
>> We may be discussing apples and oranges. You use the term
>> "over-discharged".
>> I am referring to a cell/pack that has been locked out by going
>> under-voltage,
>> meaning under that low voltage cutoff point. In the case of the cells we
>> used,
>> 3v0 was the cutoff point for the pack electronics while 2v5 was the
>> manufacturer's recommended low voltage shutoff, below which was the onset
>> of
>> deleterious and non-reversible changes.
>>
>
>The 3.0 volt cutoff point may be designed so that cells can be used from
>more than one source without having to have 2 versions of the management
>circuitry.

In our case, the 3v0 cutoff was chosen as the cells have little left to give
below that. As I previously posted, the voltage curve at constant discharge
current starts to droop noticeably below 3v3. If I had my "druthers" the LVCO
would have been around 3v25.

>In this case 'overdischarged cells that are below 3.0 volts but
>above the chemistry minimum of 2.5 volts can obviously be charged without
>danger.
>
>> Once a cell/pack went hit that 3v0 threshold, the PPM went high impedance
>> and
>> limited further discharge to uA or nA. On test, packs that reached
>> 3v0/cell
>> were still about 2v95 when we gave up monitoring their condition several
>> months
>> later, so within that half volt range there was every opportunity to
>> recover the
>> cells back into normal operation.
>>
>>
>> The PPM provided a high - but sensible - impedance to charging when in the
>> UVLO
>> state. Remember that UVLO is a protective state to prevent further
>> discharge -
>> it is NOT intended to be a terminal state. Chargers that normally operate
>> on a
>> current-limited constant-voltage will simply present their (say) 4v2
>> potential
>> to the pack, usually through their own *additional* limiting impedance as
>> they
>> do for below-safe-temp cells, to provide a trickle charge. With the low
>> rate of
>> self-discharge, this trickle will progressively bring an UVLO-ed pack back
>> into
>> the non-locked-out state and normal recharge will commence.
>>
>>
>> This is not (IMO) a *special* or *trick* charger behaviour. In service,
>> packs
>> are going to be discharged until either the load appliance (typically in
>> single-cell loads such as cellphones) or the pack electronics decides the
>> low
>> voltage threshold has been reached and UVLO occurs. If the charger wan't
>> able
>> to recover these packs they would be single use items, not rechargeables.
>>
>
>
>I stand by my statement that: chargers should make no attempt to charge any
>cell that is below its minimum voltage. This should be independant of the
>circuitry on the cell pack. The charge monitor on the cell pack should cut
>out at the minimum voltage (unless that functionality is built into the
>appliance), but it should not prevent charging as charging from the minimum
>voltage is perfectly OK. I would regard any cell pack that refused to allow
>you to charge it once the minumum voltage had been reached as badly designed
>(effectively a primary cell as you state). The refusal to charge from below
>this point should be a function of the charger *not* the cell pack (though
>IMHO there would be no disadvantage in a belt and braces approach).

Your use of the term "minimum" is confusing.

You state: "chargers should make no attempt to charge any cell that is below its
minimum voltage" yet in the same breath you follow up with: "I would regard any
cell pack that refused to allow you to charge it once the minumum voltage had
been reached as badly designed" and then: "The refusal to charge from below this
point should be a function of the charger".

There are two voltages of importance - the LVCO point and the "no-go-below"
safety-driven limit. Between those voltages, packs MUST be able to be
recovered/recharged. If not by a charger, then by what?

Sensible chargers (and I include in that my commercial designs) monitor the
cell/pack temp and terminal volts. If the voltage is below the no-go point,
they shut down. Simple. If above the no-go and below the LVCO point, and not
over-temp, proper CV charging output is applied with a low current limit. When
the cell temp is above the low temp lockout, if the cell voltage rises past the
LVCO point normal CLCV charging resumes.

"budgie" <me@privacy.net> wrote in message
news:ho5u42pi3tot40hqqank6p4seai2tv6gqn@4ax.com...
>>
>>I stand by my statement that: chargers should make no attempt to charge
>>any
>>cell that is below its minimum voltage. This should be independant of the
>>circuitry on the cell pack. The charge monitor on the cell pack should
>>cut
>>out at the minimum voltage (unless that functionality is built into the
>>appliance), but it should not prevent charging as charging from the
>>minimum
>>voltage is perfectly OK. I would regard any cell pack that refused to
>>allow
>>you to charge it once the minumum voltage had been reached as badly
>>designed
>>(effectively a primary cell as you state). The refusal to charge from
>>below
>>this point should be a function of the charger *not* the cell pack (though
>>IMHO there would be no disadvantage in a belt and braces approach).
>
> Your use of the term "minimum" is confusing.
>
> You state: "chargers should make no attempt to charge any cell that is
> below its
> minimum voltage" yet in the same breath you follow up with: "I would
> regard any
> cell pack that refused to allow you to charge it once the minumum voltage
> had
> been reached as badly designed" and then: "The refusal to charge from
> below this
> point should be a function of the charger".
>
> There are two voltages of importance - the LVCO point and the
> "no-go-below"
> safety-driven limit. Between those voltages, packs MUST be able to be
> recovered/recharged. If not by a charger, then by what?
>
> Sensible chargers (and I include in that my commercial designs) monitor
> the
> cell/pack temp and terminal volts. If the voltage is below the no-go
> point,
> they shut down. Simple. If above the no-go and below the LVCO point, and
> not
> over-temp, proper CV charging output is applied with a low current limit.
> When
> the cell temp is above the low temp lockout, if the cell voltage rises
> past the
> LVCO point normal CLCV charging resumes.

Possibly my attempts at trying to make the explanation simple. There is a
specific charge level below which the cell sustains damage due to liberating
copper from the chemistry. This precise level is less than 3.0 volts (lets
forget the 2.5 volt chemistries for now - but similar arguements apply).
The precise level is also dependant on the chemical formulation which varies
from one manufacturer to another and indeed on variations in formulation
within the same manufacturer.

In general, most manufacturers specify 3.0 volts as the minimum permitted
charge level so as to keep clear of the real minimum charge level.
Appliance manufacturers generally follow this specification (though some set
it higher at 3.2 volts or any other arbitrary figure that leaps to mind
(Windows lets you pick your own to some extent)). The level at which
charging is refused is set to a little less than this, typically 2.8 to 2.9
volts. Thus if a cell is allowed to discharge to the point where the
appliance shuts down, the charger will recharge it if it is charged
immediately, and it can be charged at full permitted current. If, however,
the cell is left in place, then there is a real risk that any small
discharge (including self discharge) discharges the cell to below the
nocharge point and the charger should not charge the cell at all (not even a
very low current). If charging is initiated before this nocharge point is
reached, it can be carried out at the full rate, because the cell integrity
has not yet been compromised. It should be noted that the tolerances on
what can be tolerated are, in many cases, very tight and there is often a
very thin dividing line between normal operation and cell abuse.

Although I refer to 'cells' in all this, it makes life simple because the
charge monitoring can be made a function of the charger alone. If batteries
are required that have a specification higher than 3.7v (nominal) and around
1.5 AH, then multiple cell constructions are necessary (though the latter
figure is rising all the time). The higher AH capacities are simple enough
because the voltage/charge characteristic permits simple parallelling of
cells to achieve this - something NiCd and Ni-MH cannot do.

However, higher voltages require series connection of either single cells or
banks of parallelled cells. Once again the parallelled bits are no problem,
but the individual cells in the series (the paralleled bits can be
considered as individual cells in this context) must be individually
monitored for charge - in particular, the charge monitor will signal if any
part of the chain reaches 3.0 volts, or in a few designs, may even cut the
battery off itself. The charge monitor will also signal if any part of the
chain is below the nocharge level or again in a few designs, actually
inhibit the charge itself.

One battery design that we have seen (not a laptop), actually monitors the
individual cells of the paralleled parts of the circuit. If an individual
cell loses capacity or discharges below the nocharge level, the monitor
circuit isolates it and allows the battery pack to continue to
charge/discharge albeit with a reduced capacity. The degree of
sophistication is, I suspect, a function of the pereived profitabilty of
your replacement battery business -v- the required reliability of the
original equipment.

This narrative is by no means exhaustive on the subject.

On Wed, 26 Apr 2006 09:40:36 +0100, "The Electric Fan Club"
<ian.shorrocks@baeMY_CLOTHESsystems.com> wrote:

>
>"budgie" <me@privacy.net> wrote in message
>news:ho5u42pi3tot40hqqank6p4seai2tv6gqn@4ax.com.. .
>>>
>>>I stand by my statement that: chargers should make no attempt to charge
>>>any
>>>cell that is below its minimum voltage. This should be independant of the
>>>circuitry on the cell pack. The charge monitor on the cell pack should
>>>cut
>>>out at the minimum voltage (unless that functionality is built into the
>>>appliance), but it should not prevent charging as charging from the
>>>minimum
>>>voltage is perfectly OK. I would regard any cell pack that refused to
>>>allow
>>>you to charge it once the minumum voltage had been reached as badly
>>>designed
>>>(effectively a primary cell as you state). The refusal to charge from
>>>below
>>>this point should be a function of the charger *not* the cell pack (though
>>>IMHO there would be no disadvantage in a belt and braces approach).
>>
>> Your use of the term "minimum" is confusing.
>>
>> You state: "chargers should make no attempt to charge any cell that is
>> below its
>> minimum voltage" yet in the same breath you follow up with: "I would
>> regard any
>> cell pack that refused to allow you to charge it once the minumum voltage
>> had
>> been reached as badly designed" and then: "The refusal to charge from
>> below this
>> point should be a function of the charger".
>>
>> There are two voltages of importance - the LVCO point and the
>> "no-go-below"
>> safety-driven limit. Between those voltages, packs MUST be able to be
>> recovered/recharged. If not by a charger, then by what?
>>
>> Sensible chargers (and I include in that my commercial designs) monitor
>> the
>> cell/pack temp and terminal volts. If the voltage is below the no-go
>> point,
>> they shut down. Simple. If above the no-go and below the LVCO point, and
>> not
>> over-temp, proper CV charging output is applied with a low current limit.
>> When
>> the cell temp is above the low temp lockout, if the cell voltage rises
>> past the
>> LVCO point normal CLCV charging resumes.
>
>Possibly my attempts at trying to make the explanation simple. There is a
>specific charge level below which the cell sustains damage due to liberating
>copper from the chemistry. This precise level is less than 3.0 volts (lets
>forget the 2.5 volt chemistries for now - but similar arguements apply).
>The precise level is also dependant on the chemical formulation which varies
>from one manufacturer to another and indeed on variations in formulation
>within the same manufacturer.
>
>In general, most manufacturers specify 3.0 volts as the minimum permitted
>charge level so as to keep clear of the real minimum charge level.
>Appliance manufacturers generally follow this specification (though some set
>it higher at 3.2 volts or any other arbitrary figure that leaps to mind
>(Windows lets you pick your own to some extent)). The level at which
>charging is refused is set to a little less than this, typically 2.8 to 2.9
>volts. Thus if a cell is allowed to discharge to the point where the
>appliance shuts down, the charger will recharge it if it is charged
>immediately, and it can be charged at full permitted current.

So far I agree although we will probably never agree on the two key voltages, as
that depends very much on the source of the cells and their chemistry.

> If, however,
>the cell is left in place, then there is a real risk that any small
>discharge (including self discharge) discharges the cell to below the
>nocharge point and the charger should not charge the cell at all (not even a
>very low current).

I will comment from the point of "dumb" pack protection modules (those that do
not communicate with a host via serial communications), as those are the only
ones we have incorporated into industrial packs to date.

If the PPM has interrupted discharge due to reaching the LVCO point, the
resulting high impedance IS *high*. Except for rebound (cured by hysteresis in
the LVCO sensing mechanism) the available discharge current is uA at most, while
self-discharge is equally insignificant. Your use of the term "immediately" is
overly dramatic - I couldn't envisage combined discharge dropping 200mV in six
months.

> If charging is initiated before this nocharge point is
>reached, it can be carried out at the full rate, because the cell integrity
>has not yet been compromised. It should be noted that the tolerances on
>what can be tolerated are, in many cases, very tight and there is often a
>very thin dividing line between normal operation and cell abuse.

The commercial PPM's we used only allowed effectively a trickle charge until the
LVCO point was reached. Similarly - but separately - the charge controller also
ensured that "normal" charging (in our case ~0.5C) did not commence until the
LVCO threshold had been crossed.

>Although I refer to 'cells' in all this, it makes life simple because the
>charge monitoring can be made a function of the charger alone. If batteries
>are required that have a specification higher than 3.7v (nominal) and around
>1.5 AH, then multiple cell constructions are necessary (though the latter
>figure is rising all the time). The higher AH capacities are simple enough
>because the voltage/charge characteristic permits simple parallelling of
>cells to achieve this - something NiCd and Ni-MH cannot do.
>
>However, higher voltages require series connection of either single cells or
>banks of parallelled cells. Once again the parallelled bits are no problem,
>but the individual cells in the series (the paralleled bits can be
>considered as individual cells in this context) must be individually
>monitored for charge - in particular, the charge monitor will signal if any
>part of the chain reaches 3.0 volts, or in a few designs, may even cut the
>battery off itself. The charge monitor will also signal if any part of the
>chain is below the nocharge level or again in a few designs, actually
>inhibit the charge itself.

The PPM's we used monitor cell voltage differentials in series strings. Once
this exceeds a predetermined amount, the pack is isolated. In fact this is a
known cause of reduction in usable pack capacity in many appliances such as
laptops, unfortunately attributed by many as simply the cells "wearing out".
Because any differences in (charging) coulomb efficiency will still effect the
SOC when charge terminates - unlike NiXX types where a continuous trickle charge
is typically applied - the cell differences not only appear cycle after cycle
but increase as cycle count mounts. This can only be properly addressed by
intrusive means - charging cells individually to restore balance at full charge.

>One battery design that we have seen (not a laptop), actually monitors the
>individual cells of the paralleled parts of the circuit. If an individual
>cell loses capacity or discharges below the nocharge level, the monitor
>circuit isolates it and allows the battery pack to continue to
>charge/discharge albeit with a reduced capacity. The degree of
>sophistication is, I suspect, a function of the pereived profitabilty of
>your replacement battery business -v- the required reliability of the
>original equipment.

It is difficult to conceive a mechanisn to effectively monitor individual cells
which are in parallel, without introducing significant series impedances.

>This narrative is by no means exhaustive on the subject.

but I suspect we are probably the only ones still reading ...

In an earlier contribution to this discussion,
budgie <me@privacy.net> wrote:

>
>> This narrative is by no means exhaustive on the subject.
>
> but I suspect we are probably the only ones still reading ...

I suspect you're right!

Whilst your detailed discussion may be of great interest to those who study
the minutiae of battery technology, it hasn't really answered my original
question, which was (in essence):

"How can I be sure that my problem is down to a failed battery rather than a
failed charging system on my laptop, in order to be confident that buying a
new battery will fix it?!
--
Cheers,
Roger
______
Email address maintained for newsgroup use only, and not regularly
monitored.. Messages sent to it may not be read for several weeks.
PLEASE REPLY TO NEWSGROUP!

In an earlier contribution to this discussion,
Roger Mills <watt.tyler@googlemail.com> wrote:

>
> How can I be sure that my problem is down to a failed battery rather
> than a failed charging system on my laptop, in order to be confident
> that buying a new battery will fix it?

As a follow-up . . .

What I didn't say earlier was that I had taken a flyer and ordered a new
battery anyway. This has now arrived and seems to be working fine - so I'm
pretty sure that the problem *was* with the battery and not with the
charger.
--
Cheers,
Roger
______
Email address maintained for newsgroup use only, and not regularly
monitored.. Messages sent to it may not be read for several weeks.
PLEASE REPLY TO NEWSGROUP!

On Wed, 26 Apr 2006 13:57:30 +0100, "Roger Mills" <watt.tyler@googlemail.com>
wrote:

>In an earlier contribution to this discussion,
>budgie <me@privacy.net> wrote:
>
>>
>>> This narrative is by no means exhaustive on the subject.
>>
>> but I suspect we are probably the only ones still reading ...
>
>I suspect you're right!

Ha! you've been eavesdroppping ;-)

>Whilst your detailed discussion may be of great interest to those who study
>the minutiae of battery technology, it hasn't really answered my original
>question, which was (in essence):
>
>"How can I be sure that my problem is down to a failed battery rather than a
>failed charging system on my laptop, in order to be confident that buying a
>new battery will fix it?!

If you read my original post I did answer that question:

"Identifying the faulty module (charger/battery) can really only be achieved by
substitution with a known healthy unit. That limits you to obtaining (access
to) another battery or another laptop."

On Wed, 26 Apr 2006 19:17:57 +0100, "Roger Mills" <watt.tyler@googlemail.com>
wrote:

>In an earlier contribution to this discussion,
>Roger Mills <watt.tyler@googlemail.com> wrote:
>
>>
>> How can I be sure that my problem is down to a failed battery rather
>> than a failed charging system on my laptop, in order to be confident
>> that buying a new battery will fix it?
>
>As a follow-up . . .
>
>What I didn't say earlier was that I had taken a flyer and ordered a new
>battery anyway. This has now arrived and seems to be working fine - so I'm
>pretty sure that the problem *was* with the battery and not with the
>charger.

Refer my other response. Good to hear.

"budgie" <me@privacy.net> wrote in message
news:b1ou42pm8v4151o93k820l7mab9p0vbdrb@4ax.com...
> On Wed, 26 Apr 2006 09:40:36 +0100, "The Electric Fan Club"
> <ian.shorrocks@baeMY_CLOTHESsystems.com> wrote:
>
>>
>>"budgie" <me@privacy.net> wrote in message
>>news:ho5u42pi3tot40hqqank6p4seai2tv6gqn@4ax.com. ..
>>>>
>>>>I stand by my statement that: chargers should make no attempt to charge
>>>>any
>>>>cell that is below its minimum voltage. This should be independant of
>>>>the
>>>>circuitry on the cell pack. The charge monitor on the cell pack should
>>>>cut
>>>>out at the minimum voltage (unless that functionality is built into the
>>>>appliance), but it should not prevent charging as charging from the
>>>>minimum
>>>>voltage is perfectly OK. I would regard any cell pack that refused to
>>>>allow
>>>>you to charge it once the minumum voltage had been reached as badly
>>>>designed
>>>>(effectively a primary cell as you state). The refusal to charge from
>>>>below
>>>>this point should be a function of the charger *not* the cell pack
>>>>(though
>>>>IMHO there would be no disadvantage in a belt and braces approach).
>>>
>>> Your use of the term "minimum" is confusing.
>>>
>>> You state: "chargers should make no attempt to charge any cell that is
>>> below its
>>> minimum voltage" yet in the same breath you follow up with: "I would
>>> regard any
>>> cell pack that refused to allow you to charge it once the minumum
>>> voltage
>>> had
>>> been reached as badly designed" and then: "The refusal to charge from
>>> below this
>>> point should be a function of the charger".
>>>
>>> There are two voltages of importance - the LVCO point and the
>>> "no-go-below"
>>> safety-driven limit. Between those voltages, packs MUST be able to be
>>> recovered/recharged. If not by a charger, then by what?
>>>
>>> Sensible chargers (and I include in that my commercial designs) monitor
>>> the
>>> cell/pack temp and terminal volts. If the voltage is below the no-go
>>> point,
>>> they shut down. Simple. If above the no-go and below the LVCO point,
>>> and
>>> not
>>> over-temp, proper CV charging output is applied with a low current
>>> limit.
>>> When
>>> the cell temp is above the low temp lockout, if the cell voltage rises
>>> past the
>>> LVCO point normal CLCV charging resumes.
>>
>>Possibly my attempts at trying to make the explanation simple. There is a
>>specific charge level below which the cell sustains damage due to
>>liberating
>>copper from the chemistry. This precise level is less than 3.0 volts
>>(lets
>>forget the 2.5 volt chemistries for now - but similar arguements apply).
>>The precise level is also dependant on the chemical formulation which
>>varies
>>from one manufacturer to another and indeed on variations in formulation
>>within the same manufacturer.
>>
>>In general, most manufacturers specify 3.0 volts as the minimum permitted
>>charge level so as to keep clear of the real minimum charge level.
>>Appliance manufacturers generally follow this specification (though some
>>set
>>it higher at 3.2 volts or any other arbitrary figure that leaps to mind
>>(Windows lets you pick your own to some extent)). The level at which
>>charging is refused is set to a little less than this, typically 2.8 to
>>2.9
>>volts. Thus if a cell is allowed to discharge to the point where the
>>appliance shuts down, the charger will recharge it if it is charged
>>immediately, and it can be charged at full permitted current.
>
> So far I agree although we will probably never agree on the two key
> voltages, as
> that depends very much on the source of the cells and their chemistry.
>

I think I said that. The voltages were presumably selected to encompass the
worst case.

>> If, however,
>>the cell is left in place, then there is a real risk that any small
>>discharge (including self discharge) discharges the cell to below the
>>nocharge point and the charger should not charge the cell at all (not even
>>a
>>very low current).
>
> I will comment from the point of "dumb" pack protection modules (those
> that do
> not communicate with a host via serial communications), as those are the
> only
> ones we have incorporated into industrial packs to date.
>
> If the PPM has interrupted discharge due to reaching the LVCO point, the
> resulting high impedance IS *high*. Except for rebound (cured by
> hysteresis in
> the LVCO sensing mechanism) the available discharge current is uA at most,
> while
> self-discharge is equally insignificant. Your use of the term
> "immediately" is
> overly dramatic - I couldn't envisage combined discharge dropping 200mV in
> six
> months.
>

Maybe. It depends on the both the cells and the equipment. I have a piece
of test equipment that will completely discharge its battery pack in just 2
weeks if never switched on. Fortunately, the battery is of a design where
it cuts its output off.

>> If charging is initiated before this nocharge point is
>>reached, it can be carried out at the full rate, because the cell
>>integrity
>>has not yet been compromised. It should be noted that the tolerances on
>>what can be tolerated are, in many cases, very tight and there is often a
>>very thin dividing line between normal operation and cell abuse.
>
> The commercial PPM's we used only allowed effectively a trickle charge
> until the
> LVCO point was reached. Similarly - but separately - the charge
> controller also
> ensured that "normal" charging (in our case ~0.5C) did not commence until
> the
> LVCO threshold had been crossed.
>
>>Although I refer to 'cells' in all this, it makes life simple because the
>>charge monitoring can be made a function of the charger alone. If
>>batteries
>>are required that have a specification higher than 3.7v (nominal) and
>>around
>>1.5 AH, then multiple cell constructions are necessary (though the latter
>>figure is rising all the time). The higher AH capacities are simple
>>enough
>>because the voltage/charge characteristic permits simple parallelling of
>>cells to achieve this - something NiCd and Ni-MH cannot do.
>>
>>However, higher voltages require series connection of either single cells
>>or
>>banks of parallelled cells. Once again the parallelled bits are no
>>problem,
>>but the individual cells in the series (the paralleled bits can be
>>considered as individual cells in this context) must be individually
>>monitored for charge - in particular, the charge monitor will signal if
>>any
>>part of the chain reaches 3.0 volts, or in a few designs, may even cut the
>>battery off itself. The charge monitor will also signal if any part of
>>the
>>chain is below the nocharge level or again in a few designs, actually
>>inhibit the charge itself.
>
> The PPM's we used monitor cell voltage differentials in series strings.
> Once
> this exceeds a predetermined amount, the pack is isolated. In fact this
> is a
> known cause of reduction in usable pack capacity in many appliances such
> as
> laptops, unfortunately attributed by many as simply the cells "wearing
> out".
> Because any differences in (charging) coulomb efficiency will still effect
> the
> SOC when charge terminates - unlike NiXX types where a continuous trickle
> charge
> is typically applied - the cell differences not only appear cycle after
> cycle
> but increase as cycle count mounts. This can only be properly addressed
> by
> intrusive means - charging cells individually to restore balance at full
> charge.
>
>>One battery design that we have seen (not a laptop), actually monitors the
>>individual cells of the paralleled parts of the circuit. If an individual
>>cell loses capacity or discharges below the nocharge level, the monitor
>>circuit isolates it and allows the battery pack to continue to
>>charge/discharge albeit with a reduced capacity. The degree of
>>sophistication is, I suspect, a function of the pereived profitabilty of
>>your replacement battery business -v- the required reliability of the
>>original equipment.
>
> It is difficult to conceive a mechanisn to effectively monitor individual
> cells
> which are in parallel, without introducing significant series impedances.
>

Well somebody clearly has.

>>This narrative is by no means exhaustive on the subject.
>
> but I suspect we are probably the only ones still reading ...

At least one other person is still reading, but I shall now go to see what
he says.

Have a nice day...