Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > comp.sys.laptops > #1867

Re: Laptop battery loses charge when off??

Show all headers | View raw

Somewhere on teh intarwebs Computer Nerd Kev wrote:
> On 17 Mar 2013, ~misfit~ wrote:
>
>> It's things like mp3 players and some older cellphones that
>> usually have fiery Li-Ion "batteries" (actually not a
>> battery at all, rather a single cell used in 'dumb' mode).
>> Part of the function of most laptop battery's electronics
>> is to monitor temps, usually in at least two places in the
>> pack - and to shut off or reduce charging current if / when
>> temps go outside of a pre-defined range.
>
> Yes, only another part of that circuitry is usually to forbid
> the charging of the cells if they are under the voltage where
> they begin to deteriorate. If this part of the circuitry is
> tricked into allowing the battery to be charged again, what's to
> say the other safety features aren't disabled as well?

What I think happens is that, in one way or another, the circuitry is 
temporarilly changed briefly (until room temperature is reached) to allow a 
trickle charge through when it normally wouldn't. If the cell is actually 
OK, just has been let drain too far, then charging will continue and, in 
effect the battery will be bought back to life.

If in fact the cell had been refused charge for some other reason - such as 
it had deteriorated due to having reached the end of it's useful life then 
it would get hot under charge, and wouldn't hold charge properly, and the 
now room-temperature monitoring circuits would pick that up and 'brick' it 
again.

My point is that (I think) all you are doing is tricking the control circuit 
for as long as it takes the battery to warm up - not permanently. If any 
'marked-defective' cells that were really only drained too far have managed 
to take enough charge in that time for the PU to re-assess them as no longer 
being defective then I would think there is no danger. It's almost the same 
thing that would occur when replacing cells; The ciruitry reassesses them 
and then treats them accordingly.

I'm told that a re-packed battery that uses the original protection and 
charging circuitry has to be cycled several times until the PU updates the 
state of the cells, stores and then starts to act on the new information. I 
think that this same proccess can be made to happen sometimes by chilling 
the battery pack and applying a charge to it while it's still cold. If cells 
were erronously marked as being dead due to sitting too long then there's a 
chance they can be given enough charge while the PU is basically asleep for 
it to then re-assess them - and sometimes that's all they needed.

There is almost no chance of thermal runaway as, soon after leaving the 
freezer the protection circuits become operational again - in fact I think 
that it's likely always operational to some degree (heh!) - just that maybe 
the sub-zero temps delete or temporarilly obfuscate stored cell info from 
VRAM.

Anyway, in most laptops there is a second redundant protection circuit on 
the planar (I know that there is / was on IBM laptops - I think that most 
others would be the same.)

>>> I completely disassembled everything but the screen then
>>> cleaned the motherboard and other complex electronics by
>>> hand before washing all the plastic and simple electronic
>>> parts in the sink. After a few minutes on, the thing still
>>> stinks of coffee, but at least not quite as bad.
>>
>> As long as it's stripped down of all 'add-on' components a
>> laptop's motherboard can be [a]safely soaked for a few
>> minutes, then washed in warm water with a little mild
>> detergent. As long as it's then rinsed thouroughly a couple
>> times in similarly warm water afterwards and completely
>> dried afterwards it should be fine[b].
>
> Yes I've heard of this being done, I've never been brave enough
> to do it myself though. My main fear is leaving moisture trapped
> in areas of the board, plus in that case some of the residue
> needed scraping with a screwdriver to remove, even after soaking
> with methylated spirits.

That's why I rinse in quite warm water a couple times - so that when all 
trace of detergent has gone the PCB is still warm. Hopefully warm enough so 
that there's not enough moisture trappen anywhere to be trouble. After the 
few times I've done it I've either left it for a few days in the hot water 
cupboard or sat it in a very low oven with the door open. (Aim for about 
25慢 above room temp and dry air for ~30 mins if done in the oven.)

>> I know of one guy in particular who worked in an island
>> community in Samoa who would sell computers; both laptops
>> and desktops, and offer a three-year warranty on them - but
>> only if they were bought back for a week at the end of the
>> first and second years. He would strip them down completely
>> and he had slightly modified a dishwasher which he used to
>> wash and dry the circuit boards of salty deposits each
>> year. If customers were particularly close to the ocean
>> he'd do it bi-annually.
>>
>> IIRC afterwards he would 'mist' the boards (as well as a
>> bunch of the stuff that he deemed too delicate to go
>> through the washer) to the point wher ethey were dripping
>> with pure isopropanol. He would then let that evaporate in
>> a drying cabinet he had made up that was connected by ducts
>> to a dehumidifier. He told me that the environment was so
>> hostile that, if such a regime wasn't undertaken computers
>> wouldn't usually last more than 18 months tops (and that
>> most companies wouldn't give / honour warranties on
>> hardware used in the islands).
>
> Facinating, I wouldn't have thought it would be a problem that
> quickly.

Apparently, yes. It was a reliable source. Those humid and salty South 
Pacific Islands can be murder on (unprotected - or well ventillated as in 
cooling airflow) PCBs - especially ones that have very fine traces and tiny 
SM components.
-- 
/Shaun.

"Humans will have advanced a long, long, way when religious belief has a 
cozy little classification in the DSM."
David Melville (in r.a.s.f1) 

Back to comp.sys.laptops | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

Laptop battery loses charge when off?? micky <NONONOmisc07@bigfoot.com> - 2013-02-24 01:57 -0500
  Re: Laptop battery loses charge when off?? Computer Nerd Kev <not@telling.you> - 2013-02-24 09:04 +0000
    Re: Laptop battery loses charge when off?? Bert <bert@iphouse.com> - 2013-02-24 15:41 +0000
      Re: Laptop battery loses charge when off?? micky <NONONOmisc07@bigfoot.com> - 2013-02-24 14:29 -0500
    Re: Laptop battery loses charge when off?? micky <NONONOmisc07@bigfoot.com> - 2013-02-24 14:22 -0500
  Re: Laptop battery loses charge when off?? Bob_Villa <pheeh.zero@gmail.com> - 2013-02-24 06:27 -0800
    Re: Laptop battery loses charge when off?? micky <NONONOmisc07@bigfoot.com> - 2013-02-24 14:37 -0500
  Re: Laptop battery loses charge when off?? Charlie Hoffpauir <invalid@invalid.com> - 2013-02-24 09:21 -0600
    Re: Laptop battery loses charge when off?? micky <NONONOmisc07@bigfoot.com> - 2013-02-24 14:40 -0500
  Re: Laptop battery loses charge when off?? micky <NONONOmisc07@bigfoot.com> - 2013-03-12 23:17 -0400
    Re: Laptop battery loses charge when off?? "~misfit~" <shaun.at.pukekohe@gmail.com> - 2013-03-14 19:17 +1300
      Re: Laptop battery loses charge when off?? micky <NONONOmisc07@bigfoot.com> - 2013-03-14 12:48 -0400
        Re: Laptop battery loses charge when off?? "~misfit~" <shaun.at.pukekohe@gmail.com> - 2013-03-15 13:15 +1300
    Re: Laptop battery loses charge when off?? Top <top1sg@suddenlink.invalid> - 2013-03-16 16:45 -0500
      Re: Laptop battery loses charge when off?? micky <NONONOmisc07@bigfoot.com> - 2013-03-16 18:31 -0400
        Re: Laptop battery loses charge when off?? not@telling.you.invalid (Computer Nerd Kev) - 2013-03-16 23:42 +0000
          Re: Laptop battery loses charge when off?? "~misfit~" <shaun.at.pukekohe@gmail.com> - 2013-03-17 15:14 +1300
            Re: Laptop battery loses charge when off?? Computer Nerd Kev <not@telling.you.invalid> - 2013-03-17 09:00 +0000
              Re: Laptop battery loses charge when off?? "~misfit~" <shaun.at.pukekohe@gmail.com> - 2013-03-18 01:29 +1300
                Re: Laptop battery loses charge when off?? Computer Nerd Kev <not@telling.you.invalid> - 2013-03-18 05:20 +0000
                Re: Laptop battery loses charge when off?? "~misfit~" <shaun.at.pukekohe@gmail.com> - 2013-03-19 11:39 +1300
                Re: Laptop battery loses charge when off?? "~misfit~" <shaun.at.pukekohe@gmail.com> - 2013-04-11 15:13 +1200
        Re: Laptop battery loses charge when off?? wrat@panix.com (the wharf rat) - 2013-03-19 15:45 +0000

csiph-web