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Re: Should I completely discharge my laptop battery?

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Once upon a time on usenet mike wrote:
> On 1/14/2015 4:35 PM, ~misfit~ wrote:
>> Once upon a time on usenet mike wrote:
>>> On 1/12/2015 3:18 PM, ~misfit~ wrote:
>>>> Once upon a time on usenet mike wrote:
>>>> [total snip]
>>>>> Are we having fun yet?
>>>>
>>>> Thanks Mike. I've copied that to notepad and saved it for when I
>>>> have a bit of time to play with.
>>>>
>>>> I have a couple of these too
>>>> http://www.dx.com/p/mp1405-5v-1a-lithium-battery-charging-board-blue-black-219454#.VLRT1MlZqUc
>>>> and used one for re-powering a mini rotary tool I got cheap that
>>>> used 3x small NiCad cells in shrink-wrap, the total size of which
>>>> was similar to a single 18650 but had little 'power' and didn't
>>>> hold much charge. I bought a new solder-tab Panasonic cell for
>>>> that job as I didn't know how good my slavaged cells were and it's hard 
>>>> to
>>>> open up the modded tool.... However it doesn't seem to like
>>>> running a motor from the 'out' pads
>>>> - maybe it's something to do with the brushes and how it works? I
>>>> tried three of these PCBs for the job and they all didn't work
>>>> right. In the end I had to wire a small momentary contact switch
>>>> between the B+ and OUT+ pads to start the motor. Once it's started
>>>> it runs fine from the 'OUT' contacts. <shrug> As you can probably
>>>> tell I only have basic knowledge (but try hard
>>>> to not take risks - I'm very aware of the inherant dangers with
>>>> Li-Ion tech and the potential for 'thermal runaway').
>>>>
>>> The website was translated into ChEnglish and doesn't make a lot of
>>> sense, but if I were to guess...
>>
>> Sadly with that site you *have* to guess a lot (unless there are
>> informed feedbacks).
>>
>>> How are you switching the power?
>>>
>>> If you're switching between the battery and the board,
>>> that may be your problem.  Sounds like the board has to be powered
>>> up continuously.  I'd measure the drain from the battery in the
>>> off state.  May be inconsequential...maybe not.
>>
>> I'm leaving the board and cell connected all the time. There doesn't
>> seem to be much in the way of constant drain. I modded it a year ago
>> and have only had to charge once in that time (it only gets light
>> use).
>>> If you're switching between the board and the motor, the turn-on
>>> transient from the motor may exceed the 3A current limit.  Maybe a
>>> big cap across the out pads will help.
>>
>> Hmmm, yes that might indeed be the problem - thanks. (I told you I
>> have only basic knowledge of electronics. However I have a cheap
>> rework station that I haven't unpacked yet which was delivered today
>> so I better learn more!) There's not much room in the enclosure for a 
>> 'big cap' - or anything
>> else for that matter. I dismantled it several times, re-soldering
>> and hot-gluing it all in place each time. The last time /was/ the
>> last time - I taped it up good (as the plastic threads for the
>> screws weren't made for repeated use and stripped quickly). I'll use
>> it as-is now I think but it's good to know how to combat this issue
>> if I use one of the other modules. Silly me; Where it says "charge 
>> current 1,000mA max" I took that to
>> mean what the board will put into the cell - not what the board
>> would take. I was charging my 3,000 A/h cell from a 500mA source and
>> it was taking hours so hooked it up to my 2,000mA plugpack. Well, I
>> shouldn't have walked away for the ~30 minutes that I did! Seems it
>> was dumping extra current as heat, there was hot glue running out of
>> it! I thought that it would just 'take' what it could handle from
>> the source? <shrug> Cheers,
>>
> Not at all clear what happened.  Too many "it" and not enough
> specificity.

The "it" was referring to the charging module - you prompted me to check the 
specs when you mentioned 3 amps.

> Lithium cells have a specification that defines the absolute maximum
> charge termination voltage and the maximum safe charge current.
> Also has a low-voltage cutout spec that tells you how far you can
> discharge it without damage.  Two problems with that.  You may not
> be able to find a spec for the cell you have in your hand.
> And if it's an EBAY cell, the capacity may be seriously exaggerated
> and you can't rely on that to estimate what you should do.

This cell in question is from a legit seller local to me and is genuine 
Panasonic.

> Your charge board manages all that.
> Typically, the voltage ramps up as the cell charges at the
> set max current, but stops ramping
> at the terminal voltage, typically 4.2V depending on the exact lithium
> technology.
> The current max is set by the charge board and current starts to
> decrease when
> the voltage hits 4.2V.  But it will charge until the current drops
> below some point determined by the setup of the charge board.
>
> The supply that powers the charge board MUST have enough voltage and
> current capacity to run the charge board under all conditions.
> Once the source current limits, the voltage to the charge board
> drops and you have no idea what it will do.  DO NOT ASSUME
> that it does anything safe.  It might, but DON'T trust that it does.

This is my whole point. I was using a USB plug-pack PSU capable of 2A yet 
the specs for the charge board says, as above, "charge current 1,000mA max". 
That's when the thing got so hot it melted hot glue used to hold it in 
place. Very inelegant. I've used the same PSU for low-drain devices and they 
work fine, no excess heat anywhere so it wasn't the fault of the PSU.

> Here's an analogy.  Sit in your easy chair and breathe thru a straw.
> It limits your supply.  You will lose control.  On second thought,
> sit in the bathtub.  You may lose control of stuff you don't want
> in your easy chair.

I haven't been able to get into the bathtub for years (well, out of it 
actually), since my back got so much worse. I even need a plastic stool in 
the shower as I can't stand long enough to wash properly....

..... but I get your analogy. I said I'm a little challenged w/r/t 
electronics. I didn't say I had an IQ less than 80. (Actually I used to me a 
member of Mensa until I couldn't keep up the membership fees due to my 
injury and loss of income / life savings.)

Thanks,
-- 
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) 

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Should I completely discharge my laptop battery? andymhancock@gmail.com - 2014-12-30 11:53 -0800
  Re: Should I completely discharge my laptop battery? "~misfit~" <shaun.at.pukekohe@gmail.com> - 2014-12-31 13:35 +1300
    Re: Should I completely discharge my laptop battery? andymhancock@gmail.com - 2014-12-31 11:06 -0800
      Re: Should I completely discharge my laptop battery? andymhancock@gmail.com - 2014-12-31 11:54 -0800
        Re: Should I completely discharge my laptop battery? andymhancock@gmail.com - 2015-01-01 15:13 -0800
      Re: Should I completely discharge my laptop battery? "~misfit~" <shaun.at.pukekohe@gmail.com> - 2015-01-01 12:29 +1300
    Re: Should I completely discharge my laptop battery? mike <ham789@netzero.net> - 2014-12-31 12:05 -0800
      Re: Should I completely discharge my laptop battery? "~misfit~" <shaun.at.pukekohe@gmail.com> - 2015-01-01 12:55 +1300
        Re: Should I completely discharge my laptop battery? andymhancock@gmail.com - 2015-01-01 14:51 -0800
          Re: Should I completely discharge my laptop battery? "~misfit~" <shaun.at.pukekohe@gmail.com> - 2015-01-02 14:16 +1300
            Re: Should I completely discharge my laptop battery? andymhancock@gmail.com - 2015-01-01 18:11 -0800
              Re: Should I completely discharge my laptop battery? mike <ham789@netzero.net> - 2015-01-02 01:15 -0800
                Re: Should I completely discharge my laptop battery? andymhancock@gmail.com - 2015-01-02 09:34 -0800
                Re: Should I completely discharge my laptop battery? mike <ham789@netzero.net> - 2015-01-02 10:46 -0800
                Re: Should I completely discharge my laptop battery? andymhancock@gmail.com - 2015-01-02 14:25 -0800
                Re: Should I completely discharge my laptop battery? "~misfit~" <shaun.at.pukekohe@gmail.com> - 2015-01-04 12:28 +1300
                Re: Should I completely discharge my laptop battery? andymhancock@gmail.com - 2015-01-03 16:48 -0800
                Re: Should I completely discharge my laptop battery? "~misfit~" <shaun.at.pukekohe@gmail.com> - 2015-01-07 14:47 +1300
                Re: Should I completely discharge my laptop battery? mike <ham789@netzero.net> - 2015-01-06 19:38 -0800
                Re: Should I completely discharge my laptop battery? "~misfit~" <shaun.at.pukekohe@gmail.com> - 2015-01-09 13:36 +1300
                Re: Should I completely discharge my laptop battery? mike <ham789@netzero.net> - 2015-01-08 17:34 -0800
                Re: Should I completely discharge my laptop battery? "~misfit~" <shaun.at.pukekohe@gmail.com> - 2015-01-10 14:59 +1300
                Re: Should I completely discharge my laptop battery? mike <ham789@netzero.net> - 2015-01-09 20:22 -0800
                Re: Should I completely discharge my laptop battery? "~misfit~" <shaun.at.pukekohe@gmail.com> - 2015-01-13 12:18 +1300
                Re: Should I completely discharge my laptop battery? mike <ham789@netzero.net> - 2015-01-12 17:20 -0800
                Re: Should I completely discharge my laptop battery? "~misfit~" <shaun.at.pukekohe@gmail.com> - 2015-01-15 13:35 +1300
                Re: Should I completely discharge my laptop battery? mike <ham789@netzero.net> - 2015-01-14 17:37 -0800
                Re: Should I completely discharge my laptop battery? "~misfit~" <shaun.at.pukekohe@gmail.com> - 2015-01-16 12:33 +1300
                Re: Should I completely discharge my laptop battery? "~misfit~" <shaun.at.pukekohe@gmail.com> - 2015-02-08 14:24 +1300
                Re: Should I completely discharge my laptop battery? mike <ham789@netzero.net> - 2015-02-07 21:02 -0800
                Re: Should I completely discharge my laptop battery? "~misfit~" <shaun.at.pukekohe@gmail.com> - 2015-02-11 11:09 +1300
                Re: Should I completely discharge my laptop battery? "~misfit~" <shaun.at.pukekohe@gmail.com> - 2015-01-03 11:47 +1300

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