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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 1/8/2015 4:36 PM, ~misfit~ wrote:
>> Once upon a time on usenet mike wrote:
>>> On 1/6/2015 5:47 PM, ~misfit~ wrote:
>>>
>>>>
>>>> Anyway now I have another six 1st tier 18650 cells to play with.
>>>> Learning their (remaining) capacity is the hardest part for me. If
>>>> I wasn't so broke I'd buy a charger / analyser like the Maha Wizard
>>>> One device that I bought ages ago for managing my Eneloops (I have
>>>> a strong dislike of primary cells). However as it is I'm stuck
>>>> with a 'dumb' charger that just charges until voltage is ~4.2v.
>>>> Then I to do a timed discharge in a flashlight. :-/ Very crude.
>>> But effective.
>>>
>>> I built a setup with programmable power supply and programmable
>>> load. Makes nice graphs,but not clear that they have any value
>>> beyond curiosity.
>>
>> I like to know cell capacity as I have some applications wher they
>> run in parallel.
>
> Try to use cells from the same pack and don't sweat it.  They're
> already paralleled in pairs in many packs.  Unless a cell is shorted,
> it's not a huge risk.

When I charged the six cells from the Viao pack some took twica as long to 
charge as others.

> The time you want 'em matched is when you run them in series.  If
> they're not matched, the pack gets imbalanced and can overdischarge
> or overcharge one.

Been there done that with NiMH. Same deal.

> I avoided all that hassle with my bike light.  I put 4 18650 cells
> in a plastic pipe and brought out the wires of all cells to a DB-9
> serial connector.  The light runs them in series.
> The charger charges them in parallel.  I did put 4 1.5 ohm resistors
> in the charger plug so that if something shorted, it would blow the
> resistor instead of the battery.


Good solution. :)

>>> I do have a suggestion.
>>> use a variable power supply and a diode.
>>> set the power supply so the output of the diode is at the low
>>> limit discharge voltage. Set the current limit sufficiently high
>>> to run the discharge load.
>
> If you don't have an adjustable power supply, it doesn't matter.

Well, I have a few ~US$5 adjustable current / voltage LED drive / battery 
charge modules. I thought I might be able to re-purpose one of those?

> The purpose of the diode and supply is to prevent overdischarge.

Yep, that's what I want.

> You set the power supply so that the diode is off and the supply
> is completely disconnected during the whole test.

Can I do that with one of the modules mentioned above? I'm talking about 
these things;
http://www.dx.com/p/buck-constant-voltage-constant-current-module-blue-dc-dc-5a-239099#.VLCG0dKUcTs
I use them mainly for driving LEDs off old laptop adapters.

> If you're gonna sit and watch a voltmeter during the whole test,
> you don't need it.

Yeah - however....

> When you do need it is when you aren't watching.  When the phone
> rings. Or the wife gets freaky.
> Or when the kid falls and hurts himself.
> If you get distracted, the diode eventually turns on, supplies
> all the load current and saves your
> cell from overdischarging below whatever voltage you set minus the
> diode drop.

.... and that's why I'd like to set something up to protect the cells during 
discharge.

>> That first thing sounds good but I'm a little challenged when it
>> come to electronics. I know basics (enough to make audio crossovers
>> etc.) and have some components around the place.
>>
>> Would you be so kind as to explain in a bit more detail? I'd be
>> obliged. Cheers,
>>
> Bottom line is that it takes a lot of equipment to get any meaningful
> data. I had fun doing it, but it's not clear that the data made any
> real difference in the
> applications.

Understood. Still, if I can do something toward protecting the cells with 
what I already have then it'd be a big help.

Cheers,
-- 
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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