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Re: Replace Li Ion battery

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On Wednesday, December 27, 2017 at 2:59:49 PM UTC-6, mike wrote:
> On 12/27/2017 5:17 AM, Winfield Hill wrote:
> > krw@notreal.com wrote...
> >> mike <ham789@netzero.net> wrote:
> >>> Andy wrote:
> >>>> mike wrote:
> >>>>> On 12/26/2017 5:31 AM, Winfield Hill wrote:
> >>>>>> mike wrote...
> >>>>>>> Andy wrote:
> >>>>>>>> I want to replace a LiIon battery with a high
> >>>>>>>> capacity one.  The old one has a third yellow wire.
> >>>>>>>> What is it for ?
> >>>>>>>
> >>>>>>> If that's the best you can do at specificity,
> >>>>>>> best not risk setting yourself on fire.
> >>>>>>
> >>>>>>     Now, now.  Many single-cell Lithium battery
> >>>>>>     packs include a thermistor to help prevent
> >>>>>>     overcharging, and dangerous overheating.
> >>>>>>     10k at 25 deg C is a common value.
> >>>>>>
> >>>>>>     I'd imagine
> >>>>>
> >>>>> Those two words suggest that YOU shouldn't be playing
> >>>>> with lithium batteries either!  Be Safe.
> >>>>> You may not be the one injured when it catches fire.
> >>>>>
> >>>>> that a big battery, replacing a
> >>>>>>     small one, would experience reduced stress,
> >>>>>>     because its charge / discharge rate would
> >>>>>>     be lower.  You do want thermal protection,
> >>>>>>     be sure to use one with the same themistor.
> >>>>
> >>>> Looks like he is safe to me.
> >>>>
> >>>> Andy
> >>>>
> >>> Sure he is.
> >>> People who give random DANGEROUS advice in response to
> >>> a question you haven't even asked don't have to worry
> >>> about their safety...or yours.
> >>>
> >>> To recap the thread...
> >>> _____________________________
> >>> I am replacing a small bomb with a big bomb.
> >>> What's the yellow wire for?
> >>>
> >>> I 'imagine' you should use a thermistor.
> >>> ___________________________
> >>
> >> I don't believe you've given a reasonable synopsis.
> >> Exactly what did Winfield (actually) *write* that
> >> you disagree with?
> >>
> >>> Am I the only one concerned that there is zero
> >>> information about the bomb or its environment?
> >>> Or that the bomb that you bought on the internet
> >>> has the same generic label, but may have radically
> >>> different characteristics that may or may not lead
> >>> to surprise detonation?
> >>
> >> But you object to Winfield's post.  His statement
> >> sounded correct to me, though perhaps not a full answer.
> >>
> >>> Do not fuck with lithium batteries unless you know
> >>> EXACTLY the specs of both cells and intimate
> >>> details of the charge/discharge cycle.
> >>> If you knew that, you wouldn't have asked about
> >>> the yellow wire.
> >>
> >> What does that have with Win's answer?
> >>
> >>> This thread contains ZERO information beyond
> >>> the color of the wire.
> >>>
> >>> Be safe.  Don't do it, or get a LOT more informed
> >>> about exactly what you're doing.  You can't do that
> >>> if your question isn't more specific than wire color.
> >>>
> >>> Life is a series of calculations of the risk/reward
> >>> ratios of your actions.
> >>> Say there's a 99% chance that you'll be ok with your project...
> >>> and 1% chance that you'll burn your house down, or that your
> >>> kid will have an eye put out when it explodes.
> >>> Do you like that risk/reward ratio?
> >>> I sure don't!
> >>
> >> What does anything above have to do with what Win actually wrote?
> >
> >   Whoa, firestorm!  It's time for me to step in and
> >   add to my remarks.  First, I specified an answer
> >   for a single-cell battery, the most common form.
> >
> >   My comments are incomplete and not relevant for a
> >   multi-cell battery, as some of the thread seems
> >   to assume. (I agree that modifying such a battery
> >   is a serious engineering exercise.)
> >
> >   We can assume the single cell charging system in
> >   question is safe, having appropriate voltage and
> >   current-limiting features, and is equipped with a
> >   cell temperature sensor (the O.P. will verify this
> >   using an ohm-meter on his existing cell).  In such
> >   a case I think it's safe to move to a larger cell,
> >   incorporating the same range thermistor.  Naturally,
> >   we assume our O.P. has relevant electronics skills.
> >
> >
> There you go.  Look at all the assumptions you made.
> Based on the composition of the original question,
> there's no basis for any of them.
> You  may have also assumed that the OP knew better than
> to solder directly to the cells.  Or that he used eye
> protection when dealing with things that might vent.
> How could you assume that the OP knew about "appropriate
> voltage and current-limiting features...?" or that the
> random lithium cell from the internet is unlikely to perform
> anywhere near expectations.  Or that a lithium cell
> designed for a laptop computer would perform poorly and
> be dangerous in a power tool or drone.  A cell with the highest
> possible claimed amp-hours is exactly what you don't want
> in a drone.
> 
> If you hang around the internet for very long, you learn
> that people have ambitions that far exceed their current
> capabilities.  Nothing wrong with that.  That's how we learn.
> 
> The problem happens when well-meaning tutors forget that
> and give them vague advice based on their own assumptions, not the
> (often unstated) design parameters and skills of the OP.
> Questioners have no way to determine whether the advice
> they're getting is good advice.  When dealing with dangerous
> devices, it's best to err of the conservative side and work
> up from there.
> 
> One of the most important characteristics of a mentor is empathy.
> The ability to assume the mindset of the student and communicate
> in HIS terms, not yours.
> 
> You can learn a lot about the mindset of the student by the
> specificity of the problem statement and the words used to
> do it.  Over the years, dealing with very smart engineers,
> I observed that there is a serious inverse relationship between
> smarts and empathy.  I've managed very smart engineers who
> had very poor communication skills.  Others were just too
> dumb to understand their precision offerings, and they were
> proud of it.
> 
> The most relevant thing you've said in this thread was,
> "(I agree that modifying such a battery
>     is a serious engineering exercise.)"
> 
> My assumption, based on the format of the original question, is that the 
> OP is not up for this exercise.
> If you want to guide him through this, that's great.
> I've got some experience here and would be glad to help.
> I object to vague statements that it'll be OK based on
> YOUR optimistic view of the OP's skills.
> This project is a minefield.  Even if you think you know what you're
> doing, you might still blow yourself up.
> 
> I'm NOT dissing the OP.  Asking questions is how we learn.
> I'm dissing the mentors who dismiss the significant personal
> risks in doing this without proper skills and equipment.

Here are more details on my project.

I bought a bike tail light.

It has a built in LiPo battery(about 800 Mah) but it only lasts a day before needing to be charged.

I plan on removing the battery and soldering wires to the board and run them to a set of 2 external protected 18650s.

Combined capacity will be about 5000 Mah.

Andy

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Thread

Replace Li Ion battery Andy <andrewkennedy775@gmail.com> - 2017-12-25 12:36 -0800
  Re: Replace Li Ion battery mike <ham789@netzero.net> - 2017-12-25 20:55 -0800
    Re: Replace Li Ion battery Winfield Hill <hill@rowland.harvard.edu> - 2017-12-26 05:31 -0800
      Re: Replace Li Ion battery Andy <andrewkennedy775@gmail.com> - 2017-12-26 12:47 -0800
        Re: Replace Li Ion battery Jeff Liebermann <jeffl@cruzio.com> - 2017-12-27 08:08 -0800
      Re: Replace Li Ion battery mike <ham789@netzero.net> - 2017-12-26 15:39 -0800
        Re: Replace Li Ion battery Andy <andrewkennedy775@gmail.com> - 2017-12-26 16:27 -0800
          Re: Replace Li Ion battery mike <ham789@netzero.net> - 2017-12-26 20:20 -0800
            Re: Replace Li Ion battery krw@notreal.com - 2017-12-26 23:44 -0500
              Re: Replace Li Ion battery Winfield Hill <hill@rowland.harvard.edu> - 2017-12-27 05:17 -0800
                Re: Replace Li Ion battery mike <ham789@netzero.net> - 2017-12-27 12:59 -0800
                Re: Replace Li Ion battery Andy <andrewkennedy775@gmail.com> - 2017-12-27 19:51 -0800
                Re: Replace Li Ion battery Jeff Liebermann <jeffl@cruzio.com> - 2017-12-27 21:20 -0800
                Re: Replace Li Ion battery Jeff Liebermann <jeffl@cruzio.com> - 2017-12-27 21:35 -0800
                Re: Replace Li Ion battery Andy <andrewkennedy775@gmail.com> - 2017-12-28 08:41 -0800
                Re: Replace Li Ion battery Andy <andrewkennedy775@gmail.com> - 2017-12-28 08:45 -0800
                Re: Replace Li Ion battery Jeff Liebermann <jeffl@cruzio.com> - 2017-12-28 20:24 -0800
                Re: Replace Li Ion battery Andy <andrewkennedy775@gmail.com> - 2017-12-28 20:30 -0800
                Re: Replace Li Ion battery mike <ham789@netzero.net> - 2017-12-29 03:39 -0800
                Re: Replace Li Ion battery Andy <andrewkennedy775@gmail.com> - 2017-12-29 07:04 -0800
                Re: Replace Li Ion battery Andy <andrewkennedy775@gmail.com> - 2017-12-29 11:00 -0800
                Re: Replace Li Ion battery Andy <andrewkennedy775@gmail.com> - 2017-12-28 06:51 -0800
                Re: Replace Li Ion battery mike <ham789@netzero.net> - 2017-12-27 22:26 -0800
                Re: Replace Li Ion battery Andy <andrewkennedy775@gmail.com> - 2017-12-28 08:34 -0800
                Re: Replace Li Ion battery mike <ham789@netzero.net> - 2017-12-28 10:50 -0800
                Re: Replace Li Ion battery Andy <andrewkennedy775@gmail.com> - 2017-12-28 11:52 -0800
                Re: Replace Li Ion battery John S <Sophi.2@invalid.org> - 2017-12-27 23:02 -0600
            Re: Replace Li Ion battery Andy <andrewkennedy775@gmail.com> - 2017-12-26 21:17 -0800

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