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[DPRG] Re: Lithium Ion Batteries

Subject: [DPRG] Re: Lithium Ion Batteries
From: John Dolecek jdolecek at gmail.com
Date: Tue Mar 30 10:33:16 CDT 2010

Ron,

The larger 'C' packs aren't more likely to grenade/melt down.  The
consequences of a melt down might be worse, but I can't verify that.  I do
believe that the different 'C' ratings are a physical characteristic of the
cells themselves.  The manufacturer is telling you the maximum discharge
rate (divided by the pack capacity).  So my 35C 5000mAh pack can discharge
at 35 * 5 = 175A.  Some are rated at both constant discharge and burst
current, but some are just rated for constant discharge and don't mention
the peak discharge under burst.  In my experience the charge rate should
never exceed 1C (5A in my case).  I've seen a couple batteries rated at
higher charge rates but it's a trade off between charge rate and pack life.

I've seen people beat the hell out of them, overcharge them, over discharge
them, etc.  I've never seen one fail catastrophically but I've seen them get
very hot and expand.  Best advice is just to keep a close eye on them
whenever you're charging them, and charge them out of the bot/rc/plane so
you can keep them away from flammables and possibly save your work if things
go tits up.

John

On Tue, Mar 30, 2010 at 7:35 AM, <DeltaGraph at aol.com> wrote:

>   Ed,
>
> >RC guys with massive batteries or at least massive discharge and
> >charge rates.  They treat the batteries like spent nuclear rods and
> >have stories of LiPo exploding and destroying small cities.
>
>  HaHa! Nice. Now, I want you to go have a cup of coffee and rewrite the
> email.  Ha!
>
> OK, question: Is a low "C" pack less likely to result in nuclear fission /
> meltdown / fire etc. than a high "C" pack?
>
> Are the raw cells the same? -- just the current limiting circuits
> different?
>
> I am using two of these in my balancing robot.
> 11.1 volt 2500mA LiPo rated at charge 2C discharge  3C-5C
>
>
> http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=6955&Product_Name=ZIPPY_Flightmax_2500mAh_Transmitter_Pack_(Futaba/JR<http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=6955&Product_Name=ZIPPY_Flightmax_2500mAh_Transmitter_Pack_%28Futaba/JR>
> )
>
> I have played with 30C packs in past. My new rule for future is to put an
> inline fuse on one lead before EVER exposing any conductors on second lead
> when I unpackage a new battery.
>
> Ron
>
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>
>
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