DPRG
DPRG List  



[DPRG] Re: Lithium Ion Batteries

Subject: [DPRG] Re: Lithium Ion Batteries
From: Ed Paradis legomaniac at gmail.com
Date: Tue Mar 30 08:02:50 CDT 2010

On Mon, Mar 29, 2010 at 10:55 PM, David <dpa at mail.isem.smu.edu> wrote:
> Most of the pilots I know
> charge them in a fire-proof container, and many store and transport them in
> a metal box or safe.  (I use a pyrex casserole dish for charging.)   They
> are in some ways really not ready for prime time.

And I hear both of these things a lot from the RC crowd whenever I
bring up LiPos.  You'd think I'd learn!

I guess what I see are two common uses:

- 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.  They're
border-line abusing the cells as far as charge and discharge are
concerned.

- my $5 cellphone that has the same crappy lipo for the past 3 years
that works great, just like the crappy cellphone before it and the one
before it.  The cells never swell, get hot, freak out, or explode.  I
don't charge them in a nuclear bunker and as far as I can tell they
don't have temperature monitoring on cell (two terminals) but perhaps
on the phone right next to the cell.

So where is the disconnect?  Is this just the difference you get when
you charge a lipo at 20C and 1/20th C ?

If so, that's fine!  I don't need to charge my robot in 30 seconds so
I can fly/drive/whatever around for another 15 minutes.  I'm looking
at "charge in an hour and run for a day".

How can the sparkfun charger get away with what it does?  Is it merely
the low charge rate? Maximum charge current is 280mA.  Rule of thumb
is that if my robot runs on about 280mA, then I should be able to
charge about as fast as I discharge.  280mA is a respectable amount of
current for a small table top robot.

These are a questions I've pondered over for a while now. I'm finally
pulling up to answer them for my mini tankbot.

Ed

More information about the DPRG mailing list