[NSRCA-discussion] LiPo Fun Fact 'O The Day

Sat Oct 10 11:38:09 AKDT 2015

Also, you're charging at 2C, too high.

From: Keith Hoard [mailto:klhoard at outlook.com] 
Sent: Saturday, October 10, 2015 15:33
To: 'nsrca-discussion' <nsrca-discussion at lists.nsrca.org>
Subject: RE: [NSRCA-discussion] LiPo Fun Fact 'O The Day

Well, there's your error.  You measured the temps in Fahrenheit, not
Celsius.

From: Ed Alt [mailto:ed_alt at hotmail.com] 
Sent: Saturday, October 10, 2015 11:11
To: Keith Hoard <klhoard at outlook.com <mailto:klhoard at outlook.com> >; NSRCA
List <nsrca-discussion at lists.nsrca.org
<mailto:nsrca-discussion at lists.nsrca.org> >
Subject: RE: [NSRCA-discussion] LiPo Fun Fact 'O The Day

There are minor effects (the endothermic reaction) and there are major
effects (the internal resistance of the cells).  The packs get warmer when
charged.  I just tried it with a pair of Gens Ace 5S 5300 30C packs at a 10A
charge rate each.  The starting point was from a storage charge.  They've
been sitting in the basement shop for months.  Pack one measured 65.1F and
pack 2 was at 65.2F before starting the charge. Here are the readings from a
brief constant current charge that I stopped at 1250 mA put into each.

At 500 mA delivered, pack 1 was 67.9 F, pack 2 67.4 F

At 650 mA, 68.5 & 67.7

At 700 mA, 70 & 68.6

At 1000 mA, 71.9 & 69.9

At 1100 mA, 72 & 70.4

At 1250 mA, 72.5 & 70.9.

Maybe you could go down to some much lower charge rate at which the
endothermic reaction cooling dominates, but that's not realistic. 

Ed

  _____  

To: ed_alt at hotmail.com <mailto:ed_alt at hotmail.com> 
CC: chuenkan at comcast.net <mailto:chuenkan at comcast.net> ;
nsrca-discussion at lists.nsrca.org <mailto:nsrca-discussion at lists.nsrca.org> 
From: klhoard at outlook.com <mailto:klhoard at outlook.com> 
Subject: RE: [NSRCA-discussion] LiPo Fun Fact 'O The Day
Date: Fri, 9 Oct 2015 23:54:24 -0500

Not silly at all.  You didn't account for the chemical reaction of the
electrolyte during the charge process.

  The term the PhD's use to describe the reaction is "endothermic"(gets
colder) and has to do with that whole "energy cannot be created or
destroyed, just moved around" rule.

    There are several papers on the internet written by the molecular
scientists who designed LiPos.

-Keith Hoard
-klhoard at outlook.com <mailto:-klhoard at outlook.com> 

From: Ed Alt
Sent: Friday, October 9, 2015 21:09
To: Keith Hoard
Cc: chuenkan at comcast.net;General <mailto:chuenkan at comcast.net;General>
pattern discussion
Subject: Re: [NSRCA-discussion] LiPo Fun Fact 'O The Day

That wasn't a guess, it was a statement of fact.  This is getting silly.

On Oct 9, 2015, at 9:09 PM, Keith Hoard <klhoard at outlook.com
<mailto:klhoard at outlook.com> > wrote:

Nope.  If you had another guess?

Sent from my iPad

On Oct 9, 2015, at 20:09, Ed Alt <ed_alt at hotmail.com
<mailto:ed_alt at hotmail.com> > wrote:

They do warm up when charging, even at low rates.  It's the physics behind
Ohms law that governs some of that.  It may not be very noticeable, but it
is happening nonetheless.

On Oct 9, 2015, at 8:03 PM, Phil Spelt via NSRCA-discussion
<nsrca-discussion at lists.nsrca.org <mailto:nsrca-discussion at lists.nsrca.org>
> wrote:

I would say "C" below:  I have never had a lipo pack get warm during
charging.  That's because i always charge somewhere between 1.8-2.0 C.  For
my electric planes I buy enough batteries so I do not have to hurry-charge
in order to get back into the air.  I charge the lipos in my starter & glow
igniter at home in the shop when I have plenty of time.  Now, in the
interest of full disclosure, I do not use $150.00 battery packs, and none of
my electric planes are for pattern.

Phil Spelt, KCRC Emeritus, Secretary
AMA 1294, Scientific Leader Member
SPA L-18, Board Member
(865) 435-1476v  (865) 604-0541c

During charging, a LiPo battery becomes:

A)     Warmer

B)     Colder

        C)   None of the above

        D)  All of the above

--Keith Hoard

--klhoard at outlook.com <mailto:klhoard at outlook.com> 

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