<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML><HEAD>
<META http-equiv=Content-Type content="text/html; charset=iso-8859-1">
<META content="MSHTML 6.00.2800.1276" name=GENERATOR>
<STYLE></STYLE>
</HEAD>
<BODY bgColor=#ffffff>
<DIV><FONT face=Arial size=2>I checked the Powerflite pack in my Alliance which
is a 2s2p configuration and the difference between the lower pair and the upper
pair was about 10 millivolts under load. Not a problem.</FONT></DIV>
<DIV><FONT face=Arial size=2>Jim</FONT></DIV>
<BLOCKQUOTE dir=ltr
style="PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #000000 2px solid; MARGIN-RIGHT: 0px">
<DIV style="FONT: 10pt arial">----- Original Message ----- </DIV>
<DIV
style="BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: black"><B>From:</B>
<A title=JOddino@socal.rr.com href="mailto:JOddino@socal.rr.com">JOddino</A>
</DIV>
<DIV style="FONT: 10pt arial"><B>To:</B> <A title=discussion@nsrca.org
href="mailto:discussion@nsrca.org">discussion@nsrca.org</A> </DIV>
<DIV style="FONT: 10pt arial"><B>Sent:</B> Friday, May 07, 2004 8:30 AM</DIV>
<DIV style="FONT: 10pt arial"><B>Subject:</B> Re: Charging concerns/questions
with NMP Lithium Ion batteries</DIV>
<DIV><BR></DIV>
<DIV><FONT face=Arial size=2>Hi Kieth,</FONT></DIV>
<DIV><FONT face=Arial size=2>I believe the NMP solves most of the problems we
have all read about. 1) it is the right type of charger for Li-Ions and
is dedicated to that chemistry by limiting the current and the voltage. 2) it
is set for two-cell packs and that cannot be changed by the operator or on its
own. 3) it limits the current to less than the 1C rate (for 2000 mAh
packs).</FONT></DIV>
<DIV><FONT face=Arial size=2>Probably its best feature vs. the other
chargers is the meter that tells the operator what is going on. After
you use it a few times you will be able to predict the current at the
beginning and during the charge cycle depending on how many flights
you had. If something is wrong, like a cell way out of wack, it will
give you an indication. Of course it tells you when the pack is charged
and if for some reason it was taking too long you would figure it out.
In other words you will learn what is normal proper charge current vs. time
and could spot an unbalanced pack. It cannot assure you a cell will not
be overcharged if the cells are not matched but I believe you would spot
it.</FONT></DIV>
<DIV><FONT face=Arial size=2>I've been using it for over a year and always
charge the packs in the plane. The total charge time is relatively short
so you can monitor it, but I have left them plugged in over night.
</FONT></DIV>
<DIV><FONT face=Arial size=2>I have only seen one pack (a Duralite which was
in a plane I bought) with a slight unbalance. It was a 2S2P
configuration and I don't have much experience with that configuration.
I have never seen a simple 2 cells in series pack unbalanced.</FONT></DIV>
<DIV><FONT face=Arial size=2>Where you really need to worry about this is in
long strings like those used in electric flight. I talked to Fred Marks
(FMA) about bringing out each node so each cell could be checked and charged
individually if required. He said they plan to do that in the
future.</FONT></DIV>
<DIV><FONT face=Arial size=2>In the mean time, I believe one could stick a pin
through the heat shrink to check the cell balance. I'll try that today
and get back to the list.</FONT></DIV>
<DIV><FONT face=Arial size=2>Regards, Jim</FONT></DIV>
<BLOCKQUOTE dir=ltr
style="PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #000000 2px solid; MARGIN-RIGHT: 0px">
<DIV
style="BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: black"><B>From:</B>
<A title=tkeithb@comcast.net href="mailto:tkeithb@comcast.net">Keith
Black</A> </DIV>
<DIV style="FONT: 10pt arial"><B>To:</B> <A title=discussion@nsrca.org
href="mailto:discussion@nsrca.org">discussion@nsrca.org</A> </DIV>
<DIV style="FONT: 10pt arial"><B>Sent:</B> Friday, May 07, 2004 12:30
AM</DIV>
<DIV style="FONT: 10pt arial"><B>Subject:</B> Charging concerns/questions
with NMP Lithium Ion batteries</DIV>
<DIV><BR></DIV>
<DIV><FONT face=Arial size=2>I'm not trying to start a "heated" debate about
the safety of lithium batteries, but I purchased a couple of these packs
just before the AMA warning and now I have some concerns and questions.
</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>My question revolves around how the NMP
batteries are built and how the NMP charger works.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>In the past I'd believed that fires with
lithium batteries are primarily due to user error when charging, typically
one of the following errors: 1) Using the wrong type of charger, 2) setting
the charger for the wrong battery type/cell count, or 3) trying to
charge cells too quickly, in excess of 1C. </FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>However, I did some research on E-Zone and
found that these packs can catch fire even on a slow charger if they are
charged beyond 4.2 volts per cell. This means if your charging a multiple
cell pack and cells differ in voltage by more than 1 volt and the charger
keeps charging until (total cells x 4.2 volts) is reached then
even slow chargers can cause a fire.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>Therefore, my question is does circuitry exist
either in the NMP battery pack or in the NMP charger to assure that a single
cell will never be charged in excess of 4.2 volts? If so, how does this
work?</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>If this circuitry exists then we can
probably feel quite safe leaving the NMP batteries inside our planes while
charging just as we do with our laptops, cell phones, cameras etc. If not
then we're taking a big chance charging inside our planes, vehicles and
houses (as has been pointed out on this list before).</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>FYI, I was shocked when I visited E-Zone and
found that the electric guys have known for a long time that fires are not
only a possibility but have occurred many times. In fact, it's common
knowledge in the electric community that precautions such as charging in a
flame proof container, not charging in vehicles or homes, never leave the
battery unattended, etc. must be observed when charging. I found
it very interesting that there are even numerous people working on various
types of fire-proof charge bags made from things like ceramic
fibers.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>Obviously the electric guys push things to the
extreme with their batteries, but if such a simple thing as exceeding 4.2
volts can catch a cell on fire then we should make sure our
batteries/chargers have circuitry to prevent this or we must take the
necessary precautions when charging.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>Here's a link to a good Lithium safety primer
on E-Zone:</FONT></DIV>
<DIV><FONT face=Arial size=2><A
href="http://www.rcgroups.com/forums/showthread.php?t=209187">http://www.rcgroups.com/forums/showthread.php?t=209187</A></FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>Thanks to anyone who can share the details of
the NMP lithium system.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>Keith Black</FONT></DIV>
<DIV><FONT face=Arial
size=2></FONT> </DIV></BLOCKQUOTE></BLOCKQUOTE></BODY></HTML>