Charging concerns/questions with NMP Lithium Ion batteries

[Ed Miller]

Ok, what built in "safety devices" does the dedicated charger have to ensure
that, in the event it has a component failure, it does not overcharge the
Lithium batteries ?? What built in safety device can I build into an
airframe to ensure that  normal day to day flight rigors does not in any way
compromise the integrity of the Lithium cell to the point it could vent ?.
All current battery technology can cause a fire if certain circumstances are
present or created, it just seems to me the intensity of a lithium cell fire
far exceeds what we as modelers can normally safe guard for. My family and
home are worth far too much to risk losing so that I can play model
airplanes. I use nicads and NimH batteries, never charge overnight while we
sleep, charging only when I am present in the shop or in the car on the way
to the field. You need to see a home with all it's possessions, memories and
history burn to it's foundation to truly understand the devastation fire
causes. Material loss is a distant second to the emotional loss suffered by
a family dealing with a fire tragedy.
Ed M.
----- Original Message ----- 
From: "Lees,John W" <jlees at mwdh2o.com>
To: <discussion at nsrca.org>
Sent: Friday, May 07, 2004 11:15 AM
Subject: RE: Charging concerns/questions with NMP Lithium Ion batteries


> Troy:
>
> I measured the output voltage on a NMP charger and got 8.89 Volts (no load
> other than the impedance of the meter)--john lees
>
> -----Original Message-----
> From: Troy Newman [mailto:troy_newman at msn.com]
> Sent: Friday, May 07, 2004 8:03 AM
> To: discussion at nsrca.org
> Subject: RE: Charging concerns/questions with NMP Lithium Ion batteries
>
>
>
> Keith,
>
> I can talk about the NMP stuff. I have been using it for a long time. It
> works very well and was designed to not have the problems with other
> systems.
>
> As for over charging using the NMP packs and charger. It is not possible.
> The charger is basically a voltage regulator that is set to 8.4V (2 cells
> means 4.2V per cell)
>
> The way the charger works is the pack is say 7.4V and the charger is at
8.4V
>
> this means current will flow from the charger to the pack. When the pack
> reaches its goal voltage...(the setting of the charger) no current will
> flow. Therefore it will not overcharge. The charger's electronics set the
> voltage it is not user adjustable.
>
> Now if you will look closely at the AMA warning it says they recommend a
> dedicated charger to the specific type and brand of pack. This means no
> variables, no charger picking cell counts and so on. No picking charge
> rates.... The NMP charger is exactly this technology. It will only charge
> the 2 cell packs. There is no charge rates to change as you can't change
> them.....The pack can only recieve so much energy at once and the design
of
> the charger is limited by the battery capacity to accept current. If the
> battery is at 8.1V it can't take as much current as when it was at
7.1V...so
>
> the charger only delivers what the battery asks for.
>
> Another analogy is a pair of balloons....ballon #1 is at 8.4psi and is a
> certain volume....Balloon #2 is 7psi.
>
> The two ballons are attached by a hose and a valve....When the air valve
is
> opened...Balloon #1 will try to inflate #2 right.....If both ballons are
> equal no pressure will flow between the 2 right?
>
> Same thing here....as the voltage comes up on the battery pack the charger
> will not deliver the current.
>
> This NMP battery system is exactly what the AMA is recommending for using
> Lithium batts.
>
> Troy Newman
>
> >From: "Keith Black" <tkeithb at comcast.net>
> >Reply-To: discussion at nsrca.org
> >To: <discussion at nsrca.org>
> >Subject: Charging concerns/questions with NMP Lithium Ion batteries
> >Date: Fri, 7 May 2004 02:30:32 -0500
> >
> >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.
> >
> >My question revolves around how the NMP batteries are built and how the
NMP
>
> >charger works.
> >
> >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.
> >
> >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.
> >
> >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?
> >
> >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).
> >
> >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.
> >
> >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.
> >
> >
> >Here's a link to a good Lithium safety primer on E-Zone:
> >http://www.rcgroups.com/forums/showthread.php?t=209187
> >
> >Thanks to anyone who can share the details of the NMP lithium system.
> >
> >Keith Black
>
>
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