Charging concerns/questions with NMP Lithium Ion batteries

Sat May 8 00:22:04 AKDT 2004

Dave,

The only failure mode I have seen on the batts is that they do not come up
to full charge after a long period of use like 1yr to 18months. My original
battery pack comes off the charger now at 7.9V not the 8.4 when it was new.
The charger still goes to zero amps....and the battery is as charged as it
will ever get. And its capacity is less as a result. These batteries seem to
be very predictable. That is the main reason I like them.

I flew about 7-8 flights this morning on the lake bed just back to back to
back...and I was getting exactly 0.15V drop per flight. I was actually
guessing the voltage under load before sticking the meter on the plane.....I
only missed on the last flight and I missed by 0.01V....Last year I was
flying before the NATS and found larger current drains...like double per
flight...Guess what I started checking my model out and found a loose motor
mount...Also current drain is directly related to servo pot and gear train
wear! So another reason to have predictable power system.

As for charger issues...as Jim Oddino stated the charger has an actual
current meter on it. Its an analog meter so you can see the actual milliamps
flowing into the battery pack. As stated by Jim also you get used to the
numbers and if you plug in and see strange values it sets the alarm off in
your brain.

When the battery is charged or taken all it can take then the rules of
electricity are proven on the am-meter. The current goes to Zero! So unless
Ohm's law fails I don't see how the charger will screw up a battery pack...

Of course anything can happen. Components can fail, I don't know what the
failure issues could be in the charger because I have never seen one. Same
with my Wall wart chargers that came with my radios never seen a failure
there either.....In my 20+ years of modeling I have cooked and burned up
Nicd packs, for various reasons  even had a couple leave a mark on the
table, floor, or in the plane.....I don't stick a battery on to charge and
go to bed. The only exception is the nicads that come with the TX or my
nicads in my B+P starter. These have dedicated chargers (hummmmm theme
here?) that are designed for this charge overnight at the c/10 rate.

As for Central Hobbies, I have been a customer of Centrals for many many
years. My relationship with them over the years has grown to allow me to
test and help refine some the products they bring to serve the pattern
modeler.

As others have said I am an advocate of their products and service. I'm not
paid, I'm a happy customer. I am also a customer of many other modeling
companies. Looking at my shop, I have Prather med fuel tubing, Radio South
CA hinges, Gator stab adjusters and some Bob Smith CA (both Thick and thin),
and a Hyde Mount on the shelf. I only advocate products and stuff that I use
myself. There are some products that I choose not to use, in favor of my
favorite version. We all have these....the Ultracote- Monocote, or Zap-BSI,
or Coolpower-Magnum....

Those that know me, know that I'm an honest straight shooter....Why would I
want to talk bad about a product that I don't use. There is enough of this
already on this list and in RCU......Product and Company bashing seems to
have grown into a 3 headed monster with the Internet. I just choose not to
play.

Rather I just tell people what I choose to use and why I use it. I never
advocate the use of a product that I don't have personal experience with.
It's your choice to take the advice or leave it.....It's is worth what you
paid for it. I know that when I spend my modeling dollars I pick the
products that I think work the best for me.

Troy Newman

----- Original Message ----- 
From: "David Lockhart" <DaveL322 at comcast.net>
To: <troy_newman at msn.com>
Sent: Friday, May 07, 2004 5:57 PM
Subject: Re: Charging concerns/questions with NMP Lithium Ion batteries

> So what is the degradation/failure mode of the battery, and then what does
> the charger do?
>
> Thanks,
>
> Dave
>
> ----- Original Message -----
> From: "Troy Newman" <troy_newman at msn.com>
> To: <discussion at nsrca.org>
> Sent: Friday, May 07, 2004 11:02 AM
> 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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> > and follow the instructions.
> >
>
>
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