Charging concerns/questions with NMP Lithium Ion batteries

[Keith Black]

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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