I've seen some interest about LiPo batteries here (the NCR forums) and have taken an interest myself. I haven't used any LiPo batteries (other than the one on my Parrot) so I don't have much experience or knowledge about them. I got the impression that there is a serious risk of fire when reading the May 2008 issue of Arvada Associated Modelers newsletter: in one of the articles in the newsletter, there is a description about all the precautions taken and still a fire that happened when charging LiPo batteries.
The article author (Gregg Schuster) gave me permission to post the contents of his article here so it is shown below. Are people here taking this much precaution when charging LiPo batteries? Is a Battery Bunker common?
Li-Po Fire – it can happen to you!
You may think it won't happen to you.....I
know I did – almost 4 years of successful charging of
Li-Po batteries! So I never really thought I would
have a problem charging on my workbench in the
basement. I set up a fairly safe area to charge in, used
a Battery Bunker ( http://.batterybunker.com/ ) and
even added a smoke detector over the charging
area.... Of course I did the cardinal sin in charging –
never leave the charging area……well…..I won’t be
charging in my basement again!On Saturday April 12th, I hooked up my Thunder
Power 1900 mah battery to the my Astroflight 109
Lithium charger and set it at 1800 mah charge rate, put
it in my battery bunker, and walked away. I have
been using the 109 successfully for three years now.
However, some people have been reporting that the
charger can jump or add an extra cell (thus more voltage)
in the middle of the charge process……you
know what comes next!I’m upstairs on the computer and hear the wife
screaming for me. I run downstairs to find the entire
basement filled with thick smoke. I clearly had
flames, smoke, and some burn marks to show for it!!!
I hope this article serves as a friendly reminder
that it can happen to you! First error - Charging in
the basement - could have easily lost the house....I
thank God for looking down on my family that night!The other saving grace....I had it in a fire proof container
with a smoke detector right above the charging
area (I put it there just for that reason)....the safety
mechanisms worked - but that will be the last time I
ever charge a battery in the house again.... Although I
had the smoke detector and the battery bunker – a
flaming LiPo will still find the little holes in the container
and in essence become a flame thrower, which
burned papers and a poster I had pinned to the wall,
melted a few things and scorched the shelf two feet
above.In regards to the Astroflight 109 – they now
have an updated chip that locks in and prevents a shift
in cell count…..you can get it for $15.00 direct from
Astroflight. If you are using this charger, you owe it
to yourself to immediately purchase the chip and update
your charger!Charge safe – as it can happen to you!
I don't have experience with those larger hobby batteries (the one in the article is the equivalent of 90 Parrot batteries), but I know that a charging bag is commonly available.
From the description of this article, the charging system was 0-fault tolerant. In the NASA programs I'm familiar with, charging systems for (large) Lithium ion batteries have to be 2-fault tolerant, so 3 separate things would have to fail in order to have a battery overcharge like that. The Parrot battery, in addition to being just really small, has a single-fault tolerant charge system; the on-board charger prevents overcharge, as does the cell protection circuitry that's mounted on the cell. If, like I do, you use a Parrot-style cell for deployments, but with the cell protection circuitry removed, then you're back to a zero-fault tolerant charge system. For me, I'm comfortable with this for the deployment cell, since the charge is just a single chip with no external parts required, so it's simple enough that it's unlikely to fail. Also cell is small enough that it seems like it wouldn't do much damage, but maybe I should do a destructive test by running the USB 5V directly to the cell, and see what happens.
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