Model Forum / Radio Controlled / Air Models / September 2010

I have read that when your pack starts to show puffing, it is reaching
the end of its life span. Puffing is anything that is not flat. Slightly
puffed will usually go away when you charge it, but will be back after it
is discharged. Puffed is when the swelling remains after a charge and you
don't get full capacity out of it. Really puffed, it will look like a
balloon and be way too hot. You generally can't use it again when it gets
to the really puffed stage.

Most people don't de-rate their stuff when they set it up. What I mean by
that is you should buy things that you only use it to 75 - 80 % of it's
capacity. Ex: If you have a 1000mAh battery, only use 800 mAh's of it. If
you have a motor that draws 25 amps at full throttle, use a 40 amp ESC.
If you do this, then your stuff will last way longer than if you don't.

If you use 100% of a batteries capacity every time, it will last maybe 40
- 50 charge cycles. If you only use 80% of a batteries capacity every
time, you could get 200 charge cycles from it.

Now for some absolutely unscientific information. Our club field is way out
in the sticks so one of the typical entertainment breaks is to shoot old
Lipo packs with a 22 to see what happens.  We have done it to about 30
packs. The battery pack is always charged up prior to execution. The results
are pretty consistent. Packs that are not puffed up, when shot, will do
everything between nothing and smoke a lot. Sometimes the pack will lay
there for a long period of time with no reaction and THEN start smoking.

Packs that are puffed up will go up in a large, intense fireball when shot.

What does this mean?
No. 1 -  It's easy to separate out the bum shooters from the good shots...
No. 2 -  I no longer keep puffed packs for any reason whatever. They are
dangerous.
No. 3 -  If you have lots of electric flyers and therefore lots of battery
packs, storage represents a big problem, especially you hang on to packs
until they are absolutely useless. Most people have far more batteries than
they do storage containers. When you store 4-5-6 packs in a single
container, that's right next to having a bomb in your workshop. When one
goes up, everything in the container goes up. You will be very lucky if you
only get the "lotsa smoke" reaction when a whole container goes up.  I use
vented ammo boxes and flower pots with a drip dish large enough to cover the
top of the pot for storage. I use the Lipo sacks only to transport packs to
and from the field. I don't believe the cheapo gray Lipo sacks from Ebay or
other Chinese suppliers would contain a runaway Zippo lighter. After seeing
the violence of the fireball explosion from our target practice, I doubt any
of these storage systems would contain the energy of a massive failure of
several packs going up. So, once again, if a pack starts showing any
abnormality, get rid of it.

FWIW..................

If you get puffing of a lipo pack, something is wrong.  Best to retire
it soon, if not immediately.

Why would it puff?

Typically I think it is from overheating caused by over working the
pack.  OR, it may be caused by a pack that is seriously out of balance
so that some cells are being over charged and some are discharged too
far.

Either way, I would replace it ASAP.  If you choose to continue a very
very slightly "soft" pack, then I would use it in a lower duty
application.

If a pack is rated for 20C that means that is the LIMIT of its
ability.  I never run them at their C rating.  I usually don't run
them at more than 80% of their C rating and more often around 60% so I
get better duration for the flight and longer life from the pack.

Ed