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SAFETY
- Handling
LIPO batteries
This is a very
important topic indeed, as the LIPO batteries that we all use with
electric helicopters can be very dangerous if they not handled
correctly.
The LIPO battery is a
great source of power, and does not have the "memory" problems
of the standard Ni-cad batteries or other problems suffered by other types
of batteries, but it does have one or two nasty drawbacks.
The first one is how
you charge them. You do not have to let them discharge all the way
down, in fact you ABSOLUTELY MUST NOT DO SO, as
there is a very good chance indeed of them catching fire.
Therefore, NEVER EVER LEAVE ONE CONNECTED IN YOUR HELICOPTER. Once you have finished flying, disconnect it and
remove it from the aircraft.
If we are talking
about the most common 11.1 Volt Lipo battery, this is made up of 3
individual cells rated at 3.7 Volts each, which means 3 cells in series
equal 11.1 Volts. The best rule of thumb to work to is to NEVER LET AN
INDIVIDUAL CELL of a LIPO battery DROP BELOW 3.5 Volts in normal use.
If
you do happen to do so, and it doesn't catch fire, there is a very good
chance that you will not be able to recharge it again at all, even with
a good LIPO charger system.
The converse of this
problem is the rate that you can charge them at. The common
formula for this is that you should never exceed what is called
1C. This value of 1C is simply the max capacity of the lipo - say
2200 Mah divided by 1000 (1C - to bring Mah to Amps) so you should only
ever charge a 2200 Mah lipo at 2.2 Amps at most.
Some people suggest
doing it at 1/2C (0.5C)to give the lipo's a longer working life, and there is
some evidence that this helps, but of course, they will take twice as
long as they are only being charged at half the 1C charging rate.
If you need to store
your Lipos for a period of time, you need to use your charger to
take them DOWN to about half their normal
power. Most decent chargers provide this as one of the options,
typically it is named STORAGE or something similar.
The external
temperature can also have adverse effects on Lipo cells. If a Lipo is
fully charged, and it gets too cold, the internal voltage can quite
easily rise, leading to a potentially dangerous charge value that could
lead to fire and explosion, so if you store your lipos in say the garage
during the winter, make sure the temperature does not drop down too much
if you have any fully or nearly fully charged lipos in there.
Finally, when you are
transporting Lipos, please be careful that they cannot be punctured by
anything, as this has been known to cause them to catch fire.
NEVER EVER LEAVE YOUR
LIPOS CONNECTED IN A HELICOPTER OR ANYTHING ELSE, THEY WILL DRAIN DOWN,
AND CAN QUITE EASILY CATCH FIRE.
WHEN
A LIPO DOES CATCH FIRE, SUCH AS A 3 CELL 11.1v DISCUSSED ABOVE, WHAT
HAPPENS IS USUALLY THAT ONE CELL EXPLODES WITH A LOT OF FIRE AND SMOKE,
BURNS ITSELF OUT, AND THEN SETS FIRE TO THE NEXT CELL. THIS MEANS
THAT YOU GET THREE SEPARATE EXPLOSIONS, AND AN AWFUL LOT OF VERY ACRID
SMOKE AND A LOT OF HEAT AND FIRE OVER A PERIOD OF SEVERAL MINUTES.
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