Lithium Batteries (Lipo, Liio, Life) - ROBBE Power Peak B7 EQ-BID Notice D'utilisation

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LIthIUM BattERIES (LiPo, LiIo, Life)

INtRODUCtION
Different types of lithium battery are available:
1. Lithium-Ion batteries with liquid electrolyte and 3.6 Volt nominal voltage - the first genera-
tion of lithium batteries, hardly ever used in modelling.
2. Lithium-Ion batteries (LiIo) with liquid electrolyte and 3.6 Volt nominal voltage - the second
generation of lithium batteries, with metal casing.
3. Lithium-Ion-Polymer batteries (LiPo) with gel electrolyte and 3.7 Volt nominal voltage -
the current generation of lithium batteries, also known as LiPo. Pressure in the cell during
charge and discharge processes is lower due to the gel electrolyte, which means that a
foil casing is adequate. This type of battery has quickly become established for model
applications due to its low weight and high energy density.
4. Lithium-Ferrum batteries (LiFe) with a nominal voltage of 3.3 Volt: the latest generation
of lithium battery, also known as A123 cells. This battery is likely to become popular in
modelling due to its ability to deliver high peak currents and high energy density.
CaPaCIty DIffERENCES
When several cells are combined to form a battery pack and discharged at a relatively high
current,
the cells heat up at different rates, as heat from the inner cell is unable to dissipate.
This causes changes to the cell's internal resistance, and reduces its output capacity. As a
result this cell is discharged earlier, and there is a risk that it may be discharged below the
cut-off voltage of 2.5 Volt.
Major differences in capacity can occur, particularly when outdoor temperatures are very
low. For example, when a LiPo battery is used in an electric helicopter, the front cell is cooled
to a greater extent by the airstream than the inner cells, which are considerably warmer. As
a result, the cold cell has a lower capacity and there is a risk that it will be discharged below
the cut-off voltage.
To avoid permanent damage to the cells, it is therefore recommended to discharge LiPo cells
only to a cut-off voltage of approx. 3 Volt. It is also particularly important to charge the cells
to the same level the next time the pack is charged.
Charging individual cells wired in parallel presents no problems, as the total current is distri-
buted amongst the individual cells according to their voltage level.
Operating Instructions
Power Peak ® B7 EQ-BID
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