17.4
LITHIUM (LiPo, LiIo, LiFe) BATTERIES
GENERAL INFORMATION
There are various basic types of Lithium battery:
1. Lithium-Ion batteries containing fluid electrolyte, with a nominal voltage of 3.6 Volts.
This is the first generation of Lithium cell, and is not often used for modelling applica-
tions.
. Lithium-Ion batteries containing fluid electrolyte, with a nominal voltage of 3.7 Volts.
This is the second generation of Lithium cell, and is housed in a metal can.
3. Lithium-Ion-Polymer batteries (LiPo) containing gel-form electrolyte, with a nominal
voltage of 3.7 Volts. This is the current generation of Lithium cell, and they have also
become known as Li-Po or Li-Poly batteries. The gel electrolyte results in a reduced
pressure build-up in the cell during charging and discharging, for which reason a foil
housing is adequate. This cell has rapidly become very popular for model purposes due
to its low weight and high energy density.
4. Lithium-Ferrum (LiFe) batteries, with a nominal voltage of 3.3 Volts. This is the latest
generation of Lithium batteries, and is also known by the abbreviation ‘A13’. This cell
is rapidly becoming popular for model purposes due to its good pulsed discharge
capacity and high energy density.
CAPACITY DIFFERENCES
If several cells are assembled to form a battery which is then discharged at a fairly high
current, the cells will heat up to different extents as the cell or cells on the inside are
unable to dissipate heat effectively.
This results in changes to the cells’ internal resistance, which in turn reduces their dis-
charge capacity. The cell concerned will then be discharged more quickly, with the dan-
ger that it will eventually be discharged below the safe final discharge voltage of .5 Volts.
Considerable differences in capacity can occur when external temperatures are very low.
For example, if a Li-poly pack is flown in an electric helicopter, the front cell will be cooled
very effectively by the normal airflow, while the inner cells become significantly warmer.
The colder cell will lose effective capacity, with the danger that it will be discharged below
the safe final discharge voltage.
To avoid the danger of permanent cell damage we recommend that Li-Po cells should
only be discharged down to a final discharge voltage of about 3 Volts. For this we rec-
ommend the MC-Balancer, No. 8636, which is capable of monitoring individual cell volt-
ages of LiPo packs containing up to seven cells. It is also essential to ensure that the cells
are charged up to the same level next time the pack is recharged.
Charging parallel-wired cells does not present problems, as the total charge current is
distributed to the individual cells according to their voltage.
Operating Instructions
Duo-Power 8S EQ
No.
8504
4
