ROBBE POWER PEAK ULTIMATE 2 Manual De Uso página 57

Operating instructions No.
POWER PEAK ULTIMATE 2 8470
CHARGE RATES
When speaking of charge and discharge currents we have all become familiar with the
concept of the charge rate (C), which represents the relationship between the charge cur-
rent and the battery capacity. For example, if a battery has a capacity of 600 mAh and is
to be charged at a rate of '1C', then a current of 600 mA has to flow.
BALANCING
A new battery, or one which has not been used for a long period, must be 'balanced'
before use. The same applies to a pack which has been deep-discharged, as this can
reverse the polarity of individual cells. A balancing charge takes around 24 to 26 hours at
a charge rate of 0.1C.
CHARGING
Charge rates of 0.1 to 0.2C are considered to constitute a normal charge. It is always
necessary to charge slightly more energy into a battery than can be removed (discharged)
again, so the charge time at the normal rate of 0.1C is not 10 hours, but 16 hours. When
normal charging is used, the overcharge factor therefore amounts to 60%.
Charging for longer than the stated time harms NiMH cells, and should be avoided, as the
excess electrical energy fed into the pack cannot be stored; instead it triggers chemical
processes which shorten the useful life of the battery.
We speak of accelerated charging when the charge current is around 0.3 to 0.5C.
In the case of NiMH batteries fast charging is generally considered to be the use of char-
ge rates higher than 0.5C. If the charge current is higher than 0.1C, the charge current
must be cut off as soon as the battery is fully charged. One useful charge termination cri-
terion is the 'digital delta peak' method. This relies upon the slight but characteristic fall-
off in the battery's voltage when the pack is fully charged; this peak is detected by the
charger when the battery is completely charged.
Batteries develop different internal crystal structures depending on the charge rate. For
this reason it is really essential to fast-charge drive / flight batteries which are to be disch-
arged at high currents. The higher the charge current, the less the fall-off in voltage during
the discharge process.
We recommend the following charge rates for NiMH batteries:
High-energy batteries: 0.5 - 1C; please observe the battery manufacturer's stated figures.
High-current batteries: usually 1C, but many cell types can be charged at 1.5 ... 2C; plea-
se check the maximum charge current figures stated by the battery manufacturer.
SELF-DISCHARGE
The rate of self-discharge of NiMH cells is around 1.5% per day at 20°C. This means that
a fully charged battery will be completely flat after being stored for about 75 days.
Batteries must therefore always be recharged immediately before use.
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