General Information; Definition Of "C-Rate; Selection Of The Suitable Charge And Discharge Current - VOLTCRAFT CHARGE MANAGER CM 420 Notice D'emploi

7. GENERAL INFORMATION

Rechargeable batteries consist of two electrodes put into an electrolyte; thus, a
rechargeable battery is a chemical element. Chemical processes are running inside this
element. Since these processes are reversible it is possible to recharge batteries.
To charge a rechargeable battery, a so-called charge voltage is required. It must exceed
the cell voltage. Moreover, the energy (mAh) supplied for charging must be higher than the
one that can be delivered afterwards. This ratio of the energy supplied to the energy drawn
is called efficiency.
The capacity that can be delivered mainly depends on the discharge current; it is decisive
for the condition of the battery. The supplied charge cannot be used as a measure,
because a proportion of it will be lost (for example converted into heat).
The capacity data given by the manufacturer is the maximum theoretical quantity of current
which can be delivered by the battery. That means that for example a battery of 2000 mAh
can theoretically deliver a current of 1000mA (= 1 A) for two hours. This value considerably
depends on many factors (condition of the battery, discharge current, temperature, etc.).
a) Definition of "C-Rate"
This is a factor (multiplier) delivering the value of the permissible charge or discharge
current independently of the battery capacity. The multiplier is the battery capacity.
The following applies: Battery capacity (in mAh) x C-Rate = Value (charge/discharge
current in mA)
Examples with rechargeable batteries at 1000 mAh and 2700 mAh:
C-Rate = 1C
1000 mAh x 1 = 1000 mA 1000 mAh x 2 = 2,000 mA
2700 mAh x 1 = 2,700 mA 2700 mAh x 2 = 5,400 mA
b) Selection of the Suitable Charge and Discharge Current
The "Charge Manager 420" offers four practically selected charge and two discharge
currents.
Charge currents:
Discharge current:
C-Rate = 2C
500 mA, 1000 mA, 1500 mA, 2000 mA
250 mA, 500 mA
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