General Information On Rechargeable Batteries; A) Definition Of „C-Rate; B) Selection Of The Suitable Charge And Discharge Current - VOLTCRAFT CHARGE MANAGER 2024 Operating Instructions Manual

8. GENERAL INFORMATION ON RECHARGEABLE
BATTERIES
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 by charge transport for charging must be higher than the one that can be delivered
afterwards. This ratio of the energy drawn to energy supplied 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 delivering the value of the permissible charge or discharge current independently of the battery capa-
city. The multiplier is the battery capacity.
The following applies: Battery capacity (in mAh) x C-Rate = Value (charge/discharge current in mA)
Examples: Rechargeable batteries at 1000 mAh and 2700 mAh:
C-Rate = 1C
1000 mAh x 1 = 1000 mA
2700 mAh x 1 = 2700 mA

b) Selection of the Suitable Charge and Discharge Current

The „Charge Manager 2024" automatically adjusts the charge current. For NiMH, NiCd batteries, you can also limit
the charge current manually. There are six practice-orientedly chosen charge current limits of 500 mA to 3000 mA
available in steps of 500 mA.
For NiZn rechargeable batteries, the variable charge current has always been set automatically by the „Charge
Manager 2024" and cannot be chosen freely.
Limitation of the charge current to 500 mA is recommended for:
• Batteries without information on charge type and a capacity of less than 1000 mAh
A charge current limitation to 1C is recommended for:
• Rechargeable batteries with a capacity of >1000 mAh and the print „Standard charge: 12 - 15 hours at xxx mA"
(„Standard charge: 12 - 15hrs. at xxx mA")
• Rechargeable batteries with the print „Fast charge: 4 - 5 hours at xxx mA" („Fast charge: 4 - 5h at xxx mA")
• Rechargeable batteries with the print „Fast rechargeable" or „Quick charging possible"
C-Rate = 2C
1000 mAh x 2 = 2000 mA
2700 mAh x 2 = 5400 mA
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