Charging efficiency

When batteries are charged and discharged, heat is released, which means that some of the energy used for charging is lost. The ratio of the charge that can be removed to the charge added during charging is called the charging efficiency :

${\displaystyle \eta ={\frac {Q_{\text{ab}}}{Q_{\text{zu}}}}}$

where η is the charging efficiency, Q _{ab is} the removable charge, and Q _{zu is} the charge added during charging.

The charging efficiency is generally between 70% and 85%. In the case of accumulators, however, its reciprocal value, the charge factor , is usually given. ${\displaystyle \kappa ={\tfrac {1}{\eta }}}$

Charge factor for different battery types: ${\displaystyle \kappa }$

• NiCd : 1.3-1.4
• NiMH : 1.4-1.5
• Lead accumulator : 1.05 - 1.2

With the help of the charging factor κ, the charging current I (in mA ) and the maximum amount of charge Q _{max of} the battery (in mAh ), the approximate charging time t (in hours ) of a battery can be determined:

${\displaystyle t=k{\frac {Q_{\text{max}}}{I}}}$

Charge time dependency (NiCd)

The charging efficiency also depends on the charging current. With NiCd one assumes a charging efficiency of 90% with 1C fast charging (ie just over an hour), on the other hand this drops to 70% with a 14-hour normal charge (0.1C), the charge factor is then around 1.4.

literature

• Egon Boss: Batteries. Lead accumulators . Robert Bosch GmbH Stuttgart, automotive equipment division, technical publications department, Stuttgart 1974, ( technical information. Bosch ), (company number: VDT-UBE 410/1 ).

credentials

1. ↑ Sven Bauer: Charging nickel-based batteries ( Memento of the original from November 22, 2015 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice. BMZ GmbH