NiMH and Nicd battery charger-regenerator circuit

This device provides charging using pulsing current method for NiMH and Nicd batteries. Between charging pulses a battery discharges by 10 times less current pulses. In some cases this method allows to regenerate dead batteries.

The circuit diagram of the charger-regenerator is shown in the figure below. It is powered by 220V or 120V AC mains, for another voltage the circuit component values can be recalculated using the online calculator located under the figure.

NiMH and Nicd battery pulse charger-regenerator circuit diagram

D1, D2 - 1N4007;
D3 - a red LED for 10 mA, the forward voltage is about 1.8 V;
C1 - 0.47μF x 400 V; C2 - 0.05μF x 400 V;
R1 - 500k...1Meg; R2 - 72 Ω
V - a NiCd or NiMH cell or a battery;

The charging/discharging current is 25 mA/2.5 mA for 220 V AC,
or 25 mA/2.5 mA for 120 V AC.
The LED D3 indicates the charging process.

AC = , [V]

F = , [Hz]

V = , [V]

N = , [Cells]

Ic = , [mA]

Id = *Ic, [mA]

VD3 = , [V]

C1 = μF

C2 = μF

R2 = Ω

AC, F - voltage and frequency of the mains;
V - voltage of the cell
N - number of cells in battery;
Ic - charging current, mA;
Id - discharging current, mA;
VD3 - forward voltage of the LED D3;
C1, C2, R2 - parameters of the circuit components

With the parameters of components shown in the figure, the circuit provides charging current 25 mA, discharging current 2.5 mA for 220V AC. Note, the full amplitude of current pulses is twice higher, 50 mA and 5 mA respectively, because the circuit uses a half-wave rectifier.

A charging time for a completely discharged battery with capacity of 250 mA/h is about 14...16 hours. The charger doesn't protect the battery from overcharge, so the voltage across the battery should be constantly monitored.