Our project is a charger that can charge 2, 4 or 6 Nicad batteries with current limiting. The batteries listed are small (AA).
Operating from the AC power line it needs 14 to 16 hours to give a full charge in groups of 2 to 6 cells, without modifications to the circuit.
All the reader has to do is put the batteries in suitable holders and connecting alligator clips to the poles, the polarity and leave from one day to the other.
The LED1 will illuminate, indicating the charge, which is very important because if a battery has a poor contact with the support current does not pass. If this occurs, the LED will indicate.
The resistor is dimensioned to provide a load circuit current of 15 mA which is required for most AA. With changing the resistor the device can also charge medium and large batteries.
In Figure 1 we have the complete diagram of the charger.
In figure 2 we have the arrangement of components in a terminal strip.
The transformer has primary winding in accordance with local AC power line and secondary 6 + 6 V at current of at least 200 mA. The resistor R1 should be at least ½ W since it tends to heat up slightly during charging.
For the connection of batteries use a holder. It is interesting to have holders of two, four and six batteries.
To use the device, just put the batteries in the holder and connect the clips .
This moment the LED glows indicating that the current is flowing. If it does not, adjust the batteries in the support, there may be some bad contact with.
Note that the wire (red) is connected to the red wire from the battery holder.
An important procedure is to let the batteries completely discharge before giving new charge, so that there is the memory effect.
D1 - 1N4004 - silicon diode
LED - common red LED
R1 - 220 Ω x 1/8 W - red, red, brown
R2 - 2.7 k Ω x 1/8 W - red, violet, red
C1 - 470 µF x 25 V - Electrolytic
S1 - SPST switch
T1 - Transformer primary according to the power line and secondary 6 + 6 V x 200 mA to 300 mA
G1, G2 - Alligator clips - red and black
Terminal strip, power cord, battery holders, box mount, wire, solder, etc.