Alkaline Battery Charger Schematic

  
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The lower charge rate, the better the charge and the less chance of a cell leaking electrolyte. Also, if a cell becomes too flat or completely flat, it will not take a good charge and will also probably leak electrolyte and possibly even pop open. The idea here is to keep them topped up. Lets say you have fresh batteries in a torch and you used it for a while. The cells have drained to around 1. 3v for example.
Alkaline Battery Charger Schematic - schematic

Put them on gentle charge with this circuit, monitor the voltage and stop when it reaches 110%. That would be 1. 65v for one cell or 3. 3v for two cells in series. Do not charge beyond 110% or there is a risk of cell leaking or even popping open / exploding. Its also advisable not to try to charge an alkaline battery that is completely flat. They don`t absorb a charge and just leak in my experience. Some of my tests I done outside in the winter (around 2 °c) and I found the cells hit 1. 65v quite fast but didn`t absorb much of it due to high internal resistance at cold temperatures. Charging should be carried out at room temperature, around 20 °c. The nice thing about using alkaline batteries is that they have no internal discharge unlike Ni-Cd and Ni-Mh rechargeable`s, and are therefore suited to low current drain applications such as remote controls, clocks or things you don`t use often such as torches. Here is a constant current supply circuit schematic diagram using the LM317 variable voltage regulator. It is a very simple circuit for charging alkaline batteries. It will provide a stable constant current which is adjustable by switching different values of resistors. The input voltage must be at least 6v higher than the battery(s) you wish to charge. The LED, BC548 and 470 © resistor provide an indication of current flow to show that your battery connections are good. They can be omitted if you wish to make the circuit...



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