The concept is indeed hugely simple and therefore pretty crude with its going. This means that though this idea is too simple, would require appropriate monitoring of the charging conditions of the battery, so that it does not get over charged or damaged.
To make this simplest battery charger circuit quickly, you would require the following bill of materials:
- One rectifier diode, 1N5402
- An incandescent bulb, having voltage rating equal to the battery which needs to be charged and current rating close to 1/10th of the battery AH.
- A transformer having voltage rating equal to twice that of the battery voltage and current twice the charging rate of the battery. That means if the battery is 12V, the transformer should be 24V, and if the AH of the battery is 7.5 then dividing this by 10 gives 750mA which becomes the recommended charging rate of the battery, multiplying this by 2 gives 1.5Amps, so this becomes the required current rating of the transformer.
After you have collected all the above material, you may simply connect the above parameters together with the help of the diagram.
The functioning of the circuit may be explained in the following manner:
When the power is switched ON, the 1N5402 diode rectifies the 24V DC to produce half wave 24V DC at the output.
Though the RMS value of this voltage may appear to be 12V, the peak voltage is still 24V, therefore it cannot be applied directly to the battery.
To blunt of this peak value, we introduce a bulb in series with the circuit. The bulb absorbs the high peak values of the voltage and provides a relatively controlled output to the battery, which becomes self regulatory through the glow of the filament intensity of the bulb (varying resistance).
The voltage and current thus automatically becomes adjusted to appropriate charging levels which becomes just suitable for the battery safe charging.
The charging of the battery can be witnessed by the gradual dimming of the bulb as the threshold charging voltage of the battery is reached.
However once the battery voltage reaches close to 14.5V, the charging must be stopped, irrespective of the bulb glow condition.