I have posted many battery charger circuits in this site, some are easy to
build but less efficient, while some are too sophisticated involving
complex construction steps. The one posted here is possibly the easiset
with its concept and also is extremely easy to build. In fact if you had
all the required material you would build it within 15 minutes of time.
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.
