High current battery charger circuit is used to charge lead acid batteries of high current value upto 200AV. The charger is automatic so when the battery is charged full, the power to the battery as well as the charger is switched off.
The circuit for this high current battery charger can be understood in following stages:
The first stage is power supply stage which consists of a transformer and bridge rectifier.
Next to the bridge rectifier network there is a filter capacitor which, for simplicity, is not taken into account here. However a 1000µF/25V capacitor can be added, between negative and positive ends of bridge, for improved output.
To charge the battery the output from power supply is given directly to it.
The next stage contain an operational amplifier viz 741 IC known as voltage comparator. This voltage comparator is put to check battery voltage during its charging. With relevant response the output from the IC is switched at pin#6.
The supply or the battery positive is connected to the pin#3 via a preset 10K resistance. This preset is being adjusted in such a way that the IC returns its output at pin no.6 in case the battery is charged fully.
The pin no.2 of the IC is connected to fix reference through voltage divider netwark comprising of 6V zener and a 10K resistance.
The IC output is provided to relay where the major controlling component is BC557 transistor.
Primarily the power to circuit is started with press of the start button. The switch powers the circuit for a moment by bypassing the relay.
Then the IC makes sensation for the battery voltage and due to low value at this stage, the IC output reacts with low out put.
This makes the relay and the transistor switched ON. The relay passes constant power and now the circuit remains ON even the start button is released, and charging of battery is started.
As soon as the battery charging reaches nearly 14V, the IC return it’s out-put to high logic level by instant sensation.
The BC557 transistor reacts to this and switches OFF the relay and as a result the power to circuit is too switched OFF.
The circuit gets completely switched OFF until unless you press the start button again and the battery, being charged, has charge under 14V.