Battery Charger Regulator

  
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Most off-the-shelf car battery chargers cannot not be left connected to the battery for long periods of time as over-charging and consequent battery damage will occur. This add-on circuit is placed in series with the battery being charged and is powered by the battery itself. In effect, the circuit uses a high-current Mosfet to control the chargin
Battery Charger Regulator - schematic

g current and it turns off when the battery voltage reaches a preset threshold. Power for the circuit is fed from the battery to 3-terminal regulator REG1 which provides 8V. LED1 indicates that the battery is connected and that power is available. The 555 timer IC is configured as an astable oscillator running at approximately 100kHz. It feeds a diode pump (D1 & D2) to generate adequate gate voltage for Mosfet Q3, enabling it to turn on with very little on resistance (typically 14 milliohms). With the Mosfet turned on, current flows from the charger`s positive terminal so that charging can proceed. The battery voltage is monitored by 10kO pot VR1.



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