![]() Once the ammeter shows zero voltage, the battery may be detached from the charger for the intended use. The connected ammeter is used for monitoring the charge condition of the battery. The IC will require a heatsink for operating optimally. R = 0.6/I, where I is the maximum desired output current limit. ![]() However with Rc along with BC547 transistor placed in the circuit at the shown position makes it capable of sensing the current that’s being delivered to the battery.Īs long as this current is within the desired safe range, the voltage remains at the specified level, however if the current tends to rise, the voltage is withdrawn by the IC and dropped, restricting the current rise any further and ensuring appropriate safety for the battery. Without the inclusion of Rc, the circuit would behave like a simple LM 317 power supply where the current wouldn't be sensed and controlled. R2 can be fine set for aligning the final output voltage with the battery. The ADJ pin of the IC is fixed to the junction of the resistor R1 and the variable resistor R2. The filtered 14 V DC is applied to the input pin of the IC. ![]() The input power to the IC is fed from an ordinary transformer/diode bridge network the voltage is around 14 volts after the filtration via C1. The IC is basically wired in its usual mode where R1 and R2 are included for the required voltage adjustment purpose. The Current Controlled 12V Battery Charger Circuit Using IC LM317 presented here shows how the IC LM317 can be configured using just a couple resistors and an ordinary transformer bridge power supply for charging a 12 volt battery with utmost accuracy. We all know how smart the IC LM317 is and it’s no surprise why this device finds so many applications requiring precise power control. When the input current at which the battery is being charged is significantly high, adding a current control becomes an important factor. Why Current Control is Important (Constant Current Setup)Ĭharging any form of chargeable battery can be critical and involves some attention to be paid. This causes less stress on the battery, and also prevents sulfation of the battery plates.įor High Current Battery Charging, the above Schematic can be Modified as Shown Below: This transforms the first design into a fully automatic 12 V charger system, which is simple to build yet entirely safe.Īlso, since there's no filter capacitor the 16 V is not applied as a continuous DC, rather as 100 Hz ON/OFF switching. You can tweak the 15V zener value until you have around 14.3 V at the output for the battery. In this design, we have used a common emitter BJT stage which has its base clamped at 15 V, which means that the emitter voltage can never go beyond 14 V.Īnd when the battery terminals tend to reach above the 14 V level, the BJT gets reversed biased and simply goes into an auto shut down mode. That said, it is advisable to remove the battery as soon as the ammeter reads near zero volts.Īuto Shut-OFF: If you want to make the above design to auto shut off when the full charge level is reached, you can easily accomplish this by adding a BJT stage with the output as shown below: Although this looks higher than the 14 V full-charge level of the 12 V battery, the battery is not actually harmed due to the low current specification of the transformer. That means, the peak voltage after rectification will be 12 x 1.41 = 16.92 V. ![]() In the above simplest layout the 12 V is the RMS output of the transformer.
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