12v/ 0.7amp constant current charger-please help me out to build this circuits.

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deepakchikane

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Dear all..
i am looking to make a small ckt to charge my battery(12v/7ah).. i have made small circuitry with lm317..
but i think it is not working in the constant current mode..

i want to make the constant current chargers..

plz help me out..!!
https://obrazki.elektroda.pl/5383882700_1371186720.jpg
 

If the battery (7Ah) is charged at 0.7A constantly, it will be fully charged in 10Hrs. And lm317 can supply a maximum of 1A. How I wish you can upload your cricuit let me analyze and make some corrections where neccessary.


I have seen your circuit, I think it should work. If it is not working, check your connections especially the pin configuration of the transistor and the variable resistor.
 

The circuit topology is OK, but the shunt resistor value is too low.
At 0.7 amps, it will drop 0.7*0.5 = 0.35 volt. The transistor may have not started conducting yet.
 

  • The value of the resistor is chosen so that when the maximum allowable current flows from the power supply, a voltage equal to the turn on voltage of the current sense transistor is developed across it. This is typically 0.6 volts, assuming that a silicon transistor is used.
  • As the voltage across the current sense resistor reaches 0.6 volts, so the current sense transistor starts to turn on.In this way it is very easy to calculate the value for the sense resistor using Ohms Law. It is simply 0.6 / maximum current.

So,i think you would need a resistor of 0.6/0.7 A = 0.85 ohm or you could use a 0.91 ohm resistor available in market.
 
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