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Batery charger Circuit !!

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A.Anand Srinivasan

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here is the circuit..... it is a car battery charger circuit... car battery is 12Vdc....
 

A.Anand Srinivasan

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it would work for non acid batteries too... rechargable batteries get charged when the voltage across them is greater than a particular threshold... so if the transformer gives a voltage greater than 12V then charging will take place...

to alert you try using some current sense circuit because as the battery starts getting charged the current to it starts dropping...
 

A.Anand Srinivasan

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ya sure.... charging dry battery wont be a problem because the headroom voltage is big enough.....

i think you would need around 13V to charge the battery fully...
 

A.Anand Srinivasan

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no it wont.... actually the cap is used to smoothen the rectified wave and hence protect the battery....
 

A.Anand Srinivasan

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the picture is in too low resolution that i'm not able to zoom it and view so the components are not clear... can you please post a higher resolution one... or give me the link where you found it.....
 

A.Anand Srinivasan

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actually the LM317 is a voltage regulator and it maintains 1.25V between its output and adjust pin... this current flows through the 2k resistance also and plus the 0.6 volt of the transistor it gives around 12V which is used to charge the battery...

the input of LM317 is a rectified wave....
 

rowokii

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I would be careful with the circuit Anand posted... it's an unregulated charger and as you suspected, after the battery has fully charged, the output voltage goes up to around 17V. Do not leave the charger connected to your battery for long time or it will degrade it.

The circuit you posted looks like(a little hard to see) it's using a 3 terminal voltage regulator (LM117?) to generate a constant voltage. For a sealed lead acid it's around 2.25V/cell, so for a 12V battery, it works out to around 13.5V.

Initially, when the battery voltage is low, the voltage drop from V+ to the base of the transistor is high enough to turn on the transistor and turn on the voltage regulator IC. As voltage increase on the battery, it drops enough voltage to turn off the transistor and turn off charging.

I would say this is closer to what you want. You can invert the signal on the collector of the transistor to turn on/off the alarm. (low voltage - battery charging, alarm off, high voltage -battery charged - alarm on.)

Cheers.
 

alisina

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this is a sample circuit of public mobile charger.
 

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