http://users.otenet.gr/~athsam/car_12v_battery_charger.htm

On reference to the link above, my group and i were to patch up the circuit and then test the charger. We did it without the transformer and the bridge rectifier. We directly connect the input to a 17Vdc power supply. But it did not work properly. The circuit can charge the 12V battery but it did not cut off once it is fully charged. The red led did not flicker as the battery is charging and did not light up once it is fully charged. We set the trimmer to null value at first, we follow the steps as we go along but still did not work properly. We try troubleshooting over and over but still could not find a solution. Can anyone help us with this? Do we need to modify the circuit? Do we need to change some of the components used? Would really appreciate the help.

 

Hi,
the web link is broken in your post (but I guessed it).

The circuit uses thyristors as switching devices. For these to work, the incoming power MUST be AC.

Once a thyristor turns on, it stays on until the current through it stops.
With a rectified AC supply, this happens 100 or 120 times per second, but if you try to use a DC supply it only stops if you turn the supply off.

If you use the AC feed it was designed for it should work fine.


If you must use DC input, I'd look at a straightforward voltage regulator circuit like an LM317 with an extra power transistor to handle the current.

But, the circuit you have is more fun. The charged light starts to pulse as the battery gets near full and as the charge completes the light stays on more with shorter off times. When really full, the light just flicks off occasionally as it trickle charges the battery. (I built some using the same principle for NiCad banks some years ago, they work fine).

 

the link has been edited above. anyway thanks for the reply. hope it helps.

 

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