Home Made Battery Charger

What I love in this battery charger circuit is its simplicity and yet working perfectly as designed. All the components are common and readily available in market.

When the charger is powered to charge a drained (discharged) battery, it continuously charges the battery for some hours (depends on the discharged level and the battery capacity) till it is fully charged up to its preset full voltage (14V for this charger).  After this, it starts trickle charging to constantly keep the battery charged and also to compensate for self discharge without damaging it. At no time will the battery voltage goes above 14V.

Below is the video of the charger working.

 
12V DC relay cuts off supply to the charger transformer to stop the charging process when needed as determined by the control circuitry, while the network of C5 and R7 protect the relay contact from arcing. The decisions to place the DC relay at the AC input before transformer and not after are: (1) to save energy that would have been wasted if transformer is working even though battery not charging, and (2) a bigger switch (mechanical or solid state relay) big enough to handle the charging current would have been required, hence higher cost.

Another strategic decision is the use of 220V AC relay to connect the control circuitry of the charger to the battery. It cuts off its connection to the battery when the charger is switched off from the utility supply. This way, the battery will not be discharged by the charger.

Of course LED1 shows the status of the charger. It comes on whenever the battery is charging.