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.

Power Inverter With Feedback For Voltage Regulation

Two things mostly inspire some of my design, it is either I need it personally or someone asks of it. The former led to this design as my former inverter could no longer meet up with my load demand and desire constant output voltage for my highly voltage sensitive appliance. In this inverter circuit, I introduce feedback circuitry for voltage regulation by modulating the pulse width of the oscillator output. When the there is a change in the voltage of the inverter battery, the rms value of the AC output voltage changes. When the load increases, voltage drop across the transformer winding increases, hence drop in the rms value of the AC voltage.
However, the feedback circuitry in this inverter circuit senses the changes, and sends the feedback to the oscillator which in return adjusts the width of the output pulse to stabilise the AC output. To really understand how this works, you can check the datasheet of oscillator IC used, SG3524.

 

The transformer use in this inverter has core dimension that give core-area equals 4860 square-mm and window area equals 2187 square-mm and can deliver power of about 1.2KVA. It is a center-tapped transformer and has winding ratio 11-0-11/300. 11/300? Yes, because the design is to deliver a modified sine-wave AC voltage output. You can use the transformer design calculator for your transformer design.

 The values of the electronic components used are well detailed in the circuit diagram. Where precision is needed to get the right value, I replaced fixed resistors with variable ones so as to adjust to get the appropriate value. VR1 is to set the frequency, VR2 to set the desired regulated AC output voltage and VR3 to set the BLVS (battery low voltage shutdown).