Today we will turn off our robots and will focus on  this particular electronic device.

Battery charger always come handy. Imagine the situation where you are on the road trip and you are taking photos with your handy camera that goes on 6V battery. On the half way your battery is dead and you need to recharge it in order to continue taking shots. In this electronic project we will help you to build your own car battery charger. Yes, you can buy some commercial solution, but where is fun in that? And this battery charger is cheaper than the one in the store. All parts for the charger can be found in local electronic store, but you can find it cheaper in online electronic stores. We recommend electronickits.com because they have quality electronic components and they are not expensive.

This  car charger can charge two types of batteries. Ordinary  12V and 6V batteries. If it is used a with transformer that can provide 4 to 5 A at a voltage between 12.6V and 16V then the 6V and 12v batteries will charge regardless the position of the switch on schematics. In fact we don’t need the switch at all.

Here is a battery charger circuit scheme:

We created this device so that battery charging current is limited to 4.2A. If we give a 600mV voltage on R1 resistor, then the T1 transistor starts to operate (conduct). T3 transistor help us to stop the charging the battery. Too much charging is avoided because the value of current on T3 is restricted. The distinction between applied voltage at T4′s collector and real voltage of the battery is balanced thru T4′s emitter junction.

The power input of T4 transistor can be calculated by multiplying load current and voltage difference we mentioned above. For 6V battery, charging power reaches 40W. After that device stops charging the battery. The rectifier diodes must provide 4A at 40V. One other thing, we must cool the T4 transistor. Heatsink must be placed on the transistor in order to cool it down.

Best way to build this electronic project is to build it on breadboard and with some good wires. Main concern is to dissipate the heat and to protect the circuit from temperature and damaging. To do that it must be placed in some kind of case. And then you have cool and cheap car battery charger. You just need to buy rechargeable batteries.