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Car Charger for 12V Batteries

The circuit has been designed to produce a battery charger for automobiles that are using 12V batteries only.

  • BTY79 – a 10A Silicon controlled rectifier with an operational temperature range from 0ºC to 125ºC
  • C106D – a 4A sensitive gate Silicon controlled rectifier that functions as reverse blocking thyristors designed for high volume consumer applications such as light, speed control, temperature, process and remote control, and warning systems where reliability of operation is important

The typical car battery chargers have simple designs that produce a few amperes during its operation while charging the battery continuously. In the event that the charger is not turned OFF, overcharging will occur with due to evaporation which looses electrolyte and might cause damage to its elements. With the design of this circuit, this type of problem can be avoided by monitoring the condition of charging of the battery via the retroactive control circuit. This is done by imposing a high current charge until the charging is complete. The LED LD2 will indicate that charging is full which will eventually deactivate the charging circuit. In creating this design, the cables that connect the transformer to the circuit should have enough cross-sectional area to prevent voltage drop when heat is produced as the current flows through.

The adjustment of the circuit comes after the design, with the adjustment of TR1 to null value. The LEDs are checked without connecting the battery initially and allowing them to turn ON. By connecting a battery, a 2A to 4A current is permitted to flow while ensuring that LD2 is turned OFF. TR1 is carefully adjusted to a few hundred milliamps until LD2 turns ON. This is done using the hydrometer technique. The correct adjustment allows LD2 to begin flickering as the battery is being charged. Connected to the battery is Q1, since it functions as a rectifier and charges the battery, which can be fired in each half cycle by R3-4 and LD2. In case an uncharged battery is connected, a low terminal voltage is obtained. When the voltage of the battery exceeds the predetermined value, Q2 is activated by the combination of C1, TR1, R2, and D2. Q1 is deactivated with the current supply cut off as the battery terminal voltage is increased where Q2 shifts the control of Q1 gate after TR1 fixed the increased battery terminal voltage above the level. A heatsink should be mounted on the bridge rectifier GR1 and Q1 to prevent overheating. A 5A DC ammeter M1, connected in parallel, is used to measure the charge current.

The circuit’s theory of design will only be applied to batteries with rating of 12V. These batteries are mainly used in a variety of vehicles used in land, air, and water such as personal watercraft like boat, yacht, Jet Skis, and other marine applications. They are also utilized widely in automobiles and motorcycles such as quad bike, RVs, snowmobile, motor scooter, utility vehicle, and riding mower. It can also be beneficial to disabled persons by providing aid to wheelchairs and mobility scooters.

Tags: car charger, 12V, batteries,

Comments on this post:

By electromania 0Score: 

5 years ago:  Can we use this circuit for other applications?

By Vava 0Score: 

5 years ago:  Wheres the list of components?

By Jack 0Score: 

5 years ago:  Hi Vava, please reload the page you will see then :)

By ahmed 0Score: 

5 years ago:  what should be the heatsink size? I am building this circuit on protoboard but after make it work I am planning to prepare a prtinted circuit board. Please give me an idea about the heatsink size

By Jack 0Score: 

5 years ago:  Hi electromina, what kind of applications do you mean? This circuit can provide large amount of current during the charging process. If your charge current must be limited due to your battery type, probably this circuit won't be suitable for it.

By Zayed 0Score: 

5 years ago:  salam ahmed! try using a heatsink that would cover the dimension of the component being supported so it will not be too large or too small

By bon bon custodio 0Score: 

5 years ago:  how long will be the charging hours? will it overheat the battery in case left charging unintentionally?

By Andrew Morales 0Score: 

5 years ago:  Hi,

Thanks for writing such an interesting article. Its really good to know about the batteries in detail. Seriously do we realize how many things in your house that need batteries? Lets count it, from the flashlight, cell phone, iPod, cameras, and many more. Knowing it should make us realize on how essential the presence of the batteries in our daily life. However, with that so many kinds of battery, which is generally different between one to another, sometimes we have some difficulties in finding the desired type.

Find the right batteries supplier is not hard if you check out because this website provides the widest selection of batteries and you can choose the right battery based on the categories. You can get the procell batteries which available in several sizes and voltage. You also can find Duracell batteries that divided into duracell plus batteries and duracell ultra batteries. All of the batteries come with cheaper price because this website provides the discount batteries in bulk, wholesale, and retail quantities.


-Andrew Morales

By Niluka 0Score: 

4 years ago:  what are the alternative SCRs for BTY79. Please reply

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