Car battery charger project

Dilshan R Jayakody s Project Repository - Simple Automatic Car

To design the entire circuit, we first design three different modules- the power supply section, the feedback and the load section.

Power Supply Design Steps:

  1. Here the desired load is a car battery with rating of about 40AH. Since the charging current of a battery should be 10% of the battery rating, the required charging current would be around 4A.
  2. Now the required transformer secondary current would be around 1.8*4, i.e. approx 8A current. Since required load voltage is 12V, we can settle for a transformer with 12V/8A rating. Now the required RMS value of AC voltage is around 12V, the peak voltage would be around 14.4V, i.e.15V.
  3. Since here we are using a bridge rectifier, the PIV for each diode should be more than four times the peak AC voltage, i.e. more than 90V. Here we select diodes 1N4001 with PIV ratings of about 100V.
  4. Since here we are also designing a regulated power supply, the maximum allowable ripple would be equal to the capacitor peak voltage minus the required minimum input voltage for the regulator. Here we are using a voltage regulator LM7812 to provide a regulated 5V supply to the relay and the 555 Timer. Thereby the ripple would be around 4V (Peak voltage of about 15V and input regulator voltage of around 8V). The filter capacitor value would thus be calculated to be around 10mF.

Feedback and Load Section Design:

Designing of the feedback and load section involves selection of resistors for the voltage divider section. Since the diode will conduct only when battery voltage reaches 14.4V, the values of resistors should be such that the positive voltage fed to the diode is at least 3V when battery voltage is around its maximum.

Keeping that in mind and with necessary calculations we select a 100 Ohm potentiometer and other resistors of 100Ohms and 820 Ohms each.

Also Read the Post –

The circuit operation commences once the power supply is available. AC power of 230V RMS is stepped down to a voltage of 15V RMS by the step down transformer. This low voltage AC voltage is then rectified by the bridge rectifier to produce an unregulated DC voltage with AC ripples. The filter capacitor allows the AC ripples to pass through it, thus producing an unregulated and filtered DC voltage across it. Here two operations take place: – 1. This unregulated DC voltage is fed directly to the DC load (The battery in this case) through a relay. 2. This unregulated DC voltage is also fed to the voltage regulator to produce a regulated 12V DC supply.

Here the relay is a 1C relay and the common point is connected to the normally closed position such that current flows through the relay to the battery and it gets charged. As current passes through the LED, it starts conducting, indicating that the battery is being charged. A part of the current also flows through the series resistors such that the battery voltage is divided using the potential divider arrangement. Initially the voltage drop across the potential divider is not enough to bias the diode. This voltage is equal to the battery voltage and thus determines the charging and discharging of the battery. Initially the potentiometer is adjusted such to its midpoint. As battery voltage increases gradually, it reaches a point where the voltage across the potential divider is enough to forward bias the diode. As the diode starts conducting the base emitter junction of the transistor Q2 is driven to saturation and the transistor is switched on.

PWR+ Pwr+ Extra Long 11 Ft Car-Charger for Philips Portable Dvd Player Dual-Screens Dc Adapter Auto Power Supply Cord (Dual)
Wireless (PWR+)
  • POWER SPECS : Output: 12V
  • FEATURES: Power device and charge battery from 12V DC outlets (car / air / boat) / Cord Length Is Extended to 11 Ft (Competitor s Products are 3-4 Ft)! / Steel-Reinforced...
  • ABOUT PWR+: Headquartered in Woodinville WA, Powering Millions of Laptops, Tablets and Electronic Gadgets and a go-to brand for premium replacement chargers and...
  • COMPATIBILITY: Philips Portable Dvd Players including Dcp852 Dcp855 Pb9001 Pb9011 Pd700 Pd7012 Pd7012r Pd7016 Pd703 Pd9 Pd9003 Pd9012 Pd9012m Pd9012p Pd9016 Pd9030...
  • MONEY BACK GUARANTEE - We are USA based Company that Wants your Repeat Business so, if You Do Not Like our Product or Don t Want It For Any Reason, We Will Happily...
Beatit 600A Peak 14000mAh 12-Volt Portable Car Jump starter Booster Battery Charger Power Pack Vehicle Emergency Kit, Compass & Built-in LED Flashlight
Automotive Parts and Accessories (BEATIT TECH)
  • [POWERFUL & COMPACT] : Jump start your vehicle (up to 5.5L(T)gas or 4.0L(T) diesel engine or Motorcycle ,oil boat and sleigh, ect) up to 30 times with 600 amps...
  • [QUICK CHARGE] : With 14mAh Capacity and our adaptive smart IQC charging technology, charge phones, tablets,camera ,kindle and other devices at speeds of up to 2.1...
  • [6 IN 1 MULTI-FUNCTION]: (Emergency jump start, USB quick charge,LED flashlight, S.O.S lighting signal for help, compass,power extend ). it can help you In any case...
  • [PROTECTION]: An safe and mistake-proof design with spark-proof technology and reverse polarity protection, which allow it to safely connect to any battery.The high...
  • [WHAT YOU GET] : Beatit Jump Starter B9, jump cable clamp, 12V wall charger, 12V car charger, use cable, A Manual,portable compressive case (Gift), 3-year Warranty...
Pwr+ 4.5mm 45W 65W 90W-Laptop-Car-Charger for HP-Envy-Pavilion Touchsmart-Sleekbook 15 17 M6 M7 Series DC-Adapter Power Supply Cord : !!! Check Connector Photo !!!
PC Accessory (PWR+)
  • POWER SPECS : Output Max: 19.5V 4.62A 90W (65W, 45W 2.31A compatible)
  • FEATURES: Power laptop and charge battery from 12V DC outlets (car / air / boat)
  • ABOUT PWR+: Headquartered in Woodinville WA, Powering Millions of Laptops, Tablets and Electronic Gadgets and a go-to brand for premium replacement chargers and...
  • COMPATIBILITY: HP Envy Touchsmart Sleekbook 11 14 15 17 M1 M6 M7 Series 854117-850 853605-001 PA-1650-63HP HSTNN-LA35 719309-003 721092-001 710413-001 710414-001...
  • MONEY BACK GUARANTEE - We are USA based Company that Wants your Repeat Business so, if You Do Not Like our Product or Don t Want It For Any Reason, We Will Happily...
FFY Fitian Portable Carrying Car Charger Power Supply Replacement Adapter for Microsoft Surface Pro 4 Core i5 and i7 Tablet Intel Core M3
Personal Computer (FFY)
  • Surface pro 4 AC/DC Adapter. Compatible with Microsoft surface pro 4 core i5 and i7 tablet, intel core M3. NOT compatible with Surface Pro 3!
  • Input: DC 12V-24V, 1.2A; Output: 15V, 1.25A; Cable length: about 3.9 feet
  • Small in size and lightweight, easy and convenient to carry
  • Power stop to charge after fully charged. Protect the charger and surface pro 4
  • Package: One car charger in the package per order
Tesla's 3-Socket Cigarette Lighter Splitter 12V/24V 120W Car Power Adapter DC Outlet Splitter with 6.5A 4-Port USB Car Charger for iPhone iPad Samsung Galaxy GPS Dashcam Radar Detector and More
Wireless (Tesla's)
  • Teslas s Advantage -- 4-Port USB charging ports with 6.5A total output enables you to rapidly charge 4 devices simultaneously. Supports iPhone 7 plus 7 6S 6 Plus/iPad...
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  • Compact and Sleek -- High-impact ABS+PC plastic surface with streamlined appearance and dirt-resistant finish, upgraded plug can stay in your car socket securely
  • High Safety Standards -- built-in PPTC auto-recovery 10amps fuse and protective circuits prevent the product and your devices from overheating, overloading or short-circuiting...

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