Automatic car charger design appears first in the do-it-yourself section. The device has been created long time ago but still meets its destiny. The cost of the device is really low.
Elements necessary to build a automatic car charger rectifier:
• Transformer model TS70/5,
• Z model housing,
• The cooling fan can be removed from the computer casing,
• An ammeter, which is necessary for measurements,
• Contactors for battery electrodes,
• The cable used to power the system may be cut off from the old device,
• Cables connected to the battery, thick,
• Bridge rectifier,
• Contact and slide contactors,
• The rest of the components were used from old electronic devices.
Construction of the transformer
We start with the construction of the transformer. We use an old transformer. We check for the current voltage. If it is too high, unwrap the coils of the coil, bend it in half, and wind it back to the core. The voltage needed to charge the battery is about 13V. So we choose the number of turns on the coil so that the 13V voltage is reached.
Exactly the same number of coils that have been wound to the transformer are required to wind up on the coil of the coil, which will be used to power the rest of the circuit. We supply this way: voltmeter, thermostat and automatic car charger.
Automatic car charger system
The system is built on the basis of two operating amplifiers, called a window discriminator. The system is used to switch on charging when the battery voltage is higher than 9V and turns off the charging when it reaches 15V, all with the 3 position relay located on the front panel, its functions are:
• continuous charging, the battery terminals supply current and voltage 12V,
• Turn off charging, no current supply to the battery terminals,
• automatic charging, the voltage of the battery is measured, depending on the voltage value, charging is switched on or disconnected.
Placement of the system in the housing available in the photos below.
Pseudoanalogy voltmeter for automatic charging system
The voltmeter was built on the basis of the UAA180 integrated circuit. Application has been observed in the application note of the system. The voltmeter is capable of measuring between 10V and 15.5V as 0.5V.
Thermostat for controlling the fan in the housing
The thermostat system was built on the basis of an operational amplifier used as a comparator. Model 1N4148 diodes have been used as a sensor of the temperature and conduction voltage (the conductivity decreases with increasing temperature). Four 1N4148 diodes were mounted on the three phase bridge rectifier heatsink. The hysteresis value is about 2-5 Celsius degrees. The temperature value from which the fan turns on can be set with a potentiometer. The optimum switching temperature of the fan is about 40 Celsius degrees. The thermostat system was placed together with a voltmeter on one the pcb board. Location of the layout shown in the pictures below.
Mounting the entire system
The photos show visible holes that were from the previous enclosure application. Drill the ventilation holes below the transformer and the top and rear walls of the fan assembly. The quality of the charging circuit, the rectifier diode bridge, the relays, the contactors, the transformer coils and the cables connected to the battery must be good at all, and any voltage drop will cause the system to load incorrectly.
Please place the contactor contact points shown in the picture below.
Automatic car charger design – summary
The rectifier diode circuit performs very well its work. The charging current values depend on the quality of the battery and its age (the charging current range is about 3 to 6 A). In automatic charging mode, firing the relay means that the battery is fully charged. In this case, you do not need to disconnect the rectifier. When we have a battery with a very old and unused battery, it may not be possible to charge it. This is caused by a low voltage value, and switching to continuous charging can damage the rectifier bridge and transformer.