31-10-2012, 06:04 PM
SMART CHARGER
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INTRODUCTION
Inorder to eliminate the difficulty of using different chargers for different voltages,we implement a circuit,which can be used to charge batteries at constant current for different voltage values.
There are many ways of battery charging but constant-current charging, in particular, is a popular method for lead-acid and Ni-Cd batteries. In this circuit, the battery is charged with a constant current that is generally one-tenth of the battery capacity in ampere-hours. So for a 4.5Ah battery, constant charging current would be 450 mA.
This battery charger has the following features:
It can charge 6V, 9V and 12V batteries. Batteries rated at other voltages can be charged by changing the values of zener diodes ZD1 and ZD2. Constant current can be set as per the battery capacity by using a potmeter and multimeter in series with the battery.
LITERATURE SURVEY
For our minor project, we searched for different topics in net as well as electronics journals like electronics for you, electronics bazaar, IEEE spectrum etc. We analyzed and studied details of various topics. We analyzed the possibility, availability of components, feasibility, cost and several other aspects regarding the project. We got quite a few topics which satisfied these criterions.After this , we shortlisted few topics. And from those our abstract based on “SMART CHARGER” was accepted. We began collecting the details of hardware components required. Then we studied details of components and working related to it which was time consuming.
BLOCK DIAGRAM EXPLANATION
TOUCH SCREEN :
A 4 -wire analog resistive touch screen is employed in this system . It is a user interface. Touch screen panel is divided into 4 parts.On touching , athe corresponding part is sensed by the touch screen controller circuit and it performs corresponding functions assigned to that part in the program
GRAPHIC LCD:
It is a user interface that displays the data.Here a touch screen is mounted on this graphic LCD. It is of the specification 128*6.
PIC MICROCONTROLLER:
A PIC microcontroller is used here which functions as a mediator between display and updation unit.It contains the program fordriving the touch screen.
PC:
The PC contains a program for updation of book details.This updated data is sent to the PIC according to the request given by the PIC as per the touch sensed on the panel.This updated data is displayed on the screen.
CIRCUIT DIAGRAM EXPLANATION
Once the battery is fully charged, it will attain certain voltage level (e.g. 13.5-14.2V in the case of a 12V battery),give indication and the charger will switch off automatically. You need not remove the battery from the circuit. If the battery is discharged be low a limit, it will give deep-discharge indication. Quiescent current is less than 5 mA and mostly due to zeners. DC source voltage (VCC) ranges from 9V to 24V. The charger is short-circuit protected.D1 is a low-forward-drop schottky diode SB560 having peak reverse voltage (PRV) of 60V at 5A or a 1N5822 diode having 40V PRV at 3A. Normally, the minimum DC source voltage should be ‘D1 drop+Full charged battery voltage+VDSS+ R2 drop,’ which is approximately ‘Full charged battery voltage+5V.’ For example, if we take full-charge voltage as 14V for a 12V battery, the source voltage should be14+5=19V. For the sake of simplicity, this constant-current battery charger circuit is divided into three sections: constant current source, overcharge protection and deep-discharge protection sections. The constant-current source is built around MOSFET T5, transistor T1, diodes D1 and D2, resistors R1, R2, R10 and R11, and potmeter VR1. Diode D2 is a low-temperature-coefficient, highly stable reference diode LM236-5. LM336-5 can also be used with reduced operating temperature range of 0 to +70°C. Gate-source voltage (VGS)of T5 is set by adjusting VR1 slightly above 4V.
By setting VGS, charging current can be fixed depending on the battery capacity. First, decide the charging current (one-tenth of the battery’s Ah capacity) and then calculate the nearest standard value of R2 as follows:R2 = 0.7/Safe fault current R2 and T1 limit the charging current if something fails or battery terminals get short-circuited accidentally. To set a charging current, while a multimeter Is connected in series with the battery and source supply is present, adjust potmeter VR1 slowly until the charging current reaches its required value. Overcharge and deep-discharge protection have been shown in dotted areas of the circuit diagram. All components in these areas are subjected to a maximum of the battery voltage and not the DC source voltage. This makes the circuit work under a wide range of source voltages and without any influence from the charging current value.
CONCLUSION
In this project a battery charger that can be used for any rated battery was designed and built. It was successfully demonstrated and working was found satisfactory.Under voltage and over voltage conditions were tested and results were satisfactory.
This project finds wide application in industrial as well as domestic appliances. Using this device standardisation of chargers is possible.