EEE, ECE & IE Project Updates
EEE, ECE & IE Project Updates |  |
- Car Battery Charger Circuit
- Solar Battery Charger Circuit
- High and Low Voltage Cutoff with Delay and Alarm
| Posted: 25 Jun 2014 06:47 AM PDT A car battery is a typical lead acid battery with about 6 cells, each of 2V such that the total battery voltage is around 12V. Typical values of battery ratings range from 20AH to 100AH. Here we are considering a car battery of rating 40AH such that it's required charging current would be around 4A. This article aims to describe the principle of operation, design and working of a simple car battery charger from AC mains supply and a feedback control section to control the battery charging. Car Battery Charger Circuit Working Principle:This is a simple car battery charger with indication. The battery is charged from a 230V, 50Hz AC mains supply. This AC voltage is rectified and filtered to obtain an unregulated DC voltage used to charge the battery through a relay. This battery voltage is constantly monitored by a feedback circuitry compromised of a potential divider, a diode and a transistor. The relay and the feedback circuitry are fed by a regulated DC voltage (obtained using a voltage regulator). As battery voltage increases beyond maximum, the feedback circuitry is designed such that the relay gets switched off and battery charging ceases. Car Battery Charger Circuit Diagram: Car Battery Charger Circuit Diagram Car Battery Charger Circuit Design: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:
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. Car Battery Charger Circuit Operation: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. As the transistor collector is connected to one end of the relay coil, the latter gets energized and the common contact point moves to the normally open position. The power supply thus gets isolated from the battery and charging of the battery stops. After some time as the battery starts discharging and the voltage at the potential divider again comes to a position such that the diode is reverse biased or in off condition, the transistor is forced to cut off and the Timer is now in off position such that there is no output. The common point of the relay moves back to its original position i.e. the normally closed position. Again the battery starts charging and the whole process repeats. Applications of Car Battery Charger Circuit:
Limitations of this Circuit:
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| Posted: 25 Jun 2014 05:39 AM PDT Solar concept is not new for us. We all know the importance of solar energy. Solar gadgets are increasing day by day. As non-renewable energy sources are decreasing, usage of solar energy is increased. This solar energy is not only used on the Earth but also used in space stations where no electrical power is available. Here is the simple circuit to charge 6V, 4.5Ah rechargeable Lead-acid battery from the solar panel. This solar charger has current and voltage regulation and also has over voltage cut off facilities. This circuit may also be used to charge any battery at constant voltage because output voltage is adjustable. (We have already seen the circuit diagram of 9v battery charger circuit using LM311 and SCR in the earlier post.) Solar Battery Charger Circuit Principle:Here the solar panel produces 12V DC. The charging current passes to LM317 voltage regulator through the diode D1. The output voltage and current are regulated by adjusting the adjust pin of LM317 voltage regulator. Solar Battery Charger Circuit Diagram: Solar Battery Charger Circuit Diagram Circuit Components:
Solar Battery Charger Circuit Design:The circuit uses a 12V solar panel and an adjustable voltage regulator LM317. Solar panel consists of 1.2V rated solar cells. Pot RV1 is used to set the output voltage to the battery. Diode D2 prevents the discharge of battery. For 6V Application:
For 12V Application:
Power Dissipation: In this project, power is limited because of the thermal resistance of LM317 voltage regulator and the heat sink. To keep the temperature below 125 degree Celsius, the power must be limited to 10W. LM317 voltage regulator internally has temperature limiting circuit so that if it gets too hot, it shuts down automatically. When battery is charging, heat sink becomes warm. When completing the charging at maximum voltage, heat sink runs hot. This heat is because of excess power that not needed in the process of charging a battery. Current Limiting: As the solar panel provides constant current, it acts as a current limiter. Therefore the circuit does not need any current limiting. Solar Charger Protection: In this circuit, capacitor C1 protects from the static discharge. Diode D1 protects from the reverse polarity. And voltage regulator IC provides voltage and current regulation. Solar Charger Specifications:
How to Operate this Solar Battery Charger Circuit?
Solar Battery Charger Circuit Advantages:
Solar Battery Charger Circuit Applications:
Limitations of this Circuit:
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| High and Low Voltage Cutoff with Delay and Alarm Posted: 25 Jun 2014 04:09 AM PDT This circuit protects the costly equipment like TVs, air conditioners, Refrigerators, etc. from high voltages as well as low voltages. If the supplied voltage is abnormal (High or low) then the circuit automatically turns of the load. This circuit also produces sound when main power resumes. Generally voltage stabilizers are used in this type of applications to maintain constant AC voltage. However due to the abnormal AC supply, relays in voltage stabilizer switches ON and OFF continuously. The frequent energization or de-energization of relays leads to the shortening the life time of appliances and the stabilizer itself. Hence it is better to use this project in order to control the appliances instead of costly stabilizers.
High and Low Voltage Cutoff with Delay and Alarm Principle:When supply voltage is high, the DC voltage at the cathode of zener diode D4 becomes greater than 5.6V. As a result, transistor Q1 is in ON and transistor Q2 gets switched off. Hence the relay RL1 de-energizes and load would be in OFF condition. Under low supply voltage condition, transistor Q1 switches to ON condition and as a result transistor Q2 switches off, making the load OFF. When normal AC supply voltage is applied, the DC voltage at the cathode of zener diode D4 is less than 5.6V, now transistor Q1 is off condition. As a result, transistor Q2 is in ON condition, hence load switches to ON by indicating the green LED. When supply is resumed after a break, 555 timer IC goes low and this triggers the 555 timer IC. The output of 555 timer IC makes sound IC to operate through the transistor Q3, at the same time, transistor Q1 switches to ON condition as the output 555 timer is connected to the base of Q1 and results transistor Q2 OFF. Thus the relay switches off the load. High and Low Voltage Cutoff with Delay and Alarm Circuit Diagram: High and Low Voltage Cut-off with Delay Alarm Circuit Diagram Circuit Components:
High and Low Voltage Cutoff with Delay and Alarm Circuit Design:In this circuit, 555 timer is configured to operate in monostable mode. In this circuit, pin4 and pin8 are shorted to avoid sudden resets. The pulse width of the 555 timer output signal is about 10 seconds. This output signal drives the speaker. Speaker gives melodious sound when power is resumed because of UM66 IC. The volume of the speaker can be controlled by using POT RV3. Green LED indicates normal AC supply voltage. Red LED is used for power indication. Here zener diode D4 along with transistor Q1 is used for comparing the input voltage. Transistor Q2 switches the load based on the output of transistor Q1. Diodes D1 and D2 are used for rectification purpose. Capacitor C1 filters the input AC ripples. How to Operate this Circuit?
High and Low Voltage Cutoff with Delay and Alarm Circuit Advantages and Applications:
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