Multiple appliances have been born to ease human efforts. And in the same run, numerous protective circuits are designed to ensure a long lifespan of those devices. We have seen those circuits claiming to protect appliances like refrigerators and air-conditioners from voltage fluctuations and brown-outs. An overvoltage protection circuit has been presented here serving multi-purpose security; under-voltage protection, switch-on delay, and regulation.
Description of Overvoltage Protection Circuit
Do not get worried with the overvoltage protection circuit diagram, though it looks complex, the circuit comprises building blocks we have been familiar with. As seen in the left part of the circuit diagram of overvoltage protection, the ladder resistance in conjunction with the modified bridge rectifier circuit has a trim-pot configuration. It guarantees the reliable sequential operations of boosting, low-voltage cut-in, bucking, and high-voltage cut-off.
The maximum limit for input line voltage is 140 V. After that, relay RL2 gets energized and the boosted voltage shows up at the N/O contact RL1 (b) of relay RL1. But, under two conditions, relay RL1 lies in a de-energized condition. First, when the input line voltage is controlled by trim-pot VR1 and is below the 170V threshold voltage level. Second, due to the initial shunting effect of capacitor C6 at the base junction of transistor T2. As the charging capacitor raises its base potential to overcome the reverse bias voltage at its emitter, the transistor T2 also gets enabled. This capacitor along with the resistor R6 determines the duration of delay, (approximately three minutes for given values in the figure).
As a result of the switching action of the transistor, relay RL1 gets energized and boosted voltage appears across the output. The bucking point is controlled by the proper adjustment of VR2 in trim-pot configuration. The output of the system is isolated when the input reaches the prohibitive voltage. The over-voltage sensing is controlled by the trim-pot VR3 to saturate the transistor. It then cuts off relay RL1 via transistors T5 and T6. Due to this, the autotransformer provides no output.
In the overvoltage protection circuit, the resistor R8 is connected to discharge the timing capacitor C6 as relay RL1 energizes. It is done such that when capacitor C6 is connected back to the base junction of transistor T2, on continuation after a power failure or an over-voltage condition, repeatability of on-delay is taken care of.
This circuit of overvoltage protecting appliances can be brought into practice by proper selection. Choosing current ratings for relay contacts (5A or 30A) and autotransformer (500VA or 4000VA, this circuit shown in the figure can be implemented to protect and regulate refrigerators and air-conditioners over a range of 200V to 240V when input voltage varies from 170V to 270V. the circuit offers multi-benefits.
Check out other protecting circuit posted in bestengineeringprojects.com
- High Low Voltage Cutout Circuit
- Auto Cut Circuit for Over and Under
- Single Phasing Preventer Circuit
- Single Phase Preventer with Under/Over Voltage Cutout
PARTS LIST OF OVERVOLTAGE PROTECTION CIRCUIT
| Resistor (all ¼-watt, ± 5% Carbon) |
| R1, R9, R10, R12, R14, R15, R17 = 2.2 KΩ
R2, R13 = 1 KΩ R3 = 3.3 KΩ R4, R5, R7, R16 = 5.6 KΩ R6 = 8.2 KΩ R8 = 100 Ω R11 = 56 KΩ VR1, VR3 = 2.2 KΩ VR2 = 4.7 KΩ |
| Capacitors |
| C1 = 1000 µF, 40V (Electrolytic capacitor)
C2 = 220 µF, 40V (Electrolytic capacitor) C3 = 100 µF, 40V (Electrolytic capacitor) C4 = 10 µF, 25V (Electrolytic capacitor) C5 = 10 µF, 25V (Electrolytic capacitor) |
| Semiconductors |
| T1, T2, T4, T5 = BC547 (Silicon NPN bi-polar junction transistor)
T3, T6 = SK100 (general purpose silicon, medium power PNP transistor) D1 – D8 = 1N4007 (Rectifier Diode) ZD1 = 7.5V zener diode LED1, LED2 = Red LED |
| Miscellaneous |
| X1 = Auto Transformer 1.5A Rating With Taps At 270V, 230V and 190V
RL1 = 6V, 100Ω DPDT Relay RL1 = 6V, 100Ω, SPST Relay |
Bro. do you have code for Automatic college bell management system