Showing posts with label mains. Show all posts
Showing posts with label mains. Show all posts
Thursday, November 6, 2014
Mains Pulser
The pulser is intended to switch the mains voltage on and off at intervals between just under a second and up to 10 minutes. This is useful, for instance, when a mains-operated equipment is to be tested for long periods, or for periodic switching of machinery. Transformer Tr1, the bridge rectifier , and regulator IC1 provide a stable 12V supply rail for IC2 and the relay. The timer is arranged so that the period-determining capacitor can be charged and discharged independently. Four time ranges can be selected by selecting capacitors with the aid of jumpers. Short-circuiting positions 1 and 2 gives the longest time, and short-circuiting none the shortest.
Mains Pulser Circuit diagram:
In the latter case, the 10µF capacitor at pins 2 and 6 of the timer IC determines the time with the relevant resistors. The value of this capacitor may be chosen slightly lower. The two preset potentiometers enable the on and off periods to be set. The 1k resistor in series with one of the presets determines the minimum discharge time. The timer IC switches a relay whose double-pole contacts switch the mains voltage. The LEDs indicate whether the mains voltage is switched through (red) or not (green). The 100mA slow fuse protects the mains transformer and low-voltage circuit. The 4 A medium slow fuse protects the relay against overload.
Wednesday, September 24, 2014
Simple AC Mains Lamp Flasher Circuit
Flashers are useful as visual metronomes, and for decoration and advertising purposes, here we learn how to build one at home. Conventional. thermal flashers make use of a bimetallic strip which alternately heats and cools, thereby breaking and making an electrical contact. Such flashers are uureliabledue to various mechanical problems. glimther, due to sparking at the contacts, their life is limited, and also their flashing rate is not constant. The solidstate electronic flasher described here suffers frdm none of the above disadvantages. A 555 timer IC operated as an astable multivibrator is used to control the on and off times of triac, which in tum controls power to the lamps. The flashing rate is determined by settings on the potentiometer, and is approximately given by
f = 43/(VR1+R2)C flashes/minute
Hence by varying the resistance included through 250K potentiometer (VR1), it is possible to adjust the flashing rate from about 6 flashes/ minute (slow) to about 60 flashes/ · minute (fast). The on and off times are almost equal due to symmetry of the astable circuit. The ST44A triac used here has a 400 PlV, 4-amp rating; With it the load must be restricted to a maximum of 500W. The triac should be clipped to at suitable electrically isolated heatsink. The unit should be assemble inside a plastic or wooden box, and on switching it on, no part of the circuitry, except the rate adjust potentiometer (which must preferably have a plastic knob) should be touched as all parts will be alive. An approximate cost of the electronic ponents used is Rs 100/-
f = 43/(VR1+R2)C flashes/minute
Hence by varying the resistance included through 250K potentiometer (VR1), it is possible to adjust the flashing rate from about 6 flashes/ minute (slow) to about 60 flashes/ · minute (fast). The on and off times are almost equal due to symmetry of the astable circuit. The ST44A triac used here has a 400 PlV, 4-amp rating; With it the load must be restricted to a maximum of 500W. The triac should be clipped to at suitable electrically isolated heatsink. The unit should be assemble inside a plastic or wooden box, and on switching it on, no part of the circuitry, except the rate adjust potentiometer (which must preferably have a plastic knob) should be touched as all parts will be alive. An approximate cost of the electronic ponents used is Rs 100/-
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