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This circuit will automatically switch on several mains-powered "slave" loads when a "master" load is turned on. For example, it will switch on the amplifier and CD player in a stereo system when the receiver is turned on. It works by sensing the current draw of the "master" device through a low value high wattage resistor using a comparator. The output of that comparator then switches on the "slave" relay. The circuit can be built into a power bar, extension cord or power center to provide a convenient set of "smart" outlets that switch on when the master appliance is powered (turn on the computer monitor and the computer, printer and other peripherals come on as well).
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|Sir, this circuit is for 110vac, I want a circuit for same purpose but on 12vdc. I want to control a 12vdc motor which draws 0.8 amps at normal working, when it get jammed it draws 4amps and that time i want to stop it. please revert. thank you sir.|
|I use a 40 amp bridge rectifier on the hot line - with the + & - terminals shorted - gives you a pair of high current diodes in series. Good voltage drop that serves as the diff. input to op amp. I add a small transformer (12 vdc) to remove the problem with high pk voltage and cap issues.|
|Current sensing using a large resistor is wasteful of power and sensing power on the neutral side can cause dangerous conditions. If R1 fails it will leave the load side of the neutral line at the potential of the hot line. A far safer way of sensing current is to use a hall effort sensor such as those provided by Allegro. These sensors provide high voltage isolation and high power level handling due to the fact that they use a magnetic field instead of a resistance to sense the current. I have used these sensors on several projects and they make life much easier. If there is enough interest I could post of example of this circuit using a hall effect sensor.|
|anybody has got this working??|
|There's nothing in this circuit to keep the voltage across C3 from rising above its rated voltage when Q1 is off (i.e. when no current is being drawn by the master load). The capacitor will try to charge up to about 170V (the peak voltage of 120 VAC RMS), but it will eventually fail (and might literally explode!) once the voltage gets significantly above the nominal 35V. A zener or even a resistor in parallel with C3 could solve this problem.|
|The values for 240VAC operation are R2 = 50K, 1W and R6 = 200K, 1W. these are calculated just using Ohms law by keeping the current at same level. if you want to increase the current then increase the wattage with same ratio, i.e doubling current will double the wattage of R2 and R6|
|Not sure this will work. To keep a 12V relay energised would need something like 50mA. So the power dissipated in R6 would be 0.050 * 0.050 * 4700 = 11.75W!|
|1. the value of r2 r6 need to be changed if you are in 240v .what is the value of this resistors. 2. if u need islorate .that is high version, about 15amp.what is rate of resistor.|
|To make a "high power version" capable of sustaining ~15A total (Master + slave peak ), I understand that I need to change the W rating of R1 and also the relay/switch model but anything else ?|
|what should be the value of r2 & r6 when connected to 240vac|
|what is the value of R2 and R6, when we want to use 240v as the supply???urgent...|
|ohms law , would indicate half the resistance , not double and it would be 4 times the wattage(power dissapation---...---...---...G.R.. . . . .|
|Ohm's should tell you that if you double the voltage in, and you want the current to stay the same, double the resistance. This will also double the power dissipation of the resistors.|
|when used at 240V. What need R2 & R6 to be. // Morten|
|The values of R2 and R6 need to be CHANGED if you are in 240V like we are in the UK. Again, what is the value or formula for R2 & R6 please?|
|What is the Values of R2 & R6
(Editor's notes: Try looking at the parts list.)
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