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switching from generator to main power line when load increases

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Newbie level 6
May 9, 2011
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hi friends! I am locking to create a mechanism for my room some thing like that

when there is less load lets say only fan is running then power should be consumed from the generator. But when load increases (i switch on other devices like lights and computer) ,all the load should be automatically shifted to the main company power line.
And similarly when again load decreases (i switch off my pc and lights) , load automatically shift back to generator.

So basically i wants a circuit or device which can automatically transfer all the load of room from generator to main line when load increases,and transfer it back to generator when load decreases.

plz help me

plz help me.
should i use micro controller,plc or some transfer switch.

Your problem can be solved without any microcontroller by using an AC relay rated to the maximum load power.
This relay can be controlled by the load as you wish. To actuate the relay, you can use a current sensor (you can make it from a small AC transformer by adding one-two turns of a heavy wire to it) which generates a voltage proportional to the current. Then you can use an operational amplifier or a suitable small-size relay driven by this voltage; the output will drive the "main" load switch to get the "stronger" source.

Such problem is an one-hour high-school project. The only problem is finding suitable components. The simpler circuit you make will be more reliable than using a microcontroller...
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