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I am making a automatic water level controller for my home,I am new to Electrical Engineering and learning things. I am using a MCU to turn ON/OFF submersible water pumps using some float switch to detect water level in overhead tank. This pump has Start Switch(Normally Open), and stop switch(Normally Closed), connected with some contactor. For my project I want to replace these mechanical switches with Relay(Electromechanical Relay)- 5V 10A, which is controlled using MCU. But I am stuck with how to interface contactor (ON/OFF) mechanism with Relay (NO and NC) contacts. I am planning to use general purpose relay, something like this but of 10A capacity: General purpose capacitor. Here is an block diagram for it. Block Diagram for interfacing Water Pump.Submersible pump here is of 2HP, 230V,Single phase. Can anyone suggest me how to do it or direct me read any such article that helps? Thanks in Advance!

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    \$\begingroup\$ why do you need an MCU? can't you just have the float switch control the pump? that would seem to be simpler and more reliable... \$\endgroup\$ – dandavis Jun 6 '17 at 12:43
  • \$\begingroup\$ Your contactor diagram makes little sense - please provide a link to the data sheet. Regardless, your connection will either produce a disaster or no result, so don't do it. If the contactor is 3-phase, SPST making connections between L and T, there will be no effect. If it is DPDT, with T3 common, there will be no effect. If it is DPDT with either T1 or T2 common, either applying power or activating the contactor will short out your AC and (hopefully) blowing your circuit breaker. So don't do it. \$\endgroup\$ – WhatRoughBeast Jun 6 '17 at 12:46
  • \$\begingroup\$ @dandavis as there will be some other features like buzzer ON/OFF, and may be later I will adding this to complete home automation, so I would need MCU \$\endgroup\$ – Archana Wadhwani Jun 6 '17 at 12:48
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    \$\begingroup\$ @ArchanaWadhwani: I would advise you to build the system in a way that can still be controlled and monitored by an MCU, but that doesn't rely on the MCU for the ever-important main operation. you still can't beat analog for mission-critical work. \$\endgroup\$ – dandavis Jun 6 '17 at 12:50
  • \$\begingroup\$ Have a look at the following image search for ideas. I would also sugegst an off the shelf level controller and then adding a float switch as an alarm input if you want to notify your home automation system. - google.com/… \$\endgroup\$ – KalleMP Jun 6 '17 at 14:28
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If you want to keep the existing manual Start/Stop buttons (highly recommended!), you will need your MCU to control two relays. The Start relay Normally Open contacts should be wired in parallel with the existing Start button, and the Stop relay Normally Closed contact wired in series with the existing Stop button. The MCU should pulse either relay for 100 mS or so (whatever time is required for reliable operation...)

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