Switch 220V with a microprocessor

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Discussion Overview

The discussion revolves around how to switch a device connected to a 220V power supply using a microprocessor output of 5V. Participants explore various methods and components, including relays, solid-state relays, and contactors, while addressing safety and operational considerations.

Discussion Character

  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant suggests using a single relay on the hot side of the 220V line, noting the need for a transistor to drive the relay due to current limitations of the microprocessor.
  • Another participant recommends solid-state relays (SSR) to avoid arcing and contact corrosion.
  • A different viewpoint proposes using X10 technology as a solution for switching the device.
  • One participant advises using a contactor instead of a relay for high voltage applications, mentioning that a power MOSFET could be sufficient to drive it with a 5V signal.
  • Another participant raises a point about the nature of 220V circuits in the U.S., emphasizing that both sides of the line are hot and suggesting that both should be switched for safety.

Areas of Agreement / Disagreement

Participants present multiple competing views on the best method to switch the device, with no consensus reached on a single approach or component.

Contextual Notes

Participants express varying assumptions about the electrical setup, including the nature of 220V circuits and the necessity of switching both lines. There are also unresolved questions regarding the specific requirements for relays and other components.

Billy_w
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Hello all,

I would like to ask how one can switch on and off a device connected to 220 V using one microprocessor output (5V). I know I should use a relay but can I use only one relay, or a cascade of two relays? Any suggestion for what type of relay I should use?

TIA,
Billy_w
 
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Billy_w said:
Hello all,

I would like to ask how one can switch on and off a device connected to 220 V using one microprocessor output (5V). I know I should use a relay but can I use only one relay, or a cascade of two relays? Any suggestion for what type of relay I should use?

TIA,
Billy_w

One relay on the hot side of the 220V line is sufficent. You will need a transistor to drive the relay though since I doubt the uP's port has enough current capacity to drive it.
 
Look into solid state relays (SSR), one of these will eliminate arcing and the resulting contact corrosion.
 
Might want to look into X10.
All set up to do this.
 
You should probably use a contactor rather than a relay for such high voltages. A simple power MOSFET is all you'd need to drive it with a 5V uP signal.

- Warren
 
Someone mentioned switching the hot side of the 220 volt line. In the U.S. BOTH sides of the line are hot on a 220 volt circuit. There IS no neutral. A clothes dryer for example is a 220 volt device and technically has a neutral because the motor runs on 120 volts. But a 220 volt device such as a water heater has NO neutral. There is a 3rd wire run but it is a ground and is not meant to carry current. In your case it is advisable to switch both of them regardless of the device used to switch.
 

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