AC Contactor Causing LCD Display to Display Gibberish When Energized

Other Hardware Displays
1

Dear Team,
I built an ATS controlled by Arduino with LCD. Whenever the Contactor energizes, sometimes, the LCD would display gibberish or unknown alphabet but the code would still run on the background. I energize the ac-220v contactors through a 4 channel relay module sold online with optocouplers;

Sometimes, the Arduino will freeze and stop running the code (The LCD will freeze).
I have tried insulating the Arduino box with a damper-foam but no effect. What can I do to stop the interference from the ac-contactor on my Arduino?

Note I connected the LCD through an I2C to A4/A5 of Arduino. If i disconnect the ac-contactor coil voltage cable (A1-Live) the Arduino/LCD runs smoothly without any problem provided the contactors does not energize.

2

Go on. You are trying to use an interface designed for Inter-Integrated-Circuits (I2C) in the middle of an Electrical Storm.

I2C is intended to link i.c.s on the same pcb. Not via trailing wires (that act as antennas)

Two solutions:

  1. Screen the connecting cable.
  2. Re-initialise the LCD regularly.

Your relays are optically isolated. I would use separate power supplies. One for Contactor + Relay and one for Arduino.

David.

3

Start by putting a 220 or 470 µF capacitor across the 5 V and ground connections on the display itself (or the I2C backpack).

4

It would be much easier to answer your question if yo posted a schematic, not a frizzy thing showing all power, ground and interconnections. Include mains power source connections for the system as well. Is this a three phase system or single phase. Are the contactors and controls in the same enclosure. More information only help you get an answer that will work.

5

The contactor needs a surge supressor on the coil leads.

6

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