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I have 5V relay circuit to control 3 220V fluorescent lamps using ESP-01. What I found sometimes the relay get stuck on "ON position" randomly. I have multiple of these around my house. I'm just wondering if this is some circuit design issue or poor quality components or anything else. please share your thoughts.

BOM List:

  • 100nF Capacitor (C1)
  • 10uF Capacitor (C2)
  • 1N4148 (D1)
  • 2.54mm,2×4Double row female (H1)
  • KF1000-2P (J1) (220V Power Source)
  • KF1000-3P (J2)
  • 2N2222 (Q1)
  • 510 Ohm Resistor (R2)
  • SRD-05VDC-SL-C (RLY1)
  • WX-DC12003 (U2) (220V AC to 5V DC)
  • LD1117V33 (U3)

enter image description here enter image description here

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  • \$\begingroup\$ So is the ESP really controlling the relay on so the issue is thay ESP is stuck and keeps relay on, or do the relay contacts just weld together? \$\endgroup\$
    – Justme
    Jan 31, 2022 at 15:38
  • \$\begingroup\$ Not the first to have this problem. This looks like an almost identical question, same relays switching fluorescent lighting. forum.arduino.cc/t/relay-switch-stuck-in-one-state/421401 \$\endgroup\$
    – GodJihyo
    Jan 31, 2022 at 15:48
  • \$\begingroup\$ What is the ballast rating of the relay? (or tungsten rating if the fluorescent ballasts are electronic / no-buzz / no-flicker). \$\endgroup\$ Feb 1, 2022 at 3:12

4 Answers 4

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Your relay is not capable of reliably handing the surge due to the electronic ballast. This tends to be more of a problem at 220VAC compared to 120VAC. It's a design issue- the relay is reliable when used within ratings.

A relay such as this one (the TV-8 version) has a much better chance of working reliably, however the cost, power requirements and size are all higher.

Even a TV-5 rated relay should help- some are available in a compatible package, however the power requirement is typically more like 560mW than 360mW and the contact material will be different (usually AgSnO rather than AgCdO).

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Flourescent lamps tend to have a large inrush current when powered. This can easily cause the contact inside a relay to "weld" stuck, when you power it on.

The easiest solution to this is probably to change the relay to a more powerful one, or to an SSR (Solid-State-Relay).

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  • \$\begingroup\$ Old fluorescents have enormous inductive kick when interrupted at the wrong instant in the AC cycle. New electronic-ballast fluorescents have inrush (like incandescents) to charge the capacitors in their switching power supplies. \$\endgroup\$ Feb 1, 2022 at 3:16
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Tungsten ratings are applicable to modern fluorescents with electronic ballasts, these don't hum or flicker, and start fine when cold. I love 'em. Ballast ratings are applicable to older fluorescents with big inductive transformers inside - easy to know if you have one; they hum!

This relay does have RU Recognition and a spec sheet.

enter image description here

Form C version of these relays isn't permitted over 125VAC at all.
I'll be gracious and assume you have Form A.

No specification of a tungsten rating.

No specification of a ballast rating.

There's an inductive rating, but maximum 120VAC when used that way.

These are simply not fit for purpose.

ObDisclaimer: Installing things like this into houses is foolhardy, and a Code violation. Meaning insurance won't pay and you'll be sued for the burn-down or accident. Do not mess around with AC mains! Unless you are learning to learn the full chapter-and-verse of Codes and standards in your jurisdiction, and pull permits from local authorities where called for. The DIY stack specializes in this. Most places require approved equipment (not mail-order hobby stuff) - UL Listing, BSI kite mark, etc. To switch or dim AC mains, feel free to use the many approved COTS plug-in controls that use WiFi or other protocols.

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An NTC inrush current limiter, in series with the fluorescent lamp, could solve the problem.

Cold resistance of the NTC thermistor would limit the inrush current during initial turn-on.

With the thermistor heating up following continuous flow of current, its resistance would reduce to a very low level that would allow the operating current to flow for normal operation.

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