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schematic

simulate this circuit – Schematic created using CircuitLab

I am trying to control an LED bulb using a solid-state relay, the problem is, the bulb is flickering from time to time, if it is turned on it momentarily turns off then back on and vice versa.

I am using Nodemcu8266 to control 5v relay module and the relay controls 220v LED bulb.

I have googled it, and found that I need an RC snubber circuit to absorb that surge, I have used 100nf tantalum capacitor and 220ohm 1\4 watt resistor, but when I turn the relay off bulb glows in low brightness so current is flowing through this RC circuit.

How I can fix this flowing?

How to choose the right values for RC snubber circuit? this is the relay module I am using

This is the relay module I am using, from DC side I connect 5v, GND and signal wire from digital pin of Nodemcu8266

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  • \$\begingroup\$ Please show a circuit, you can edit the question and draw one with the tool. \$\endgroup\$
    – Voltage Spike ♦
    Commented Feb 24, 2023 at 23:52
  • \$\begingroup\$ Tantalum capacitors are polar, they are unsuitable for this role. The capacitor also needs to be rated for your peak voltage, so 350V at least. But I'm unconvinced that a snubber is really what you need here. It sounds like there's something else going on with your SSR or the drive from your ESP8266. What specific SSR are you using? How is the ESP8266 connected to that SSR? Please also edit to add in your code. \$\endgroup\$
    – Polynomial
    Commented Feb 25, 2023 at 0:41
  • \$\begingroup\$ SSR may have snubber inside. \$\endgroup\$
    – user263983
    Commented Feb 25, 2023 at 0:59
  • \$\begingroup\$ Please furnish details of the SSR module. \$\endgroup\$
    – vu2nan
    Commented Feb 25, 2023 at 4:49

1 Answer 1

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Snubber circuits are generally only needed when you are switching highly inductive loads (such as motors, or relay coils); I suspect the inductance of your LED bulb is quite low, so you don't need a snubber.

The solid-state relay (SSR) data sheet specifies a minimum load of 0.1 amps. The actual load presented by your LED bulb will be complex (since it contains a power converter to step down the mains voltage), but it may well draw less than than 0.1A, or maybe the pulsed nature of that current makes it unsuitable for switching with an SSR.

The simplest solution would be to replace the SSR with a conventional relay, which won't care what waveform it is switching.

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  • \$\begingroup\$ My problem I guess not with LED bulb itself as a load, in normal case everything works perfectly but I tested it while my washing machine is working, every time it starts / stops rotation my LED blinks whether it turned on or off, the same behavior happens with conventional relay, and I need to understand what is going on? \$\endgroup\$
    – Ahmed_4EGA
    Commented Feb 25, 2023 at 22:18
  • \$\begingroup\$ According to the data sheet, the SSR needs at least 5 mA to switch on, and it is impossible for that amount of current to be generated in the SSR inputs when your washing machine switches on or off. So the problem must be in the Nodemcu device (or its power supply), or the connections to the SSR. \$\endgroup\$
    – jayben
    Commented Feb 26, 2023 at 8:59
  • \$\begingroup\$ The relay is active low trigger, maybe the problem with floating signal (not pulled high) so it is distracted by EM generated noise? \$\endgroup\$
    – Ahmed_4EGA
    Commented Feb 26, 2023 at 12:23

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