Help with spec on solid state relay

Hardware
1

Hi All. I’m planning to add a solid state relay to my WLED / ESP32 setup to switch the AC Live to my 5V power supply. To test the setup I’ve been using a basic 5A relay that came in an old Arduino starter kit, and it’s been working well. But, because of the environment my WLED controller is in, I’d prefer to use an SSR to keep noise down compared to the mechanical relay.

The problem I’m running into is specifying the current rating I need for the relay.

  • The system is SK6812 LED strips (total 288 LEDs) theoretically drawing up to 86.5W at 100% RGBW.

  • My 5V PSU (Mean Well LRS-100-5) is listed as 86% efficiency, so some back-of-an-envelope maths suggests an AC draw of around 0.42A@ 240V.

  • Using a basic wall-socket energy monitor seems to confirm that AC power draw at 100% RGBW is around 0.42A.

BUT:

  • The PSU datasheet lists an input AC current of “1.2A/230V (Typ.)”

  • The PSU is physically labelled as input 2.1A (see photo)

  • The PSU datasheet lists an inrush current of 50A/230V

I will always derate the system by selecting a relay that is over-speced by a good 20-30% (minimum), but can anyone give some advice on what current rating I should be looking for in an SSR? Should I be trusting the wall energy meter that suggests my LEDs draw around 0.5A? Or at minimum should I spec for the 2.1A listed on the PSU physical label? Or, do I need to significantly over-spec from this to allow for inrush whenever the lights are powered on?

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2

The safe solution is to meet or exceed the current capacity of the power supply.
For your situation, it seems like ~3A SSR would work fine, last a long time (with the built-in safety margin), tolerate startup current spikes better (than say a 2.1A SSR), and stay worry-free and hands-off.

If you want to be really safe, insert a mechanical relay in front of the SSR, controllable by WLED. Enable the SSR with WLED but add a small time delay. This approach is super safe, has no leakage, prolongs SSR & relay contact life, and buffers the 5V signal to the LED strip to keep things running worry-free for a long time.

There are many ways to meet the needs. Sometimes, it’s as simple as adding well matched capacitors in the right places.

3

Thanks @huggy-d1. Looking at all the SSR options and specs is a little overwhelming. And a little eye-watering to look at the component price when you get up above the 3A rating.

Lots of research for me this weekend. :slight_smile: