Arduino Relay Board

Sylvia Else wrote: ===============

** So the relay is rated for 230/240V AC? ** That is not enough clearance for 240V.

Be fine for 12VDC or AC though.

** Then don't.

....... Phil

Yes.

Sylvia.

I imagine you have something like Trading Standards with which you could raise a CE accreditation query. However it is a bit niche and they may reasonably give priority to verifying (e.g.) childs' toys...

gap 240v to LVDC should be 5mm ?

It's that self-certification thing, innit? In Principle anyone can slap a CE sign on a board. Consequences will only arise if somone complains.

Are you sure that the label is the EU conformity label and not the very similar-looking China Export label.

In principle, the EU CE label is a declaration by the manufacturer that the product conforms to the relevant safety requirements. It is up to the conscience of the manufacturer how well this is done.

You beat me to it.

I was going to say that the CE was probably the China Export instead of the EU CE for safety.

torsdag den 3. februar 2022 kl. 16.33.20 UTC+1 skrev Ralph Mowery:

afaik the "China Export" is just an urban myth, in reality it was just someone that didn't follow the spec for how the CE mark should look

If the ckt connected to the small race is truly isolated from mains gnd then the impedance is extremely high and any arc over cannot deliver any energy to speak of.

Sylvia Else snipped-for-privacy@email.invalid wrote in news: snipped-for-privacy@mid.individual.net:

It runs on DC, right? Not an AC device form the looks and size of it. So "isolation" is all about "line isolation" on the AC side of a system.

That appears to be DC driven, but you would isolate at the AC side of the DC supply, not at that PCB assy. Likely a dongle type, plastic encapsulated fully isolated wall wart. Many do not even have a transformer in them nowadays.

And a diode across the relay drive circuit will quell any back EMF. For most relays. You could use an SSR. They make those pretty small form factor these days too.

Do they make any voltage claims for this module?

As you say the diode trace goes close to the contact trace but they have about 4mm clearance between the exposed conductore. They've put solder mask and silk screen on the traces, I guess they're trying to call that silkscreen suplimental insulation, but it seems to stop short of where it should be. Maybe they are just apeing someone elses design which had better layout.

More worrying, the exposed relay common contact pin is close to header pin 1, it looks like less than 2mm clearance there.

Some designers will route a groove around the common pin to give better isolation between the coil and the contacts, but I much prefer relays that have the coil terminals at one end and the contacts at the other end.

This is the product page:

You may note that the picture doesn't match. The data sheet provided is for the relay itself, rather than the module.

At the time of posting I hadn't realised where the common pin was. As you've observed, it represents another isolation concern.

Sylvia.

the picture is a different module, the diode is smd and there's a cutout around the common pin

I hadn't noticed the cut-out, but yes, it's different. There's a pale grey "Image is for illustrative purposes only" caveat underneath. A downside of the illustrated module though is that it has no mounting holes. Still, it makes the point that the job could have been done properly by someone who knows what they're doing.

Sylvia.

I decided to sacrifice the relay itself to examine its construction:

If the coil wire were to break off its pin there, it could get horribly close to the mains connected (brass?) plate.

I salvaged four of these from my dead UPS:

They've clearly been designed so that there's no credible failure mode that would connect the load to the coil.

Sylvia.

Sylvia Else snipped-for-privacy@email.invalid wrote in news: snipped-for-privacy@mid.individual.net:

That is a pretty sad assembly. Hand tweaked lead positions after soldering too, I'm sure.

Those are nice industry pro grade parts.

And? The cheapest of relays are cheapy made. If you need safety look up intrinsically safe relays, and no don't then try buy buy fakes ones from amazon or alibaba.

Let me guess, one Omron relay costs the same as 5 chinese house-special relay boards.

I don't know about the law where you live, but where I am, products are required to be safe, and the requirement is not relaxed just because the product is cheap.

Sylvia.