Songle Relay board safety concerns with 240V


I was wanting to get some opinions on the safety of using these types of relay boards for UK 240VAC mains appliances.

Relay boards

I have these installed as part of a DIY heating control system via an esp32. It works really well.

But despite the UL stamp, and the fact they claim to be rated to 10A at 240V, I have also read that the separation from the common contact to the coil is not adequate. So, a potential failure could cause Mains voltage bridging across to the SELV side (5v) resulting in catastrophic failure and a potential fire hazard.

As much as I have enjoyed automating my house, it’s not worth burning my house down for.

Does anyone have any knowledge of these boards and whether they should be used for UK mains voltage.

Thanks in advance

I use those only as a intermediator. The version with WiFi. Just as a interface to get the smart part. They get fed with 24V~ on the contacts, which switches a industrial 240V~ DIN rail contactors. This way they only have to switch very small power and the heavy load is taken by the contactor.

My experience says that long term, these relays are unreliable. Two 4 relay boards that control the lights in my shop just failed a few days after each other.

I had two relays fail such that they wouldn’t open. This is a very dangerous scenario because the contacts are no longer being held tightly together and will exhibit higher resistance. Depending on current draw, they may heat up. And indeed, with about 8A of current draw I ended up with discolouration on the board and the relay case.

The 2nd board failed with only a few mA through one of the relays. Being used as a switch to control a heater at 24VAC. After several years of clicking on and off the contacts became intermittent. Typical failure was inability to make contact. Occasionally would not separate. A minor annoyance in this case because nothing in my shop could be damaged by under/over temperature.

Both these symptoms tells me that these cheap relays have very poor contact coating. Indeed if you look at the cost of a decent relay (Omron, etc.) then a single relay is twice the cost of one of these boards.

I am now in the process of designing my own relay board and replacing everything critical with “Songle” printed on it.

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Take a look at the reviews and q&a here

Thanks for all the replies. It’s interesting reading.

I have used these boards for just over a year now and in terms of reliability I’ve had no issue. But have started to consider the implications of these should a fault occur.

I’m leaning towards the idea of using them as an intermediate relay to switch a 5V supply to a OMRON Relay. But, will do some research on the certification on these relays too.

I find it quite worrying that devices that claim to be certified are available for home DIYers (Like myself) to install on Mains Voltages. Despite our best interests, are we inadvertently introducing fire hazards to our houses?

Once again, thanks for the replies

That is why most countries have certification laws.

Agreed, but certification laws do not prevent the end user buying uncertified products. Unfortunately, the law does not prevent the sale of these goods meaning the consumer can unwittingly buy a product that they think is safe, when infact it is not.
The Songle relay boards are a good example of that. The Songle Relay itself appears to have certification markings on it, but then that is likely just for the Relay and not for the board it’s connected to. So, with the best intentions, you could easily be fooled into thinking it’s safe.

Yeah but most places prohibit connecting uncertified devices to anything but quite low voltage.

You can’t stop a person sticking the end of a metal knife in a socket either.

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Ha ha! Very true!

But at least in the UK we’ve tried to account for idiots by having a shutter mechanism in the socket that requires the Earth Pin to be engaged before the Live Terminal is exposed. But, you can’t stop them all

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Unscrew a light bulb and stick your fingers in then :slight_smile:

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