For switching 240V, I have used a great product from Altronics… K 2930 opto-isolated mains relay kit. Unfortunately, they no longer make/sell them. This unit also provides a detect feature, so your micro can confirm if the relay is actually on.. which my project uses effectively.
Given they are no longer available, I could post the circuit and construction notes pdf if you want to make one… but not sure if this would violate copyright. I’ll check with Altronics…
Cheers, T.
[EDIT] PS This was a Silicon Chip project…
Update.. I talked to Altronics, they actually are possibly going to make another production run of these (they already have over 100 back-orders!)… So, if it works for you, keep an eye on their website.
I could not find an alternative product that does what this kit does… so will be happy to see it resumed. As a fall-back, Silicon Chip still have a few PCBs (I bought a couple as spares)
My unit has been working reliably for a year, drawing 8.5 Amps
Hope it helps… T
Hi Andrew
Take note of Trevor’s post. This relay module will do as you want.
The Silicon Chip article is in Oct 2018 issue. It is headed “Opto-Isolated Mains Relay”. The printed version of this issue is still available from Silicon Chip
The PCB for this is apparently available from the Silicon Chip store (10 available at this time) Cat no SC4702 for $6.75. PCB only, you would have to populate it.
Parts list
Or if you want to roll your own the PDF version of the PCB pattern is available as a free download ID no 10107181
Cheers Bob
PS: Picture of the finished product is on Altronics web site.
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Hi Bob
Very nice but complex alternative. It provides mains clock frequency back to you which not everyone needs. As well as purchasing the kit, the need for a 24vDC supply for driving the relay away from the Isolated side is quite a cost. The actual relay contacts are rated the same as the product from Core under discussion in this thread. Note that the real safety benefits are that the kit has a pcb that fits into a particular solid plastic box and has a mains fuse. If you take Core’s product, put it in a similar plastic box with a fuse and bring 3 wires +v, IN1 and IN2 (not the GND) out through a decent quality socket, you can have the isolation and safety to drive 2 loads at low cost. Add that resistor you recommended if you like. Of course both the kits and the Core boards are only for people experienced with electronics and mains voltages.
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Hi Andrew
Quite so but something has also come up with respect to the Core board in a previous thread.
Jane said quite rightly that while the RELAY is rated for mains operation THE BOARD IS NOT. Without searching around I think from memory it is something like 30 something VACWhich I think is specified in the description text or spec list. This would accommodate 24VAC watering solenoids but potentially unsafe for a 240VAC pump.
I have been reading Silicon Chip from when it was “Radio and Hobbies” and later publication names nd over the years I have found their designs pretty vigilant when it comes to 240VAC mains requirements and I would be pretty confident that as this is described as an “Opto-Coupled Mains Relay” device the PCB itself would comply to requirements. i am not going to check, I will just believe them.
As for monitoring relay operation:
That is about what you could expect without an extra set of contacts. The Core device has an indicator LED but that one tells you that the relay has been asked to operate, NOT that it has actually done so.. This feedback to the user is also opto isolated so all connections to a controlling device ARE suitably isolated.
Why would you want to do that ?? This part of the circuit is isolated from the outside world as are the mains bits. In fact this is not a bad idea as all these bits are elevated to somewhere near contact potential WRT earth thus minimising any potential problems in that area and the main area of potential risk is the actual board clearances between Opto Coupler input and output.
As with all this type of thing. Keep your fingers well out of it while alive.
If it can be arranged a mains isolating transformer is a good idea for safety. NOT a “Variac” These are Auto Transformers and DO NOT isolate the mains. These with any sort of power rating are a bit expensive I think but depending on projected use could be a worthy investment.
Actually if the environment is any ways harsh operating the whole set up (pump and all) via an isolating transformer might not be such a bad idea. Or change your pump to something like 24V.
Cheers Bob
PS: That SC PCB has a cutout in the board between input and output of the Opto Couplers for further (air gap) isolation
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