About 8 years ago I built a pond controller using a raspberry pi, this worked quite well but after problems with the SD card getting corrupted several times I have decided to redesign using an Arduino. Here's a picture of the original installation from 2016.
A few years in the 8 way relay board burned out and I thought it was just a bad connection, so I replaced it and made sure all connections were tight. I am using 1.5mm solid copper wire, taken from twin and earth mains cable.
Anyway, when I dismantled it all recently I discovered the relay board has burnt again. (amazing it was still working) Here are some pictures...
I suspect the problem is the screw terminals corroding either because they are cheap or dissimilar metals but I would appreciate some input from other people.
For the new version I am going to use a recessed GRP UK meter cupboard, the fused switches I am going to replace with a consumer unit and 3A MCBS.
Does look like the terminals first corroded, and the increased resistance then cause heat, which again increased the resistance a bit and then things started to melt.
I'd say the corrosion is cause by moisture. You should package the relay board inside a waterproof enclosure. Probably a good idea to varnish the back of the PCB as well.
That only works if you keep drying out the gel pack otherwise it just gets saturated with water and stops working.
Maybe a small heater, which could be just a high power resistor on a heatsink.
Those relays are cheap, if you are having problems with them then buy some industrial quality relays, although I suspect you'd need a bigger enclosure.
I did original have a problem with condensation inside the filter house, but the electronics box had a door with a rubber seal. Interesting that the no 8 relay contacts are fine, this is the main pump that is pretty much on 24/7. Whereas the worst ones are the air pumps which switch on/off 4 times a day. Also the PI and my custom PCB have held up really well.
They do appear to be, but once you have them out, you'll have a hard time putting something else through the hole of the PCB. Also i do not believe they are the issue. Seeing you are using solid wire, there can not even be moisture that gets in between the strands. I still maintain that a fully waterproof enclosure is the way to go.
Also it appears that the bottom of the PCB is where the initial issue may have been. Hence my suggestion of the varnishing of the bottom, and probably some clearance from the actual mounting floor rather than screwing it tightly onto would (or plastic. Don't think PE is safe to screw on when using AC ! The static on the surface is enough to make contact)
Another thing is of course that i think the PCB traces are actually to thin for AC mains.
For my relay boards i mask the PCB traces for AC mains, put a layer of solder on and then varnish. You could solder some copper wire between the Screw terminals and the relay. It is only short distance, but the 200W pump in particular is getting quite close to the rating of what i assume a 10A relays
Edit : sorry had it a factor 10 wrong. The total rating is not in question, still it looks like more current flowed around the board than the 1 or 2 A max per channel)
Mainly though, use a IP68 waterproof enclosure and use a separate enclosure for the low-voltage electronics control section.
The relay board was mounted on a 3d printed support, approximately 10mm off the wood, but I will add some conformal coating to the next version as it can't hurt.
I beg to differ on your beg to differ. The 'relays' work fine, it's the connections, operator/designer that is the problem.
Waterproofing is very important. Can’t underestimate that part,,,, sprayfoam, tape, sealant all your holes mating surfaces.
That being said, if you look at the some of the contacts and other equipment,,, there is no signs of corrosion/heat. Most surprisingly, on your largest motor load. Why? .
One thing I do not like about these relays is they do not state if terminals are good for copper/aluminum. They also do not post the HP rating of the contacts/terminals. Its one thing to post an inductive rating BUT they never state an inductive rating @220-240VAC… in my country’s safety certifications, these relays are not allowed to supply a load with a voltage greater than 120VAC.
I think the issue is more to do with a poor relay than anything… as @PerryBebbington has mentioned, sometimes its better to go with an actual “commercial/industrial” product. In total, you have 485-500 watts (2/3 HP) of inductive motor loads passing through this board. Thats a lot for something without a HP rating anywhere in its data sheet
I have to agree with everyone else and say that the relays you are using are not the best for the job.
You could look into solid state relays to cut out the arcing, at least for the 5 240v motors. I saw some CRYDOM on eBay where you could buy 5 for around the $60 which I guess is around 50 pounds UK, I saw cheaper on Amazon they got mixed reviews but might be worth a try. Give them a little separation and mount them on an aluminum plate.
I would be interested to know if others have had good results with this kind of relay.
Clearly this hobby board is unsuitable for this application.
If you're skilled, the terminals could be removed and wired out to a proper terminal strip.
The relay contracts in those relays are very poor quality.
They very often go high resistance causing heat, then failing, then causing the burning you see.
If you continue using those relay boards, you will burn down your home.
Does your insurance company cover fire if you make this kind of apparatus ?
Condensation is tricky - You can seal a perfectly dry container but there is humidity in the air (water vapor in gaseous state). As the temperature goes down you hit the due point (100% relative humidity) and you get condensation.
If the condensation freezes things can get even worse for electronics.
Look at the ratings on the relay plastic enclosure. Do they show a rating for electric motors? No they don't and the OP has discovered why they don't have a rating for motors. How many are controlling motors?
I think the focus on the Relays is not justified. The PCB HASSL burn away, The screw-terminals partly melted. If the issue was with the relays, the damage would be there. The points of a relay generally burn in when there is a lot of switching going on.
Suggest these relay boards only be used with low current resistive loads.
These board relays are okay as interposing relays to a final stage relay or contactor.
Example, Look at KRP type relays (Potter & Brumfield).
These final stage relays should be located near the load, have kickback diodes across their coils, SWC across their contacts, and the load should be fused. Ground fault detection must be considered.
The 'relays' work fine, it's the connections, operator/designer that is the problem.
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