Has anyone found a nice small mains relay (230V coil, and 230V switching). The smaller the better (switched load is tiny - I need for the logic rather than the switching capacity). Either solder lug, or with the option of a mounting base. SPDT would be fine.
I needed one in my C/H wiring, got a maplin one, bought a spare at the time, have never needed it in ~10 years, looks like this one, no guarantee they've not substituted a different manufacturer in the meantime of course ...
Yup I saw that, and to be fair it would do, although I was hoping for something small enough that it could be lost in the back of a normal depth of back box...
I thought I'd have something like that in a junkbox, but they're all low v coils. Rapid do a fair range.
NT
Yup same here - I am sure I had a sub miniature one somewhere that was only about 1 cm on each axis - its been knocking about for years, and now I finally need it...
(although that was probably a LV coil as well)
you can certianly get mains/mains ones at electrical wholesalers, but they call them contactors.
They tend to be quite large DIN mounting things though...
I have a couple of mains ones providing feedback into home automation. They are not completely reliable, because the fraction of a milliamp signal current through the contacts is not enough to keep (what are designed as mains voltage contacts) clean. This can be an issue when using contacts designed for mains voltage with 5V and next to no current - ideally you would use different contact metals for that.
One that has been reliable for 13 years now is a Finder one which comes from CPC. (It also has mains contacts, but so far, they have worked OK at 5V and almost no current.)
I've never seen a small relay with a mains coil. Could it be it's easy enough to do with a low volts one - but not mains?
See recent thread about relays? "DIN relay recommendation (make at least)" Omron MY21. I used them for mains switching in the old system for ten year in the new system they are just isolation between the system mains side and low voltage monitoring (1-Wire). They just work, roughly 3/4" wide 1" high and 1 1/4" deep. Fits DIN rail socket or the blade terminals look as if they might accept 1/8" spades.
They are rather thin on the ground these days. ISTR last time needing to use a nominal 110V relay coil with a series resistor when replacing a failed UK mains relay of somewhat larger size than you want.
Closest minature I can see would be something on 60VDC with a bridge rectifier and series resistor to suit. eg
Depends how much messing about you can live with.
Depends on what you call small, the one I used is roughly the size of a Tic-Tac box ...
I have arranged the wiring with a three pole fan isolator switch mounted high on the wall near the fan. I have taken a 3&E feed to it from the light fitting so that I have L, N, and switched Live.
From the switch I then have a cable out to the humidistat and also one to the fan. I was using the switch position to do all the interconnects, so it would have been nice to have a tiny relay one could lob into the dry lining backbox of the switch...
Since it looks like I will need to go for a larger relay, I will probably mount it on the back of the dry lining box that the switch is in (the wall cavity its in, is plenty deep enough). That way its easy enough to get to in the future.
Right. Smallest ones I have here have the coil on its own measuring 25mm in diameter and 15mm deep.
My thinking was that there will be a lower limit for the winding wire in terms of the insulation at 240v. As well as obviously contact size and spacing.
I have a similar problem with switching small loads. I plan to have a fancy continental style boiler installed in the Spring, but to call for DHW when using weather compensation you need to simulate the NTC thermistor that is built in to continental style hot water cylinders.
I want to stick with traditional S-plan controls, so have ordered the Finder 40.52.8.230.5000 (PCB Mount Relay 230VAC 8A DPDT AgNi + Au contacts) from Rapid, with the Finder 95.75SMA DIN rail socket to interface mains switching with the low-voltage boiler input.
Finder write in their general technical information: "With 2 gold contacts in parallel, it is possible to switch 1 mW, 0.1 V / 1 mA." I don't know what current a boiler controller sends through a thermistor
-- it cannot be high to limit self-heating of the thermistor. I do hope I will get away with it!
AgNi + Au contacts are nearly universal, but beware the tale of woe about the submarine that failed to dive:
Regards,
Melvin A
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