Can anyone recommend a relay (or make of relay) please? I'm going to have to build some logic for a central heating system.
Immutable parametrics are:
DIN mount,
6A AC restive (with a good slice of inductive, enough for a CH water pump)
230V contacts and coils. SPST is sufficient Reliable long term. No solid state - I like the simplicity of mechanical.
Quietness is not important. Pluggable is cute but not essential if reliable. Isolation (3mm contact gap) is not required.
It's easy enough to pick a random one from Farnell, but I'm out of touch with who the good makes are and there's so much junk manufactured these days.
I use one of the Finder ranges from CPC/Farnell, first column and a bit on the catalogue page 3470:
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There are 3 ranges 10A SPDT, 16A SPDT, and 8A DPDT. Confusingly, the 10A SPDT needs the 8A DPDT socket, and you parallel up the pins to meet the current rating (although there's only one set of contacts).
I have a pair of DPDT ones controlling a mid-position valve, and I use the SP ones for lighting driven by home automation.
I'd say you'll pay through the nose for DIN rail mounting. I'd be inclined to use a PCB and cheap as chips relays. Not sure if there are any junk relays out there - I've never come across them from a reputable electronics supplier. I'd probably use low voltage coils though if possible. DC makes it easier to 'block' etc with diodes.
All my sources (Z wave relays) will be mains based and I do not fancy my PCB skills avoiding mains flashovers, not to mention the time it would take.
If I do this right I'll only need a few relays and the rest of the unit will be done with Wago Topjob DIN terminals anyway, so it makes sense to go all DIN for this. Easy to alter if needed.
What we'll have is:
Radiator call4heat -> turns CH pump on
Shower room UFH call4heat -> opens that valve + turns on UFH mixer pump
CH pump
Conservatory UFH call4heat -> opens that valve + turns on UFH mixer pump
CH pump
Conservatory Myson air blower call4heat -> powers air blower -> Conservatory UFH call4heat above[1]
[1] Because we want to keep the conservatory floor very lightly heated periodically but the room can remain cool, then flat out over a weekend, but there's also a CH powered air blower for rapid warm up, but that should also force the UFH on for a comfortable floor.
It's really a lot of OR logic, and you are right, diodes would be simpler if I had a DC control circuit anyway.
The exact number of relays depends on how much I assume a random Z Wave "relay" device is actually a relay drive with zero volt output switching.
Me being me, I will probably assume nothing and stick a few more relays in - no telling what a replacement Z Wave device will look like in 5 years - might have gone solid state.
Naturally I will also have a small bank of override switches for a) bleeding the system; b) if it goes t*ts up :)
Cheers - Tim
PS I measured the heat loss of the conservatory over the weekend - more or less 2kW with 20C inside, 0C outside - which is what I'd calculated, so felt quite pleased there (the calc, not the heat loss!) In short, it's fine to use it randomly and UFH will work well for perhaps 2/3 of the year when it's not very cold outside, but in winter, we'll not want the 6 hour warm up time for 3 hours of use here and there, so the hot air blower should make that more reasonable.
Omron where what i used here in the old heating system. Mainly 'cause they met the spec, very similar spec to yours. They have now been repurposed to provide isolation between the new heating system mains side and 1-Wire 8 channel monitoring chip.
Omron MY21N, possibly type 1671Y1 but that might be a batch/serial number. Made in Japan or were... have LED indication of energised coil, passive indication of operated and a manual momentary opearate button. Plugs into a holder that fits DIN rail. They "just work" and have for >10 years switch both mains in the old system or 5 V in the new.
No zone valve(s) to open first, that then switch the pump on when open?
Plus indiactes to me that the orginal source turns everything on at the same time. As I'm sure you are aware the pumps shouldn't run until the valves are open...
The OMRONs I was looking at also have the cool LED indicator plus override tab. Bit wasted here as they'll be in a box and I'll probably have a mimic panel for fun (and debugging). But they are not expensive relays given the specification.
I did not notice a minimum current rating for the contacts (some other makes did carry this datum) - given the coils are a few mA, I ought to check that as I might need a relay driving a relay for some of the logic.
One reason why I'd use low volts for the 'logic' side. Low voltage low current relays are pennies. You could keep the high current mains ones seperate.
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