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From: Theo <theom+news@chiark.greenend.org.uk>
Newsgroups: comp.sys.raspberry-pi
Subject: Re: relay modules?
Date: 10 Apr 2024 16:58:49 +0100 (BST)
Organization: University of Cambridge, England
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Mike Scott <usenet.16@scottsonline.org.uk.invalid> wrote:
> Hi all. Two separate projects which will need a relay of some sort to 
> run from a Pi or similar.
> 
> I'm really looking for something plug-and-go rather than build-your-own 
> (especially item 2 below)
> 
> First is a dpdt relay to switch around 12-20 V at a couple of amps. spdt 
> are easy to come by; the only dpdt ones I've found are on aliexpress, 
> but their longevity is possibly open to question :-{
> 
> Second is something to switch mains safely - a full 13A to run a 3kW 
> heater. I've drawn a blank: best I can think of is to butcher one of 
> those wireless mains switch modules, which would at least provide a good 
> isolation gap :-)

Are you looking for a module to integrate into your own project, or
something with an enclosure (ie a thing with a case and a handy USB cable or
whatever?)

Relay boards for the Pi, either by GPIO or USB, are common.  Look on ebay or
the usual Pi retailers (PiHut, Pimoroni, Adafruit, etc).  For DPDT look for
'reverse polarity switch'.

If you want something packaged then that's a bit harder, especially if you
want an enclosure with mains inside.  Those wireless switch modules are nice
in that they provide all the isolation for you - just RF goes in.

Another option is a 'fire alarm relay' which come in a nice thing to fit a
wall mounted mains backbox.  Often the coil voltage is 12V or 24V
though, and maybe only 5A switching current.

If you want to switch 3kW, I would look at either a solid-state relay (I
would recommend a known brand like Crydom, since the Chinese ones often lie
about current capacity) or a contactor.  A DIN rail enclosure plus a DIN
mount contactor solves the isolation problems.

Theo