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 :-)

TIA for any ideas.

--
Mike Scott
Harlow, England

Mike,

> Second is something to switch mains safely - a full 13A to run a 3kW
> heater.

You could take a peek at so-called "solid state relais". And as your heater
is a resistive load, it should be no problem to control it with even a
simple one (no zero-pass detection needed, as is needed for inductive
loads).

One thing to check is what your heater pulls in the first seconds or so (up
until its fully heated). That current might well be more than the 13A that
it draws after those first few seconds.

The last thing to check is (ofcourse) the voltage those solid-state relays
"switch on" on. The Pi's 3.3 volt is on the low end, so you will likely
need something to connect it to a higher voltage. A simple open-collector
transistor should work though.

Regards,
Rudy Wieser

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 :-{
>
Try CPC (cpc.farnell.com), but you will probably need some sort of
'driver' between the Pi digital output and the relay coil.
Alternatively, as suggested here, a solid state switch or even an opto
isolator.

> 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 :-)
>
Again CPC will probably have something, but again you'll need
something between the Pi and the 'whatever'.

Are there not ready made relay modules for the Pi?

--
Chris Green
·

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

In article <uv5qtf$te0a$1@dont-email.me>,
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 :-)

I used a solid state relay to control an oven some years back - the
Pi's 3.3v output was good enough to fire the relay although it's LED
was rather dim.

The oven was only 2.2Kw though, but I used a relay rated for something
like 40 amps (that's probably chinese amps, but it never failed in the
5 or so years I used it near daily when I was running my small bakery)

For a 3Kw project (Atmega, not a Pi) I used one of the SparkFun "Beefcake" relays.
I think it did need a 5v signal though. You'll need a driver transitor from a Pi.

https://www.sparkfun.com/products/13815

I built that into a control system in a micro-brewery 'washing machine'
about 5 or 6 years back and its still running today.

Gordon

On 10/04/2024 11:50, Mike Scott 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 :-)
>
> TIA for any ideas.
>

I built my own, and have spare PCBS. It has buffers to drive the relays
, led drivers and a built in mains power supply to run the pi as well.

Only switches 10A at 230V though. However a purely resistive load like a
3KW heater might well be OK

You can use *two* relays to do DPDT. :-)

Serious European made relays cost quite a bit.

Nearly all electronics these days comes ultimately from china.

Looking through my 'usual suspects' supply list it seems that solid
state relays have overtaken big power contactors for switching high
mains current.

What I would try to do is get a board with four low power relays on it,
and use one to drive a big fuck off panel mounted *solid state relay*.
Two more do DPDT.

Won't be cheap though...

--
There’s a mighty big difference between good, sound reasons and reasons
that sound good.

Burton Hillis (William Vaughn, American columnist)

On 10/04/2024 11:50, Mike Scott 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 :-{
>
a bank of 4 SPST relays will do the job if you wire them thoughtfully.
e.g.
https://tinyurl.com/4vw34usb

> 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 :-)
>
I use one of these to control my 3kW immersion heater to soak up excess
solar power.
https://tinyurl.com/mv4az28r

They're reasonably easy to reprogram to run from your own wifi.
e.g. https://www.elektroda.com/rtvforum/topic3912748-30.html

> TIA for any ideas.
>

--
Nev
It causes me a great deal of regret and remorse
that so many people are unable to understand what I write.

On 10/04/2024 14:16, Chris Green wrote:
> 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 :-{
>>
> Try CPC (cpc.farnell.com), but you will probably need some sort of
> 'driver' between the Pi digital output and the relay coil.
> Alternatively, as suggested here, a solid state switch or even an opto
> isolator.
>
>
>> 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 :-)
>>
> Again CPC will probably have something, but again you'll need
> something between the Pi and the 'whatever'.
>
> Are there not ready made relay modules for the Pi?
>
There are, but most are lower power and SPDT.

Which is why I built my own...

BUT although it would be a fun project, even getting hold of big solid
state relays is difficult.

--
"First, find out who are the people you can not criticise. They are your
oppressors."
- George Orwell

On 10/04/2024 11:50, Mike Scott 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 :-)
>

I've got lots of the wireless mains plug/sockets. I felt that my
competence level demanded a good isolation gap ;-).

Generally they have been good. A couple of caveats:

1) Try to get ones with Tasmota pre-installed (Some are flashable, but
this can be difficult). i.e. This gives you control purely in your own
LAN. You don't want to rely on some cloud service in China.

2) I have seen comments about them breaking at high wattage. I have used
one on a 2.4 kW fan heater. It worked fine, but that was for short
periods, not all day, every day.

> TIA for any ideas.
>

On 10/04/2024 20:09, Gordon Henderson wrote:
> In article <uv5qtf$te0a$1@dont-email.me>,
> 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 :-)
>
> I used a solid state relay to control an oven some years back - the
> Pi's 3.3v output was good enough to fire the relay although it's LED
> was rather dim.
>
> The oven was only 2.2Kw though, but I used a relay rated for something
> like 40 amps (that's probably chinese amps, but it never failed in the
> 5 or so years I used it near daily when I was running my small bakery)
>
> For a 3Kw project (Atmega, not a Pi) I used one of the SparkFun "Beefcake" relays.
> I think it did need a 5v signal though. You'll need a driver transitor from a Pi.
>
> https://www.sparkfun.com/products/13815
>

Good find - the relay is available separately at a sane price.

I might try and source some

https://www.aliexpress.com/item/4001135871051.html

Looking to make up some boards with mains relays on and PI Pico Ws and a
mains PSU to go into the backbox of a UK mains socket to act as smart
sockets...

> I built that into a control system in a micro-brewery 'washing machine'
> about 5 or 6 years back and its still running today.
>
That says a lot more than any ali-express recommendation.

> Gordon

--
“The ultimate result of shielding men from the effects of folly is to
fill the world with fools.”

Herbert Spencer

In article <uv5qtf$te0a$1@dont-email.me>, usenet.16
@scottsonline.org.uk.invalid says...
>
> Hi all. Two separate projects which will need a relay of some sort to
> run from a Pi or similar.

:

> 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 :-)

I've used (an earlier model of) these

https://energenie4u.co.uk/catalogue/product/ENER002-2PI

for that purpose (though I've only been switching a few tens of watts, I
*think* these are 3kW rated)

John

On 11/04/2024 21:27, John Aldridge wrote:
> In article <uv5qtf$te0a$1@dont-email.me>, usenet.16
> @scottsonline.org.uk.invalid says...
>>
>> Hi all. Two separate projects which will need a relay of some sort to
>> run from a Pi or similar.
>
> :
>
>> 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 :-)
>
> I've used (an earlier model of) these
>
> https://energenie4u.co.uk/catalogue/product/ENER002-2PI
>
> for that purpose (though I've only been switching a few tens of watts, I
> *think* these are 3kW rated)
>
> John

Thanks all for comments.

The above looks very interesting, and I'd not seen the like before. I
guess it could be persuaded to work with a pico instead.

For the dpdt low voltage stuff, I've opted for the ali-ex offering; if
it blows up, at least it'll not take me with it :-}

Again, thanks to all.

--
Mike Scott
Harlow, England

In article <uv890f$1jse4$1@dont-email.me>,
The Natural Philosopher <tnp@invalid.invalid> wrote:
>BUT although it would be a fun project, even getting hold of big solid
>state relays is difficult.

They're pretty readily available through (for instance) Amazon:

https://amzn.to/449j7O0

Make sure you get one that uses DC input to switch an AC output. I have one
switching the 600W bed heater in a 3D printer. It's controlled by the 12V
bed-heater output on the printer motherboard, but this one should be
directly controllable by a Raspberry Pi GPIO pin. If that proves to not
quite be the case, a transistor and resistor would let you switch the SSR
with 5V instead of 3.3V.

--
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