Australian Law safe way to externally turn on/off 240v power.  - Page 1
Forum section: electronics / beginners

author: FearTec
author_rank: Regular Contributor
timestamp: May 09, 2020, 01:38:35 am
content: Hi, long time watcher of eevblog but no expert in controlling 240vI have a load of arduino's (Uno, Mega(s)), WeMos Mini D1(s) and Raspberry Pi Zero's and would like to put a 240v fan and a motion sensor over our cars litter box.I recall recall seeing a certified 240v power pack that has the relay inside that does the power switching and has an isolated external input from a micro that fires the relay.I have made dad a 240v home brew controller (heat and cold), but high power scares me.I figure am external plug? would be the safest way to control high voltage. What's the best off the shelf power controlling device that's safe to use in Australia.I can code well (fearby dot com) and the circuit should be OK.Thanks in advance

author: Dubbie
author_rank: Unknown
timestamp: May 09, 2020, 02:05:30 am
content: something like a solid state relay with logic level input is probably the safest way if you are a bit unsure what you are doinghttps://www.jaycar.co.nz/solid-state-relay-5vdc-control-ac-load/p/SY4088You will need to make sure you construct your circuit with appropriate clearances and insulation for the "hot" side.

author: beanflying
author_rank: Super Contributor
timestamp: May 09, 2020, 02:21:50 am
content: You also need to understand there is 'safe' and 'legal' and what happens if it ends badly with insurance should the smoke come out. I won't be trying to dissuade you but just understand playing with mains and in particular unattended mains devices comes with risks.An SSR as mentioned or the quick and dirty way is one of these 30A Relay boardseBay auction: #172347665538I have had one of these on a Level switch running a 250W Pump on an Espresso machine for the last few years. The reason for the 30A is that inductive loads on startup require the contacts to typically be derated you can actually see on the top of the relay a 1/2HP rating while 30Ax240 is obviously way more.

author: FearTec
author_rank: Regular Contributor
timestamp: May 09, 2020, 02:40:02 am
content: Thanks for the replies. I just want a way to detect the cat using the litter box and turning on an extraction fan to outside and maybe a notification (I have motion sensors and micros).Working from home us not nice wiry litter smell. I have a 240v high powered fan (I got from dick smiths years ago that would suck a ping ping ball through a hose.I don't want to splices 240v wires I just want to plug the fan (with its 240v plug) into an off the shelf device. I recall seeing and plug with 2 male breadboard wires into the plug that you could trigger and if would turn off/off the 240v.From memory the plug was pre certified, had the internal micro and relay that detected the external trigger (breadboard wires) from the external micro and work the relay. I'm a software not a hardware nerd.

author: beanflying
author_rank: Super Contributor
timestamp: May 09, 2020, 02:57:22 am
content: If you don't want to break into the mains wiring then look at one of these and change the appropriate switch to be controlled by a sensorhttps://www.jaycar.com.au/remote-controlled-mains-outlet-controller/p/MS6148There is no need for a micro just hack the remote control.

author: themadhippy
author_rank: Super Contributor
timestamp: May 09, 2020, 03:25:22 am
content: save all the messing around,just get a pir controlled socket,something likehttps://smarthome-online.co.uk/product_info.php/smartwares-remote-control-socket-and-indoor-pir-kit-p-61But with Australian connections

author: Cubdriver
author_rank: Unknown
timestamp: May 09, 2020, 03:54:54 am
content: Could you just use a wall wart feeding a 12V computer-type muffin fan, and switch the 12V line between the power supply and the fan with a small relay? That should eliminate any concerns with switching mains voltage...-Pat

author: Brumby
author_rank: Unknown
timestamp: May 09, 2020, 06:01:57 am
content: As I understand it, if you want to operate a home-made device, "legal" in Australia only requires that device to be plugged into a power point through the standard wall plug - so if something goes wrong, it can be quickly disconnected. "Safe" is quite another matter.If you want to sell such a device, however, then that is a whole different ball game (not that you are considering that).You can certainly do your own 240V wiring inside the device, but as has been suggested above bybeanflyingandthemadhippy, there are other options commercially available where you can avoid fiddling with that.

author: wizard69
author_rank: Super Contributor
timestamp: May 10, 2020, 01:18:11 am
content: The best answer here, for somebody afraid of AC power is t take a local industrial electricity course. That is if you can find one locally. These courses are usually aimed at electricians that want to advance beyond house wiring or commercial installations. The focus is on motor controls and the like that usually are not covered in depth in Electrician training. In any event such a course would introduce you to safe electrical control practices and hopefully local regulation.I mention this because I took such a course pretty much fresh out of high school even though that wasn't my employment direction. It has paid off many times in my professional employment, and saved me huge bucks at home. It is an occupation that is closely related to the electronics industry so it really helps with questions like this one. I can't remember the exact number of weeks / months but I think it was 3 months of "night" school at the time. Probably one of the better bucks spent post secondary education.

author: james_s
author_rank: Super Contributor
timestamp: May 10, 2020, 05:32:33 am
content: There's nothing magic or difficult about making a safe mains powered device. Make good solid connections, lay out the wiring cleanly and make sure there's no way the low voltage wiring can come into contact with the mains voltage wiring. Mount it all in a sturdy plastic box and you should be good to go.Or just buy something off the shelf, like the PIR or remote controlled sockets someone else suggested.

author: AVGresponding
author_rank: Super Contributor
timestamp: May 10, 2020, 07:59:27 am
content: Quote from: james_s on May 10, 2020, 05:32:33 amYep, and just to be clear, this does not include margarine tubs (a well known DIY phenomenon amongst sparkies).If you're going to include much in the way of control electronics, it wouldn't be a bad idea to consider opto-isolators to interface between the electronics and the relay coil, belt and braces and all that.Big Clive bangs on about separation, clearance, and creepage regularly on his channel when he tears stuff down, might be worth watching some of his vids to get a nice visual idea what that means.

author: sleemanj
author_rank: Super Contributor
timestamp: May 10, 2020, 09:59:47 am
content: 12v desk fans exist.If your kitty is really stinky then car radiator fans could blow a gale, at pretty high current!No need to deal with mains more than plugging in a power supply.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: May 10, 2020, 11:33:32 am
content: If you have experience with the Wemos D1 mini, then you know the ESP8266.A lot of WiFi remote switches use the ESP8266, as it's probably the cheapest WiFi solution around.The SonOff S20 for example uses an ESP8266 (At least it did in 2017), and in the version I have there are pads for a programming connector on the PCB.But use an external power supply as long as the case is open, because it uses a capacitive dropper and the whole circuit is live when powered from Mains.

author: Cerebus
author_rank: Super Contributor
timestamp: May 10, 2020, 01:11:52 pm
content: Quote from: themadhippy on May 09, 2020, 03:25:22 amQuote from: LaurieEdwards on May 10, 2020, 07:11:22 amThe problem with a commercial PIR is that the good ones go out of their way to tune them so that theydon'trespond to Tiddles/Fang wandering about and triggering them all the time. That might prove problematic for this use case.

author: Brumby
author_rank: Unknown
timestamp: May 10, 2020, 01:16:58 pm
content: Quote from: Cerebus on May 10, 2020, 01:11:52 pmPerhaps they won't respond at normal range - but I suspect the sensor will be a lot closer to the feline's "action station".

author: Syntax Error
author_rank: Frequent Contributor
timestamp: May 10, 2020, 02:06:49 pm
content: At first I thought about suggesting a wireless smart plug, such as those from TP-Link or Philips, in your kitty-pong ventilator. Then I rembered plug-in power sockets with a built-in wide angle PIR. This might be simple, quick, low cost about AU$25, safe AND legal method?There are some effective odour control litters out there, designed for flat dwellers. Just don't make the fan too loud, otherwise the cat will stop using the litter tray and use the front porch instead.

author: FearTec
author_rank: Regular Contributor
timestamp: May 12, 2020, 08:49:50 pm
content: I might give this a go to allow remote control over WiFihttps://youtu.be/O_cgfj6SiTY