Powering Remote control switch (with Relay) from the same mains supply - Page 1
Forum section: electronics / beginners

author: 4kruby
author_rank: Contributor
timestamp: July 22, 2021, 08:24:11 am
content: Hello,I have never done switching mains voltage. I have worked separately with mains supply and also have a bit of experience in electronics.I have a circuit similar to this one :http://embedded-lab.com/blog/wp-content/uploads/2011/07/IR_RemoteCkt-550x375.jpgNow, the problem is with powering the project. For a simpler solution, the electronics control part can be powered by a battery and the Line wire can be switched using the relay.But what if I want to power the project directly from the mains using a SMPS in between? I have few thoughts (just thoughts) can anyone provide their valuable feedback?I am having in mind to place the circuit (with SMPS) after the main switch (in the switch board). The SMPS will be connected in parallel with the load (and before the load). After the SMPS, the LINE wire will be controlled by the relay. Is there any flaw in this design?Thanks.

author: Manul
author_rank: Super Contributor
timestamp: July 22, 2021, 09:08:42 am
content: You need to connect your SMPS before the relay. In other words, to the point where mains voltage is present all the time. So not in parallel with load. If in doubt, draw a schematic and post it here.

author: 4kruby
author_rank: Contributor
timestamp: July 22, 2021, 10:32:11 am
content: Thanks for your reply.What I meant is like the attached picture.In that the SMPS is connected across the load right? No?

author: Manul
author_rank: Super Contributor
timestamp: July 22, 2021, 04:04:52 pm
content: What I meant is that you obviously don't want to turn off your SMPS when you turn off load with relay, so it should not be in parallel with load. Your schematic is correct, but I would not call such arrangement "parallel with load" or "across the load", because there is a relay in between which can be on or off. Normally, "parallel" or "across" literally means that there is a direct connection.

author: Terry Bites
author_rank: Super Contributor
timestamp: July 23, 2021, 03:45:16 pm
content: You can signal over mains if you want. Just like network over mains. There are loads of ways to do it:https://www.homemade-circuits.com/remote-control-using-mains-power-line-communication/

author: 4kruby
author_rank: Contributor
timestamp: July 27, 2021, 09:39:04 pm
content: Quote from: Manul on July 22, 2021, 04:04:52 pmAh yes. Thank you. I was not considering the relay (I was assuming a direct connection - say when the relay is ON, then it literally is across the load) so it skipped my head.Quote from: Terry Bites on July 23, 2021, 03:45:16 pmThanks for the link. This looks promising to try. I have vaguely heard about PLC. But never ventured into it more than that. This topic looks interesting.

author: perieanuo
author_rank: Frequent Contributor
timestamp: July 28, 2021, 06:12:52 am
content: Quote from: 4kruby on July 22, 2021, 08:24:11 amput the LED in collector T2, that way you also monitor T2the schematic you draw by hand won't work, causality...[edit->i deleted unclear stuff]

author: 4kruby
author_rank: Contributor
timestamp: July 28, 2021, 01:58:05 pm
content: Quote from: perieanuo on July 28, 2021, 06:12:52 amHello,Thanks for your reply. I got your first statement. But I just based my circuit on this example, and I didn't include the indicated LED itselfAnd for the second point, I am not sure what you are trying to suggest. Is it coherent with the pic attached in post #3?Thanks.

author: perieanuo
author_rank: Frequent Contributor
timestamp: July 29, 2021, 06:12:50 am
content: Quote from: 4kruby on July 28, 2021, 01:58:05 pmon second point, yes i was referring to post 3, the schematic you draw by pencil (you didn't mention it was you in fact), that one:Quote from: 4kruby on July 22, 2021, 10:32:11 amwhat i say is simple: it's a cause-effect direct connection: series switch controlled by RELAY can't be closed for simple cause: your smps has no power in order to activate that relay. it's some classic cause-effect negation, well it's a little bit philosophy. the effect cannot happen because the cause (the powered smps) doesn't exists, to put this simplewhat i proposed is to move the switch just before the load, and smps powered directly from mains

author: 4kruby
author_rank: Contributor
timestamp: August 02, 2021, 04:21:51 am
content: Okay,I got you. You wanted the Circuit and SMPS to be always powered as long as there is mains supply. But what I was trying here is, I don't want the circuit to be operational always. I just wanted it to activate only when needed. That is the reason it is placed after the appliance(a light bulb) switch.Basically, I am trying to connect the appliance to the NC contact of the relay. So, the effect desired is, if the remote control is not used, we can normally operate it without the need of the remote. But if needed, the switch needs to be ON and we can control to switchoff and switchon the appliance with remote.Thanks.