How to shield a live wire at 240V ?

[_q12x_]

I have a electronic board with leds (made by me) that is driving a relay. When that relay is closing it’s contacts, is actually switching the 240V for the light bulb switch in my room. This board is quite long, like 50cm (half a meter). The relay is in the left corner, and the live wires from it goes in behind the board to the hole in the wall for the mains switch. I also have a mild steel sheet behind my board that is grounded. It is shielding the interference of the 50Hz from the live wires from the wall to my sensitive circuit. But even If I have this grounded metal shield behind my board, the live wires from the relay are still affecting my entire circuit board, keeping it ON all the time. If I am disconecting the live wires from the relay, the board is functioning very well. Another IF, is if I disconnect the ground from the metal shield, the circuit board goes nuts. So the shield is doing it's job fine, but only for the live wires inside the wall !!! But not for the wires from the relay to the live switch.
- I want a way to shield these wires !
Thank you !

 

[_q12x_]

I was contemplating your sketch.
I marked with orange boxes, the potential reverberation of the components and wires from the 50Hz.
I was thinking I will need a secondary power supply only for commanding the relay itself, but that vibration can transit also to my first circuit that is commanding the relay and its second power supply. Damn, this is hard. What kind of 50Hz isolation are there? Or better, what a 5kHz or 5GHz isolation is looking like? Im not speaking about capacitors or electronic circuits, but physical isolation, like concrete or rubber or some Faraday cage.... Im out of ideas.

But in the same time, this other guy idea is very logical as well. Since the entire board does not react to the 50Hz if SCM is removed and replaced by the pot, then the entire problem is simply filtering that single module.

 

[marconi]

May I ask first how the resistor and capacitor has been connected in your sensing circuit?

Do you have details on the 5V relay you are using to switch the 220V ac to the lamp? What is the resistance of its coil please? I would like to look up its specification.

It looks like this relay has an internal LED indicator - the blue lamp which sometimes glows dimly. Did the relay have this LED when you bought it or did you fit one? I think that you will find this LED has only started to glow dimly since you added the two diodes. Could you temporarily short these two diodes so that the 5V activation supply is connected directly to the coil please? When you do this does the LED only glow when 5V is applied?

Is this relay wired as in my attachment? A 100nF capacitor will only present a reactance (ac resistance) across the coil of 32 000 Ohms. Not much to have any effect. C needs to be higher to have any noticeable filtering effect on 50Hz voltages appearing in the relay's coil.

I have some more to discuss with you but think it is best to do it in stages.

 

[marconi]

Two diagrams to ponder are attached. On the left when the lamp is off and on the right when the lamp is on. The yellow capacitors indicate mutual capacitance between 5V and 220V ac and the brown ones between 5V and earth (the neutral is earthed so it is at or only a few volts above earth potential).

I will address your #121 but I do not want to give you electrical indigestion!

 

[marconi]

Here is an idea for a second relay in the switch box controlled by the relay connected to the 555. The 100uF and 470
Ohm reduce the induced mains voltage fed back to the 555 circuit and further. The 10uF between base and emitter of the transistor controlling the first relay is more mains filtering. Note how the twisted pair is either connected brtween 0 and 5V or both to 0V. Through the 5V supply decoupling capacitor - the 1000uF I suggested you add- the 0 and 5V are effectively connected together for ac voltages ie 50Hz . This means the pair of wires between the 555 relay and switch box relay will effectively be at the same ac voltage and tied to the 0V rail.

 

[_q12x_]

- Good morning mister @marconi !
May I ask first how the resistor and capacitor has been connected in your sensing circuit?
-The first suggestion that also is in the movie that you've seen, are those 2 components linked to pin5wire.

I've got an update after the movie, where the gray boxes are the same components as before, and the black boxes are the new updates. But this second version, is doing a bit more harm than good. The wings leds are a bit more uncontrolable and random comparative to the 1st version.

Do you have details on the 5V relay you are using to switch the 220V ac to the lamp? What is the resistance of its coil please? I would like to look up its specification.
I already give you this information before, but is ok.
These values are measured by me: Internal coil resistance = 128R; At 5V it draws 40mA.
Usually it stays around 30mA, in my wings circuit.
I didn't searched for its datasheet until now when you asked me for it. Bad from my part. I usually search for IC and transistors, but not so much for other components. I assume too much.
Here is it's file: https://img.ozdisan.com/ETicaret_Dosya/445413_4369639.pdf
and this is how it looks in reality:

It looks like this relay has an internal LED indicator - the blue lamp which sometimes glows dimly. Did the relay have this LED when you bought it or did you fit one?
It does not have anything. I added to it a command circuit, specified in my big circuit diagram.
It is exactly this circuit here:

but made with smd's by miself. That relay in the circuit is this orange relay. The "lamp" you are refering is a smd LED but in it is a super tiny dot of light, probably 1/3 of a mm. Super tiny, I am barely see it with naked eye. The camera lenses makes a halo around it, make it appear bigger than it is.
So the relay does not have any additional circuit on outside of it. Here is how I made it:
(in one of my artpages)

I think that you will find this LED has only started to glow dimly since you added the two diodes.
I think you are right. I didnt thought of it at all. Yes, it very much be because of the diodes I introduced. Very interesting indeed. But why? Is the question. So I am right? some residual is traveling along those wires after all. I wanted to stop the interference with those diodes and it turned out to make a continuous rectified current flow and bright the led. Imagine that. Heh.
Could you temporarily short these two diodes so that the 5V activation supply is connected directly to the coil please?
No need. I remember when the diodes were not mounted and absolutely no light in that led in particularly or any others around that area. I would have spotted them. Because is the way I mount it on the wall, first I link the 220 wires and then mount the board on the wall and secure it. So Im looking directly to that area every time im mounting it.
I marked with a blue square, this blue led and its circuit, here:

When you do this does the LED only glow when 5V is applied?
It only glows when is disconected from 5V and the relay switch contacts are connected to the 220 inside the wall. It is effectively catching some current from those switch contacts of the relay itself. I think is catching an electric field or maybe the vibration from the 50Hz that is influencing the coil in the relay that is acting as an dinamo or transformer perhaps? How wonderful strange, now that I am thinking about it. Haha. No?

Is this relay wired as in my attachment?
This is how it is wired:

It is exactly as in this circuit I draw. I didnt draw this to look pretty. Well, that too. Haha, but I did it in the first place to be as practical and illustrative of the current (updated) circuit I have in use. I am very methodical individual from little age, but hated for that by the majority and kept poor as f*ck, with no life or future whatsoever. Capitalism happened and nothing matters anymore, right? What a sh*t life.

A 100nF capacitor will only present a reactance (ac resistance) across the coil of 32 000 Ohms. Not much to have any effect. C needs to be higher to have any noticeable filtering effect on 50Hz voltages appearing in the relay's coil.
Hmm... thanks for that. I will change it with a larger and electrolytic cap, and update you after that. I have much to learn about filtering with capacitors. But this was a very practical lesson to me.

I have some more to discuss with you, but think it is best to do it in stages.
Best. Thank you so far, you prove a very good friend so far. We will make this thing work. You will see.
I am encouraging myself actually right now. Haha.

 

[_q12x_]

New updates, new progress:

q20210206 Wings Circuit Update by q12a on DeviantArt

www.deviantart.com

 

[marconi]

Good morning. We expect snow and rain over the next few days which means ideal weather to go in my shed. First, thank you for your very clear reports.

1. Sensing Ciruit Module (SCM) - 10kOhms and 100nF low pass filter. The series combination of these two components with pin 5 fed from where the join together is acting as a low pass filter. The question we ask ourselves now is what is the frequency above which signals are attenuated/reduced. A simple calculation is to find the frequency fc when the voltage drop across the resistor is the same as that across the capacitor. Beyond this frequency the capacitor will have a low voltage drop than the resistor has.

We can write down R = Xc = 1/(2 x pi x fc x C); Xc being the reactance or resistance to alternating current of the capacitor at frequency fc. The resistor R has the same resistance to unidirectional or alternating currents.

10000 = 1/(2 x 3 x fc x 100 x 10EXP-9) = 1/(6 x fc x 1 x 10EXP-7) = 10 000 000/(6 x fc) [using 3 for pi]

Re-arranging for fc gives:

fc = 10 000 000/( 10 000 x 6) = 1000/6 = 166Hz

A quick check; Xc = 1/(2 x 3 x 166 x 100 x 10EXP-9) = 1/(1000 x 100 x 10EXP-9) = 1/(1 x 10EXP-4) = 10000 Ohms.

For more on simple RC circuits and alternating currents for low pass and high pass filters see:

What is an RC Circuit ? - Circuit Globe - https://circuitglobe.com/what-is-an-rc-resistor-capacitor-circuit.html

and https://www.electronics-tutorials.ws/filter/filter_2.html

and https://www.electronics-tutorials.ws/filter/filter_3.html

https://www.arrow.com/en/research-and-events/articles/using-capacitors-to-filter-electrical-noise

At a frequency of 166Hz the voltage drop across the resistor or capacitor is 0.707 of the total voltage across both of them. The figure of 0.707 is explained in the links above.

The question we ask ourselves now is whether this cut off frequency is low enough noting that it is a 50Hz signal we want to detect the amplitude of to produce what I termed Vs. First thought is that the harmonics of the 50Hz mains are 100, 150, 200...Hz. At 166Hz, the low pass filter will allow through it significant amounts of signal ip to the 3rd (150) and fourth (200) harmonic. I am minded to reduce fc by increasing C to more strictly concentrate on the 50Hz frequency signal.

I will be starting on my sensing circuit today using the 2N2007 like you have. I must go now. I will be on-line later but cannot say when right now.

I hope the above has been helpful and not been 'teaching you to suck eggs' which means something you already know very well.

 

[_q12x_]

Good luck with the sensing circuit replication.
I am not a math guy, I never was. You on the other hand are more talented than me in this domain.
My primary objective is to find the cause inside the circuit board. Then the problem is half resolved.

 

[marconi]

Back to the SCM and the position of R1 the 100 Ohm resistor. This resistor is in a poor place because when the LED turns on, the current of the LED I1 will flow through R1 and cause the voltage between A and B to drop by about 100 x 0.0005 = 0.1 Volts (assuming 0.5 mA through the LED and 4.7kOhms combination - 2V across the LED and 2.5V across the 4.7k and 0.5 V collector-emitter).

The voltage across 2n2007 circuit will thus fall and so will the source drain current which in turn will reduce the bias to the LED transistor. The voltage collector to emitter will rise a little which rreduces the voltage across the 4700 Ohm which in turn reduces the current through the LED.

The voltage dropped across the 100 Ohm thus rises a little. This now increases the voltage across the 2n2007 so the drain source current rises leading to increased base current into the LED. The little combination of the 2n2007 FET circuit and the 2n3904 BJT oscillate at a frequency dependent on their characteristics and the 10uF and 100Ohm resistor. This is sometimes called 'motor-boating' because when it happens in audio amplifiers it sound like a motor boat engine phut -phut -phut....

Motorboating (electronics) - Wikipedia - https://en.wikipedia.org/wiki/Motorboating_(electronics)#:~:text=In%20electronics%2C%20motorboating%20is%20a,output%20from%20speakers%20or%20earphones.

To avoid this R1 needs to be moved to the left as I have shown in my diagram.

Even then, because the current flowing in the FET circuit is so much smaller than that in the BJT it is likely that even then the large changes in current flows when the LED turns on and off will impact on the biasing and hence current through the FET. By way of analogy it is rather like a mouse (the FET) sleeping in the same bed(circuit board) as an elephant (the BJT)! For this reason in my sensing circuit there will not be an LED indicator located alongside and switched by the 2n2007.

points A and B are top and bottom of the 10uF. I forgot to put them on the diagram.

 

[_q12x_]

Thank you for the correction of the resistor location.
Very interesting the motorboating low frequency. I definitely don't know much about fv in general. And I think I know what you are talking about, now that you mention it. I might hear it in the past, in radio stations or between fv while I was scrolling in old radios. Very good explanation of it also, bravo.
Also very good explanation with the mouse and the elephant. I absolutly didnt think in this terms at all as you put it. In my mind, every transistor is the same size, phisically, but now I understand from you that from power or current flow point of view(pov) of the transistor, they are LIKE having different dimensions.
You didnt mention how your sensing circuit worked so far.
Maybe it will help you more if you know where I get the circuit. It was actually suggested to me by a friend from another forum. So I didnt find it myself alone.
This is the sensing circuit I built on my board, see the video:

 

[_q12x_]

I've fully read the motorboating wiki page and I extracted 2 conclusions to my problem from it:
Here they are:
Just read the red lines markings I made.
1-

2-

Very interesting that you remember this thing and apply it to my problem. As I mentioned already, I imagine that a possible cause and explanation for the disturbance of the SCM is exactly in the moment when the 2 relay output (contact latch) are touching the mains wires. I higly suspect that fv of 50Hz is traveling along the relay wires and its isolation and traveling up on it's 5V supply wires like the explanation from wikipedia for RF.

 

[Dreaded]

I have a electronic board with leds (made by me) that is driving a relay. When that relay is closing it’s contacts, is actually switching the 240V for the light bulb switch in my room. This board is quite long, like 50cm (half a meter). The relay is in the left corner, and the live wires from it goes in behind the board to the hole in the wall for the mains switch. I also have a mild steel sheet behind my board that is grounded. It is shielding the interference of the 50Hz from the live wires from the wall to my sensitive circuit. But even If I have this grounded metal shield behind my board, the live wires from the relay are still affecting my entire circuit board, keeping it ON all the time. If I am disconecting the live wires from the relay, the board is functioning very well. Another IF, is if I disconnect the ground from the metal shield, the circuit board goes nuts. So the shield is doing it's job fine, but only for the live wires inside the wall !!! But not for the wires from the relay to the live switch.
- I want a way to shield these wires !
Thank you !

I need to know what the relay is powering, the amount of current that is flowing through that relay and what else is on the same circuit of the main, it could also be coming through the main from outside. Lets say it is a motor. florescent light, or even a malfunctioning electronic device that is on the same circuit then the interference may be coming from that device. There is only three ways to eliminate the interference. One is capacitive/inductive circuit that cancels the frequency of the interference added to the electronic board, finding the source of the interference and eliminating it by removing the device or isolating it from the circuit. The 50 or 60 cycle is not the problem it is a higher frequency riding on that 50/60 hz that appears to be the problem.

If the power is same only a couple amps then a lost cost device can be purchase to eliminate that interference. But if it is a heavy current then you might have to have real expensive device.

An example is in the industry I work in they had 100s of motors running. We had bad interference in a PLC network and tried using small capacitive/inductive to reduce the interference which worked to an extent but did not work well enough to solve the problem. We ended up finding the source of the interference which happened to be a 50 hp motor with a winding going bad. When we replaced that motor the interference stopped.

Also moving the relay off that board might solve your problem.

 

[marconi]

Good morning. Some very helpful references - thank you. I was gathering together the components yesterday, many of which were well hidden in various drawers. Today is the day to start constructing my SCM.

You are gaining a good understanding of how the mains and parts of your own circuitry are interfering and disrupting the operation of your proximity switch.

The little video was useful. It does seem to work well but we both can see this circuit, when demonstrated, is not near any unearthed mains equipment or mains wiring which would interfere or disrupt its operation, which your is near.

 

[Dreaded]

You may have two problems. One is that your relay is located to close to the electronics board. You can put this relay a couple feet away in its on grounded metal box and stop a lot of the interference. The control wiring for that relay may have to have a filter of some type on it to prevent the interference from traveling back on those control wires.

Since you stated it is a 5vdc suppling you electronics device then I will ask where is the power for that power supply coming from. If it is the same 220 circuit then you need a better power supply or to filter that dc5volt more.
The interference can be coming into your electronics at more then one place.

 

[marconi]

Attached is a picture of the subminiature coaxial cable which arrived yesterday afternoon. I have placed a piece of spaghetti next to the stripped end so you can see how thin it is. I will be using this to shield the wiring between my SCM and the antenna and the rest of the circuitry.