Power supplying a circuit ith just live line (Vcc) without neutral line (GND)

[PersianMan]

I saw a smart switch with just live line as input.
There was any battery in the circuit and the body of switch was completely isolated from the wall.
The input voltage of switch is 220vAC and there was no transformer. This switch can be controllable remotely by RF.
How can i design a circuit for controlling a relay with just live line of 220vAC?
Can we make a dummy GND for electronic circuit?

 

[Hero999]

It's more likely it was powered by the mains. When it's off it's connected between the live and neutral, when it's on, it might drop a volt or two and rob the power from the load, more likely it uses bootstrapping or phase control to take the power required for the receiver.

Another option is to just use a passive receiver and take the power from the remote but I don't think it's likely.

 

[PersianMan]

Dear Hero999,
Thanks for your reply.
1. You said: "When it's off it's connected between the live and neutral", But as i said there isn't any neutral line. Although when the switch ON, You are right.
2. The switch can work manually by push a button for every way too, e.g. two push button for 2-way switch. So our idea not right when you said: "Another option is to just use a passive receiver and take the power from the remote."

Is it possible to make a dummy ground in a 5v circuit?

 

[Hero999]

Duplicate post removed.

 

[Hero999]

No, a circuit needs both a line and return to work, otherwise it wouldn't be a complete circuit.

The switch is in series with a load which will be connected to neutral.

The switch is electronic and pushing the buttons turns a transistor or TRIAC on and off.

Awhile ago I designed a 7555 lamp dimmer which is connected in series with a load.

The 555 could be replaced with a microcontroller, a low dropout regulator and an RF module. The lamp can't be left on permanently (100% duty cycle) otherwise the the voltage on C1 will drop too low for the 555 (or microcontroller) to work so it will would to be turned off for 1ms every second, depending on the current and voltage.

**broken link removed**
Two wire dimmer

A similar thing could be done using mains electricity, I'll post a schematic, if you're interested.

 

[Wade Hassler]

I saw a smart switch with just live line as input.
There was any battery in the circuit and the body of switch was completely isolated from the wall.
The input voltage of switch is 220vAC and there was no transformer. This switch can be controllable remotely by RF.
How can i design a circuit for controlling a relay with just live line of 220vAC?
Can we make a dummy GND for electronic circuit?

See here how a dimmer-switch works
Light dimmer circuits
This shows how to dim a light without a neutral: the lamp is never completely on- enough time is left over for the triac to be triggered.

If a small rectifier/capacitor are added to the circuit, a radio can be powered.

There is *almost* always a building ground ('grounding' conductor) wire in the junction box, even when there is no neutral ('grounded' conductor). So, if you trust your electrical system completely, you could use the building ground as a neutral. But it's a bad(illegal?) bet.

Wade Hassler

 

[PersianMan]

Dear Friends,
I think it's not possible to use this idea. It's completely different.

My idea: Using the line connected to lamp as neutral line for Electronic circuit. I think it's better if we use a capacitor in series as attached figure.

 

[Wade Hassler]

Dear Friends,
I think it's not possible to use this idea. It's completely different.

My idea: Using the line connected to lamp as neutral line for Electronic circuit. I think it's better if we use a capacitor in series as attached figure.

View attachment 41020

I don't think you're quite there yet: when the switch closes, the power supply has no input. Perhaps a very-low-current circuit, combined with a largish energy-storage capacitor, would do it.

 

[Hero999]

That won't work.

Where do you get the 24VDC from?

If it's via the capacitor, i.e. a transformerless power supply, it'll only work when the switch is open.

Here's an idea.

Tr1 can't be on for too long, otherwise there won't be enough power for the MCU.

R3 is a current limiting resistor enabling the MCU to perform zero crossing (when Tr1 is off anyway).

Tr1 could be an SCR but it has the disadvantage of having to wait until the end of the cycle to turn off.

The voltage on C2 could be monitored so Tr1 is shut off if it drops below something like 7V, in order to preserve the 5V supply.

 

[PersianMan]

Dear Wade Hasseler,
My idea was completely wrong. After charging the capacitor in series with a diode (1N4007), The electronic circuit will be OFF.

DearHero999,
Why do you use TRIAC? I don't need to dimmer.
If D1 is Zener type, Why did you add a Regulator after that?
This idea has a small problem, When the Relay is Open, The lamp is in the 5v closed circuit and so it's not power saving idea. Maybe the lamp will be ON with a low light.

 

[Hero999]

1) You can use a TRIAC as a switch - it doesn't have to be used as a dimmer. Incidentally look up phase control dimming and you'll see that the TRIAC is being used as a switch.

2) I thought about using a 5.1V zener but zeners aren't very good at really low bias currents so I decided to use an 18V zener to pre-regulate the voltage to another 5V regulator. The regulator must be a low quiescent current type. The 5V part of the circuit is only good for a few mA, it's a very low powered circuit

3) What do you mean? Are you talking about my circuit or yours? There is no relay in my circuit. This is not supposed to be a power saving idea, it will draw a small current when the switch is off but it won't be enough to light a bulb, even very dimly.

 

[PersianMan]

Dear friend - Hero999,
Thanks for your comments.
1. OK! the dimmer can be usable as switch and dimmer. but this switch is within the power supply circuit. How can it turn ON and OFF the Lamp (220vAC circuit)? We need to a Relay yet?
Could you please about the functionof TRIAc in the circuit?
2. If we use TRIAC as switch or dimmer we can use a high power lamp!?
3. Very good to use the Zener Diode as pre-regulator.

 

[Hero999]

There is no need for a relay.

1) Turning on Tr1 will short circuit the bridge rectifier so the only thing that will limit the load is the lamp in series with the AC side. When Tr1 is on, the circuit is powered by C1. Tr1 can't be left on for too long, otherwise the charge on C1 will run out so Tr1 needs to be turned off for a short period of time every cycle to recharge C1.

2) The circuit can be used as a high powered lamp dimmer or a switch.

I've never done this before, it's just an idea, you might hve to change a few of the component values so it can do what you want. C1 must be rated to 400V and R2 must be a 3W power resistor.

 

[badbeat]

has anyone here made any success with Hero999 idea? or does anyone have a working solution? hope u guys are still here to help....buzzzzzzz

 

[Mr RB]

No need to revive an old thread, this is already being covered in this current thread;
https://www.electro-tech-online.com...ess-power-supply-with-only-live-wire.134152/?

 

[MrAl]

Hello,

Wow this is an old thread. Interesting ideas like the ones we came up with. But what would be interesting would be if someone would simply throw a scope on a store bought cheapy dimmer and see if it holds back part of the line waveform. That would appear to power the bulb with not a sine wave, but the very first sections of the sine wave would be missing so it would shoot up suddenly, then continue as the normal sine wave. That would tell us if they are doing it this way too. I would bet they are, otherwise they might have to use a current transformer for the times when the triac is turned on.

 

[badbeat]

Many thanks to MrRB for being a good Samaritan by directing us to the current thread. I shall look into it....right away!