A question of feasibility - no neutral wire

Reply

  #1  
Old 01-31-19, 03:20 AM
Member
Thread Starter
Join Date: Jan 2019
Location: Israel
Posts: 3
Received 0 Votes on 0 Posts
Lightbulb A question of feasibility - no neutral wire

Hi,,
I'm wondering whetther it is possible to design a circuit that will be able to opertae somehow with only a phase wire connected with no neutral.
The pupose of the circuit (a PCB/ non-linear components can be involved) is to switch an outlet, while the circuit will be connected only to a signle hot wire - no grounding / neutral connected.
I had a conversation with a friend of my - an electrical engineer who suggested to use a diode and determine a 0.7v potential.

Here is an illustrasion:



P.S, the circuit is be controlled by RF / Wifi modules, the querstion is raelted to the power supply for these.
Thanks.
 

Last edited by NCinov; 01-31-19 at 04:12 AM.
Sponsored Links
  #2  
Old 01-31-19, 06:10 AM
Member
Join Date: Sep 2002
Location: welland ontario
Posts: 7,012
Received 110 Votes on 100 Posts
It is not possible to operate any circuit AC or DC with only a single wire.
 
  #3  
Old 01-31-19, 06:33 AM
Member
Join Date: Nov 2015
Posts: 1,281
Received 22 Votes on 20 Posts
I had a conversation with a friend of my - an electrical engineer who suggested to use a diode and determine a 0.7v potential.
That only works when there is current flowing through the wire. Meaning the switch has to be on and the device on the other side has to be powered up all the time.
This completely defeats purpose of the module you are trying to build.

There are some motion sensor switches that does not use neutral. It gets neutral from ground wire, but this works because it is very low current device. I would not try that with any RF or Wifi modules.

One thing you can do is place RF or Wifi switch at the outlet or the device and require existing switch loop to supply hot and neutral instead.
Then you can install a controller at where switch used to be.
 
  #4  
Old 01-31-19, 12:44 PM
Forum Topic Moderator
Join Date: Feb 2005
Location: Near Lansing, Michigan
Posts: 10,944
Received 42 Votes on 40 Posts
There is nothing I can think of practical use. You could make some sort of physics experiment that bleeds charge out into the atmosphere or emits RF radiation which creates a very, very low power circuit from the charged wire back to the earth. But neither of these is sufficient for any practical purpose other than demonstrating scientific principles.

To do any sort of useful work, a two-wire circuit is required.
 
  #5  
Old 01-31-19, 12:46 PM
Member
Thread Starter
Join Date: Jan 2019
Location: Israel
Posts: 3
Received 0 Votes on 0 Posts
Thanks for supporting.
One thing you can do is place RF or Wifi switch at the outlet or the device and require existing switch loop to supply hot and neutral instead.
Then you can install a controller at where switch used to be.
If I understand right, you're saying to use the outlet socket (which includes 3 wires) for a RF/wifi module + switch?
in this case it can be a local solution but not a versatile.
I'm trying to figure out how manufacutrers offer smart switches with no neutral or battery required.
An example is Lutron Caseta
http://www.casetawireless.com


 
  #6  
Old 01-31-19, 12:49 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Northern NJ - USA
Posts: 54,166
Received 475 Votes on 445 Posts
Devices that operate with no neutral is not a new idea. It's called power stealing. As the load draws power thru the device..... a small battery or capacitor charges. That small charge runs the electronics. This type of device typically requires a minimum load of 40 watts connected. That usually eliminates using that type of device with LED lights.

The problem with wifi devices is that they require more power to operate then they can steal. The small charge is enough to run the on/off circuit but not to keep the wifi link active.

I saw your Lutron link. Yes.... those also use power stealing and require a minimum of 25 watts of connected load. They've managed to reduce the wifi load enough to make it work.
Lutron Caseta specs (pdf)
 
  #7  
Old 01-31-19, 01:40 PM
Member
Thread Starter
Join Date: Jan 2019
Location: Israel
Posts: 3
Received 0 Votes on 0 Posts
They've managed to reduce the wifi load enough to make it work.
So the wifi link that is available on the device became weaker due to low power stealing ability, therefore a hub/gateway is required? To make the link physically closer?

also I'll appreciate if you'll attach more information about this power stealing method.
 
  #8  
Old 01-31-19, 01:55 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Northern NJ - USA
Posts: 54,166
Received 475 Votes on 445 Posts
I've used those Lutron devices before but just for close wireless use. I've never connected them into a hub or router.

Power stealing is putting a small battery or high storage capacitor in series with the load. When the switch is off..... it charges. When the switch is turned on..... the device is no longer charging. There is just enough left to turn the light back off. In the case of a wifi or wireless link..... the unit needs to be in constant contact with the hub or listening for a wireless command. That requires power. In order to be able to run a wireless link on a system like this the current must be very low and I would think of very low transmit power.

The circuit Lutron uses will be proprietary as it is their highly guarded design.
 
  #9  
Old 01-31-19, 02:22 PM
Member
Join Date: Oct 2005
Location: USA
Posts: 1,432
Received 13 Votes on 13 Posts
I see two wires in the drawing. I made a radio when I was 11, it had a short antenna and a connection to a window screen. It drove a set of sensitive headphones, with no other energy source.

Not seeing a huge issue charging a supercap or even a Li cell and doing lots of things with it. Wireless or otherwise. The trick is allowing a tiny current when load is OFF.
 
  #10  
Old 01-31-19, 02:24 PM
Member
Join Date: Sep 2002
Location: welland ontario
Posts: 7,012
Received 110 Votes on 100 Posts
I'm trying to figure out how manufacutrers offer smart switches with no neutral or battery required.
Ok now we know what you are asking. Those devices do not operate on a single wire. They have a line and a load that continues on to the neutral through the load device, like the light bulb. It flows a tiny current through the load even when it is off. That is why CFL and LED often blink when off with these devices. If you were to remove all the loads from them, they would not function.

To summarize, they have neutral connection through the load.
 
Reply

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread
 
Ask a Question
Question Title:
Description:
Your question will be posted in: