Author Topic: Noise injection for magnetic in-wall mains wire tracing  (Read 256 times)

0 Members and 1 Guest are viewing this topic.

Offline Axk

  • Regular Contributor
  • *
  • Posts: 185
  • Country: by
Noise injection for magnetic in-wall mains wire tracing
« on: October 18, 2020, 07:11:28 pm »
I'm thinking about something similar to what this guy made:


but using a dedicated "noise-generator" instead of the CFL bulb.

Is 10mA peak current at 100 KHz enough for this?
I'm thinking of the following design using a 555 timer, an NPN transistor and a 5W power resistor (I will also add an input fuse) with 10mA peak current (~ 3mA average):



It works in the simulation and the power dissipation on the power resistor is around 1W and 300mW on the 300K resistor so I think it should work.
My only concern is if the current is enough, but I suppose at such high frequencies it should be enough to pick up with a 15mH radial inductor (the largest value my local supplier has) and an opamp?

I think this should work better than electric-field based capacitive sensors in my case because I have some old wiring which presumably has places with bad insulation so I have entire walls that trigger my capacitive sensor.

What do you think?
« Last Edit: October 18, 2020, 07:16:34 pm by Axk »
 

Offline Axk

  • Regular Contributor
  • *
  • Posts: 185
  • Country: by
Re: Noise injection for magnetic in-wall mains wire tracing
« Reply #1 on: October 18, 2020, 07:21:30 pm »
Just changed the NPN to a real transistor model in the simulation and now it doesn't switch off.
Have to figure out why.
Guess it could be some sort of a leakage current that's always there...
 

Offline Axk

  • Regular Contributor
  • *
  • Posts: 185
  • Country: by
Re: Noise injection for magnetic in-wall mains wire tracing
« Reply #2 on: October 18, 2020, 07:32:21 pm »
Thinking more about it I guess I need a faster transistor.
 

Offline Benta

  • Super Contributor
  • ***
  • Posts: 2629
  • Country: de
Re: Noise injection for magnetic in-wall mains wire tracing
« Reply #3 on: October 18, 2020, 07:43:39 pm »
I think you need to learn some basic physics first.

Youtube (or whatever) is a wonderful playing ground for kooks with no clue.

Inductive sensing of current running through a wire that's perpendicular to the end of a coil won't fly. What this guy's actually sensing is capacitive coupling into the windings of the coil.

That can be done done much easier by just holding an electrode close to the wire and amplifying the signal. Which, by the way, is how pretty much all "cable finders" work. You'll even find them integrated into hand drills etc. and they work fine.

Your bad insulation would give you other problems, such as getting a shock when touching the wall. In that case you have bigger problems.

 
The following users thanked this post: Axk

Offline Axk

  • Regular Contributor
  • *
  • Posts: 185
  • Country: by
Re: Noise injection for magnetic in-wall mains wire tracing
« Reply #4 on: October 18, 2020, 08:47:24 pm »
Ups, didn't think about the orientation.

Do magnetic coupling based wire tracers exist then? Will it work if I orient the coil correctly or the magnetic coupling is just not strong enough?
Tracing the wires is the first step to replacing them.
« Last Edit: October 18, 2020, 08:52:03 pm by Axk »
 

Offline pwlps

  • Frequent Contributor
  • **
  • Posts: 266
  • Country: fr
Re: Noise injection for magnetic in-wall mains wire tracing
« Reply #5 on: October 18, 2020, 09:50:45 pm »
Do magnetic coupling based wire tracers exist then?

Found this one:
https://megger.com/cable-route-tracer-accutrace
 
The following users thanked this post: Axk

Offline Axk

  • Regular Contributor
  • *
  • Posts: 185
  • Country: by
Re: Noise injection for magnetic in-wall mains wire tracing
« Reply #6 on: October 18, 2020, 10:13:15 pm »
Great find, thanks!
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf