How to make a good wire detector in a wall?

[Aleksandar-]

Hi.
For make wire detector in a wall, it is given here that the total length of the coil wire should be 10-12 cm, but no coil diameter was given, how long it should be?

Thanks.

 

[rjenkinsgb]

To detect power cables, it would work by capacitance - the length and shape of the pickup should not be critical, just a short stub or flat spiral should work.

Commercial "voltstick" type non-contact voltage devices only have a very short stub probe, and the audio frequency cable tracers I use also have just short probes, around 20 - 25mm.
eg.

Fluke VoltAlert | Fluke 1AC II Non-Contact Voltage Tester | Fluke

Safely test for energized circuits with non-contact voltage tester Fluke 1 AC II. Fluke Volt Stick even detect miss-wires of an electrical outlet.

www.fluke.com

Tempo Tone Probe Cable Tracker Kit PTS

A low cost toner kit designed for identifying and tracing wires or cable within a group without damaging the insulation. Supplied in a sturdy cordura twin-pocket pouch. Kit comprises: Tempo PTS 100 Tone Tracker Probe Works with any oscillator 500Hz to 1.2 kHz Sensitivity control 30dB adjustment...

www.millsltd.com

 

[Aleksandar-]

Where on that electronic scheme I could add a piece of this type

here

to see the battery usage percentage?

 

[rjenkinsgb]

Just connect it directly across the circuit power, positive after the switch (with buzzer positive) and negative to battery / circuit negative.

What battery are you using? If it's not a type that meter supports, you will not get an accurate percentage.

eg. A "9V" battery starts at around 9V and gradually drops to about 6V over its life, before it is considered completely exhausted.
With that meter, setting it for two lithium cells is probably as near as you will get to an appropriate range for a 9V battery.

 

[Aleksandar-]

positive after the switch (with buzzer positive) and negative to battery / circuit negative.

You think like this: ?

What battery are you using?

I use a rectangular 9V battery.

 

[rjenkinsgb]

You think like this: ?

Exactly.

The battery meter reads directly from the battery, as long as the power switch is on.

 

[Aleksandar-]

the length and shape of the pickup should not be critical...

But can anyone is able to estimate the dimensions of that spiral based on the recording, though it was written in the recording that, for example, only a straight wire did not produce a strong enough signal.

 

[rjenkinsgb]

You are forming a capacitor plate - the spiral is emulating a flat area of metal, that picks up a signal from a powered cable by capacitive coupling.
The size and turns are not critical as it is not a coil in the tuned or resonant sense.

Try something like 10 - 15mm diameter.

If the circuit was better designed and sensitive enough, it should work with a tiny stub of wire.

 

[Nigel Goodwin]

But can anyone is able to estimate the dimensions of that spiral based on the recording, though it was written in the recording that, for example, only a straight wire did not produce a strong enough signal.

There's a picture in your original link, it's not at all critical, make it similar to that picture.

 

[Aleksandar-]

Try something like 10 - 15mm diameter.

I would say it's less than 10mm in the picture.


Did you pay attention to this part of recording:

especially what was written here

 

[rjenkinsgb]

There are hundreds of versions of that (very badly designed) circuit on the internet.

It is very bad because the base of the first transistor has no bias and if it detects any voltage and the transistor conducts, the base-emitter diode will cause the sensitivity to drop at the same time, by pushing the base negative of the conduction point.

You cannot expect good operation - a bigger pickup area also means more voltage, more rectifier effect and more "unbiasing" of the transistor, if it was even in a state to conduct to start with...

As a toy, just use any piece of wire or a small area of metal like a small coin. it will work to some extent but never well or reliably.


Use a properly designed circuit and a tiny probe will detect a live cable at a good distance; this looks to be a pretty good design:
**broken link removed**

 

[KeepItSimpleStupid]

Circuit Cellar had an article about a wire tracer. It wasn;t a few parts. It could do underground as well.

I have an older version of the Ideal Suretrace. https://www.idealindustries.ca/products/electrical/electrical-testing/circuit-tracers.html Not cheap, unfortunately. You can actually find the short.

What happened in my case, is that some manufacture relied on box dimensions and did not protect the side screws on a daisy-chained outlet, so one day a circuit developed a short. I was able to guess it's path and bisected the circuit until I found the short. A screw on an outlet against the enclosure. The box dimensions were off. it was a 1960's enclosure with no tapped ground holes.