Sensing voltage in a wire without removing insulation

[premkumar9]

Hi,
Is there any way to check whether 12V DC is present in a wire or not without removing the insulation?

 

[alec_t]

Do you have access to either end of the wire?
How much current does the wire carry?

 

[Mikebits]

Sounds like a non contact voltage tester, never used one though.
https://www.google.com/search?q=det...e=utf-8#q=non+contact+voltage+tester&tbm=shop

 

[Externet]

I do it all the time... piercing the insulation with a sewing needle.
I also made a oscilloscope probe from a ballpoint pen with a sewing needle in place of the ball, protuding ~2mm. If you want to go fancy, get piercing probes:
----> http://i01.i.aliimg.com/wsphoto/v4/...tive-test-Clip-with-1pair-free-back-probe.jpg

 

[Mikebits]

I do it all the time... piercing the insulation with a sewing needle.
I also made a oscilloscope probe from a ballpoint pen with a sewing needle in place of the ball, protuding ~2mm. If you want to go fancy, get piercing probes:
----> http://i01.i.aliimg.com/wsphoto/v4/...tive-test-Clip-with-1pair-free-back-probe.jpg

You still need a return path.

 

[jpanhalt]

Mikebits

Your link seems to be all AC voltage detectors. Are you sure they will detect 12VDC when there is no current? There are, of course, similar detectors for DC current.

John

 

[chemelec]

You still need a return path.

Use Two Sewing Needles.
One for Hot and One for Neutral.

I do this also.

 

[crutschow]

Here's an electrostatic field sensor that may do what you want, but it's rather expensive.
You can also build a simple field sensor but you would likely have to do some sort of calibration to know what voltage you are detecting.

 

[KeepItSimpleStupid]

How much current is flowing?

 

[premkumar9]

Here's an electrostatic field sensor that may do what you want, but it's rather expensive.
You can also build a simple field sensor but you would likely have to do some sort of calibration to know what voltage you are detecting.

Thank you very much for the information. I don't need to measure the actual voltage. I only need to know whether the voltage is present or not.

 

[premkumar9]

How much current is flowing?

Even with no current I must be able to sense the voltage.

 

[premkumar9]

THANK YOU ALL FOR THE VALUABLE INFORMATION AND GUIDANCE

 

[large_ghostman]

I dont know how good this is but..................... a year or so back I tried using a electro leaf (cant remember the name of the device) thingy used for static electric, you get static near it and the gold leaf rises in the jar. I got it real cheap off ebay, a couple of times I got the leaf to raise when a DC wire was near the top plate. But it wasnt 100% reliable and although I intended to follow up on it I didnt bother in the end, so I dont know if it works or could be made to work but.......... Might be interesting to dig it out again and play with it

 

[large_ghostman]

The other thought I had was does inductance vary if you put a coil of AC around a wire and then pass dc through the wire? Does anything measurable change in the AC field?? Hmmmm another path I might have a look into, I have been into bio chemistry for a while so electronics have been secondary to that

 

[crutschow]

The other thought I had was does inductance vary if you put a coil of AC around a wire and then pass dc through the wire? Does anything measurable change in the AC field?? Hmmmm another path I might have a look into, I have been into bio chemistry for a while so electronics have been secondary to that

Yes, something similar to that is done for the AC/DC clamp-on probes built for oscilloscope use, but that measures current through the wire, not voltage.

 

[large_ghostman]

I might mess with this a bit, I can see no real use for met at the moment but its a good excuse to dust off the soldering iron and put this away for a while

 

[crutschow]

That gives a me thought.
If you made a coil by wrapping many turns of wire around an iron core (nail) you might be able to detect the electric field by swiping the coil close to the wire. That should give a small pulse of voltage, but I don't know how hard it would be to get a readily detectable voltage using a standard voltmeter.

The best core shape would probably be a U with the ends of the U just wide enough to pass the wire and then swipe the wire through the center of the U.

Edit: Cancel that thought. See Post #20.

 

[large_ghostman]

That gives a me thought.
If you made a coil by wrapping many turns of wire around an iron core (nail) you might be able to detect the electric field by swiping the coil close to the wire. That should give a small pulse of voltage, but I don't know how hard it would be to get a readily detectable voltage using a standard voltmeter.

The best core shape would probably be a U with the ends of the U just wide enough to pass the wire and then swipe the wire through the center of the U.

Not sure I am going to explain this well...............
But instead of one U shaped coil and swiping the wire through, could you instead have two U shaped coils a smallish distance apart and switch (electrically speaking) between the two? I think the idea he wants is to detect the voltage but maybe without having to actually be there.
So 2 Coils U shaped and connected switch between the two pretty fast and read the difference (if any) with a ADC??? Man its late and my brain is churning out rubbish :S

 

[magvitron]

if you could turn ON/OFF the DC supply to the wire rapidly, you could use a CMOS IC with input open sand tying a small wire as antenna to detect the pulses. Just a thought.

 

[crutschow]

Not sure I am going to explain this well...............
But instead of one U shaped coil and swiping the wire through, could you instead have two U shaped coils a smallish distance apart and switch (electrically speaking) between the two? I think the idea he wants is to detect the voltage but maybe without having to actually be there.
So 2 Coils U shaped and connected switch between the two pretty fast and read the difference (if any) with a ADC??? Man its late and my brain is churning out rubbish :S

After some further though I've concluded that my scheme won't work. I was trying to look at it from a relativistic point-of-view but made an incorrect assumption I believe.
The wire still has to carry a current to generate a voltage in the moving coil.