Voltstick Question

[Hawkmoon]

I've got flu at moment so if this is a stupid/Electrical Trainee/diy type question then illness will be my excuse ....


How do voltsticks sense live cables but not neutral cables?

 

[snowhead]

but not neutral cables?

They will, if the Neutral isn't connected at the source,, maybe a clue there.

 

[Hawkmoon]

They will, if the Neutral isn't connected at the source,, maybe a clue there.

Don't follow what you mean

 

[Darkwood]

They use a u shape receiver antenna in their tip which is tuned to pick up very low frequencies ...specifically in the region of 50hz and the control circuit filters out many false sources like static etc .. they tune into the voltage itself and ref' it to you by capcitive coupling usually but other methods exists. typically looking for >90v this then means N isn't picked up as its potential in reference is 0v

 

[Badged01]

Thats an interesting question/observation! Dont think it will work on the magnetic field from current flow as both L & N will emit fields. I'm gonna go with something along the lines of Darkwoods answer in that somehow the voltstick senses the voltage then references it against you holding the stick as a nominal zero (or the battery -Ve). So "Live" shows 230V and it lights, "Neutral" shows 0V and it don't light.

Must get one and have a play ......

 

[Hawkmoon]

It 'references' pd to you even though it's insulated? The negative of the battery is electrically separate though?

As the neutral is emitting same em and frequency never really understood how it made the distinction

 

[Badged01]

Isn't there a special part of the voltstick that you touch/hold? I assume will allow the reference to be made?

 

[Darkwood]

It 'references' pd to you even though it's insulated? The negative of the battery is electrically separate though?

As the neutral is emitting same em and frequency never really understood how it made the distinction

I edited it to delete confusion ... they can work in various ways but they look at the voltage waveform hence the live wire, the N is the line at 0v on the waveform chart so doesn't register as its a straight line as it uses you as a reference and you are in contact with mass earth - its capacitive coupling so its regardless that you are holding a plastic object.

 

[Hawkmoon]

Isn't there a special part of the voltstick that you touch/hold? I assume will allow the reference to be made?

No I have used them resting on floorboards (while switching elsewhere) and they still 'work'

 

[Badged01]

Brain can't comprehend the physics of it at the moment, seemed such a damn simple thing when I first thought about it! So it even works without you touching it? Must be a bright bofffin out there somewhere who has the definitive answer .....

 

[Hawkmoon]

Just trying to get my head round your second post DW

 

[snowhead]

Isn't there a special part of the voltstick that you touch/hold? I assume will allow the reference to be made?

You don't need to touch them.

Look no hands;

 

[Badged01]

And what a weird coincidence, was only playing with my avatar this morning and added a voltstick for impact .... fate!

 

[Darkwood]

Look up capacitive coupling and how it works and you will understand how some volts sticks dont need to be held to light up as they ref' the AC waveform to that of the DC battery circuit to establish if something is live.

• 

The waveform abobe shows the voltage rise and fall this is what the pens are looking at - the traight line in the middle is 0v and a reflection of the N wire... don't confuse this with current which is reflected the same in L and N

 

[Badged01]

Did you touch it first to get the light then leave it --- somehow the signal is locked in from you?

Does it do the same if you leave it on the cable with it unpluged (no power) then plug in so you have power and you havent touched it?

 

[Hawkmoon]

Did you touch it first to get the light then leave it --- somehow the signal is locked in from you?

Does it do the same if you leave it on the cable with it unpluged (no power) then plug in so you have power and you havent touched it?

As this

 

[snowhead]

Did you touch it first to get the light then leave it --- somehow the signal is locked in from you?

When I took the photo, Yes, see below.

Does it do the same if you leave it on the cable with it unpluged (no power) then plug in so you have power and you havent touched it?

Yes, I've now tried it by placing on the cable and switching on afterwards.
It makes no difference, it still lights up.

They look for frequency within a 50 /60 hz range and with my Fluke with a voltage over 200v.

Neutral has 50 hz on it but not 200+v

You can get them for 120volt detection.

 

[Hawkmoon]

Look up capacitive coupling and how it works and you will understand how some volts sticks dont need to be held to light up as they ref' the AC waveform to that of the DC battery circuit to establish if something is live.

• 

The waveform abobe shows the voltage rise and fall this is what the pens are looking at - the traight line in the middle is 0v and a reflection of the N wire... don't confuse this with current which is reflected the same in L and N

But all the voltstick will see is an oscillating magnetic field from both live and neutral cables alternately (ac wave), how is the dc battery circuit 'common' to either of these? (if you get what I mean)

The voltstick just senses two conductors doing exactly the same thing (at different times).


Or am I just not getting this? lol

 

[Hawkmoon]

Also why was this thread moved?? I wasn't asking 'where can I buy one'!!!!

This post was about theory - posted where the 'brains' mostly hang out (DW etc)


Why move this and leave posts like:

'What screwdriver do you find best'
'Honeywell Galaxy G2'
'Megger 1730'

?????????

 

[Darkwood]

But all the voltstick will see is an oscillating magnetic field from both live and neutral cables alternately (ac wave), how is the dc battery circuit 'common' to either of these? (if you get what I mean)

The voltstick just senses two conductors doing exactly the same thing (at different times).

Or am I just not getting this? lol

These modern volt sticks don't work like the old ones sensing a magnetic field which pulls in a leaf contact they use a control circuit board to filter false signals etc they use capacitive coupling this allows it to use the voltage waveform of the Live wire to switch components in the dc circuit they are only looking for voltage level and its cyclic waveform not current flow this cyclic component of the voltage is only present in the live conductor at the voltages the pen is sensitive to.

Capacitive coupling could be done in a few ways as ive mentioned it can use the dc battery circuit or the capacitive effect of everything around the pen that is not within its voltage pick-up range.

This is slightly out of my field of knowledge but im just theorising and putting the pieces together with what i do know .... but eether-either-or the best place to put these testers is the bin!