EEVblog #267 - Voltage Detection Stick Teardown

[EEVblog]

I did a quick check on the main IC, and it's showing pin 4 is ground and pin 11 is Vcc. Hmm...

Dave.

[T4P]

  Custom Logic maybe ?

[firewalker]

Was the audio really bad on this episode or it was just my idea?

Alexander.

[david77]

Could it maybe be an opamp, LM324 or similar? They have power on 4 & 11.

[EEVblog]

Was the audio really bad on this episode or it was just my idea?

Yes, the in front of camera audio is crap.
I need to fix this, my shotgun just picks up too much crap in the new lab.

Dave.

[FreeThinker]

Hi Dave
Do you find these voltage sticks useful? More of a novelty in my opinion but what do others think?

[IanB]

Do you find these voltage sticks useful? More of a novelty in my opinion but what do others think?

I've been using mine a lot lately when replacing electric sockets. It's really handy to check which wires and outlets are live when a breaker is tripped and which ones are off. Much quicker just to touch the detector to a wire than to mess around with meter probes.

[sacherjj]

Was the audio really bad on this episode or it was just my idea?

Yes, the in front of camera audio is crap.
I need to fix this, my shotgun just picks up too much crap in the new lab.

Wireless lapel mic?

[Rufus]

I did a quick check on the main IC, and it's showing pin 4 is ground and pin 11 is Vcc. Hmm...

Probably a quad CMOS op-amp then.

[saturation]

Its very helpful doing electrical work.  When you see wires, even if you powered down the circuit breakers for whatever you're working on, you case easily find the live wire.

Hi Dave
Do you find these voltage sticks useful? More of a novelty in my opinion but what do others think?

[FreeThinker]

I've found them either way too sensitive (ie you cannot trace individual wires) or very erratic and failing to light up (similar wires out of phase cancelling each other out?) Never liked or trusted them, prefer a contact probe, a little more hassle but very reliable. Not a lot of price difference between the two but a world of difference in function/reliability.

[SeanB]

I still like contact probes, I have 2. A cheap Steinel that uses neons and a VDR to drive the LED's, and an old moving iron unit that does double duty as a voltage tester and voltmeter/ earth leakage tester ( if I press the button while one lead is on grounded metal) with ultra sharp steel probes.

[HackedFridgeMagnet]

My volt stick is probably one of my favourite tools. But really only useful for mains powered circuits.
Great for tracing domestic/building mains circuits back to the switchboard.
I asked a sparky once whether he trusted them, he said he trusts it when it's glowing.
I bought a Fluke one,  I have never known it to not detect if a circuit is live.

[david77]

I've tried several volt sticks, all different brands and haven't found one that I could fully trust. Sometimes they are over sensitive and react 10cm away from a live wire, sometimes you stick them into the live side of a socket and they do not light up.
That's rubbish. These things are unneccesary and can sometimes be dangerous, making you believe a wire is not live until you touch it and learn your lesson. I'd lump them into the toy section together with the screwdrivers with neon indicators.

The only way to determine what's live and what's not is to use a meter or better still something designed for the job, like this:
http://www.conrad.de/medias/global/ce/1000_1999/1200/1250/1253/125379_BB_00_FB.EPS_1000.jpg.

[HackedFridgeMagnet]

Hi david77
I think your right, don't use them if you don't trust them.
I am not sure if you understood the full meaning of what I said

I asked a sparky once whether he trusted them, he said he trusts it when it's glowing.

That means he trusts it when the volt stick is saying it is dangerous, but doesn't trust it when it is saying it is not dangerous.

As for me, I trust it to read the efield strength between its antenna and its ground. If you are working in an area with a lot of stray efields, such as in a switchboard, then you should be using your multimeter, if you are somewhere else in the building, trying to figure out what circuit a particular wire or mains outlet is on, it is just so much quicker.

[hlavac]

Dave, I have better explanation of the patented frontend circuit discussed in the video.

The cap and resistor between B and C together with the next inverter and its input protection diodes act as a pulse shortener.
It sends a short pulse out every time the input transitions from low to high.
If the input is stuck on either logic level there will be no pulses going out.
These pulses charge the second cap thru the diode while the resistor in parallel with it discharges it.
This means that the cap voltage will rise over the logic high level threshold if there are enough pulses in a time span to charge the cap more than it is discharged by the resistor.
So output of the inverter behind the second cap will signal continous presence of series of low to high transitions on the input, that is the AC signal capacitively coupled onto the probe tip.

 

[Alexei.Polkhanov]

Yes it sounds right. This is almost exactly what circuit description section in patent say (lines 15 to 20, left column). I understand that the output will look like smoothed-out DC , almost like from switching DC-DC converter.

[eV1Te]

It would be interesting to compare the circuit design in the Fluke voltalert to the patent and the one that Dave tested now. Maybe Fluke hasn't scraped the labels of their ICs 

[elCap]

I have a volt stick from Tequipment.net (their own brand) which is totally useless. Do not buy it!! Its red LED turns on when there is no voltage, and off when close to a voltage source. But sometimes opposite. Having it close to an earth connection lights up the LED.
Printed on it is the same patent number as on the one Dave did the teardown of. I will do a destructive teardown of it to see if it's same design.

I have to buy a Fluke which I was aiming for in the first place (Tequ. cannot send Fluke items abroad).

[IanB]

I have volt sticks from Fluke and Klein Tools. Both of them work equally effectively at telling live wires from unenergized wires. On a two core cable they can tell the live conductor from the neutral conductor by touching to one side of the cable or the other. They are helpful in tracing a particular cable in a cable run where I want to know which cable is live or not. When I use them on mains wiring I get neither false positives nor false negatives. Performance may vary but I have no problem with the performance of these items. If it lights up and beeps when I touch a mains conductor, that conductor is live, no question.

[FreeThinker]

I have volt sticks from Fluke and Klein Tools. Both of them work equally effectively at telling live wires from unenergized wires. On a two core cable they can tell the live conductor from the neutral conductor by touching to one side of the cable or the other. They are helpful in tracing a particular cable in a cable run where I want to know which cable is live or not. When I use them on mains wiring I get neither false positives nor false negatives. Performance may vary but I have no problem with the performance of these items. If it lights up and beeps when I touch a mains conductor, that conductor is live, no question.

Unfortunately WHEN it doesn't light up on a live conductor are when the problems start.

[Ed.Kloonk]

I have volt sticks from Fluke and Klein Tools. Both of them work equally effectively at telling live wires from unenergized wires. On a two core cable they can tell the live conductor from the neutral conductor by touching to one side of the cable or the other. They are helpful in tracing a particular cable in a cable run where I want to know which cable is live or not. When I use them on mains wiring I get neither false positives nor false negatives. Performance may vary but I have no problem with the performance of these items. If it lights up and beeps when I touch a mains conductor, that conductor is live, no question.

Unfortunately WHEN it doesn't light up on a live conductor are when the problems start.

I'd say it would be the end to all your problems.

[IanB]

Unfortunately WHEN it doesn't light up on a live conductor are when the problems start.

I've tested it a lot and that's never happened. So far my confidence is sustained.

[saturation]

Same here.  Many of them boot with built in self check, part of their firmware.  If you touch it it will chirp and is quick user based self check.  Lastly, you can check its response to a known live wire as tested by your DMM, before you go hunting among cables of unknown state.

Unfortunately WHEN it doesn't light up on a live conductor are when the problems start.

I've tested it a lot and that's never happened. So far my confidence is sustained.

[FreeThinker]

Unfortunately WHEN it doesn't light up on a live conductor are when the problems start.

I've tested it a lot and that's never happened. So far my confidence is sustained.

And how many times would it take for a failure to 'shock' you out of your confidence?
Ok Voltage sticks do work, but the whole concept of them is fundamentally flawed as a safety check and as a fault finder leave a lot to be desired. If you must use one use it with care, if you have an alternative method use that in preference. Not to mention the variability of these things, the one Dave stripped down was of OK construction as I am sure is the Fluke but believe me the one hung low brigade are not so particular and these are 'Badge engineered' by some of the big names so just take care