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Author: Subject: Strange earthing problem
wg48
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[*] posted on 16-1-2019 at 20:26
Strange earthing problem


I was removing some electronic components from an old pcb when I noticed some leakage current from my electric soldering iron. That is not good. Not only can it damage sensitive semiconductors its potentially dangerous as the iron is supposed to be earthed. In case I imagined the slight tingle I felt i checked with a neon tester. Yes the iron was alive but only slightly as the neon glow was dim.

Obviously I assumed the earth connection was broken so I checked continuity between the soldering iron tip and the earth prong of its power supply plug. Less than one ohm suggested the problem could be in the socket wiring. I checked the continuity of the earth socket with other earth sockets that was OK.

Eventually I plugged back in the soldering iron back in and and checked the continuity between the soldering iron tip and the earth wire of a lead plugged in to a nearby socket that was ok. I also checked if the earth of that lead was live no glow.

Apparently the soldering iron is earthed but when its turned on the tip is slightly alive ???. How can that happen if its connected to the power earth and the power earth is not live. That is impossible. I assume my tests must be in error.
I will check again tomorrow and hopefully the mistake I must have made will not be repeated.

The only possibility I can think of is if the electronic temperature control is generating a sufficiently high frequency that given the inductance of the earth lead it manages to create a voltage at the tip even though the DC resistance to earth is less than an ohm. That seems very improbable.

I will solve the problem tomorrow hopefully.


[Edited on 17-1-2019 by wg48]




Borosilicate glass:
Good temperature resistance and good thermal shock resistance but finite.
For normal, standard service typically 200-230°C, for short-term (minutes) service max 400°C
Maximum thermal shock resistance is 160°C
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[*] posted on 16-1-2019 at 21:05


Maybe there's an intermittent ground connection between the iron and its cord, the cord and the plug, or (unlikely) the plug and the wall socket. it feels like practically every device with a cord fails like that eventually-conductors break apart while still covered in insulation or (evidently ineffective) strain reliefs, and from there on out it conducts sporadically depending on the position of the cord.

I've always heard that M- and GHz signals don't tingle or shock, but do absolutely horrendous internal thermal damage if the intensity is strong enough. Perhaps a wierd pulse harmonic would be different?

The element should be insulated from the tip, and the tip should be grounded, although I've seen an untold number of two prong ungrounded irons. Mine is one of those, so if I suddenly disappear from a discussion of an ongoing electronic build, that might conceivably be the reason:D

Did you simultaneously test for stray voltage and for continuity with ground? If so, Could part of the tip assembly be live and the other grounded? If not, you could be right about VHF from the controller, or (Hopefully not) the whole grounding system of you house might not be earthed. Or we're bumbling our way around the answer with out ever contacting it.

[Edited on 17-1-2019 by Vomaturge]
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[*] posted on 17-1-2019 at 00:37


Check for ac voltage between wall socket earth and your physical earth,
by physical earth I mean you, the floor, the bench etc.
Spread some aluminium foil on the ground and some on the bench and measure Vac between the foils, and between the foils and mains earth.

P.S. various 'stray' leakage paths are common,
they are usually of high impedance so rarely felt by us,
but often enough current to light a neon,
or break down a semiconductor junction etc.
e.g. the capacitors in a line filter allow a small current from line to earth/chassis.
if the chassis is not 'earthed' then it will be 'live' via the line filter,
nothing is a perfect insulator, even diamond appears to have measurable resistivity
and humidity makes everything conductive to some degree......

[Edited on 17-1-2019 by Sulaiman]




CAUTION : Hobby Chemist, not Professional or even Amateur
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wg48
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[*] posted on 17-1-2019 at 03:16


Back into the workshop first thing this morning.

Got a glow on the iron tip.
Quickly made a high current continuity tester (12V Pb battery and a 12V 25W bulb).
NO continuity to the earth of an adjacent socket.
Checked again with the multimeter no continuity.
Dismantled iron earth connection looked good.
Dismantled control box earth connection looked good.
Checked continuity tip to plug now its good.
Powered it back up no glow, thats makes sense.
I bent the lead into the mouldered on power plug NO continuity

Vomature was correct its an intermittent open circuit fault on the earth connection of the plug. . I will replace it.

Sulaiman: Yes that,s always a good idea to check that if there is a problem. The earth connections was checked when the power I first installed the power years ago now. Actually I have an earth rod/s just outside of the workshop door so I could use that. I am using the house earth connection via a cable to the house. It would be better to use the earth rod and I can then use the spare wire for power to reduce voltage drop. (lights flick when the heating comes on or goes off.

Eventually I want to put an earth leakage trip in workshop. (presently using one in the house) That is what the earth rod will be for and to earth the tin roof not that much lightning gets near to my house as I am at the bottom of a narrow valley

On a different note: The soldering iron is an Aldi special. Ok It was a lot cheaper (10% of) than Weller but its crap in comparison.

In spite of the low cost as the control box seems just about heavy enough to contain a transformer I foolishly assumed it was a low voltage iron. Actually the weight was an iron plate in the bottom of the case. I had to add one to the soldering iron holder to stop it moving or falling over.

In my experience 240V powered iron do not last very long (as little as a few weeks if used all day) probably because the heating wire is so thin its oxidation makes it go open circuit. The Aldi one may last a bit longer as it switches to 200C after several minutes. That should increase the element life but it means you have to wait for it to heat up.

Also it has a narrow BRASS bit that screws in to the iron via an even narrower thread thats almost same length as the bit is wide. So heat conduction to the actually soldering tip is poor probably 10% of a Weller's and low thermal mass too. That mean you have to up the temperature to solder thick wire or wait for the heat to transfer. The higher temperature with a brass bit means the bit is desolving even quicker that plain copper one. Weller bits are iron plated with the thermostat built in to the bit so a very short delay on supplying extra heat during soldering.

PS DON'T USE a NOT EARTHED iron on semiconductors or unplug if you do.

PSS. I should have spent the £100+ on a Weller but who can resist what you think is a bargain LOL.

Below is a 24V Weller with an earth. The Rolls Rorce of soldering irons. It has iron plated copper tip That is temperature control via a magnetic alloy pill on the opposite end of the bit to its tip. When the alloy is above it Curie temperature it looses its magnetic properties, that activates the thermostat with a very short delay

That costs about £100 and you still need a 24Vac power pack for it.

RRiron.JPG - 23kB

[Edited on 17-1-2019 by wg48]




Borosilicate glass:
Good temperature resistance and good thermal shock resistance but finite.
For normal, standard service typically 200-230°C, for short-term (minutes) service max 400°C
Maximum thermal shock resistance is 160°C
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[*] posted on 17-1-2019 at 13:20


Quote: Originally posted by wg48  

Below is a 24V Weller with an earth. The Rolls Rorce of soldering irons.

[Edited on 17-1-2019 by wg48]


You mean one of those magnastat irons that generate so much noise when they switch they can trigger a 'scope 3m away?

I suggest you try out a Metcal. I fell in love with Metcal irons a decade ago and haven't looked back since. Used to like Weller, but have also used Hakko and Pace irons. But the Metcal is a delight to use. They too use the Curie point of the tip to regulate temperature, but the tip is directly heated by RF induction so they are able to provide very stable temperature control and loads of power (mine is 60W ) with a low mass tip, and a very fast response.

The last time I got a tickle off the earth in my house it was because the main cable into the house had got water in it and neutral wire had corroded through. That was 2 days without power and $2k to replace the buried cable. Glad your fix was so much simpler.




[Edited on 17-1-2019 by Twospoons]




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[*] posted on 17-1-2019 at 22:25


Complicated. That's why I hate analog current/voltage. It has something called earth, something we don't have in batteries.
Maybe we have it in some other dc sources like electrostatic. Even that is complicated. How can electricity travel through insulators? Because it is extremely high?
Also what is purpose of earth? Isn't it just to prevent our death, and maybe if we don't have null to carry electricity.
But I doubt that electricity is supposed to be flowing to earth just like that, usually, normally.
That would cause huge loss? That means we have serious problem? That is extreme and dangerous?
I am saying that because many people everywhere said that it is normal that electricity is flowing to ground always!
Btw, why lightning, thunderstorm flow into earth? Anybody discovered anything ever? Even a bit?
Maybe there is magical clock or being that eats electricity??? :mad::o
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[*] posted on 18-1-2019 at 02:54


Quote: Originally posted by Twospoons  
Quote: Originally posted by wg48  

Below is a 24V Weller with an earth. The Rolls Rorce of soldering irons.

[Edited on 17-1-2019 by wg48]


You mean one of those magnastat irons that generate so much noise when they switch they can trigger a 'scope 3m away?

I suggest you try out a Metcal. I fell in love with Metcal irons a decade ago and haven't looked back since. Used to like Weller, but have also used Hakko and Pace irons. But the Metcal is a delight to use. They too use the Curie point of the tip to regulate temperature, but the tip is directly heated by RF induction so they are able to provide very stable temperature control and loads of power (mine is 60W ) with a low mass tip, and a very fast response.


I stand corrected. Hakko an RF heated soldering iron obviously IS the Rolls Royce of soldering irons and from a quick google they have a Rolls Royce price too.

I assume because the heat is generated in or on the surface of the bit and does not have to travel through insulation and interfaces as in a Weller the response time to a drop in temperature is comparatively instantaneous, supper nice.

Because I have to crank up the temperature of my iron to compensate for the poor conduction the tip oxidises then the flux boils off and carbonizes when I try to re-tin it and of cause carbon does not tin. So it has to be scraped but the surface reoxedises before it can be re-tinned but the flux boils off and carbonizes again. Just making the bit from thicker iron clad copper with a better thermal connection to the heat source would have improved its performance dramatically.

I should also add it has a three year guarantee or it did until I replaced the plug and damaged the labels over the screw holes to open it LOL. I guess its an economic solution for the occasional soldering job.



[Edited on 18-1-2019 by wg48]




Borosilicate glass:
Good temperature resistance and good thermal shock resistance but finite.
For normal, standard service typically 200-230°C, for short-term (minutes) service max 400°C
Maximum thermal shock resistance is 160°C
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[*] posted on 20-1-2019 at 04:22


Oops: sorry I got the Hakko and Metcal mixed up in my previous post.
The Hakko is not RF heated it just a heating element intagrated in to the tip with a thermocouple for temperature measurement. So its probably not as fast a response to a drop in tip temperature as the Metacal assuming the Meatcal is directly heated. I was unable to confirm its the direct heating of the actual tip as opposed to a heating element in thermal contact via electrical insulating material.

From my research I think the temperature control is achieved by the change in skin depth of the magnet material of or in the tip at the Curie temperature of the magnetic material. So the disadvantage is the temperature is not adjustable via a control knob. The tip must be changed to vary the controlled temperature.




Borosilicate glass:
Good temperature resistance and good thermal shock resistance but finite.
For normal, standard service typically 200-230°C, for short-term (minutes) service max 400°C
Maximum thermal shock resistance is 160°C
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