Solved: RFID coil and superglue

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I wound a 18cm x 20cm RFID coil big enough for my cat go walk through with 55 turns of 30 gauge magnet wire.  I measured the inductance with a cheapo meter to be 2.4 mH and the resistance as 15 Ohm.  When I hooked it up to my RFID circuit it worked great and I got a detection range of about 6" with a standard fob.  

 

Then I soaked the coil with super glue to keep the wires from moving and make the coil rigid.  My RFID circuit quit working.  I measured the inductance and it had changed to 1.6 mH and the resistance was still 15 Ohm.

 

Does anyone know what happened?  I neglected to measure capacitance before.  I didnt think cyanoacrylate was magnetic.  I dont think it melted the magnet wire coating shorting  out some wires as the coil resistance was unchanged.  very strange.

 

I started winding another coil but ran out of wire.  I will have to wait 3 days for more wire to come before I can wind another coil and measure capacitance.

 

Never mind.  When the glue dried the inductance went back up.

Last Edited: Mon. Aug 7, 2017 - 03:47 AM
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Probably the wet glue is conductive? which messes with your inductor in multiple ways.

Paul van der Hoeven.
Bunch of old projects with AVR's:
http://www.hoevendesign.com

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Paulvdh wrote:
Probably the wet glue is conductive? which messes with your inductor in multiple ways.

 

Yeah, it was just me being dumb.  Again.

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Super glue should NOT be conductive or magnetic! Capacitance measurements won't mean much. After the glue dried, is it working again? Not clear from your last post!

 

Jim

Jim Wagner Oregon Research Electronics, Consulting Div. Tangent, OR, USA http://www.orelectronics.net

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ka7ehk wrote:
After the glue dried, is it working again?

Well, the cat tried to come through when the glue was still wet.  So now it is hard to tell, with the attached and very angry cat.

You can put lipstick on a pig, but it is still a pig.

I've never met a pig I didn't like, as long as you have some salt and pepper.

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The glue is almost dry in most places.  I measured the inductance and now I get 2.8 mH, up from 2.4 before the glue.  Probably because all the wires are close together.  So yes, it is working again, only sporadically.  I need to wait for the glue to be dry everywhere and try again.  The solvent in the glue must be conductive, for the inductance to drop by 35% when wet.  I will keep you informed as time passes and I get the wire to wind another one for comparison.

 

Luckily, the cat didnt get stuck, but if she jumps up on top of my toolbox, which happens sometimes, she might find her food stuck to the coil, which is up there drying.

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Food, Feet, Paws ?

 

Just read up on wikipedia on Cyanoacrylate:

https://en.wikipedia.org/wiki/Cy...

 

No hint of conductivity while wet.

Ans cyanoacrlate does not "dry" It polymerises in the presence of water (specifically hydroxide ions)

 

@mark

Are you in for an experiment? Try to measure conductivity or other parameters of wet glue?

And apparently it catches fire if you mix it with cotton.

Paul van der Hoeven.
Bunch of old projects with AVR's:
http://www.hoevendesign.com

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So is this some form of cat scan?

John Samperi

Ampertronics Pty. Ltd.

www.ampertronics.com.au

* Electronic Design * Custom Products * Contract Assembly

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It's weird.  The glue has been sitting for almost 24 hours and now the inductance measuures 2.6 mH, but what is really weird is there is a dead spot on the axis of the coil at a distance of about 2-3 inches from the plane of the coil.  It didnt do this before I added the glue.  Maybe parts of it are still wet.  It is too bad.  Coating the coil with the glue holds all the wires together and makes the whole coil fairly rigid, but whatever effect the glue or the filler in the glue has on the coil makes it unreliable.  Maybe in a couple of days it will work correctly.  It is very odd that the coil detects the fob at 6 inches along the centerline of the coil but not at 2-3 inches.  I will have to find another way to rigidfy the coil, I guess.  I ordered 800 feet of magnet wire and it should be here in a few days, and then I can start from scratch.

 

Yes, John.  This is for a cat scan.

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The older HID readers I used - The large ones had a rigid plastic frame that the coil was wound around very tightly and a few drops of nail paint, or HV enamel was put on four corners, and that was it.  The wires wee not sealed.  For the weatherproof ones they were potted but I remember the manufacturer saying that they needed to wair for a full cure before they could test them.

 

Superglue does not take 24+ hours to set up. 

 

Jim

If you want a career with a known path - become an undertaker. Dead people don't sue! - Kartman

Please Read: Code-of-Conduct

Atmel Studio6.2/AS7, DipTrace, Quartus, MPLAB user

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When the wires were still stretched tightly on the fixture I made to wind them the coil worked really well.  I think that is the best way to hold the wires.

 

The superglue I used was the gel type and I used quite a lot.  It might have been old when I bought it.  I dont know.  There were still wet sticky spots after 16 hours.  It is all dry now, and the coil still has a dead spot about 2 inches from the plane of the coil.  I'm not sure what the deal is, but in the future I am going to wind the wires tightly around a frame, and leave it be.

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Superglue was not a good choice. As mentioned bail polish at a pinch or i used some circuit board laquer recently for a similar task.

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jgmdesign wrote:
Superglue does not take 24+ hours to set up. 

I think what happened is I had some big globs of glue that set on the surface and formed a membrane that prevented humidity from getting to the underlying glue.  Like I said, I was using the gel type, and i still got glue on my fingers yesterday when I handled it, and it still reeks of superglue  

 

As I remember from my medical device days, the Loctite rep told us the clean room had to have a relative humidity greater than 40% for the adhesive to set.  We were using the wicking type in that case.

 

As to the dead spot 2 inches away, I suspect it is from not holding the coil very flat.  I am going to play around with that coil a little more before I toss it.

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Kartman wrote:
Superglue was not a good choice.

 

Clearly.

 

Kartman wrote:
As mentioned bail polish at a pinch or i used some circuit board laquer recently for a similar task.
 

 

I dont know what bail polish is, but I think I have some old clear nail polish that would have been a better choice, as you say.  I'm not so sure I want to pot the coil any more.  I think holding it tight in a frame is the better way to go.

 

All in all, though, I am pleased my home made coil worked as well as it did (before I super glued it) with my home made detection circuit using an EM4095 chip and a bunch of capacitors.  I think a 6" detection range with a cheapo fob is respectable.

Last Edited: Thu. Aug 3, 2017 - 06:37 PM
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Smashing the coil between two pieces of foam core does not get rid of the dead spot.  There are some out of place wires in a couple of corners.  Maybe that is the problem.  In any case, that coil is going into the recycle box.

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MarkThomas wrote:
In any case, that coil is going into the recycle box.


So it kind of recoiled, then... [It's pun-week here at 'freaks, but I'm ducking anyway... ]

Happy 75th anniversary to one of the best movies ever made! Rick Blane [Bogart]: "Of all the gin joints, in all the towns, in all the world, she walks into mine."

 

"Some questions have no answers."[C Baird] "There comes a point where the spoon-feeding has to stop and the independent thinking has to start." [C Lawson] "There are always ways to disagree, without being disagreeable."[E Weddington] "Words represent concepts. Use the wrong words, communicate the wrong concept." [J Morin] "Persistence only goes so far if you set yourself up for failure." [Kartman]

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perhaps the glue would cure quicker with a cat-alyst ... ?

 

 

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JohanEkdahl wrote:
MarkThomas wrote:
In any case, that coil is going into the recycle box.

 

So it kind of recoiled, then... [It's pun-week here at 'freaks, but I'm ducking anyway... ]

Quack, quack...

 

Ross McKenzie ValuSoft Melbourne Australia

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This could get acrylonious.

"Experience is what enables you to recognise a mistake the second time you make it."

"Good judgement comes from experience.  Experience comes from bad judgement."

"When you hear hoofbeats, think horses, not unicorns."

"Fast.  Cheap.  Good.  Pick two."

"Read a lot.  Write a lot."

"We see a lot of arses on handlebars around here." - [J Ekdahl]

 

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Wire you guys making fun of my project?

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we didn't mean to hurt your felines ...

 

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awneil wrote:
we didn't mean to hurt your felines ...

Groan.  Good job to all.

You can put lipstick on a pig, but it is still a pig.

I've never met a pig I didn't like, as long as you have some salt and pepper.

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Lee, have you become enameled of this thread?

"Experience is what enables you to recognise a mistake the second time you make it."

"Good judgement comes from experience.  Experience comes from bad judgement."

"When you hear hoofbeats, think horses, not unicorns."

"Fast.  Cheap.  Good.  Pick two."

"Read a lot.  Write a lot."

"We see a lot of arses on handlebars around here." - [J Ekdahl]

 

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I think it's just a wind-up

 

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These puns are making me recoil.

John Samperi

Ampertronics Pty. Ltd.

www.ampertronics.com.au

* Electronic Design * Custom Products * Contract Assembly

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I thought it might induce that kind of respon ...

 

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MarkThomas wrote:

Wire you guys making fun of my project?

 

Of course we are! We make fun of our own projects.

274,207,281-1 The largest known Mersenne Prime

Measure twice, cry, go back to the hardware store

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OK, my turn.  While I approach the subject with some reluctance, :),  I suspect you probably had a shorted turn.  In a previous life I worked at a place that made low frequency magnetic anti theft systems.  Big panels you walked between that contained large resonant coils at just hundreds of Hz.  A shorted turn would produce the effects you see.  Actually the most obvious effect was a lowering of the Q of the overall resonant circuit.  If whatever you were using to measure inductance also showed Q, or loss tangent, etc....    We would just measure the voltage on the resonating caps as compared to the drive voltage.  If it was within the right ratio, the Q was OK and thus the efficiency and resulting magnetic field were OK too.  

 

Dave

 

 

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I'm getting saturated.

"Experience is what enables you to recognise a mistake the second time you make it."

"Good judgement comes from experience.  Experience comes from bad judgement."

"When you hear hoofbeats, think horses, not unicorns."

"Fast.  Cheap.  Good.  Pick two."

"Read a lot.  Write a lot."

"We see a lot of arses on handlebars around here." - [J Ekdahl]

 

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This current problem is capricious.  

 

I measured the coil resistance before and after the super glue, and it was 15 Ohm both times.  If I have a shorted wire in the coil it couldnt have taken out to many turns.  Can problems happen with just one turn shorted out?  I wouldnt think so.  

 

I just measured the inductance with my cheapo meter and it was down to 1.5 mH, so I didnt even try it with my RFID circuit.  The coil has been bounced around some so it is probably not real flat.  What was really mysterious was the dead spot on the axis about 2-3 inches out when the glue was mostly dry.  It worked fine further away and closer in.  Creepy.

 

I have found a much better way to hold and wind the coils with no glue and now I am getting a range of 18.5 cm with an 18cm x 20cm coil.  I am starting to think bigger, but I dont know what I would do with a coil I could walk through.  What would induce me to make such a thing?

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That 1.5 mH measurement was a mistake.  I made the measurement with an active RFID coil right next to it, and it coupled in to the meter measuring the superglue coil.  It actually measured 2.5 mH, which is about what I expected.  It works with the RFID circuit and has no dead spot in the middle.  It doesnt have great range, but it acts like a crummy coil should.  So the mystery is solved, so to speak.  The wet solvent in the superglue must have had some conductivity and affected the coil until it all set up.

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My understanding is that superglue polymerizes it the absence of air.  So blobs of coating could take some time to dry.

 

Perhaps hot melt might be an acceptable solution, or the age old "varnish".

 

Would be interesting how the final product performs when caught in the rain.

 

 

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superglue must have had some conductivity and affected the coil until it all set up.

I wouldn't expect it to have much if any conductivity, or you would have noticed a change in the resistance.  But perhaps its magnetic permeability is different in its non-polimerised state.  A brief Google search finds at least two GoogleBooks offerings which touch on the subject of the magnetic properties of cyanoacrylate.

 

Would be interesting how the final product performs when caught in the rain.

And the feel of the ocean.  And the taste of champagne.

 

"Experience is what enables you to recognise a mistake the second time you make it."

"Good judgement comes from experience.  Experience comes from bad judgement."

"When you hear hoofbeats, think horses, not unicorns."

"Fast.  Cheap.  Good.  Pick two."

"Read a lot.  Write a lot."

"We see a lot of arses on handlebars around here." - [J Ekdahl]

 

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I'm sure your will find the Purrrrrr...fict solution to this eventually! 

 

 

Jim

Last Edited: Mon. Aug 7, 2017 - 01:21 PM
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that'll be the cat's whiskers!

 

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lundquist wrote:
Dave

Someone had better caution [relatively] new 'Freak Dave about inserting an on-topic reply into a thread that has degenerated into punning. ;)

 

Oh, wait -- isn't it supposed to be the other way around, cautioning [relatively] new participants to >>stay<< on topic?

You can put lipstick on a pig, but it is still a pig.

I've never met a pig I didn't like, as long as you have some salt and pepper.

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Yes Theusch is right, this has "strayed" to far.

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its a bit of fun, no need to be stuck up about it

 

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This tread must have 9-lives as it just will not die....

 

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My understanding is that the polymerization process requires water molecules to happen (cat-l-eyes), which is why 40% humidity is required.

 

I'm glad this thread is marked solved.

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I think the problem was that your super glue was still liquid in places and effecting things.

 

There is a catalyst you can buy https://www.amazon.com/Pacer-Tec...

 

Used to use a loctite product for cleaning out screw holes for the same purpose. In Model Airplanes, there's even a CA that WILL NOT SET until you use the catalyst. Never used it myself, but some guys loved it. Realize, it's been 34 years since I flew R/C airplanes.

274,207,281-1 The largest known Mersenne Prime

Measure twice, cry, go back to the hardware store

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Torby wrote:
I think the problem was that your super glue was still liquid in places and effecting things.

 

I think you are right about that.  Now that it is totally cured the coil behaves as I would expect from a coil of that quality.

 

I have used the Loctite Accelerator with Loctite adhesives.  It tends to cause blooming and gets white powder on the parts, but it sure makes the glue set up in a hurry.

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Oops, someone already used cat-alyst.  

 

Why is there such a resistance to this thread decaying away?  Could dB that everyone has to get their say. I dont think it is reVolting. but there is a potential for it to go on and on.

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All in all, a sticky subject.

 

JohnRob was left speechless.

Stuck Like Glue

Sugarland

...

I'm stuck on you

Whoa-oh, whoa-oh
Stuck like glue
You and me baby
We're stuck like glue

You can put lipstick on a pig, but it is still a pig.

I've never met a pig I didn't like, as long as you have some salt and pepper.

Last Edited: Mon. Aug 7, 2017 - 11:14 PM
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theusch wrote:
JohnRob was left speechless.

 

I wondered what that meant.  I though maybe he diode and went to heaven.

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And we love puns. Too bad we don't have zbaird to compose limericks any more.

 

274,207,281-1 The largest known Mersenne Prime

Measure twice, cry, go back to the hardware store