can hot glue kill a coil?

[punagold]

I got some new wire and wound a new RX and TX coil. Today, for the first time, I got a response from my coil when I tested it. I did this several times with different objects. Because my coils are quite large, i wanted to test them before I stiffened them up. After the successful test, I set them to the perfect shape for the proper inductance and hot glued them (individual) so that they would hold their shape. Now I get zero response. I was so happy to finally get it working and now nothing. The only measurement slightly off is the resistance of the RX. It is at 9.3 instead of 8.9, and this has to do with the coax cable hookup, but this did not change from the successful test.

So, is there any way the hot glue did something to the coil? Still has same resistance and inductance. As a last resort I will wind new coils tomorrow and see if they work with out hot glue again. Damn!

[baum7154]

I got some new wire and wound a new RX and TX coil. Today, for the first time, I got a response from my coil when I tested it. I did this several times with different objects. Because my coils are quite large, i wanted to test them before I stiffened them up. After the successful test, I set them to the perfect shape for the proper inductance and hot glued them (individual) so that they would hold their shape. Now I get zero response. I was so happy to finally get it working and now nothing. The only measurement slightly off is the resistance of the RX. It is at 9.3 instead of 8.9, and this has to do with the coax cable hookup, but this did not change from the successful test.

So, is there any way the hot glue did something to the coil? Still has same resistance and inductance. As a last resort I will wind new coils tomorrow and see if they work with out hot glue again. Damn!

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When you got your coil to respond did you have coax attached? How much coax? Keep it as short as possible. Coax adds a lot of capacitance that slows coils down. Did you flood your entire coil with hot glue ? If so then yes that too can slow a coil down. Is this for a PI detector?

Dan

[punagold]

Yes, my coax was attached. It is the original coax for my PI. I did try to coat all sides of my coil in order to stiffen it up. Is hot glue different than resin? My plan, if I can get this to work, is to eventually coat it in epoxy. Would that cause the same problem? Thanks for the reply Dan.

[baum7154]

Flooding any coil with hot glue, wax, resin, anything that replaces air will slow it down. Air is the best and that is why spider wound coils with their air spaces are so good. By the way adding the shielding also slows coils down significantly. Spiral coils while very fast must be shielded and because of their broad geometry are among the most difficult to shield and even then they are slowed way down by the shielding.

Dan

[Silver Dollar]

My basket type PI coil has hotmelt to hold the windings and it works fine. I used it on a DD coil
and it allowed movement and so didn't work so hot (pun intended!).

[baum7154]

My basket type PI coil has hotmelt to hold the windings and it works fine. I used it on a DD coil
and it allowed movement and so didn't work so hot (pun intended!).

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The key word here is 'Flood' and just securing the coil with a dots of hot glue won't have the negative effect of filling between the windings.

Regards,

Dan

[Amnesiac]

I think I done the same. First I made a coil and flood it with hot glue. I would like to coil had a good shape. I had a 0,2 mm wire, 260 rolls, 90 Ohm resistance. Then I connected 47uF capacitor and connect this to oscilloscope. Resonance was very weak, about 14 MHz... I wonder, how could it happened. Maybe glue can destroy wire isolation, or have a paramagnetic or ferromagnetic properties? However hot glue is not good idea for DD coil.

[baum7154]

Are you talking about a PI coil? If so, Flooding a coil with any dielectric but air will have a negative consequence on the coils speed. That is why builder go to the trouble to wind coils with as much air space a practical in their coils in order to operate at short sample delays.


Dan

[Qiaozhi]

I think I done the same. First I made a coil and flood it with hot glue. I would like to coil had a good shape. I had a 0,2 mm wire, 260 rolls, 90 Ohm resistance. Then I connected 47uF capacitor and connect this to oscilloscope. Resonance was very weak, about 14 MHz... I wonder, how could it happened. Maybe glue can destroy wire isolation, or have a paramagnetic or ferromagnetic properties? However hot glue is not good idea for DD coil.

There should be no problem initially fixing the coils in position with hot glue. After that you can flood the coil shell with epoxy for a more permanent solution. Have a look at Fig. 10-25 on page 142 of "Inside the METAL DETECTOR - Edition 2" for an example of a DD coil constructed for the Raptor VLF detector. This was fixed used only hot glue, and worked just fine.

[Amnesiac]

Thanks for your responses. I had done DD coil for IDX PRO. Maybe you have right and I done some mistakes in rolls counting, or something else. On the next week I'm going to do new coil without hot glue and try to harmonize it. Maybe they are a various kinds of hot glues? Some kinds are safe for the coils and some are not?

[rickb]

Amnesiac:

This does not make sense.
You said .2 mm, 260 rolls (turns?) 90 ohms, 47 uF cap, 14 MHz resonance.
If I use .2 mm, 260 turns, and 250 mm inner diameter in the coil calculator, I get 112 mH. An LC resonance calculator says approximately 69 Hz not 14 MHz. Even if my selected coil size is 1/2 or double your size, you will not get 14 MHz.

.2 mm wire is about 205 ohms per 304 meters, therefore, you used about 133 meters of wire.

Push reset and try again.

[Amnesiac]

47 nF of course, sorry for my mistake. I found the reason of my failure. I just connect oscilloscope in wrong way. I was found resonant ferquency abou 3895 Hz. In my case hot glue didn't destroy the coil. Thank You very much for your advices and attention.

[rickb]

Amnesiac:

What is the radius of your coil? In my calculation I accidentally used 250 mm as the radius instead of diameter, so my figures were off also. With 125 mm radius, 49 mH and 47 nF, I get 3316 Hz. Is this for an IB det.? 90 ohms for an IB tx coil will result in low Q, .5 mm wire would be better. For an rx coil .2 mm is ok. Was it your intent to use this low of a freq for an IB det.?

Rick

[Amnesiac]

Radius of my coil is 255 mm. I used this template:.

• Tx - 0,6 mm 34 turns, 1uF,
• Rx - 0,2mm 260 turns, 47nF

I made this coils for IDX Pro. I tuned Tx to 6590 Hz and Rx to 4600 Hz. In Rx I had to unwrap a few turns to got a correct ferq. Do You think it is too low ferq?
PS. Sorry for my english