New spin on a old friend. 3Dss holllow core wind.

[waltr]

If the were me, I'd dip the whole thing in shellac or epoxy to hold everything in place, let it cure fully. Like they did with old fashioned transformers, you know, the ones with the lovely "sweet" electrical smell.

I find some type of old electronics smell quite pleasant but I'm not sure if potting 3dss windings is such a good idea, as it increases the capacitance and is advised against by some people (see 1st page). Then again I haven't seen any actual test results, so maybe it can be an alright compromise between speed and rigidity.

I don't think he meant potting the coil but just a dip and drain to have where the wires touch each other bonded together. This should help coil rigidity a lot to ensure the wires do not move during use.

[Cazavor]

I see. No experience with epoxy here but if dipping leaves air between most of the wire gaps then it should work quite well indeed.

[waltr]

I see. No experience with epoxy here but if dipping leaves air between most of the wire gaps then it should work quite well indeed.

shellac is typically thin and runs nearly as well as water so most would drip of.
Also not sure of epoxy since most seem to be much more viscous and may not drip off as well. Maybe it can be thinned.

I have had good success using Polyurethane of VLF coils to bond the windings together. Does not seem to effect the finial inductance. This may also work well as a binder and is thin enough to drip off leaving lots of air space.

[godigit1]

Thanks guys for the suggestions I tried polyurethane on some pvc coated wire it did work but brushing it on . My main purpose is to remove the toothpicks.
Nothing sticks well to silicon.
I think my best option is the foam It only failed before because wrapping on the litz was not chemical resistant.
Locktite door and window expands less and is more consistent than the big gap type foams.

Looking at radar dom tech urethane foam is one of the best insulators.
Plus you can sand shape and shield directly to it and its light .
My thoughts anyway ill foam the coil tonight been ive had 3 days off in 6 weeks i come home fired up but run down quickly lately.

[godigit1]

Well done with the coil. Looks very good and SRF is also way up there. Silicone wire has a lower dielectric constant than PVC, which may be one of the factors. My wrap ended up 25-27 mm outer diameter.

If you're using a regular coil calculator then I think it makes sense for 3DSS wrap to have a lower inductance for the same amount of turns, as the wires are spaced further apart and are not completely aligned with each other, cancelling some of the magnetic flux. 270 uH is likely correct, I got a similar value when I measured 30 turns of my coil during winding.

For the clevis I clamped the plastic sheet between a piece of wood and a metal bar with two screws and folded it around the edges as necessary. Its not that perfect either, one half is a good few mm higher than the other. It is also easy to overdo it with the heat when working with ABS, I charred one spot slightly. The plastic sheet is cut from a license plate holder.

I haven't got the chance to do a proper test with the coil yet, as I have been having some problems with my Hammerhead II type detector. But I think I pinned down the issue today - intermittent coil connection between the BNC socket and plug. I didn't suspect that at all since those parts were brand new. Soon.



I find some type of old electronics smell quite pleasant but I'm not sure if potting 3dss windings is such a good idea, as it increases the capacitance and is advised against by some people (see 1st page). Then again I haven't seen any actual test results, so maybe it can be an alright compromise between speed and rigidity.

Hi Cazavor,
I think your right about the inductance its just a much larger variance than I,m used to seeing I'm usually within two to three wraps of the calculator.
The silicon wire may be some of it it has the highest voltage rating of any of the wires I've used.
Sold as low impedance wire.
I have my op amp apart but will get some testing done after I complete the coil I want to fully package it See where the SRF ends up.
Thanks for the info on the Clevas and good luck with your H H .

[Cazavor]

Hi Cazavor,
I think your right about the inductance its just a much larger variance than I,m used to seeing I'm usually within two to three wraps of the calculator.
The silicon wire may be some of it it has the highest voltage rating of any of the wires I've used.
Sold as low impedance wire.
I have my op amp apart but will get some testing done after I complete the coil I want to fully package it See where the SRF ends up.
Thanks for the info on the Clevas and good luck with your H H .

Thanks. The wire I bought didn't even have a voltage rating heh. What detector are you going to use your coil with?

[godigit1]

Thanks. The wire I bought didn't even have a voltage rating heh. What detector are you going to use your coil with?

That's a bummer about your wire being spliced. Shorter lengths can be used to make dual field coils. Wondering about your coil Srf. When you tested it was that after the cable was attached ? Thinking you should have had a higher initial Srf.
I'm curious of the larger surface area of your coil and sensitivity I've been debating with myself about spacing Vs inductance and capacitance trade offs.


I will be testing the coil on a Mpp that can sample at 5us but will also be trying it on other Pis if it looks good. Have a modded HH coming (Mirage) soon to build probably be the first coil for testing that since my inductance came up low.

I foamed the coil and rough trimmed it all went well no dissolved wire coating this time.



Best Regards

[Goaty]

A good effort godigit. I have been watching and reading with interest as I'm sure many others have too.
Just as an aside - can you still identify the start & end of your windings as I can't see any markings?

[godigit1]

A good effort godigit. I have been watching and reading with interest as I'm sure many others have too.
Just as an aside - can you still identify the start & end of your windings as I can't see any markings?

Hi Goaty,
I twisted the positive wire cleanly and folded the end over to mark it the other I left a mess, I know its not the best way but I was in a hurry. the coil top was put down on the paper I used to foam it. it up in the picture.
If any one tries this use the party tooth picks they don't stick to the foam. The raw wood glues in pretty good.
Thanks

[godigit1]

Sorry for my long periods between posts, I have finally got the coil ready to package.

Here are some pictures of the coil along the way for anyone who wants to see the build.

The coil shaped and ready to be wrapped.





I decided to shield this coil even though it is self shielding thinking it might handle bad ground or salt water better. (experimenting)
For the shielding I wrapped the coil with paper medical tape then sprayed it with polyurethane to kinda make a shell
and base for the carbon spray.

for the shield connection i used 4 strands of wire taken from the 30 strand wire I used for the coil. I spiral wraped the wire around the coil with 1 inch spacing, two wires both directions and twisted opposite around the coil.
The wires were tacked with dots of super glue every 3/4 inch or so.

Here is a pic of the wires up close.



So it works out that connection to the carbon shielding is consistent around the coil.
I used Mg chemicals carbon shield the one for work stations it seems pretty durable.

Here is the coil shielded.



Further Specs,

Original SRF was 1.536 megs
after foaming no change at all.
After shield wire 1.471 megs
after carbon
No change in SRF.
I have not tested SRF with Cable yet.

Shield resistance is averaging 430 to 580 ohms per inch.
Shield resistance between the gap not touching the connection wires is 1.21K.

The coil is pretty fast and to my surprise and dismay the shielding actually speeds up the coil.
I can disconnect and reconnect the shield and watch the op amp speed up slightly when connected.
Everything Iv'e read so far says shielding slows the coil down.

This is the first coil Iv'e shielded so can anyone help to explain this?

Here are some scope shots of the coil.



This shot is of the coil at fet shut off and pre amp, this is with shield unconnected.
Coil damping resistor set up at 1230 ohms.



I still have to do some target testing but so far the coil behaves very well.

[surfdetector]

All of the attachments say invalid when I attempt to view them.

[MartyJ1963]

@Gdigit,,,Can't view your attachments,,Clicking on them just takes me to the main Forum page. Regards, Marty

[6666]

Great post but attachments are toast

[godigit1]

Sorry guys just got home from work and found your posts.
Not sure what happened this is when I wish I could edit the last post.

So ll put these in order as from the last post sorry anyone has to jump around.

Ok here is the coil after rough cut shaped. And the second picture is of the paper tape wrap.

Shaped



Paper wrap.



Here is the coil with the shield wire attached.



The coil with shielding.



I think I remember something about not more than 4 photos per post Im not sure so Imm going to post the scope shots below.
If anyone knows if the 4 attachment thing is valid or not please let me Know .
Thanks

[godigit1]

Looks like that worked .
here are the scope shots.

The coil fly back.
Measurement is AX, on the cursors.
Voltage peak on the fly back is 500 Volts since you cant see it. sorry



And the op amp.



Sorry again on the first post Thanks guys for letting me know.

Be Well