spiral pi coil

[godigit1]

For interest
https://www.nuggetfinder.com.au/spiral-wound-coils

Thank you very much. Exactly what Ive been starting to work with low loss forms made of foam and or what I started calling my formless coils.
Also I see the foam they used did not eat the seathing from the litz.
this helps to confirm my thought that maybe I had got some bad cheap litz off ebay on my last 3d ss disaster.
Also thank you it kinda gives me confirmation Im going in a worthwhile direction.
Hope you are feeling back to yourself.

[godigit1]

hi all, so i made another coil wound exactly the same as before only this time i used .5mm magnet wire,
8" flat spiral basket coil, 30 turns, 590uh, 4.3ohms, 3.5nf and srf of 1.1069hz.
that is as it stands i will probably remove some windings just to drop the uh a bit, there was definitely some thing amiss with the other one.
something i thought about was when using calculators for this type of coil, the uh always seemed low compared to what was expected for a given number of windings.
and i think there is actually more than 30, if you count them on one side its 30 but does the surface area of the 30 windings on the other side of the coil matter?.
is it 30 windings or more due to the windings on the other side of the coil form?.

If you are using both sides of the form each side counts as a wind on your coil, sounds like you have that figured out allready.
Will be interested in where you can sample sample this coil when you get it finished and shielded.
Thanks

[green]

sorry green, 30 turns, 590uh, 3.5nf and srf of 110693.162 hz.
sorry about that, its not quite what a calculator says it should be(110754.17429501114), but in the ballpark.

Are you adding 3.5nf across the coil and then measuring 110.7kHz or calculating 3.5nf from coil SRF=110.7kHZ(no external capacitor)? Think a bundle wound coil would have a higher SRF.

[godigit1]

First I'm just learning. I'm not saying you are wrong. Just saying we are not thinking the same. Probably means at least one of us wrong. One thing worse than being wrong is not knowing it. Helps if someone corrects or suggests something different.

The leads were not twisted on these coils when I tested them should I retest that way?

Just did a test with a shielded mono coil I have. 31inch twisted pair lead, 100nf capacitor across coil(SRF 29760kHz, 286uH) 31inch twisted pair lead, no capacitor(SRF 1.563MHz, 36pf) 31inch lead not twisted, no capacitor(2.1MHz, 20pf) no lead, no capacitor(2.56MHz, 14pf) The lead not twisted did add some capacitance, not as much as twisted. Probably should state if no lead, or with lead and what type of lead when giving SRF or coil capacitance.

Thanks for testing the twisted pair Vs untwisted. interesting results. kinda confirms the capacitance and proximity thing. If I used the leads from the coil I had planned on making my own shielded cable for them. But I also have some nice belden cable Ive been wanting to try Im going to have to test it for capacitance once i get there.

I started to make 3 forms for a verticle stack to wrap with different spacings, figured its the easiest way to wrap with some spacing.

I know you did a verticle stack and shielded it in the past with very nice results is this the coil you are testing the leads on?
Nice low capacitance its going to be interesting to me messing with some the spacing.
The coil example 6666 just posted shows a loose wrap but not much spacing. But with a urathane closed cell foam you have to pick up some dialectric value.
So far the best foam Ive found is the locktite seems to be the most consistant and rigid.
Thanks

[green]

Thanks for testing the twisted pair Vs untwisted. interesting results. kinda confirms the capacitance and proximity thing. If I used the leads from the coil I had planned on making my own shielded cable for them. But I also have some nice belden cable Ive been wanting to try Im going to have to test it for capacitance once i get there.

I started to make 3 forms for a verticle stack to wrap with different spacings, figured its the easiest way to wrap with some spacing.

I know you did a verticle stack and shielded it in the past with very nice results is this the coil you are testing the leads on?
Nice low capacitance its going to be interesting to me messing with some the spacing.
The coil example 6666 just posted shows a loose wrap but not much spacing. But with a urathane closed cell foam you have to pick up some dialectric value.
So far the best foam Ive found is the locktite seems to be the most consistant and rigid.
Thanks

Not sure how the coil is wound. It's potted in foam shielded top and bottom with graphite paint, probably flat basket. Did forget to connect shield to one of the coil leads when measuring yesterday. Connecting the shield would lower the SRF readings. Think number differences for twisted pair lead and not twisted are valid.

Might have to try locktite foam. I have used GE and Great Stuff, seem to work.

Including a test I've posted before. All the coils have the same number of turns and same ID(200mm). A bundle coil, 23turns AWG28 magnet wire 200mmID calculates 335uH. Insulation on the wires does add some spacing. Appears added spacing did lower inductance. Litz wire coil comes out of saturation first. Not a big difference between any of the coils except coil D(AWG24 solid), takes longer to come out of saturation. The vertical coils look a little less in Litz_7 but better in Litz_4. Be interesting if you can find a magic coil.

[sinclairuser]

hi, no green 3.5nf capacitance is what the coil measures(without coil lead), as is 590uh, put in the calculator it comes to 110754.17429501114hz, but it measures 110693.162hz.
hope that clears that up.
like i said in the ballpark.

aly.

[green]

hi, no green 3.5nf capacitance is what the coil measures(without coil lead), as is 590uh, put in the calculator it comes to 110754.17429501114hz, but it measures 110693.162hz.
hope that clears that up.
like i said in the ballpark.

aly.

Thanks for the reply, wasn't expecting a SRF of 111kHz. My spiral coils measure over 2MHz without the shield. Maybe yours being close to 600uH has something to do with the low SRF?

[godigit1]

Not sure how the coil is wound. It's potted in foam shielded top and bottom with graphite paint, probably flat basket. Did forget to connect shield to one of the coil leads when measuring yesterday. Connecting the shield would lower the SRF readings. Think number differences for twisted pair lead and not twisted are valid.

Might have to try locktite foam. I have used GE and Great Stuff, seem to work.

Including a test I've posted before. All the coils have the same number of turns and same ID(200mm). A bundle coil, 23turns AWG28 magnet wire 200mmID calculates 335uH. Insulation on the wires does add some spacing. Appears added spacing did lower inductance. Litz wire coil comes out of saturation first. Not a big difference between any of the coils except coil D(AWG24 solid), takes longer to come out of saturation. The vertical coils look a little less in Litz_7 but better in Litz_4. Be interesting if you can find a magic coil.

Its hard to tell for me on the litz 4 graph, at the bottom where the colors all come togeteher they mingle and to me it looks llike coil B is 1 usec faster. but coil E has a faster rise time. wonder if thats partially due to the low inductance?

As far as a magic coil no I think thats allready hear they cost 1700 Bucks. I just wanted to try adjusting coil perimeters a different way using one peice of wire length to see what the different capacitances and inductances do. Been messing with designing or moddind coils want to twist my own wire so i should learn what each varyable does, such as larger wire mass with lower inductance, Will it just slow down the coil? Who can answer that for me. I have no tutor i have to learn imperically.
Maybe im just making nice antennas.

[green]

Its hard to tell for me on the litz 4 graph, at the bottom where the colors all come togeteher they mingle and to me it looks llike coil B is 1 usec faster. but coil E has a faster rise time. wonder if thats partially due to the low inductance?

As far as a magic coil no I think thats allready hear they cost 1700 Bucks. I just wanted to try adjusting coil perimeters a different way using one peice of wire length to see what the different capacitances and inductances do. Been messing with designing or moddind coils want to twist my own wire so i should learn what each varyable does, such as larger wire mass with lower inductance, Will it just slow down the coil? Who can answer that for me. I have no tutor i have to learn imperically.
Maybe im just making nice antennas.

Litz_4, vertical coils F and H have highest signal at 5us. Litz_7, vertical coil H has lowest signal at 14inches. Think coil diameter is some of the reason, vertical coils have the smallest mean diameter. Smaller coils are better at short distances(target was close to get good signal when recording), worse at longer distances. Litz_4, vertical coils F and H come out of saturation sooner than coil B. Think coil E(Litz)is the fastest because the larger wire used in the other coils act as a target causing longer time to come out of saturation, only about 1us difference between Litz and AWG28(AWG24 longer time)made a spiral coil with AWG19 magnet wire(over 10us to come out of saturation).

[green]

hi, no green 3.5nf capacitance is what the coil measures(without coil lead), as is 590uh, put in the calculator it comes to 110754.17429501114hz, but it measures 110693.162hz.
hope that clears that up.
like i said in the ballpark.

aly.

How do you measure coil capacitance? I measure SRF and calculate capacitance with inductance. Looks like you measure capacitance some way and calculate SRF with inductance?

[sinclairuser]

How do you measure coil capacitance? I measure SRF and calculate capacitance with inductance. Looks like you measure capacitance some way and calculate SRF with inductance?

this calculator is quite accurate https://m0ukd.com/calculators/resona...ce-lc-circuit/

though it requires accurate capacitance i measure the capacitance with a fluke PM6303A bench lcr meter, i also have a capacitance and esr tester i was given by one of the old boys years ago that has a magic eye valve old but still useful.
it doesn't matter if which way you do it, it seems there are calculators out there that take different approaches to make calculations, the beauty of them is you can use the different calculators to double check the numbers.
thanks,
aly.

[green]

this calculator is quite accurate https://m0ukd.com/calculators/resona...ce-lc-circuit/

though it requires accurate capacitance i measure the capacitance with a fluke PM6303A bench lcr meter, i also have a capacitance and esr tester i was given by one of the old boys years ago that has a magic eye valve old but still useful.
it doesn't matter if which way you do it, it seems there are calculators out there that take different approaches to make calculations, the beauty of them is you can use the different calculators to double check the numbers.
thanks,
aly.

Thanks again for the reply. Apologize for the repeats. Still trying to figure out how you can wind a spiral coil with 3.5nf capacitance. Spiral coil should be a fast coil. Looks like you are cross checking by measuring capacitance, inductance and SRF. I don't measure capacitance, but I cross check with Rd=pi*L*SRF. Our SRF and capacitance measurements are "lot" different. Do a lot of your coils measure SRF less than 200kHz? Any thoughts why SRF is so low? If you have a scope could you try measuring SRF the way I do? Clip scope ground lead to scope probe making a loop. Lay loop on the test coil, place test coil near a operating PI coil to excite resonance and read resonant decay with scope. Wondering if my procedure has a problem. Thanks

[godigit1]

Hi Guys
Ive found this calclulator useful. Solves for capacitance Freq And inductance.
Double checking to C= 1/(2pi*2pi*L*Srf*Srf) its been good so far.
http://www.1728.org/resfreq.htm

Have you rewraped your coil yet?
Looking back at your photos of the first coil it does look like there are 30 wraps on just the one side of the form. If thats the case that would explaine the extra resistance on the last coil and high inductance on this coil.

[godigit1]

Litz_4, vertical coils F and H have highest signal at 5us. Litz_7, vertical coil H has lowest signal at 14inches. Think coil diameter is some of the reason, vertical coils have the smallest mean diameter. Smaller coils are better at short distances(target was close to get good signal when recording), worse at longer distances. Litz_4, vertical coils F and H come out of saturation sooner than coil B. Think coil E(Litz)is the fastest because the larger wire used in the other coils act as a target causing longer time to come out of saturation, only about 1us difference between Litz and AWG28(AWG24 longer time)made a spiral coil with AWG19 magnet wire(over 10us to come out of saturation).

Thanks for explaining I was looking at the graph wrong realized that later after I posted.

Started to make the verticle test coils then decided it was not practicle for the test. With the increased spacing and 28 wraps the coils would be too tall.
Still trying to decide between flat spiral or a verticle stack 7 high 4 wide.
Both have advantages but thinking the flat will be better for testing where the inductance is concearned.

[godigit1]

I think you will have better luck with the magnet wire especially if you added a spacing between wraps.

Why do you think adding space between the wraps would make it better? I think spacing reduces inductance and probably increases capacitance especially if enough turns are added for the same inductance?

Are your 3 foot leads twisted? I get about 1pf/inch when I use AWG24 twisted pair for lead. I wound a bundle coil awhile back with AWG 28magnet wire, inductance very close to calculated using the coil calculator. Calculated inductance winding the same coil with Teflon coated wire calulates about the same inductance I get winding the spiral coil using magnet wire with no spacing.

Hi Green,
Ive been reading so much it took me a while to find where I was getting adding spacing will reduce capacitance.
Comes down to type of capacitance in a coil its parasitic capacitance as there is not actually two plates seperated.

Here is a little bit of the wicki on it

.When two conductors at different potentials are close to one another, they are affected by each other's electric field and store opposite electric charges like a capacitor. Changing the potential v between the conductors requires a current i into or out of the conductors to charge or discharge them.{\displaystyle i=C{\frac {dv}{dt}}\,}where C is the capacitance between the conductors. For example, an inductor often acts as though it includes a parallel capacitor, because of its closely spaced windings. When a potential difference exists across the coil, wires lying adjacent to each other are at different potentials. They act like the plates of a capacitor, and store charge. Any change in the voltage across the coil requires extra current to charge and discharge these small 'capacitors'. When the voltage changes only slowly, as in low-frequency circuits, the extra current is usually negligible, but when the voltage changes quickly the extra current is larger and can affect the operation of the circuit.
Coils for high frequencies are often basket-wound to minimise parasitic capacitance.
Effects


I re- wound the spool coil with a layer of silicon flex tape between every five wraps it is .040mills thick.
Both the inductance and capacitance dropped and the srf rose.
original Spool coil
540 uh
588khz
135.6pf


spacing added
384uh
1.136mhz
51.1pf


this is the 8 coil with too much spacing notice the low voltages


I also tested a couple other coils a 3dss
8"
302uh
1.136 mhz
64.99pf

And the real suprise for me is a folded mono designed for the TDI
280 uh
500khz
361pf
Im thinking it has to do with the shieldind.
Is there a specific way to test a shielded coil should I be hooking up the shield?

So im thinking on a spiral coil the wire proximity is low as only the edges of the wires are in close proximity. (it may allready be the sweet spot)
Im also thinking spacing added to the spiral coil will have a greater effect than some other coil types due to all the wires being on the same plane.
what does this come down too for me?
I think any coil design can be further optimized for capacitance by adjusting the spacing or angles that the wires may cross.
Just building allot of the same coils to find ths out is time consuming. I wonder if there would be a way to model this as a varible in spice. Way out of my league for now.

Thanks again for all your help and information you offer to the forum.
And I think all the members would agree as we understand the time and effort that goes into it all.
Best Regards.