Fast coil with teflon wrapping wire

[nick_f]

Hi Thinkerer,
If you have 23 turns, I would say your coil will have quite a bit over 300uH. I got to about 290uH with 20 turns with my PVC wire!
With 24 turns, if I remember right, I had about 385uH. The coil has about the same diameter as yours, 280mm.
Did you measure the inductance of your 280mm diameter/23 turns coil?
I tried last evening to make my coil, but I failed.
The two mistakes I made were: - after I winded the wire into the coil, I used some polyester sewing thread to keep it in place, as I usually do. But after that I took the coil off the jog and tried to wind the spiral wrap around the coil. Toward the end, some of the turns were much shorter, while others were very long. I have to follow bbsailor's advice and to pult the spiral while the coil is still on the jig. Second mistake - because the diameter of the coil was larger than the internal diameter of the spiral, its lenght decreased, so my spiral wrap in the end wasn't long enough.
I will try again tonight, I hope I will have better luck.
The shielding from a video cable is not good for the purpose of shielding the coil, it is a mess to try working with it, I quit soon after I took the shielding out.
Regards,
Nicolae

[Tinkerer]

Hi Thinkerer,
If you have 23 turns, I would say your coil will have quite a bit over 300uH. I got to about 290uH with 20 turns with my PVC wire!
With 24 turns, if I remember right, I had about 385uH. The coil has about the same diameter as yours, 280mm.
Did you measure the inductance of your 280mm diameter/23 turns coil?
I tried last evening to make my coil, but I failed.
The two mistakes I made were: - after I winded the wire into the coil, I used some polyester sewing thread to keep it in place, as I usually do. But after that I took the coil off the jog and tried to wind the spiral wrap around the coil. Toward the end, some of the turns were much shorter, while others were very long. I have to follow bbsailor's advice and to pult the spiral while the coil is still on the jig. Second mistake - because the diameter of the coil was larger than the internal diameter of the spiral, its lenght decreased, so my spiral wrap in the end wasn't long enough.
I will try again tonight, I hope I will have better luck.
The shielding from a video cable is not good for the purpose of shielding the coil, it is a mess to try working with it, I quit soon after I took the shielding out.
Regards,
Nicolae

Hi Nicolae,
well, it seldom turns out quite the way one wants on the first try.
I got 325uH and 0.8 Ohm. Increasing the inter wire spacing reduces the inductance somewhat. The resistance is a bit of a surprise. So it must be #20 wire.
What I end up with is 1 Ohm for the Mosfet, 0.1 Ohm for the series resistor that I use to measure the coil current, and 0.2 Ohm for the cable, total 2.1
for a TC of about 155uS or about 1.32A coil current at 41uS TX time.

The former bucking coil does not work with the new coil, so tomorrow I will wind a new one.

I changed the timing schedule of the PIC, keeping the same 416.5uS cycle, but reduced the TX from 50uS to 41uS, so the overall power consumption is reduced a bit.

All the best

Tinkerer

[nick_f]

Hi Tinkerer,
I hope your coil will perform very well. What is the configuration of your coils?
As far as I understand, the bucking coil is used on (Induction Balance) detectors that have concentrical coils. The bucking coil cancels the field in the Rx coil. Are you using the same configuration?

So you are using a PIC for generating the delays? Did you write the code? Do you have access to the source code? I want to try something with a PIC as well.

Regards,
Nicolae

[Tinkerer]

Hi Tinkerer,
I hope your coil will perform very well. What is the configuration of your coils?
As far as I understand, the bucking coil is used on (Induction Balance) detectors that have concentrical coils. The bucking coil cancels the field in the Rx coil. Are you using the same configuration?

So you are using a PIC for generating the delays? Did you write the code? Do you have access to the source code? I want to try something with a PIC as well.

Regards,
Nicolae

Yes, I use the Concentric Induction Balanced Coil, CIBC.
TX coil = 280mm outside diameter, bundle wound, 10mm bundle diameter.
23 turns
325uH
0.8 Ohm

Bucking coil = 140mm diameter, about 8 or 9 turns

RX coil, 140mm diameter, bundle wound, hmmm, I just realize that I don't know the amount of turns. I usually do not worry about the amount of turns, I measure the wire length and use the same wire length for the TX and the RX coils.
300uH
2.6 Ohm including 5 feet of HDTV cable

I use the PIC16F690 for the timing and write the code myself. However, I am very much a beginner at programming. Later I intend to migrate to the PIC18F4550. I would much appreciate if I could get help with that.

Tinkerer

[nick_f]

Hi Tinkerer,
Thanks for the info. What is that a bundle wound? Is there a presentation of this type of coils?
What's the capacitance of HDTV cable, per meter?
With the source code, I would help you, but I am also a beginner. If I do any progress with the code, I can send it to you. Do you use a LCD for control?

Regards,
Nicolae

[porkluvr]

problem with MiscEl

Tinkerer,Please help me With MiscEl. I love its apparent flexibility but I can't get my desired function to work.

What is wrong with my coil diameter entry? Meters is the default unit of measure for the Diameter box, so .28 should be interpretreted as 280mm, right? I am confused.

[Tinkerer]

Tinkerer,Please help me With MiscEl. I love its apparent flexibility but I can't get my desired function to work.

What is wrong with my coil diameter entry? Meters is the default unit of measure for the Diameter box, so .28 should be interpretreted as 280mm, right? I am confused.

Use 280m and 12m.

You have to cheat with the wire diameter. Use first the copper diameter and then do it again with the copper plus insulation to get the wire length.
For the fill factor I calculate the surface area with a normal calculator.

For PI reference I use the outer diameter of the coil, since it has to fit within a coil form, but for Misc.El you have to use the average diameter.

So my TX coil as described above, has 280mm outer diameter.

Tinkerer

[Tinkerer]

Hi Tinkerer,
Thanks for the info. What is that a bundle wound? Is there a presentation of this type of coils?
What's the capacitance of HDTV cable, per meter?
With the source code, I would help you, but I am also a beginner. If I do any progress with the code, I can send it to you. Do you use a LCD for control?

Regards,
Nicolae

porkluvr has posted the answer for the bundle.
I have no idea about the capacitance of the HDTV cable.

I think I have found a solution for the capacitance problems with the PI. It does not seem to bother me anymore, but I need further experimenting to see where the boundaries are.

Tinkerer

[Tinkerer]

PIC timing schedule

Here is the timing schedule

[Tinkerer]

Polypropylene spacer coil

OK, so here is the TX coil as promised. It does work.
I will move this coil thread to the other coil threads now.

Tinkerer

[nick_f]

Hi Porkluvr,

Thank you for the information and formulas. I bought from ebay some teflon insulated multistranded wire, various sizes including AWG22, it should arrive next week. Unfortunately it is silver coated, but I couldn't find any that is tin coated. I also want to buy the Scotch 24 tape, maybe I will buy it in a week or two. I will let you know about the characteristics of the coil, once I made it.
I also bought some good quality audio shielded cable, I am very happy with it. It is flexible (multistranded core), has good shield, made of copper and tin foil and it has a low capacitance per meter (1.5m has 100pf). For people in Australia, I bought it from Jaycar Electronic, code WB1508 (Electus).

This is the description of this cable:

Single Core OFC Screened Audio Cable

High quality OFC mono audio cable, double screened for extra shielding. Ideal for making your own RCA leads etc.
- Conductor Material: OFC
- Insulation Material: PPE
- Stranding: 45/0.12mm
- Braid Stranding: 96/0.10 + Alum
- Conductor Resistance: 0.0365ohms/M
- Capacitance: 66.8pf/1M
- Impedance: 65ohms@1m
- Colour: Black.
- Roll length 100 Metres
- Sold per metre QTY 1+$2.35 100+$1.95 500+$1.70

[porkluvr]

Hello Nick. You should do well with your wire selection. Don't worry too much about the tin coating for now but keep that in mind when you run across 18 ga., if there is a choice between tin and silver - you know what to choose. That looks like good audio cable.

Here is a stateside surplus dealer that I want to purchase from when I get the chance. At the current time their only offering in teflon, stranded, tin coated 18 ga. is double thickness teflon, but that may not be a bad thing. It might be more bulky than desired but it shouldn't add much weight.
http://www.surplussales.com/Wire-Cable/Wire4.html

They also carry ferrite rods suitable for probes. (ICH) ROD7.5/50-3C80 (recommended by bbsailor).
http://www.surplussales.com/Inductor...s/FerRods.html

You have a scope so you should be able to see where you can make improvements, but your 22ga. should work OK. I don't know what you are using but you will probably need to have a very fast settling preamp before you can make use of advantages offered by the fastest coils, getting down into the single-digit microsecond delays.

I'm learning as I go along and hopefully I know enough already so that I won't be terribly dissapointed with results on my prototype in work.
I'd like to forget that I still have one PCB to layout, and then two to construct (not counting the power board which will be easy) before I will be needing to get my wire. Yeah, and I'd better get busy with finishing the receiver design that the unfinished PCB will represent, too.

I'm wanting to implement three channels but maybe I should start with only two, and then finish what's been started. Three is too much to juggle, especially since I'm confounded as to how channel three should work.
(Shoot, two channels confuse me, for that matter!) Ahhh, I waste too much time thinking and not doing.
Let us hear how you do!