Litz wire size for coils

[godigit1]

Hey guys thanks for spinning me in the right direction. This thread as been a eye opener for me.
I found this statement on q and wire and it helped me to under stand a little better.


Parallel resonant circuit: Impedance peaks at resonance.

A low Q due to a high resistance in series with the inductor produces a low peak on a broad response curve for a parallel resonant circuit. (Figure below) conversely, a high Q is due to a low resistance in series with the inductor. This produces a higher peak in the narrower response curve. The high Q is achieved by winding the inductor with larger diameter (smaller gague), lower resistance wire

This is the link to the full article if any one is interested.
http://www.allaboutcircuits.com/text...onant-circuit/


Best Regards

[FatBob]

I've made a few coils with regular wire and Litz and am ready to make a perfect coil but
I have found the Litz is a bit fragile. I had a coil with 4 foot leads in a box when I moved
and the leads broke internally where they came out of the housing. Also they can break on
the former for the race track/basket weave type. And using super glue to firm them up
can cause shorts to form inside the coil.

So does anyone have some tips on how to make a perfect coil using Litz? I got some new
housings from DB coils https://sites.google.com/site/dbcoil...m-style-shells and I'm
itching to build something!

[Chet]

Litz wire reduces the eddy current losses and does improve the Quality (Q) of the coil especially at a resonant unloaded frequency. The PI coil with the damping resistor operates below the self-resonant frequency in a somewhat broad band mode.
The high self-resonant frequencies from Green’s charts provide an indication that the PI can use an early target detection sample window. They show that coil self-capacitance, cable capacitance, and diode and MOSFET output capacitances are reasonably low.
Any gain in performance using Litz versus solid wire needs to be demonstrated by methods such as Green’s measurements. Especially the entire transmit/receive performance comparison of coils on fixed short time constant targets.
Most of the commercial coil manufactures now build their coils with Litz wire. I haven’t been able to find any direct measurements comparing solid wire with Litz wire coils.
Have another fine day,
Chet

[green]

Wanting to see if I can see the residual eddy current decay of coils wound with different wire. Where I'm at and what I'm thinking. I have two coils, spider wound with solid wire, one AWG24 and one AWG28. Don't have Litz wire but I have AWG34 magnet wire. Think of twisting 4 strands of #34, same resistance as AWG 28 and winding a coil. 23 turns, same as other coils. Including some data on the two coils. Coils not shielded, about 12 inches Teflon coated twisted pair for lead wire. Thinking it makes sense to leave the coil resonance as high as possible to allow early sampling for the comparison. Need to connect coils to a coil driver and pre amp and compare decays, scope and maybe LT spice simulation of the same circuit. The scope resonance pictures were taken with the coil connected to the coil driver with no damping resistor and the pre amp disconnected with a x10 probe across the coil. The resonance is higher with the scope probe disconnected laying close to the mosfet. Suggestions appreciated.

http://www.geotech1.com/forums/showt...042#post213042

Teleno suggested a vertical coil in the thread above. Think I'll add 1 or 2 vertical coils to the Litz wire comparison. Including a chart of coil information. Should I add more columns? All coils, 200mm I.D., 23 turns. The main purpose of the test, see if coil shows in the decay curve. Other comparisons to look for? I could try the Litz vertical also if I test on the spider wire coil form, unwind and wind on a vertical form. Fr is circuit resonance with Rdamping and input resistor disconnected. Measured with scope probe near mosfet and with scope probe across coil.

[Chet]

Attached is an example of a vertical basket coil that should be considered. The dowels should be shorter. Toothpicks may not be strong enough.
Have a good day,
Chet

[FatBob]

Here's a 10" Litz 3D Race Track Basket Weave Gutter Mount Coil I just made using 175/46 Litz;



I used Gutter glue (tri-polymer based formula that is semi-self leveling) to affix the windings
(I hope there's no metal in there!). I couldn't figure a way to route the Litz safely up to
the control box so will use some Fishfinder 2 lead wire for that.

(10" 175 Litz 3D Race Track Basket Weave Gutter Mount Fish Finder coil?)

[green]

Attached is an example of a vertical basket coil that should be considered. The dowels should be shorter. Toothpicks may not be strong enough.
Have a good day,
Chet

The toothpicks were strong enough for AWG28 solid magnet wire. I'll add it to the list of coils reply#64.

[Chet]

Hi Green,
Great looking coil; looks like toothpicks will work.
Have a good day,
Chet

[godigit1]

Hi Green,
Another great looking coil. I've had good luck with the toothpicks on a dart board. A finish nail can be used for stiffer wires.
I use a small awl to pre pierce or punch the dart board then insert the picks with a pin driver I made from brass. You can make very fast forms. A cheap board is about 9 bucks and totally reusable. .
I have a couple of new vertical winds to see what you guys think about. And the 3dss can stack in a vertical way by using configurations of three toothpicks but advancing forward in a row instead of like a slot if that makes any sense. I will ad some pictures when I get back home again.
(On The Prowl )


So far no luck but its more about just getting out there!

As far as coil resonate testing I am failing so far I cannot make it happen and I'm pretty sure that my signal generator is insufficient. I have one made for testing acoustic amps and I think the circuit is damped some how. I'm going to build one out of a arduno or propeller when I get home.

I know the comparisons and graphs you are doing are very time consuming and your efforts are greatly appreciated. I'm wondering if another perimeter to evaluate coil wire may be by coils that are the same inductance using different wires as you are might be useful.
Is This a useful approach?
I will be happy to do allot of testing and I will, but I'm still not up to speed, and It appears my lab or I are lacking. But not for long.

Have a great one!

[baum7154]

As far as coil resonate testing I am failing so far I cannot make it happen and I'm pretty sure that my signal generator is insufficient. I have one made for testing acoustic amps and I think the circuit is damped some how. I'm going to build one out of a arduno or propeller when I get home.

Godigit1
-----------------------------------------
Do you know if your generator goes to 1mHz +? Most of the fast coils of 300uh to 350uh with feedlines attached resonate in the range of 900kHz to 1.5mHz. Slower ones lower than that. Your coil at self resonance should dramatically PEAK in voltage without any damping resistor.

Dan

[godigit1]

Hi Dan,

I have been trying a tenma 72-910 audio oscillator with a max range of 200 k to 1 meg square wave only. The output is damped at 600 Ohm so its not gonna do it for me I guess.
Ill look at the specs for the arduino one I was planning on building. But this may be one of those things where I should just spring for the right tool.
Ive been using this set up but maybe I should try without the resistor next time and with the proper tool.



Thanks for your help.
digit

[chemelec]

200 khz is probably not high enough.
Most of my coils are Over 1 Mhz.

You mIght add a Parallel Capacitor (10 or 22pF) to the coil, to get it in Range with only 200 Khz, But than you need to use My JavaScript Calculator to determine the Actual Free Air resonance.
Calculator is located at: chemelec.com

[green]

Hi Dan,

I have been trying a tenma 72-910 audio oscillator with a max range of 200 k to 1 meg square wave only. The output is damped at 600 Ohm so its not gonna do it for me I guess.
Ill look at the specs for the arduino one I was planning on building. But this may be one of those things where I should just spring for the right tool.
Ive been using this set up but maybe I should try without the resistor next time and with the proper tool.



Thanks for your help.
digit

Try a 100 ohm resistor in series with a 1N4148 diode in stead of the 1M resistor and excite the coil with a 1khz square wave. Wasn't thinking about sapping the signal generator. Maybe start with a 1k resistor in series and turn the amplitude up slowly.

[baum7154]

In the above example you will measure the frequency of the coil ringing with the scope to determine self resonant frequency. Should do nicely but i wonder if the 100 ohm plus the 600 ohm of the gen will damp the coil too much to give true SRF.

Dan

[Chet]

Hi Digit
Release all of the attenuation buttons and then tune very slowly from 500k to 1meg. You should be able to see a weak second harmonic around 600-700k. The second harmonic will be somewhere around 1.2-1.4 meg double the basic frequency.
Good luck,
Chet