Nikola Telsa Coil

[chemelec]

At the Request of a guy in Slovenia, Eu. I made one of Nikola Tesla's coils in a 10 inch diameter.
Also another in a 9 inch OD for my testing.

Tesla, Patent number 512340, dated Jan 9 1894.

Definately Interesting.

I'm in the process of testing it on my PI Unit.

If results prove bennifical, I will post further info.

[Carl-NC]

Looks like an odd way to make a double winding... don't see the advantage. :confused:

- Carl

P.S. -- I see you're headed for an adventure this summer!

[Unregistered]

I wonder why he wound it so that one winding is

90 degrees out of phase with the other? He must have had something in mind when he did it.

[fairdinkum]

tesla coils

I think he wound it this way to try to cut down on the capacitive coupling between turns so it would take a higher voltage without arcing over.
Tesla used this configuration under his tower, along with a shaft going down into the ground with a tuning device, and in this position it was his earth.
Thinking about it maybe it would be less useful as a detector coil due its capacitive coupling with the ground??????
FD

[chemelec]

Patent 512340, Written Portion.


Yes Carl, The Trip Should be Interesting.

[Cossaro]

new way?

section 15, second column...

"...increase the capacity of any give coil..."

This method increase the energy stored in parassitic capacitance of any adiacent spire to obtain a lower resonance without added capacitor components.

This effect is not the target for good PI coil.

[chemelec]

Checking out the definition of Parastatic Capacitance in Inductors, According to the "ARRL Handbook". (American Radio Relay League for Radio Amateurs)
Basically it say that Parastatic Capacitance only Exist at Frequencies ABOVE Self Resonance.
That is Really High Up, Well Beyond the Frequencies of any metal detector.
At least this is the way I understand it.

Now as to my Two New Test Coils and my test Data.

Both Coils are 5.125 inches ID and 7.75 Inches OD.
Both coils Total 40 turns total.
Both coils measure .77 Ohms.

The Single Coil measure 405 uH
The Tesla Dual Coil measures 407 uH
(They were both the same inductance before applying the Epoxy, But than they both changed a bit after coating them.)

The Single Coil has a SHARPLY Pronounced Free Air Resonance of 1.695 Mhz

The Dual Coil has a Very SLIGHT Free Air Resonance at 240 Khz. I suspect this is due to a slight In-balance between the two opposing coils.

These Free Air resonance tests were performed from 0 Hz, up to 2.2 Mhz. Thats the total range of "Kenwood, FG273" Function Generator.

Using these coils on my Pulse-1 Detector, With Normal Control settings:
Yes I Think the Dual coil is a Bit more Senstive, in Overall Performance.
Comparing both coils on detecting a 1/2 Gram Gold Nugget, the Dual coil is Definately More Sensitive.

Based on my test results above, I think I'm going to try to make a Smaller Tesla Coil, Simular to a 3 1/2 Inch coil that I already have.

Comments Welcome
Gary

[bbsailor]

Gary,

You said:
(They were both the same inductance before applying the Epoxy, But than they both changed a bit after coating them.)

My comments:

The slight change in inductance with the expoxy added is due to the close proximity of the epoxy which changes the dielectric constant of the space immediately around the coil.

The lower self resonance of the Telsa Dual-lead Coil is due to the phase cancellation of the winding looping back on itself out of phase. If you take a pen and shade-in the dual wire spiral all the way around starting at point A, you will come out at the lower wire at point B which gets looped back to the other wire.

If you switch between a spiral single traditional coil and then switch to the Telsa loop back dual version, you should see a different coil radiated field intensity. I would be interested, as a result of your expeiments, to hear how much the field intensity changes between the single coil radiated field and the Telsa coil dual vesion radiated field.

Who knows, but this might function like the figure-of-eight noise canceling coil to cancel external noise, and possibly ground changes, and become more sensitive to smaller targets.

Backyard research may reveal some surprises!

bbsailor

[chemelec]

bbsailor

Gary,

You said:
(They were both the same inductance before applying the Epoxy, But than they both changed a bit after coating them.)

My comments:

The slight change in inductance with the expoxy added is due to the close proximity of the epoxy which changes the dielectric constant of the space immediately around the coil.

The lower self resonance of the Telsa Dual-lead Coil is due to the phase cancellation of the winding looping back on itself out of phase. If you take a pen and shade-in the dual wire spiral all the way around starting at point A, you will come out at the lower wire at point B which gets looped back to the other wire.

If you switch between a spiral single traditional coil and then switch to the Telsa loop back dual version, you should see a different coil radiated field intensity. I would be interested, as a result of your expeiments, to hear how much the field intensity changes between the single coil radiated field and the Telsa coil dual vesion radiated field.

Who knows, but this might function like the figure-of-eight noise canceling coil to cancel external noise, and possibly ground changes, and become more sensitive to smaller targets.

Backyard research may reveal some surprises!

bbsailor

Yes bbsailor, I know why the Inductance changes with the epoxy. I also usually leave the coils for a few days befoore testing them. That way the Epoxy is good and hard.

I also new that the coils cancel because of out of phase windings.

That Self Resonant point is Barely Noticable on the scope. I Don't think it is actually a Self Resonance, I think its because of slight differences between the two coils. It is a Totally different frequency than the Single coil and responds differently.
I Can't actually Find a Resonance like a Normal coil yet. But I'm going to fire up my old TUBE RF Generator and check it out further.

Lots of Fun Winding these. Got it down to 2 minutes winding time for an 8 inch coil. But Gluing it is another thing.

MORE TO COME......Gary

[chemelec]

Still Playing:
I wound another Tesla coil with 80 turns total, 26AWG and 3 3/4 inch Outside diameter.

I never designed my jig for this small of wire and this Tesla coil didn't turn out very good as some of the turns overlapped on one side, making it somewhat oval and the two coils are Not properly Equil in capacitance.
Winding Two Small wires simutanously is a bit tricky.

In any case, it detects a 0.5 gram Gold nugget at 2 inches.
Thats a good 1/2 inch greater than my normal coil of the same size, turns and wire gauge.

I will try it again, but I'm out of epoxy for a few days till I go to another town and get some.

[chemelec]

bbsailor wrote:

If you switch between a spiral single traditional coil and then switch to the Telsa loop back dual version, you should see a different coil radiated field intensity. I would be interested, as a result of your expeiments, to hear how much the field intensity changes between the single coil radiated field and the Telsa coil dual vesion radiated field.

bbsailor, How do you do this? Iron Filings?
I don't have any, and doubt there are any sources near me.

Your Suggestions?

[bbsailor]

Gary,

Hook up another coil near the Standard/Telsa dual coil and connect this other coil directly to a scope. Then, when the standard coil is pulsed and then switched to the Telsa dual coil, you can see the effect on the induced radiated field on the coil connected to the scope. I suspect there will be quite a field cancellation in the Telsa coil. Your test should prove interesting if the Telsa coil produces enough of an induced field that can be useful as a PI coil.

I suspect the TX field will be cancelled in the dual Telsa coil design as well as the RX field from a target. But this coil might be a good test coil to eliminate external coil noise to debug internal PI circuit noise while having a coil loading the circuit.

See if the Dual Telsa coil is more quiet than the traditional mono coil?

bbsailor

[chemelec]

Considering the Detection results I'm getting with it, Obviously it is Transmitting Good.

But I believe Back EMF is reduced substantially.

I'll run some tests on his tomorrow.

Gary

Gary,

Hook up another coil near the Standard/Telsa dual coil and connect this other coil directly to a scope. Then, when the standard coil is pulsed and then switched to the Telsa dual coil, you can see the effect on the induced radiated field on the coil connected to the scope. I suspect there will be quite a field cancellation in the Telsa coil. Your test should prove interesting if the Telsa coil produces enough of an induced field that can be useful as a PI coil.

I suspect the TX field will be cancelled in the dual Telsa coil design as well as the RX field from a target. But this coil might be a good test coil to eliminate external coil noise to debug internal PI circuit noise while having a coil loading the circuit.

See if the Dual Telsa coil is more quiet than the traditional mono coil?

bbsailor

[Leto]

TESLA COIL

Hi to all,

Well I'm the guy from Slovenia who requested Tesla coil from Gary. Here are my results with two spiral coils both 28cm OD and 10cm ID, 1mm wire diameter, pvc insulated

(these were not made for performance but for comparison).

Normal (N) coil has 26turns and Tesla (T) coil 13 + 13 turns.

50 eu cent: (N) 25cm, (T) 24cm

US quarter: (N) 22cm, (T) 23.5cm

silver coin: (N) 19cm, (T) 21cm

golden ring: (N) 12.5cm, (T) 17.5cm



I had many theories about this coil, but everything really (except using it in PI detector) is explained in written portion of patent above. Techno talk of that days (112 years ago) is almost the same, but in Tesla style - very compact.

Thanks to Gary for his measurements and test data, I'm hardly waiting for his nice wound coils.

Note that almost every coil can be wound in Tesla configuration (honey comb, spider, basket..). Plenty of space for experimenting.

[chemelec]

Leto, Not sure if you measured the inductance of that coil, but I would suspect its Much Less than 100uH.



Here is another Tesla Coil I made this morning.
I Never counted the turns but the total inductance is 610 uH. (somewhat higher than I should use.

Its 1 inch ID and 4.25 OD, wound with 24 AWG.

Using my Pulse-2 and trying for best setting I can detect a 1/2 gram gold nugget at just under 3 inches and a 1/8 gram gold nugget at about 1/2 inch.

It definately appears that this type of coil Significantly reduces back EMF as I could reduce the dead time to a much lower setting.

However with such a small coil, Larger objects not so good.
A large mans gold ring at 8 inches.