Nikola Telsa Coil

[Cossaro]

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.

the pulse rate won't be the operative "self-resonant" frequency.

For my GoldDetector-PI i consider the pulse-delay in relation to inductance.
The better coil i made, 350 uH, can be "sampled" at 9 uS with a TX of 80 uS (5A used).
Can you test this TeslaCoil with similar conditions? I need to compare the decay fly-back for ther 2 coils

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.

this confirm what i say,
single spiral coil = high Q Factor,
Tesla... lower Q an lower self resonance.

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.

i suspect the new coil is better "tuned" to your MD preamp and integrator.

Can you post the decay picture for the single and tesla coil with the same division unit on your scope? This help us to see the exact sample point (you can mark with some img-editor).

i made 3 good-on-air spiral coils and never used on field,
to much weight,
to much capacitance on ground exposition,
absence of shield...

I never resolve those problems, i go back to "eric foster-like coil"

[chemelec]

Sorry, I am no longer doing any electronics till SEPEMBER.

With Spring here, Summer Comming I have too many other things to do.
Also a Trip to Europe in July and August.
I also won't be on this forum or the many others I visit, Very often in the next few months.

However, That Lower Frequency Resonance I Mentioned is Almost Non-Existant.
I Doubt it will affect Anything on Any Detector.

Take care........Gary

the pulse rate won't be the operative "self-resonant" frequency.

For my GoldDetector-PI i consider the pulse-delay in relation to inductance.
The better coil i made, 350 uH, can be "sampled" at 9 uS with a TX of 80 uS (5A used).
Can you test this TeslaCoil with similar conditions? I need to compare the decay fly-back for ther 2 coils



this confirm what i say,
single spiral coil = high Q Factor,
Tesla... lower Q an lower self resonance.



i suspect the new coil is better "tuned" to your MD preamp and integrator.

Can you post the decay picture for the single and tesla coil with the same division unit on your scope? This help us to see the exact sample point (you can mark with some img-editor).

i made 3 good-on-air spiral coils and never used on field,
to much weight,
to much capacitance on ground exposition,
absence of shield...

I never resolve those problems, i go back to "eric foster-like coil"

[Cossaro]

[QUOTE/Chmelec]
However, That Lower Frequency Resonance I Mentioned is Almost Non-Existant.
I Doubt it will affect Anything on Any Detector.
[QUOTE]

the analysis of the decay is the basis for detection in PI-family detector .

Mono coils are frequently used in this kind of electronics and the MAJOR quantity of information are condensed in the first 10-15 microsecond after the TX signal.

If you'll try to discriminate between ferrous and non-ferrous object you need to sample immediately after the TX.

The self-resonance frequency, the Q-factor and the inductance of the coil define the limit for decay analysis.

If you'll happy to discriminate between ferrous and non-ferrous you need a coil with higher self-resonance, high Q-factor and pre-defined induction value.

With long decay (simptom of low Q-factor and low self-resonace coil!) you loose all the items essentials to discriminate.

best rgds.

Fernando.

[chemelec]

Cossaro, The Self Resonance on my NORMAL, single flat Radial coils is typically about 1.75 to 2.5 Mhz, Depending on the size between 12 to 8 inches respectively.

This Slight Resonance I am detecting on this Tesla Coil is Not the actual Coil Resonance.
I believe it is a Small ERROR resonance created by Small differences between the two windings. No Coil is Perfect. This is a VERY Tiny Bump on the scope, Not the normal Very High SPIKE.

I have tested these Tesla Coils up to 100 Mhz and I do NOT Detect a Normal Resonance at Any Frequency. Just this one Tiny Bump.

I would recommend you Try one of these flat Tesla Coils, Properly Wound.
They Definately have Increase Sensitivity to SMALL Objects.

[Unregistered]

Cossaro,
I would recommend you Try one of these flat Tesla Coils, Properly Wound.
They Definately have Increase Sensitivity to SMALL Objects.

I won't exclude this test in a future.

[Cossaro]

sorry...

I won't exclude this test in a future.

sorry, reply as unregistered!

[chemelec]

Hows this for a Coil? Just Expermenting!

4 Wires, A Double Tesla Coil.

[chemelec]

Hows this for a Coil? Just Expermenting!

4 Wires, A Double Tesla Coil.

Now, Having Finished this coil:
8.1 inches in OD.
Total is 36 Turns of 26 AWG.
Coil Width is .8 inches.
Mean Radius is 3.65 inches
Inductance is 461 uH.

Doing Tests with this coil on my Pi Detector, it detects my gold ring at 12 inches and it detects a 6.5 inch diameter Paint Can Lid at 27 Inches.

[AdrianM]

Now, Having Finished this coil:
8.1 inches in OD.
Total is 36 Turns of 26 AWG.
Coil Width is .8 inches.
Mean Radius is 3.65 inches
Inductance is 461 uH.

Doing Tests with this coil on my Pi Detector, it detects my gold ring at 12 inches and it detects a 6.5 inch diameter Paint Can Lid at 27 Inches.

Please forgive me for digging up this extremely old post, but I simply can't understand why such apparently astounding results as these didn't prompt further discussion

What has happened to this scheme in the four long years that have elapsed? moodz seems to have been the most recent experimenter to have taken it up and has shown how to make a differential coil to the Tesla design. I'm starting to wonder if this has gone "underground"

[chemelec]

Please forgive me for digging up this extremely old post, but I simply can't understand why such apparently astounding results as these didn't prompt further discussion

What has happened to this scheme in the four long years that have elapsed? moodz seems to have been the most recent experimenter to have taken it up and has shown how to make a differential coil to the Tesla design. I'm starting to wonder if this has gone "underground"

I find a Vertical Wound Coil Doesn't work as wel as a Radial Coil.
I Think because all the coil is not at the same distance from the object.

And if you want one of my Radial Tesla coils to play with, that can be arranged.

[AdrianM]

I find a Vertical Wound Coil Doesn't work as wel as a Radial Coil.
I Think because all the coil is not at the same distance from the object.

It might be, although I don't think this is a problem for a solenoid otherwise they'd be wound radially wouldn't they?

However, this could be a reference to my awful ribbon cable lashup Oddly, it's the fastest and deepest experimental coil I've made so far! (which may of course mean absolutely nothing!).

When you made that double (4 wire) Tesla, how did you combine the windings? I've been driving mine in the same way as moodz (auto transformer style) - using the "centre tap" at ground and switching just one end of the coil to -ve. Then for detection the signal is taken from both ends of the coil which flyback above and below ground allowing the signal to be recovered differentially. This is one of the great advantages of a differential coil like this - common mode noise signals are cancelled so shielding (that would otherwise slow up the flyback) can be eliminated altogether.


I'd love to have a play with one of your superbly made coils but I wouldn't be able to justify the shipping costs when I could do with the all the coil building practice I can afford here

[AdrianM]

Mythbusting

There's a lot of mythology surrounding Mr. Tesla, and researching this patented coil I've come across some fantastical claims. One that seems to crop up the most often is that the bifilar winding generates a greater magnetic flux for the same Ampere Turns all else being equal. That's an extraordinary claim that Tesla himself never made, as far as I'm aware, and it will be trivial to confirm or deny.

My mythbuster setup consists of two near identical 50 turn air-cored solenoid windings (the one on the right is bifilar wound as per the patent, and the one on the left is conventionally wound). These are connected in series to ensure identical current in each (developed from a PSU with a 50Watt halogen lamp as ballast) which I've dialled up to 4Amps. Mechanically they oppose each other on a calibrated track (aluminium ruler) and between them sits a compass. In the absence of the electromagnetic fields, this is aligned to Magnetic North. Now the coils can be moved to their respective nulls; the position where their opposing fields cancel each other out leaving the compass pointing to North.



The above picture is with the current off and the whole rig aligned to Magnetic North.

Next, with the current on and both coils placed 10cm from the compass, the fields null (as standard physics dictates) so the needle stays where it was. So much for there being a greater flux from the Tesla winding. To prove the methodology, moving either coil upsets the balance - even by just a millimeter. Here the coil on the left is being moved by 10mm.





Looks like this particular myth is busted. The coil does still have useful properties (i.e. the ones Tesla himself claims) but these only emerge in an AC analysis.

[bklein]

I'm not really getting what you are trying to say. Are you saying your air coil test samples are wound exactly like the iron core nail samples in your reference?
Why not just make the nail samples like your reference, battery supply, and do the compass test with them?

[AdrianM]

bklein,
I was trying to eliminate as many variables as possible here - the problem with having an iron core is that it tends to retain it's own magnetic field (Remanence). Maybe this has accounted for people getting different magnetisation from their testing?

An iron core in each solenoid would multiply the field (through its higher magnetic permeability) by the same amount (I'm pretty certain) so I think it's one varaiable that can be safely taken out. Not that I won't try it to make sure

[AdrianM]

Yep, the laws of physics are still holding here I had to demagnetise the nails before using this rig - there was a strong pull from both without any current flowing. Again the null is obtained when the electromagnets are equidistant from the compass. A few less turns but a greater flux than before but still the same result - the myth is still busted!

I won't be running this again with a battery in case anyone thinks that would make a difference. It probably would - but only because the current would fall as time went on. Maybe this is also why people think the Tesla winding makes a more powerful electromagnet - if they used it first they might indeed be able to pick up more paperclips