tesla coil primary diameter

Thread Starter

pager48

Joined Nov 25, 2018
161
what impacts and effects i the primary tesla coil diameter? what happens if the primary is wound right over a very well insulated secondary?
 

BR-549

Joined Sep 22, 2013
4,938
Tesla had many coil and circuit configurations. There are lots of factors. Where is your circuit and what are you trying to improve?
 

MisterBill2

Joined Jan 23, 2018
8,422
The magnetic field of the primary needs to cover most of the secondary, and so ver close spacings will probably have much lower performance.
 

MisterBill2

Joined Jan 23, 2018
8,422
Probably that also, but it has always puzzled me as to how the large coil near the bottom affects the whole secondary. But clearly the magnetic field drives a lot of the secondary. AND, it turns out that they should resonate at the same frequency. Or at least, the secondary should be driven at it's resonant frequency. But I have seen quite a few Tesla coils with no top dome at all, often a cap that looks a lot like a funnel. VanDe Graff generators are the ones that always have the dome on top. It serves as half of the charge storage capacitor.
 

MisterBill2

Joined Jan 23, 2018
8,422
But the ones without don't work to full potential.
I have no clues about that assertion. A Tesla coil is a high frequency device, while the VanDeraff generator produces high voltage static electricity. Two totally different things. Clearly the Tesla coil does need to be resonant at the drive frequency, perhaps the dome serves as a capacitor to help with the resonance. A web search may possibly turn up some correct information, I know there was a thread here a few months back about some fake version of a Tesla coil, rather devoid of any technical understanding about such things as oscillators and resonance.
 

shortbus

Joined Sep 30, 2009
8,467
I know there was a thread here a few months back about some fake version of a Tesla coil, rather devoid of any technical understanding about such things as oscillators and resonance.
Yeah a lot of what is on Youtube being called a Tesla coil is not. And the young people today don't understand that it isn't.

I know what a Van de Graaff is , and have a small one. I have built many Whimshurst machines. And have a partially built Diorod project. I love sparks. The Van de Graaff was used in the early development of the atomic bomb.
 

MisterBill2

Joined Jan 23, 2018
8,422
I did a search for Tesla Coils and it seems that most of them do have some large smooth conductive thing on top. And I found a definition that stated that what makes it a Tesla coil instead of just a transformer is that both primary and secondary resonate at the same frequency. So I stand educated a bit. It appears that to do it best takes a bit of math, or adjustment. Or, possibly luck?
 

Yaakov

Joined Jan 27, 2019
2,895
Clearly the Tesla coil does need to be resonant at the drive frequency, perhaps the dome serves as a capacitor to help with the resonance.
The (usually toroidal) hat on a Tesla coil is a capacitive load, very much like the capacity hat on a short HF mobile antenna. It’s there for the tank circuit in the secondary.

So, you have that right.
 

MisterBill2

Joined Jan 23, 2018
8,422
The (usually toroidal) hat on a Tesla coil is a capacitive load, very much like the capacity hat on a short HF mobile antenna. It’s there for the tank circuit in the secondary.

So, you have that right.
About a half of the pictures that I found showed domes, many of the torroid-shaped ones seemed to be made of the expandible aluminum duct material, some wrapped in aluminum foil, some not. None of those looked especially smooth.
 

Yaakov

Joined Jan 27, 2019
2,895
About a half of the pictures that I found showed domes, many of the torroid-shaped ones seemed to be made of the expandible aluminum duct material, some wrapped in aluminum foil, some not. None of those looked especially smooth.
The only reasons they'd need to be smooth is to avoid discharge from pointy edges but unlike the VDG generator, the "dome" is not for accumulating charge. In the case of the VDG, pointy bits cause discharging in a way that isn't very relevant to the Tesla coil.

The Tesla dome is just a capacitor to make the secondary tank circuit resonate. Obviously, even without it the coil could work, for some values of work.

I actually spent a few years maintaining the original, massive VDG as a museum exhibit in Boston about 30 years ago or so.
 
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