My first tesla coil need some help before getting started. / Tesla Coils / Forums

Forums

4hv.org :: Forums :: Tesla Coils

« Previous topic | Next topic »

My first tesla coil need some help before getting started.

1 2 next

Move Thread

LAN_403

Zeeb

Wed Feb 08 2012, 07:16PM

Registered Member #4398 Joined: Wed Feb 08 2012, 07:04PM
Location:
Posts: 10

Hello, i want to build a tesla coil and am currently looking into some information about how they work. Iâ€™m having some trouble understanding how the discharge terminal works. I know it acts as a capacitor but why does it need to be round? And how much should its capacitance be? Should it be higher or lower than the secondary coil?

As my first project I decided to only use a neon sign transformer that has an output of 4000v and 0,050A these numbers gives me the inductance of the secondary coil. Which is equal to 915.8 uH

The self-capacitance is at 6,545 pF for the secondary coil. now should the torus be higher or lower then this and why should it be higher or lower?

Inducktion

Wed Feb 08 2012, 07:57PM

Registered Member #3637 Joined: Fri Jan 21 2011, 11:07PM
Location: Buffalo, NY
Posts: 1068

There is no real capacitor; The capacitance is from the top of your tesla coil to ground.

The reasoning for roundness is probably just due to the way it looks, and also surface area. (more surface area = more capacitance)

Dr. ISOTOP

Wed Feb 08 2012, 08:06PM

Registered Member #2919 Joined: Fri Jun 11 2010, 06:30PM
Location: Cambridge, MA
Posts: 652

Inducktion wrote ...

There is no real capacitor; The capacitance is from the top of your tesla coil to ground.

The reasoning for roundness is probably just due to the way it looks, and also surface area. (more surface area = more capacitance)

Also the roundness helps prevent energy loss due to premature breakout.

Zeeb

Wed Feb 08 2012, 08:26PM

Registered Member #4398 Joined: Wed Feb 08 2012, 07:04PM
Location:
Posts: 10

Thanks for the quick response guys. I checked with some other sites to confirm my calculations and I got pretty much different answers on every site for the value of inductance

Using the site above I get 26,129 microhenries
(this site use cm)

Using this one i get 9167.94 microhenries
(this use mm)

I might be wrong here be shouldnâ€™t everything be in their SI-unit when performing calculations (meters)
So I tried performing the formula on paper

L = Radius^2 X turns^2 / 9*Radius + 10* Length
My secondary coil will have a diameter of 7,6 cm and height of 45,7 cm around 900 turns of copper wire

Iâ€™m going to use meter for my calculations

7,6/100 = 0,076 m in diameter

Radius = 0,076 / 2 = 0,038

Length = 0,457 m

L = (0,038^2 * 900^2) / (9*0,038 + 10 * 0,457) = 164902â€¦

Iâ€™m rather confused since I get 3 different answers.. could anyone clarify what is going on here?

Herr Zapp

Thu Feb 09 2012, 04:37AM

Registered Member #480 Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644

Zeeb -

A much more useful tool for designing your entire Tesla coil is JAVATC, a sophisticated (but free) CAD design application available at:

You can run the program from the website, or download a local version.

This tool will help you calculate ALL the parameters for your TC, and easily see how changes in dimensions or electrical values affect resonance.

Herr Zapp

Zeeb

Thu Feb 09 2012, 11:38AM

Registered Member #4398 Joined: Wed Feb 08 2012, 07:04PM
Location:
Posts: 10

Thanks for the link Herr Zapp. However Iâ€™m doing this for a school project so I need to be able to explain for my class mates how the calculations are made for each part of the tesla. I could not find any formulas that explain the calculations that are made on the site you posted. (sorry if I missed it) however thanks to the link you provided I think I understand what went wrong in my calculations

Both sites I linked in the previous post use the formula
L = Radius^2 X turns^2 / 9*Radius + 10* Length

should note I'm using a helical coil

Now the (10 * length) part is supposed to be from the ground plane to the top of the secondary coil or is it as i thought the length of the secondary coil?
I guess I'll have to figure out how big the coil support should be before I can continue.

Also, regarding the top load. As I understand it the larger your top load is the more power you need. Now Iâ€™m using a rather small power source 4000v 0,050A which produce 200W. Iâ€™m planning on using a toroid design. How big should its minor and major diameter be? for optimal spark visibilty

Herr Zapp

Fri Feb 10 2012, 01:38AM

Registered Member #480 Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644

Zeeb -

Back at classictesla.com, under "Basics all coiler's should know", click "Formulas for Tesla coils".

This is a compilation of just about every formula that's useful for TC design (at least for conventional spark-gap coils).

This compilation of formulas, used in conjunction with JAVATC, should provide everything you need.

Herr Zapp

Tetris

Fri Feb 10 2012, 03:27AM

Registered Member #4016 Joined: Thu Jul 21 2011, 01:52AM
Location: Gainesville, FL
Posts: 660

use

Also I think your NST is too low a voltage. 7500V is the least. There are ones twice that, but I still recommend going with the 7.5kV.

Herr Zapp

Fri Feb 10 2012, 05:00AM

Registered Member #480 Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644

Zeeb -

Your 4KV, 50ma NST can give great performance in a smaller "desktop" Tesla coil, but with the low primary voltage the spark gap will have to be carefully built and adjusted.

Gary Lau has hosted a "perpetual competition" for small TC performance using a tiny 4KV, 20ma NST as the "standard" power source. Typical streamer length for a well-tuned small coil is 12-14", with one builder reporting 18" streamers.

The specs for each of the coils can be seen at:

Herr Zapp

Zeeb

Fri Feb 10 2012, 01:53PM

Registered Member #4398 Joined: Wed Feb 08 2012, 07:04PM
Location:
Posts: 10

Great, thanks Herr Zapp. the formulas are finally starting to come together :) as for the mini coils i think my toroid with 314 mm width and 100 mm height might just do fine after seeing those mini-coils

1 2 next

Moderator(s): Chris Russell, Noelle, Alex, Tesladownunder, Dave Marshall, Dave Billington, Bjørn, Steve Conner, Wolfram, Kizmo, Mads Barnkob