torid topload sizing / Tesla Coils / Forums

Forums

4hv.org :: Forums :: Tesla Coils

« Previous topic | Next topic »

torid topload sizing

Move Thread

LAN_403

Stuart

Thu Oct 09 2008, 10:13PM

Registered Member #1747 Joined: Wed Oct 08 2008, 12:57PM
Location:
Posts: 6

Hi,

Another newbie question, had a search but as cant see how to search only the tesla forum so i get millions of results from other forums... anyway.

Ive put all the numbers so far at the bottom of this message for reference.

Ive calculated i need a 7.433pF topload. The table below shows the tube diameter (D2@deep fried neon calculator) in 10mm increments and the corresponding overall diameter (D1@DFN calcs) to give as close to 7.433pF.

Tube Dia Overall Dia Cap
20 225 7.44
30 185 7.43
40 172 7.42
50 170 7.45
60 172 7.44
70 176 7.41
80 182 7.46
90 190 7.45

I have to stop above 90mm tube diameter otherwise the tube diameter doubled is more than the overall radius.

Any recomendations for what size would be good? im looking at 60mm as i can get some of that aluminium tube as used in performance car air induction systems.

_________________________________
Data as its looking (on paper) I will wind the transformer then obtain voltage and current data before going further but things wont be too far diffirent i hope.

Transformer v = 10000v @ 50mA
(transformer from 650w microwave wound for 5-0-5kV, 100mA may be possible with some oil cooling and short runs but will need to test)
Tank cap = 15.92nF

Primary inner dia = 155mm
Primary turns = 10
Diameter = 10mm (i have some lying about)
Spacing = 10mm
Inductance = 34.27uH
Resonant frequency = 215.5kHz

Secondary Diameter = 150mm
Turns = 900
Copper Dia = 0.470mm
Copper insulation = 0.045mm
Inductance = 33.5mH
Self Cap = 8.85pF

Topload cap required = 7.433pF
Topload torrid size = as table above

Thanks,
Stuart

Coronafix

Fri Oct 10 2008, 01:34AM

Registered Member #160 Joined: Mon Feb 13 2006, 02:07AM
Location: Melbourne, Australia
Posts: 938

First of all you are better off using a larger cap value as that value will be charging at resonance.
1.4X 15.9nF = 22nF
This will allow you to use less turns on the primary.
With a 150mm diameter secondary, you want to use a topload that is large enough to
hold the charge. You could use 150mm diameter tubing (ac duct) and have a 500mm diameter overall.

Stuart

Fri Oct 10 2008, 10:25PM

Registered Member #1747 Joined: Wed Oct 08 2008, 12:57PM
Location:
Posts: 6

Hi,

I have seen some things todo with using a higer cap value than resonance. Has the 1.4 factor anything to do with convering RMS to peak or is 1.4 just a good factor?

Also, if i increase the cap value to 22nF, the resonance freq changes from 215kHz to 183kHz.

Which freq should i use for the topload calcs? im thinking the calculated value for 22nF.

I have not seen any calculations for working out optimal number of primary turns (if such a thing exists), 8-10 seams a common figure then experimenting with taps.
Somebody in another post said "First you construct the capacitor to meet requirements of your power supply, and then you use largest number of primary turns with lowest possible resoant frequency for the secondary." How do you find the balance of the two? im guessing there is a calc or rule of thumb or is this experimentation?

Thanks,
Stuart

Coronafix

Fri Oct 10 2008, 11:49PM

Registered Member #160 Joined: Mon Feb 13 2006, 02:07AM
Location: Melbourne, Australia
Posts: 938

Stuart wrote ...

I have seen some things todo with using a higer cap value than resonance. Has the 1.4 factor anything to do with convering RMS to peak or is 1.4 just a good factor?

It's just a good factor, there could be another reason but I don't think so.

Stuart wrote ...

I have not seen any calculations for working out optimal number of primary turns (if such a thing exists), 8-10 seams a common figure then experimenting with taps.
Somebody in another post said "First you construct the capacitor to meet requirements of your power supply, and then you use largest number of primary turns with lowest possible resoant frequency for the secondary." How do you find the balance of the two? im guessing there is a calc or rule of thumb or is this experimentation?

Building from the transformer up is usually the best way because this is the fixed value item, the other things can be varied.
Once you have a transformer you can calculate the tank cap, then you can design a primary with as many turns as you can.
My large coil has about 17 turns of 6mm copper pipe, that's because that's as much as I had.
The cap and primary coil will then give you the lowest possible frequency you can achieve, but you don't want to build a coil to exactly that because as spark loading lowers the resonant frequency (a few %IIRC) so the tuning has to be done by experimentation.
So I would suggest you design the coil to have a frequency where you are tapped at about half the turns on the primary, you can then add more toploads to lower the frequency and you have enough primary coil to move out to.
Hope this helps. Don't know if you've seen this already

Hazmatt_(The Underdog)

Sat Oct 11 2008, 12:48AM

Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735

Here is an answer for the cap size:

I've been using the toroid size of 2x Cself, but I'm still investigating that a bit and haven't come up with a justification just yet, but hopefully I will soon. ^^

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