1. Home
  2. Electronics Design
  3. Use of Cylinder to Simulate ES Sphere

Use of Cylinder to Simulate ES Sphere

I need a conductive sphere so that when DC is applied, negative charge migrates to the outer surface.

To economize, it was suggested to substitute an aluminum cylinder. Of course, "as is" the charge would bleed off the ends instead of sitting upon the outer radius.

The envisioned solution is to place inward-facing, metal hemispheres over the ends so their convex surface redirects negative charge back into the tube. This sounds plausible enough to try. My question is how to affix the hemispheres.

Can they be simply clamped over the ends of the tube, as in a mechanical fit, or would they need to be soldered all around the adjoining edge?

If the latter, could the solder be replaced with something "easier" like conductive grease?

Would the cut edges of the hemispheres need to "blend in" with the ends of the tube, or can they be larger in diameter and sort of over-hang?

The applied signal would be around 20KV, at a 20KHz pulse rate, so corona discharge enters into the picture.

Any and all ideas appreciated.

Art Brooks

Reply to
abrooks
Loading thread data ...

Why?

You will have higher field gradients at the ends of the cylinder, and at 20 kV that would give you corona discharge.

A tube with bulbous ends is a better approximation to a sphere than a flat- ended cyclinder, and less likely to give you high enough filed gradients to give you corona discharge at 20kV.

Clamping would be fine. The charges involved are tiny

My guess is that that would work just as well as solder - tiny charges mean tiny currents and very little voltage drop in the conductive grease.

Clamping is going to entail occasional local contact, but again the longer paths through the occasional metal-to-metal contacts don't have much induct ance - 10nH per inch is a very crude rule of thumb - and since you've got v ery little current the extra voltage drop over these inductances aren't goi ng to be large.

Blending in is better, but a slip=on fit is going to be good enough in mo st applications.

Again, what are you trying to do here? In-house lighting bolts?

Tell us what you are intending to do - and why - and we can probably be mor e helpful.

--
Bill Sloman, Sydney
Reply to
Bill Sloman

flat-ended cyclinder, and less likely to give you high enough filed gradients to give you corona discharge at 20kV.

Thank you for your reply.

Did you notice my description specified that the convex surface of the hemispheres faces _inward_ to reinforce the lateral migration of charge toward the tubes outer surface?

IOW the asembly isn't intended to approximate the smooth outer surface of a sphere. There is a "sharp" outer edge where the inverted hemispheres (cut sphere) are joined to the tube's openings.

I am thinking to use a clamp consisting of two acrylic end plates connected by threaded rods. A layer of silicone rubber would be sandwiched in to cover the tube's sharp edge and inhibit coronal discharge.

I would leave the mechanical contact between tube and hemisphere non-continuous. Carbon grease is a bit messy.

How does that sound?

It is an enclosure for an experimental piezo transformer utilizing cylindrical componets.

Art Brooks

Reply to
abrooks

I did. I'd hoped you'd got confused and didn't actually mean it. My impression is that it wouldn't work in the way that you have in mind. There's a nice self-consistent heap of physics involved which you could probably read up on with advantage.

This is probably a bad idea.

The corona would still occur on the surface of the silicone rubber, and the ozone produced will chew up the rubber fairly quickly. Silicone rubber is an insulator when compared with metals, but it's a conductor compared with air.

Sensible, if you do have some metal-to-metal contact.

So a piezo-electric transformer for making a higher voltage from a lower voltage? It's practicable, but scarcely practical.

--
Bill Sloman, Sydney
Reply to
Bill Sloman

More like "conductive epoxy".

One connection may be all you need between components, however if a full join is needed between dissimilar, not easily soldered normally elements, conductive epoxy would be the choice to make "good wetting" of the surfaces involved, and therefore good bonding and some modicum of structural support of the constructed elements as well.

Reply to
Archimedes' Lever

How big a sphere? What's it for?

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC 
Optics, Electro-optics, Photonics, Analog Electronics 

160 North State Road #203 
Briarcliff Manor NY 10510 USA 
+1 845 480 2058 

hobbs at electrooptical dot net 
http://electrooptical.net
Reply to
Phil Hobbs

If a sphere is impractical, I'm not sure how a cylinder and two hemispheres is less impractical. Have you considered a toroid? Flexible aluminum dryer duct is a great material.

Reply to
Ralph Barone

Machine half shell or spheres with a step down that can be pressed into the ends of the tube.

At one time you used to be able to buy metal dome caps for grease cap covers. They come chromed if you wish in various sizes..

I deal with much higher voltages, 20k is nothing..

Jamie

Reply to
Jamie

I doubt it. The field strength would be nonuniform as compared to a sphere but you wouldn't "bleed off" charge. Probably.

Get an old world globe. Or buy a plastic ball and stick foil on it.

How big do you want this to be?

Pulsed? Not DC? What is the pulse width and rate?

What are you trying to accomplish?

--

John Larkin                  Highland Technology Inc 
www.highlandtechnology.com   jlarkin at highlandtechnology dot com    

Precision electronic instrumentation 
Picosecond-resolution Digital Delay and Pulse generators 
Custom timing and laser controllers 
Photonics and fiberoptic TTL data links 
VME  analog, thermocouple, LVDT, synchro, tachometer 
Multichannel arbitrary waveform generators
Reply to
John Larkin

Is it possible to use metallised (helium)balloon as Sphere?. Are they conductive enough?

Reply to
LM

How big a sphere?

Something like this perhaps?

12" seems to the largest, but the various vendors have smaller conductive spheres available. 
--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558
Reply to
Jeff Liebermann

probably read up on with advantage.

The charge would naturally accumulate upon the outer surface of the tube, as well as the inward-facing, convex surface of the hemispheres. The way I visualize the result is that any unwanted charge migration toward the ends of the tube would be repelled by the like charge sitting on the hemisphere.

If this is incorrect, please explain why. The concept is to orient all charge perpendicularly to the central axis of the tube.

Is there a good solution?

ozone produced will chew up the rubber fairly quickly. Silicone rubber is an insulator when compared with metals, but it's a conductor compared with air.

Maybe silicone sealent then. A fairly common remedy for corona problems.

Art Brooks

Reply to
abrooks

OK, it is not just about obtaining spheres at the correct sizes. It is also that a tube has an axial component, whereas a sphere has a central one. I believe the former is required for my intended application.

Additionally, they are easier to nest one-within-the-other. Have you ever costed having nested spheres machined to order :->

Art Brooks

Reply to
abrooks

Just get the Fischer Price job and have them plated.

Reply to
DecadentLinuxUserNumeroUno

probably read up on with advantage.

no. on on the outward facing concave face (but not much there)

formatting link

easy in theory, hard in practice ... you need an infinite tube.

what's it supposed to do?

--
?? 100% natural 

--- news://freenews.netfront.net/ - complaints: news@netfront.net ---
Reply to
Jasen Betts

hemispheres

dryer

Well for one i wouldn't be machining them, there are many much less expensive ways to get metal half spheres. Depending on dimensions and tolerance stamping, forging, casting and other processes come easily to mind. Talk to a shop that can do all of these things and ask them how to do it inexpensively.

?-)

Reply to
josephkk

Just buy Tesla coil parts and accessories on ebay.

After you waste several days dicking around you loose days of your life. How much is your time worth? To me, the price of properly polished Aluminum hemispheres and toroids is worth it, when you consider the difficulties with coming up with your own fabs, which would likely be crap at least the first time through.

Reply to
DecadentLinuxUserNumeroUno

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.