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Tesla coil Emi considerations

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genious 7

Wed Jan 19 2011, 04:03PM

Registered Member #2887 Joined: Sat May 29 2010, 11:10PM
Location: Panama City, Panama
Posts: 107

I am considering building a tesla coil. Altough being my tesla coil, I have a bit of experience with flybacks and ZVS. Nevertheless, I want to know what considerations I must take to make the Tesla coil interfere with the least possible; both in terms of mains backfeeding and the emi present around the coil. As of know, I still haven't decided between a sgtc and a sstc (or drsstc). Which type of coil is more Emi friendly?

Besides stuff such as good coil grounding, what other things can be done to reduce the Emi around the coil (except Faraday cage). I'm not looking for zero emission, just as small as possible. My aim is a medium sized coil. Any recommendations on how to design a line filter, since over here in Panama I haven't seen preassembled units as of yet. (If you know where, tell me).

If you have any suggestions towards emi reduction, please share them.

PS: I'm going to Taipei during the vaccations. Any place where I could buy GDT cores and/or line filters, or other discrete components in small quantities?

Luca

Wed Jan 19 2011, 05:06PM

Registered Member #2481 Joined: Mon Nov 23 2009, 03:07PM
Location: ITALY
Posts: 134

Hi Michael,
to reduce conducted emissions you can simply put an EMI line filter on your power input. You can use a pre-assempled one or you can build your own filter, is not that difficult...

On the other hand, radiated emissions are much more complicated to stop, and a coil will always radiate some power... I have recently (almost) concluded my first medium-sized DRSSTC and when I power it, my (digital) TV signal is corruptted and at full power is totally disturbed...

Regards,

Luca

genious 7

Thu Jan 20 2011, 12:06AM

Registered Member #2887 Joined: Sat May 29 2010, 11:10PM
Location: Panama City, Panama
Posts: 107

Thanks for answering. I've been looking at specifications for line filters and I think I'll build my own. Regarding Tesla coil types, which tesla coil has less radiated emmisions (sstc, sgtc, drsstc, etc.). I am not looking for zero emmisions, just trying to get a low or reasonable level which won't bother neighbor's electronics or damage permanently my own.

hsieh

Thu Jan 20 2011, 12:47AM

Registered Member #1412 Joined: Thu Mar 27 2008, 04:07PM
Location: Taipei Taiwan
Posts: 278

Michael Chen wrote ...

PS: I'm going to Taipei during the vaccations. Any place where I could buy GDT cores and/or line filters, or other discrete components in small quantities?

I live in Taipei.I remember seeing line filers in many many stores that sale electronic components.

This store is near Taipei railway station.(in the underground Taipei City Mall

)I remember seeing EMI core in this store too,which can be used as GDT core.Many other stores also sale these components.

HV Enthusiast

Thu Jan 20 2011, 01:10AM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

A faraday cage is going to do very little with shielding radiated emissions from a Tesla coil unless your aperture size is VERY small. Also, the faraday cage will not do anything for magnetic field shielding.

genious 7

Thu Jan 20 2011, 09:24AM

Registered Member #2887 Joined: Sat May 29 2010, 11:10PM
Location: Panama City, Panama
Posts: 107

seeing EMI core in this store too,which can be used as GDT core.

Someone correct me if I am wrong, but aren't we suposed not to use Emi filter cores as gdt. I think I read somewhere that they are designed to be lossy at high frequency, and should be avoided for this type of use. Nevertheless, I'm going to visit the store when I can, as it seems pretty much what I was looking for.

One question: can I buy a random inductor over there, remove the wire, and use the core, or there is a chance I might end up with a choke or other iron pownder core?

Still wanting to knoww which tesla coil is friendlier to other devices (sgtc, sstc, drsstc). I kinda recall that less Emi is generated when employing a breakout point since less energy is stored before releasing the streamer, but I'm not sure. Could someone confirm or refute this statement?

PS: sent from my laptop in Taipei. If you know a good store, don't hesitate to post. There are never too many electronic stores.

Steve Conner

Thu Jan 20 2011, 09:58AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Here is my answer to the EMI problem:

Line filter intended for a variable speed motor drive + a complete Faraday cage.

SSTCs are much more EMI-friendly than spark gap coils, because the spark gap generates a lot of really high frequency noise. Enough to destroy almost any EMI filter you might try to fit to the gap.

However, if you let a SSTC arc to nearby objects, that can create bad EMI. The shorter the arcs, the worse it will be.

hsieh

Thu Jan 20 2011, 01:09PM

Registered Member #1412 Joined: Thu Mar 27 2008, 04:07PM
Location: Taipei Taiwan
Posts: 278

Michael Chen wrote ...

PS: sent from my laptop in Taipei. If you know a good store, don't hesitate to post. There are never too many electronic stores.

electronics stores in Taipei are mainly located in or near Guang Hua Digital Plaza

, or this one

the last one is in a messy tranditional market but there are a lot of good store nearby or in it .You can find vacuum tubes and audio related thing there.

There are also other good electronics store in Taipei.Some of them sell components that are difficult to find in other stores.Some is cheaper than others.
Can you speak Chinese?

Maybe we can meet and I can tell you in detail where to find electronic components in Taipei.I'm a student major in EE(and a electronics enthusiast) at a school in taipei.Most people major in EE in Taiwan are not electronic enthusiasts.

Someone told me that common inductor cores are not suitble for GDT.

Luca

Thu Jan 20 2011, 03:23PM

Registered Member #2481 Joined: Mon Nov 23 2009, 03:07PM
Location: ITALY
Posts: 134

Michael Chen wrote ...

seeing EMI core in this store too,which can be used as GDT core.

I do not agree. Ferrite materials coomonly used for EMI filtering (such as NiZn) are lossy above tens of MHz, while typical gate driving frequency are in the hundreds of kHz...

Regards,

Luca

HV Enthusiast

Thu Jan 20 2011, 07:34PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

Luca wrote ...

Michael Chen wrote ...

seeing EMI core in this store too,which can be used as GDT core.

I do not agree. Ferrite materials coomonly used for EMI filtering (such as NiZn) are lossy above tens of MHz, while typical gate driving frequency are in the hundreds of kHz...

Regards,

Luca

Not really. The fundamental pulse rate is in the kHz, but if you want to pass a rectangular wave shape with fast rise / fall times - as is typical with switching transistors, you need a core with decent permeability up into the MHz. For example, Fair-Rite type 78 material (MnZ) which is common for these types of applications has permeability up to several MHz.

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