Tabletop Tesla Coil

Step 7 The power supply

For power I use an Allanson 7,500 volt neon sign transformer. It is current limited. As Mitch Tilbury writes in The Ultimate Tesla Coil Design and Construction Guide:

"Small Tesla coils that typically use NSTs will not require circuit protection as the NST is current limited and will draw less line current than the 15-A [15 amps] rating that is typical for building electrical outlets." (page 275)

I installed two RF chokes on the lines running to the coil. These are snap-on types sold at Radio Shack. They are there to block or reduce RF interference.

The Allanson unit is handy in that it has a pull-chain switch with a long string attached. You can easily stand two or three feet away and turn the apparatus on and off from a safe position. I mounted the NST on a pine plaque, well-shellacked, and put four hard rubber feet on the plaque to raise it and give it a more finished appearance.

Comments

[disappearingshadow]

http://www.ebay.ca/itm/LOW-GLOW-NEON-9500-VOLT-TRANSFORMER-FITS-LOWGLOW-AND-MANY-OTHER-NEON-BRANDS-/380430895286?pt=Motors_Car_Truck_Parts_Accessories&hash=item589372c8b6
I was thinking of getting this one. Do you think it would work with this project?

[Mr. Apol]

It will definitely not work. These Low-glow modules are solid state power supplies with Ground Fault Interrupt protection. This means they will not power a spark gap at all. Do not use these for Tesla coil power supplies.

Paul

[disappearingshadow]

Okay thanks :D how about this one?
http://www.ebay.ca/itm/New-10kv-30mA-Neon-Power-Supply-Neon-Transformer-UL-Series-A410EL-/150798592048?pt=LH_DefaultDomain_0&hash=item231c4be830

[Mr. Apol]

Nope. See the mention in the description that it has "open circuit protection?" That's GFI.

You need something like this: http://www.ebay.com/itm/NEON-TRANSFORMER-7-500-VOLTS-For-Neon-Signs-Jacobs-Ladder-or-Tesla-Coil-/330719105373?pt=BI_Circuit_Breakers_Transformers&hash=item4d0065115d#ht_507wt_934


Paul

[disappearingshadow]

I am having a lot of trouble trying to find one in Canada. I don't supposed you know any good sites.

[Mr. Apol]

Try the phone directory for Sign Shops, Neon Signs, etc. A lot of shops are changing over to solid state GFI transformers and getting rid of the old fashioned iron-brick type of transformer. You may be able to buy one from them. They might even give them away, just to get rid of them. You can also try oil burner ignition transformers (OBITs, they're called). Avoid GFI units again. You can also build power supplies based on automobile ignition coils.

Good luck. Try in person where you live, or any nearby city.

Paul

[disappearingshadow]

I went to a neon sigh place and they gave me Ann allanson power pak it has 35 ma 7200v complies with secondary ground fault protection requirements please tell me it works

[Mr. Apol]

Does it look like this?

http://www.google.com/products/catalog?q=Allanson+power+pak&um=1&ie=UTF-8&tbm=shop&cid=9228341418964618920&sa=X&ei=3c2XT7LeHaX02QWH3sGIBw&ved=0CEQQ8wIwAg

If so, it won't work. It has GFI protection.

Here's a simple rule of thumb about NSTs. If it's big and heavy, it will probably work in a Tesla coil. If it's small and light, it's solid state and has GFI.

Here's a listing on eBay Canada for a non GFI unit:

http://www.ebay.ca/itm/15-000-Volt-Allanson-Neon-Sign-Transformer-Lighting-Unit-Non-GFI-Tesla-Coil-/120900954333?pt=BI_Circuit_Breakers_Transformers&hash=item1c264228dd#ht_500wt_950

and

http://www.ebay.ca/itm/neon-sign-transformer-9-000-volts-france-ground-fault-/300699999724?pt=BI_Circuit_Breakers_Transformers&hash=item46031dddec#ht_500wt_950

more are listed if you search for "neon transformer."

Paul

[Crtek]

can i use a CRT monitor instead of this?

[Mr. Apol]

You can use a flyback transformer, found in a CRT. I have no experience using the whole CRT itself, but I'll bet you can find someone who has, somewhere on the Net.

[punkzter]

Do you have any insight for using/taking apart the CRT to get the flyback?

Also, does the spark gap need to be as complicated as yours? I have seen some that are just two screws. Thanks!

[Mr. Apol]

If you open up an old CRT or TV, make sure the capacitors are discharged. Some of them can hold a serious jolt. The flyback transformer is usually off in one corner of the chassis. You can find it by tracing the high voltage cable back from the picture tube to the flyback. The HV cable usually has a suction cup type end on the CRT itself.

See

http://www.instructables.com/id/How-to-find-the-primary-and-the-secondary-coils-of/

for a description of finding the primary and secondary coils on a flyback. This Instructable also has pictures of a flyback, so you can recognized one when you see it.

You can make a simple two part spark gap, sure. It will work, but it will overheat quickly, reducing the output of your coil. Blowing the gap with air helps. The best static spark gap I know is the "hyperbaric" gap described here:

http://www.stephenhobley.com/blog/2008/09/10/petes-quick-hyperbaric-spark-gap-tm/

It's easy to build and works great, with or without an air source to quench the spark.

Good luck,

Paul

[punkzter]

So I wouldn't have to hook it up to a vacuum cleaner for it to work?

[Mr. Apol]

No, the hyperbaric gap works with or without a vacuum attached--but it is many times more powerful if you do use an air source. The difference is very marked.

Paul

[Evilthingamabober]

I have an old 7.5kv negetive ion generator transformer that isn't current limited. How can I make a ballast for it?

[Mr. Apol]

I am not quite sure what you mean. You have a 7.5 kV ion generator, or a transformer that powers an ion generator?

Paul

[Evilthingamabober]

It's a 7.5 ion generator, here's a pic. The needle array was cut off.

[Mr. Apol]

Others feel free to weigh in, but I have a couple of these ion generators, and they put out DC at low amperage. They are not strong enough to power a Tesla coil. They can power a simple Marx generator, charge Leyden jars, etc., but they don't have the power to make the spark gap of a Tesla coil fire. DC requires some kind of pulse generator to work with a Tesla coil also.

Paul

[chriskarr]

While you're correct about the ion generator being insufficient for a Tesla coil, you aren't completely correct about one thing.

In a DC Tesla coil, you don't need to have a pulsed supply but, rather, a constant-current supply and an inductor. The inductor stores the DC energy in its core and windings in the form of magnetic flux and allows the current (after it's charged) to pass through and into the capacitor. Once the capacitor is charged to a sufficient voltage to fire the spark gap, it will do so, at which point the potential in the transformer drops to near-zero and the magnetic flux experiences reversals. Since the gap is still conducting at this point, your core's magnetic flux 'dumps' its charge into the spark gap, as well, increasing your voltage to near two times the supply voltage. This does, however, require a rotary spark gap to occur.

[itsachen]

Where did you buy your PS? How much did it cost?

[Mr. Apol]

I bought the neon sign transformer off eBay for $8, plus shipping. I hear you can sometimes pick them up for scrap at a sign shop, just for asking. Just yesterday I picked up an oil burner ignition transformer (OBIT) for $4 off eBay. 10kV, 23 mA , etc. Paul