Tesla Coil

[Bent]

Here\s an picture/schematic of a autotransformer: Note, there is no isolated or discrete secondary winding, a autotransformer uses a common winding on the input side and on the output side.

If you imaging the secondary tap as being adjustable, as in a slider/wiper, you have a variable transformer, or Variac

Until recently, General Radio held the copyright on the name Variac - so we called them varaible autotransformers, but the product name became the trade name as they manufactured the majority of them.

[Mike B]

I made a mounting base for the primary tank cap out of HDPE (high density polyethylene). Made it with 2 grooves that I cut with the saw that fit the polycarbonate sheets perfectly. Glued it with silicone bathtub caulk that sticks to anything.

Or so I thought. Gave it the test and it fell apart. Looked up gluing polyethylene and found that nothing sticks to polyethylene.

Cut the piece and screwed it.



You can see the groove in the trimmed off pieces -

I learn new stuff every day.

[Mike B]

Done.



This was a lotta work.

But will be worth it if it keeps the secondary of the transformer intact.

Plus, it looks really cool. How about them brass balls baby? Yeah, it takes balls of brass to build a good Tesla coil.



The base is a scrap piece of polycarbonate I picked up at Tap Plastics for $10. The normal price was $35. I love the scrap bin at Tap.

Going to be assembly time soon.

[Pete Apruzzese]

YouTube- BRIDE OF FRANKENSTEIN - Creation Scene

[Bent]

I'm missing something here on the theory of operation of a tesla coil.
Please correct me if I'm wrong, but a variable voltage source is connected to a high voltage step-up transformer (should all be 60 hz at this point, right?), which the output of is connected to a tuned tank cct (tuned for frequency much higher than 60 hz...) and also allowed to cr4eate an arc across a defined spark gap.
Now, do the high frequencies induced onto the high voltage side of the tesla dischrge unit (at the showboat end of the rig) reslut from the harmonics generated by the spark gap?

[Mike B]

Yup.

The primary gap is just a fast switch. When the voltage rises high enough it fires and discharges the primary cap into the primary coil which rings back and pumps up the cap again.

Meanwhile, back at the business end, the secondary cap (the top load) is driving sparks and dissipating the energy transmitted by the primary (which is still ringing through the primary spark) until the the gap quenches and the process continues.

The variac will not be needed after the coil is tuned. It's useful for running at reduced power (with small spark gap spacing) to tune. It will also be useful for setting up the safety gaps.

[Mike B]

I should have added that the primary and the secondary are resonant at the same frequency. This frequency is shifted slightly by the spark loading, so the best way to tune the coil is by spark length and audible noise when running.

All of the tuning is done by tapping the primary coil. If anything changes (top load, primary cap) the coil needs to be re-tuned.

And last, but not least, there is the coupling. Tesla coils are loosely coupled transformers ~20%. More coupling makes bigger sparks, but too much coupling makes "racing sparks" that run along the sides of the secondary and destroy the insulation.

Coupling is adjusted by moving the secondary with respect to the primary.

It's going to be loads of fun playing with this toy.

[Mike B]

This is the best most complete Tesla site that I've found on the web.

If you are interested in coils, check this one out for sure.

http://www.richieburnett.co.uk/operation.html#operation

[Bent]

thanks

[Randy Rhoton]

C'mon! Quit teasing us and turn that thing on!

[Mike B]

There is nothing to turn on yet.

It will be at least as long from now as when I started.

[Mike B]

Some idiot didn't seat the pipe all the way.

I am proud of this. I fucked this up so good, I will have to redo the whole piece. Ordered up more fittings. Of course I fucked up the piece with 8 fittings and not the one with 4 -

Oh well, shit happens. I wouldn't even have posted this except for my advice to Stefan in the "growth" thread.

And yes, I am very happy for not beating myself up over it.

[Rich Kraus]

seems like what piece is messed up is relative. I think id remake the top piece to match the bottom. (unless there was a specific measured requirement that was missed.)

ordered? to get the pvc with the fancy beveled ends?

[Mike B]

Yeah, these are "furniture" grade fittings and won't even flow water because they are blocked internally. But that's the only way a "4 way" is made I think.

Nah, the piece with the 4 fittings is right, I measured it, all dimensions are the same.

I just didn't fully seat one pipe in the other piece. The other 3 holes work fine as you can see.

[Mike B]

Ah, back to some good ole wood work.



Also cut the ply for the spark gap.

[Mike B]

Done.



Works good too, drew off some nice sparks from both ends of the secondary to ground.

The incandescent lamp across the primary of the transformer tells me if the transformer is hot. An AC panel meter and an neon light let me know if the thing is powered on the control side and what the voltage is.

Now for the interesting part -

[Mike B]

Done.



This has taken a lot of time. I've re-designed it 3 times.

First I was going to mount it integral to the bottom with a hole cut through to let in the air. Nah, fan will suck up dirt and leaves.

Then it was going to be modular, but 4 series gaps. Nah, after I saw how hot arcs can get, I thought better and went with a larger thermal mass design.

This is the final. 2 series gaps, lotta thermal mass, lotta air flow, larger gaps that the air can blow through.



Now on to the capacitor safety gap and then the final assembly can begin.

[John Celardo]

Hey Mike, how's the project going? A movie called the Sorcerore's Apprentice opened today, and in the first paragraph of the New York Times review there's mention of a giant Tesla coil. Check it out.

[Mike B]

Slow and steady John. Almost ready to start winding the primary coil. The secondary I just bought along with the toroid.

Also building a little side project, a Jacobs ladder. Easy and since I already have a nice high voltage supply, why not?

[Jack Van]

I want to see it connected to Chads nut sack. That would be smokin cool.

[chadci]

Originally Posted by Jack Van

I want to see it connected to Chads nut sack. That would be smokin cool.

YouTube- Simpsons ZAP

[LarryB]

[Ken McDaniel]

As cool as that was, I can't help but fixate on the dude in the bike shorts. Is that some kind of Tesla-coiling outfit?

[Zak]

Rubber pants for protection. Duuuuuh Ken!!!!

[JeffC]

Originally Posted by Ken McDaniel

As cool as that was, I can't help but fixate on the dude in the bike shorts.

Shit. I thought that was just the Navy????

Stay safe Ken.