Terry Blake's Tesla Coil
with oil-filled secondary

RATCB Teslathon 2003

see the videos


Photo courtesy of Dan McCauley

This is a totally excellent shot. There are three things going on here.
1) There are 2 plasma plumes rising from discontinuities on the strike rail.
2) There is electrical breakout from the toroid.
3) There is a power arc shorting out the secondary. The winding was not damaged by this.

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GIF from photos courtesy of Dan McCauley

This Tesla coil is 25" tall with an acrylic base that is 24" x 24".
Orange fiberglass insulators are used for supports and an additional 12" of height.
The 4.5"x24"x1/8" acrylic tube secondary is wound with #26 magnet wire for a winding length of 23" (1300 turns).
The secondary is enclosed by another acrylic tube (5"x24"x1/8"), with the 1/8" gap filled with mineral oil.
The 13 turn, flat-spiral primary is 1/4" copper water tubing, with acrylic supports and base, tuned with a clamp.
The capacitor is a 0.03 uF @45 KV Maxwell.
The power supply is a 14.4KV (1.5 KVA rated) Potential Transformer (run at about 3KVA).
The power supply is protected with dual RC filters plus spark-gap.
The R is 2 x 1,000 ohms @ 225 Watts and C is 2 x 500 pF. The Rs get very hot.
Current limiting is provided by a 500 foot roll of 12 Gauge wire.
An Asynchronous Rotary Spark Gap was used. Propeller style.
For safety, the ARSG was shielded with 1/4" polycarbonate sheet and 1/4" tinted acrylic sheet (12"x12").
The acrylic sheet reduces UV light and the polycarbonate (Lexan) sheet should contain a rotor explosion.

Rotary Spark Gaps

Multiple toploads were used (put on top of a 6"x1.75"spun aluminum from John Freau):
1) 13" x 4" spun aluminum from John Freau.
2) 12" gazing ball from some garden place.
3) 24" x 6" spun aluminum from a bulk buy.

Why did I build an oil-filled secondary?
1) sounded like a cool thing to do
2) turns out that it looks really cool
3) winding is impervious to power arcs from discharge terminal (I HATE WHEN THAT HAPPENS)
4) winding has increased protection from racing sparks
5) should handle tighter coupling and/or higher power levels

What is up with those plasma plumes?
They are caused by sharp edges on the strike rail. Specifically, the strike rail has a gap in it, to avoid the shorted-turn issue. The gap has two rather sharp edges that I never tried to round out (right side). Also, I connected the strike rail to ground using a clamp that itself has some sharp edges (left side). I had never seen the plasma plumes until I tried the rather large 24"x6" toroid at home. I thought the effect was way cool, and I hoped that it would still work at the Teslathon. It did, and Dan McCauley was able to get some fantastic photos. It reminds me of the Boston spaceship talking off. The plumes reduce in intensity as the sparks break out. So I think that the power lost in this corona is not too bad.

I think this adds another dimension of interest to a Tesla Coil. I intend to play around with adding more controlled disturbances to the strike-rail to further enhance the plumes.

These are a mix of photos taken from three different sources.
The filenames are keyed as follows: video (TB_...), my digital camera (P8...), and Dan McCauley's digital camera (dm_...).

Setup by the van. Note alternate primary for bipolar use of secondary.

Ready to hook it up. Using clip-leads made from 10ga Monster Cable. Very flexible.
A John Freau 6"x1.75" toroid is used as a base for the other toploads.

Always put your rotary gaps into an enclosure. This one combines acrylic with polycarbonate.

Gotta have some targets. Bill Downs sets up 3 at multiple levels and distances.

Now put on a John Freau 13"x4" toroid. John makes very nice toroids.
I have seen the videos, but I still am amazed at the results.

All set up and ready to rock.

I am wondering if it will actually hit that target to the right?

Strike rail. Easy.

Strike rail and first target. Better.

ARSG enclosure. Guess that was a little too close. Hehe.

Oooo. It hit the support. Very close, but no cigar.

Take out the second target. Nice.

Now back for the killer blow. YES.

OK. Time for the 12" gazing ball.

This arc is very different from that of a toroid. It tends to be driven up to the top.
It has no desire to stay on the side, but drifts all over.

The ball does not shield the smaller toroid very well, and it sometimes breaks out.
But the secondary windings are not getting fried.

Jeeze. It finally hit something other than the strike rail.
Maybe I could have done a better job tuning for that topload.

Sue Gaeta showing where she saw some power arcing going on.
Ed Wingate is relaxing way in back.

Now for the big one. The 24" x 6" toroid.

Expecting it to fall off, like last year.

Goes right for the tough one. No problem at all.

Here's the plasma plumes. Power level is just below spark breakout.

Of course, the fantasic shot Dan got.

John Freau talking shop.

Bert Hickman having a closer look.

The potential transformer. I got about 3 KVA out of it.

Gary Lau checking for heat buildup in current limiting ballast. It is getting very warm.
These 500 foot spools of 12 gauge work fine at 25 amps for runs up to 5 minutes.

The RC filter network that protects my transformer. The resistors get hot.

Entire photo gallery of my tesla Coil

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