Some Jacob's Ladder Fun

[Robert3z]

Part 1: The Large Ladder

Before starting my DRSSTC I had to build a large Jacob's Ladder for a friend's business. It obviously HAD to be safe. This meant no NST's, OBiT's, etc. that run on 60Hz. Needed to be enclosed thoroughly and high frequency. I built the Information Unlimited JACK-50, a 5' design that runs 16-18 KVAC at 15-50KHz. Guessing about 1KVA or so, didn't think to use a clip-on meter on the AC line - oh well. Here is a link.

https://www.amazing1.com/products/jacobs-ladder-5-foot-plasma-arc.html

The kit is run by a small full bridge unit (chopper) that outputs a 300V p-p square wave with the usual gate driver circuits, gate transformers, etc. What distinguishes this kit is that it has you scratch build a high freq ferrite core grounded center tap transformer. I found this very instructive, very difficult  by hand, and pretty cool. Some of the really tough parts were locating structural pieces for the transformer that fit together (bobbins, etc.) I used polycarbonate tubing in 1/16" x 1 1/2" for the bobbins, and larger for the enclosure. You do have to vacuum pot it to prevent arcs and corona.

I used Ferroxcube 3C91 or 3C94 Ferrite in the U100/57/25-3C94 size. Either material will work due to the frequency range.
https://www.digikey.com/en/products/detail/ferroxcube/U100-57-25-3C94/7041696

The arcs are huge, white, and fuzzy - it will bridge electrodes at up to 4" or more with a 1" thick arc. Downloadable plans do have some small issues (obsolete parts, etc.) but do work and are, IMO worth the 10.00 for just the transformer design. One of the really nice features is the cooling fan for the full bridge is dual-purpose. Someone very carefully designed ports in the base to provide air to prevent arc hangup and give a smooth arc climb.

Here are some pics of the test setup - the first set of electrodes were made from steel coat hangers and without the fan, suffered quite a bit of damage from hangups. I also applied salt and baking soda dissolved in water for a little entertainment    There are other fun chemicals - don't use any Barium compounds, vapor is toxic.

Cheers / Robert

[Robert3z]

Part 2: the Small Ladder

After making the large ladder for a friend, I wanted my own but didn't want to spend anything.
I had an Allanson 250VA 10KVAC OBiT laying around, and used it for the (much more dangerous) arc generator. I also wanted fan assist because it works great. So I took a small 12VDC CPU fan I had from scrap and built a regulated 7812 12VDC Power Supply with a small transformer for it. Used 1/16" x 3' 308 Stainless TIG welding rods for the electrodes, and spent quite a bit of time getting electrode shape perfect. Electrode shape is critically important as I found out, and with less voltage and power than the larger unit, more important.
I spent some time adjusting box pressure with a vent, and finally got it perfect. Here are some stills - I may get a youtube account if anyone is interested.

On durability - I am certain that a stack of 2 minute run times will probably kill the OBiT, even though they are supposed to be rated for "continuous duty, so I follow the 30 second rule. 30 second run times with cooldown.
Running the ladder off my monster 3.5KVA Variac at 100% does increase the arc length, but worries me on the transformer. No change in brightness obviously since OBiT's are current limited.

Nice, entertaining toy!

Cheers / Robert

 











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[abstruse1]

To really spice things up, drop a bundle of bottle rockets down the tube