Saturday, July 18, 2020

Bonsai Lightning!

We live in a residential space - there are limits to exactly what magnitude of lightning we can tolerate in the kitchen, after all. Why not make a dwarf kind of lightning?

I recently ran across a $9 miniature Tesla Coil kit. It seemed too good to be true, but it works (there were a few missing or helpful but absent parts: a nut for the screw to hold the transistor to the heat sink, and a hot glue gun really helps!).

This is not a link that generates any kickbacks or credits, I include it for those who are interested:

My son and I assembled the kit in about an hour (teaching the whole way, and making several repairs to self-inflicted damage to a few parts along the way). It worked on the first try when we were done, so I rate this as a decent design.

Key notes:

1. The secondary coil has a tendency to unwind - a drop of hot glue at each end of the winding saved a lot of rewinding time.

2. The high voltage end of the secondary (the little wire sticking up in air) is literally a tiny strand of copper wire. We hot glued it to a plastic drinking straw that we anchored on the inside of the coil to give it some stability.

3. Solder bridges are easy to make when soldering parts into the circuit board - especially if your assistant is enthusiastic with the solder.

4. Always solder in an area with good ventilation and wash hands after!

5. Put something underneath your soldering area that cannot catch fire - we used some fiberglass fabric (just the glass fabric!).

6. You need a 12V DC power supply that can provide at least 400ma of current, which they do mention but I repeat it here since we forgot.

My son says "The Tesla Coil is a complex circuit, but one of the easiest circuits to assemble. If your parent's say it is ok to build a Tesla Coil by Nikolai Tesla, fire up your soldering iron and get a 12 Volt power supply. Don't use a one-cell battery holder, since it does not work. When things don't work, it is not exciting. If you do have to happen to have a 12V power supply and everything you need in the kit, you can build it."

The lightning that is generated is small and at a very high frequency - the primary frequency of the oscillator appears to be around 200ns, or 5 MHz.

This is a frequency where the electricity will not penetrate deeply into human skin - however - lots of things can change that, so really no touching the high voltage end of the coil!

At 5MHz the skin depth is only about two micrometers, which is enough to be felt and cause pain - though the bigger danger is burns. There is enough power in the output to cause thermal burns from your skin heating up in the area of the spark, which is the more likely injury mode.

Also be aware that this device is a hazard to some electronics if they get too close - smart watches and cell phones come to mind.

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