The Fryback!

Ladies and gentlemen of the world, I present to you a marvelous device that will revitalize your health and bring wondrous wealth and prosperity to your families and all future generations. Straight from Nikolai Tesla’s labs I bring you a fantastic revelation in high voltage transformer technology, made with nothing but the latest and greatest materials this magnificent transformer will supply all the milliamperes you’ll ever need along with more than nine thousand volts! Such mind boggling wonders can be experienced with this remarkable transformer…

Because I had nothing to do and had an empty piece of ferrite I decided to make the largest AC flyback transformer that I could. Now if you don’t care how I made it you can skip to the video at the end of the page, but if you do you may read the text below and learn how to make your own.

 First you’ll need to find a suitable ferrite core. The one I had to use was made at least 50 years ago and was part of an old flyback who’s winding pretty much fell apart. Because I’m a klutz the core has a crack in it, though when repaired with superglue it’s good as new.  What’s special about this core is it has a huge winding window, and that allows for quite a large secondary. Cores such as this can be found online if you look hard enough, one this size might cost you $14. 

I had a bunch of 28AWG magnet wire and nothing to do with it, so I decided to use this wire to make the transformer’s secondary. It’ a little thicker than I’d like, but the thinner stuff I had was 40AWG which was way too thin. I chose to make a disk shaped secondary for a number of reasons;

  • Because there are few windings per layer, inter-winding capacitance is reduced and the transformer can run at higher frequencies.
  • Because there are few windings per layer, there will not be a large voltage difference between layers; something that could cause arcs.
  • Because a disk shaped secondary is not very fat I can use tape to make it.
  • Disk shaped secondaries look cool.

Ideally I should have used kapton tape to make the transformer since it has very good dielectric strength but I had to make do with what I could get at the hardware store. Therefore I bought some red electrical tape and some teflon pipe thread tape. I bought the nice 3M tape that comes in the little plastic containers because it is very stretchy and very sticky, perfect for making the transformer. After some testing I found that the electrical tape failed at 800V while the teflon tape failed at 1kV. Because of this I’d need a couple layers of tape to prevent failure.

The first step was to find a nice cardboard tube and wrap some electrical tape on it, then wind some wire around that. In order to prevent failure the wire must not come close to the edges of the tape. I managed to fit about 23 windings nicely in the middle.

 The next step was to provide some insulation for the layer by wrapping 5 layers of teflon tape around it nice and tight. Since teflon is very deformable it conforms to the windings and squeezes out air that could cause corona. This is a plus since corona would eat away at the insulation.

Then one layer of electrical tape was wound to so the next layer of windings could be put on. After that I repeated these steps until my brain melted and I ended up with 40 layers; a task that took 25 hours, a super mighty and a two liter of loganberry to accomplish.

As magnet wire is rather fragile I attached some silicone insulated wire to the windings and used cyanoacrylate adhesive to secure it in place. I chose silicone wire because it is very flexible and it can stand up to HV quite well. Not only that but super glue sticks to it very well. Unfortunately it costs a little more than regular plastic insulated wire.

 

Since tape isn’t perfect it would in time slip off center and ruin the secondary. To prevent this I bought a can of liquid electrical tape at the hardware store and coated the secondary with it. This will both keep the windings in place and make the secondary look better. 

Every transformer needs two windings to work, so the primary winding was made by taking two strands of 18AWG wire and wrapping a 4+4 turn center tapped primary around a paper and tape form. Notches were cut in the coilform to prevent rotation.

 

After adding some tape to the core pieces to make an air gap I slid the core in the paper tubes and the friction held it in place. When powered up the core will clamp together because of the magnetic field, so no external clamp is needed. And here we have the largest disk AC flyback yet made, a transformer which I have aptly named “the fryback”.

When powered by a ZVS and run at 36V the fryback makes some 5 inch long, 2.5cm fat arcs. The voltage is about 20kV while the current must be 100mA or more. That’s all well and good, but when fed 48V the fryback really shows what it’s capable of. It outputs 8kV (11kVrms) and the current is… a lot. The arcs I can draw from it are 1 foot long!

The fryback can’t handle more than 48V because the core gets very hot at that voltage and it is probably in saturation. The secondary could theoretically handle much more power though because it stays nice and cool, and because the interwinding voltage is only 1250V while I used 4kV worth of insulation.

And what you’ve all been waiting for; the video. ∎

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