Flybacks

I did quite a few experiments with flyback transformers salvaged from old TV’s or computer monitors.

Single transistor driver

My first flyback driver was the famous single transistor flyback driver. For the transistor, I used the MJE13009. I used it to drive a DC flyback from an old monitor. It produced only weak, purple sparks but that was enough to get me addicted. Unfortunately I don’t have any movies or pictures from this experiments anymore.

ZVS driver

After a while, I got bored with the little sparks from the single transistor driver. So what do you do then? Build a more powerful driver of course! I’ve chosen for this driver because it’s simple but powerful. I built it and it looks like this:

Component values are not too critical, there’s some space to experiment with different values. I used 15 V zeners instead of 12 V, RGP10D diodes as recovery diodes and a 660 nF cap instead of 680 nF. By changing the value of the capacitor, you can change the frequency at which the driver is running and thereby the output of the flyback. However, the value of 660 nF worked best for me. For the coil, I just took a toroidal core taken from an old PC power supply and wound on as many turns as possible. Despite this non-scientific method it works just fine.

So time for some sparks… with 12 V input from an old computer power supply my DC flyback already produced hotter arcs than with the single transistor driver. But still, they weren’t that big. Then, a friend of mine gave me a very old AC flyback. I removed the original primary and wound my own primary consisting of 5+5 turns. I hooked the flyback up to the driver and the arcs from this old thing were already much more impressive than the arcs from the newer DC flyback! The AC flyback seems to pump much more current into the arc.

But still, the arcs weren’t that large. Unfortunately I didn’t have a better power supply than that old PC PSU (which gives 12 V at 8 A). However, that changed when I acquired four 12000 μF 40 V capacitors (€ 3,00 for two capacitors including a mounting bracket) and two 35 A bridge rectifiers. I already had a powerful transformer (a MOT rewound for 17 V~ output) so a 24 V 1000 W power supply was constructed quickly. The output of the flyback amazed me and made me hungry for more. So I hooked the caps and the bridge rectifiers up in a voltage doubler arrangement. Now I had 48 V at 1000 W to pump into my ZVS driver! And, as expected, the arcs were really long, hot and scary. The arc jumps over a distance of about 2 cm and can then be stretched to almost 10 cm.

Here you can see my setup with the voltage doubler:

As you can see, I only used one diode from each bridge rectifier (for the voltage doubler you need two separate diodes, and using the rectifiers was a cheap way to get 35 A diodes).

I have made some movies for you:

• DC flyback, 12 V input
• AC flyback, 12 V input
• AC flyback, 24 V input
• AC flyback, 48 V input (actually 45 V as the doubler doesn’t function perfectly)
• Jacobsladder driven by the AC flyback with 45 V input

At the moment of writing, however, my trusty AC flyback is dead. I was pulling arcs from it when the output suddenly collapsed and a cloud of smoke came from the flyback. When I quickly turned off the power, I could still see the enclosure of the secondary coil glow red hot. Apparently the flyback overheated and arced over internally. I removed the secondary coil also so I can use the ferrite core for something different.

I have tested a newer DC flyback on 45 V input, and it seems to produce a slightly larger voltage, but when stretched out, the arc is much thinner than with the AC FB.

Singing arc

Mainly because I had nothing better to do, I decided to make a very simple “singing arc” with my ZVS driver. Yep, that’s right, an arc making music instead of the usual “arc-sound”! To accomplish this, I placed a transistor in the supply line to the ZVS. The emitter is connected to the GND of the power supply, the collector to the “GND” input of the ZVS and the base to the output of a small amplifier (with a 1k resistor in series). I used a TIP122 transistor. That is a darlington transistor with a h_fe of 1000 and an I_c of 5 A continuous. The supply voltage I used was 12 V, because at higher voltages the ZVS would draw too much current for the transistor to handle.

The results are, as expected, pretty bad. The music is dominated by the noise of the arc. Also, when the volume of the music drops below a certain level, nothing is heard anymore. Listen for yourself in this movie in which I let the arc play a part of the intro from Meat Loafs “Bat out of hell”.