Posted April 20, 2024
A few years ago I was (and I still am) interested in electrical engineering and learning about how electricity works. I built circuits and repaired various different electronic devices around my house that were broken. My favorite part however, was working with high voltage. The cheapest and most effective gateway drug into high voltage that I encountered was actually the humble microwave oven.
Believe it or not, microwave ovens are actually deceptively simple. It really consists of 3 main parts:
The control panel is pretty self explanatory, it lets the user input the time into the microwave oven, change settings, and etc. In fact, a control panel isn’t really necessary, all that the control panel does is turn the transformer on and off, which could potentially be done manually. The magnetron is the part that actually generates the microwave radiation needed to cook your food. The high voltage transformer is what provides the necessary power for the magnetron to actually work. The transformer is what we will be focusing on.
If you’re unfamiliar with transformers and how they work, I would recommend learning a bit about them here. Otherwise, let’s continue.
The transformer within a microwave oven is very special. Most high voltage transformers that you can easily get a hold of are very…limited. Usually these transformers output a high voltage (around 5,000 volts max), but have at a pretty low current (less than 5 milliamps). While this can potentially hurt you and leave burns, it is usually not enough to kill you. Microwave oven transformers are very different.
While microwave oven transformers are pretty easy to get a hold of, they can output a scary amount of power. The average microwave oven transformer can output anywhere from 2,000 to 4,000 volts at around 500 milliamps (or 0.5 amps). That’s around 1-2 thousand watts of power!
With high voltage like this, you can do some really cool stuff. But first, a disclaimer:
Disclaimer
This should go without saying, but do NOT work with microwave ovens and microwave oven transformers unless you know 100% what you are doing! These things can easily kill you.
Human skin is usually 100 killoohms, this means that if you touch even a 2,000 volt microwave transformer, then you could have at least 20 milliamps flow through your body1. This is enough current to seize your muscles so you can’t let go. 💀
I am NOT responsible for anything stupid that you do.
This is the transformer that I pulled out of a microwave oven. Like most transformers there’s two coils, the primary and the secondary2. These are illustrated below:
By hooking up the primary side of the transformer to 120 volts AC (a.k.a. Mains electricity) and attaching wires to the secondary side, I was able to get some pretty cool arcs. I achieved this by bridging the gap between the secondary side with a nail. This setup is called a Jacob’s Ladder.
We can do better. We can build a self-sustaining (non-manual) Jacob’s Ladder…but how?
In order to create a self-sustaining and self-starting Jacob’s Ladder I needed more power. But how exactly can we add more power to this circuit? One microwave oven transformer already draws a lot of power, but how about two microwave oven transformers? That’s right, I got a hold of another microwave oven transformer.
Careful consideration is needed in order to hook up two of these microwave oven transformers. I wired the two transformers in series with a “center tap” going straight to ground (otherwise my breaker would trip). This gives me anywhere from 4,000 volts to 8,000 volts AC. Next I need to turn that AC voltage into DC voltage.
Sadly, I did not have enough high voltage components to make a true AC to DC conversion system…but I hobbled one together anyways. I was able to use two microwave oven capacitors as resistors3 since I didn’t have any high power resistors on hand. In order to turn AC into “DC” I took and very simple [but stupid] approach. During the negative AC cycle, all the current is dumped into a pair of diodes…that’s it. Does it waste a lot of power? Yes. But does it work? Yes. I made a schematic below in order to better illustrate the circuit.
And here is the final product. A working Jacob’s Ladder!
I’m not sure if you noticed in that video, but my breaker popped. This circuit just draws too much power. I could improve this circuit, but I think I’ve decided to end my project here. That being said, I think this was enough high voltage fun for one day. :)
These are actually very conservative estimates. In reality, much more current is likely to flow through your body…which would kill you even faster. ↩︎
Most microwave oven transformers actually have a third coil (see the image). This coil usually generates a very low voltage with a high current capability. This is used to heat the magnetron filament, however we are not concerned with it. ↩︎
For those who don’t know, capacitors behave similar to resistors when passing AC current through them due to capacitive reactance. ↩︎