Providing output of a kilowatt long-term and in excess of 4 kVA short-term, undoubtedly it is the most powerful single-phase power supply I’ve made, and the scariest of them all! Whether you want to power up medium size Tesla coils, arc-weld through any sensitive electronic evidence or commit suicide using one of the most horrendous ways, this beast always gets the job done.
Shame that living in a flat gives no possibility of obtaining three phase power. In such a case I’d go for 1.5 meter long arcs with a beastly 15 kVA stack 🙂
Just what sorcery is inside? None! Purely, just parts from 4 microwave ovens. Yes, you’ve guessed it right – two microwave oven transformers (MOTs) with their primaries paralleled and secondaries in anti-phase, to double the voltage of a single MOT (2100 volts ac) to 4200 V. To put both transformers in resonance, a capacity of 2-3 microfarads rated at least 3kV= is put in series with each transformer output (center tapped to ground, yielding two 2kV~ outputs against ground). In my case I used four oil-filled microwave oven capacitors rated 1uF each in a 2×2 configuration. Don’t omit these – you’ll thank me later.
A MOT is, however, a fine example of maximum savings on materials. Some are even wound with aluminum primaries, lacquered orange to look like copper… (remember, chinks are masters when it comes to fakes!) So even these 1000W-rated MOTs pictured above are really just 250-300 watt transformers long-term and cannot be used for their “rated” powers, or God forbid arcing, without active cooling. That’s why there’s a fan inside the guts of your microwave. For this setup to survive, you will need at least two of them fans, in close proximity to your MOTs.
What I did above is far from enough! Should have used a bigger cage…
Unless you have a circuit breaker rated 25A and more, don’t try connecting more than one microwave oven transformer to your mains directly, or the huge inrush current will cause it to trip most of the cases. I used a soft-start circuit obtained from one of the microwaves I disassembled, and works like a charm. Basically, it connects those MOTs for a fraction of second to mains, through a few-ohm 30W resistor. Then a relay shorts it out, connecting them directly. Despite drawing 10 amps at idle, this method never trips my class B “10A” breaker. Or, well, at least the power up itself doesn’t. 🙂
If you don’t want to use fans to cool those transformers down, you can limit output current with stacks of chokes out of mercury or sodium lamps. And, as mentioned above, I used microwave oven capacitors to get those MOTs in resonance. However, if you plan using different capacitors rated the minimum voltage as described above, discharge them before playing inside. Most oil filled microwave oven capacitors discharge themselves within few seconds as they have an internal bleeder resistor encapsulated.
My setup draws a juice of 10.7A~ rms from 240V, at idle. Arcing and fiddling with the output made the ammeter to jump between the 20 and 25A markers, so watch your electricity bill 😉
That’s all folks – I suppose there’s no need to draw a schematic for this, as the wiring and the soft-start solution have been documented thoroughly above. Contrary, if you really needed a circuit schematic for a setup like this, you should swiftly click on “Low voltage circuits” on the side menu…