HV Power supplies

In the left picture the arrangment of the MOT's for my 6MOT array can be seen. The white stuff is made from HDPE kitchen board which is perfectly oil resistant as far as I can see and easy to work with.

As one can see, the wiring is far too thin for the expected current, but under oil everything works cold to the touch
The whole array is submerged under oil inside a blue HDPE container. This ends up with almost 50KG of oil and metal... I used the finished supply up to 10KVA on short runs and it performs really great at 12KV Output. I usually balast this setup with one or two additional MOT in series with the input current for 2,5 or 5KVA.

This is how I tested the supply for the first time after assembly. You can still see the big air bubbles escaping from the xformers.
With 12V in I achieved over 800V out without load. Always keep that in mind while working with this kind of setup. Although 12V in sounds very safe the 800V out will give you a nasty zap ( been there, done that, got the t-shirt ;-)

One older pic of the ordinary 2-coil setup with the old 4MOT supply.
This Supply only existed for some 2 Weeks and was dismatled in favour of my new 6-MOT Version.

The power capability of the 4MOT was really good, but for the upcoming magnifier experiments I wanted something with higher input voltages. As you might guess from the picture I did not have any ballasting but a very well sized supply cable.

On top of the stacks box one can see a Siemens type line filter and power switch. I never switch on the supply with this switch but use it as additional safety disconnect while working on or near the xformers.

Here I powered up the MOT-stack for the first time with an impromptu jacobs ladder as load. I used one MOT with the secondary shorted in series with the 240V input. Switching on would trigger the 16Amps breaker once in a while.
Currently I use a 40Amps service but I would rather go back to 16Amps for logistic reasons as 40Amps single phase is not available everywhere I want to run my coil....

This is a new transformer I found via ebay for 8EU, which is pretty cheap but had to pay almost 10 times the price for shipping to my door. Nevertheless a pretty good deal after all. The core is even easier to seperate than I hoped it to be.
Originally it was intended for use in a Siemens frequency inverter and was rated 380Vin 165Vout in aoutotransformer configuration and tha lable stated 10KVA. Now I wonder how far this core can be stressed before saturating.
From the size I'd guess around 4 or 5KVA max.

Here you can see the transformer partially disassembled. When I saw it for the first time I feared the core was welded together and could not be taken apart at all. But as you can see one can easily remove the parts of the core that carry the windings.
I counted the original winding with 160 turns on the 380 volts side, which sounds pretty low. I still have to check if this value is OK for single phase "non-autotransformer" operation.
The basic idea is to keep the central winding ( or part of it ) for 230V input. Then I would rewind each of the two outer windings with aproximately 2600 turns of 0,4 or even 0.6mm magnet wire and have some whooping 400mA at 12KV RMS.

The mandatory jacobs ladder pic. This is the former 6MOT-stack, but only 5 MOTs are currently conneted after one transformer arced over internally.

For security reasons I decided to give the MOT I use for ballasting a home and get rid of the exposed wires. I happened to have a suitable case at hand.

The finished ballast. Since then I added a third connection for ground. It is connected to the MOT's core and can make up a central point for other ground connections.

The Ballast hooked up to the MOT-stack. This was before I added the ground connection.

Hers is a pic of the one of the outer MOT's that failed in the 6MOT-pack. This was due to a massive voltage rise that occoured while the RSG was out of phase and the safetygap got disconnected and failed to fire. A real beginner's mistake that simply must not happen. Now I am looking for a replacement. I intended to use the smaller MOT to the left, but it turned out its secondary winding is open and has a short to the core. I could have forseen that when I found the microwave oven under a bridge and obviously its fomer owner had thrown it over the banister 30 feet down ;-) cruel word...