Here we will look at some of the configurations in which MOTs may be used to develop High Voltage power supplies. The first is the Single transformer AC output.
This configuration does not present much promise for use as a Tesla Coil power supply in a disruptive discharge type coil. The output voltage is too low to jump a spark gap of any usable distance. If one were able to get the spark gap to fire, it would be very hard to get it to go out. It would have a tendency to power arc. I have experimented with this configuration using a single static gap blown by a five horsepower two stage air compressor. It was all the air compressor could do to blow out the arc. This was tried on the Tesla coil pictured at <link> (use back button on browser to return). The power arcs blown out of the spark gap were about 10 to 12 inches high. Streamers off the toroid were 4 to 6 inches long. It worked, but not very efficient!
Next, two transformers connected in series.
This configuration is actually usable. The voltage is low, but high enough to jump a spark gap reliably. Gap losses will be high, and some form of external current limiting in series with the primary is recommended. If a large tank capacitor is used, an appreciable amount of energy can be delivered to the primary. Several people have reported success using this configuration. Other people have seriesed more than two MOTs to obtain higher voltages using various strategies. The main problem is that the winding to core insulation is not good for more than a couple hundred volts so there is a tendency for the insulation to break down. Some have isolated the transformers under oil, others have used extra transformers hooked up backwards to provide the primary voltage at higher potentials for the outer transformers leaving the cores floating. I have not explored any of these methods, so I will not try to describe them further.
Next we will look at some DC sources. The first DC source we will consider is the level shifter. This circuit has been used with success by several people. The output is pulsed DC. Rather than look at a single circuit, as that was covered in the microwave oven power supply discussion, we will look at a popular configuration.
This circuit produces a pulsed DC output of 5.6 X the VRMS output of a single transformer in the unloaded condition. The pulse rate is equal to the line frequency. This circuit works well with a synchronous rotary spark gap. The voltage output looks like this in a loaded condition:
And the current across a resistive load :
Here is a model for a double half wave doubler circuit.
Here is the Voltage envelope with the resistive load.
Here is the current waveform for the resistive load.
One more variation is of interest here. This is the full wave voltage doubler circuit using a single MOT.
Output Voltage waveform:
And the current waveform into a 100K ohm resistor:
More to come