Original poster: David Speck <Dave@xxxxxxxxxxxxxxxx> Prof Scheinberg,All the MOTs I've worked with have magnetic shunts in them. They look like a flat stack of lamination pieces about 1/4" to 3/8" thick, inserted in the winding space between the primary and secondary windings. The most desirable transformers come from the earliest Litton or Amana RadaRange ovens. Those monsters were rated for something like 1500 watts nominal, much better than the wimpy little 900 watt units in the current production Sanyo or Samsung ovens. Commercial MWOs also have very overrated transformers, as they are expected to be in pretty much continuous operation. The transformers in domestic MWOs run very hot, and are minimally rated, with the assumption of a very low duty cycle. In normal operation, the magnetron tube behaves like a 4 kV Zener diode. The magnetic shunts limit the transformer output current to prevent the runaway consumption of current during oven operation. The shunting function of a MOT shunt in not as dramatic as that of a NST. While you can theoretically run a NST indefinitely with the secondary shorted, OTOH, even with the shunts in place, a shorted MOT will still draw enough power to burn up, hence the need for external ballasting of MOT stacks. In my experience, most TC builders drive out the shunts to get a bit more power output from their transformer stacks. Oil immersion is a big help in improving the power handing capabilities of series MOT stacks. Better stock up on MOTs while you can get them. The newest ovens use a solid state high frequency oscillator, like a TV flyback transformer on steroids, instead of the heavy iron transformers of the original ovens. So far, no one has found an appropriate TC application for the new inverter systems.
Dave Tesla list wrote:
Original poster: norman@xxxxxxxxxxxxxxxxxxxxxxxxx I have read several web sites about MOTs and tesla coils. From these sites I have gathered that MOTs do not have shunts. That is why they need to be balasted. Now I am reading all these posts about removing MOT shunts. What's going on?I have built a tesla coil but it uses an NST. I have not seen a MOT, so I haveno first hand knowledge of their construction.The information that I have read on this list over the last few months has beeninvaluable in getting my coil to work. Thanks, Prof. Norm Scheinberg, City College of New York, EE Dept.