John S. wrote:
[snip] I destroyed 8 MOTs before I realized the secret....take the shunts out and make a good ballast. Removing the shunts made the MOTs run much cooler. In fact, with them in, the oil would be hot to the touch just after a few quick minute long runs. I think that the heat contributed to their failure. Now I can run the coil much longer and the oil never gets warmer than ambient temp. I haven't lost a transformer since.
Interesting observations, John. MOT shunts are one area where nobody really seems to be in agreement, at least from I have noticed over the last decade or so on the list. I have read some suggesting to leave them in, some suggesting to take them out, and some saying that it really doesn't matter.
I do know that they are not anywhere near as significant as in an NST, but considering the intended application of a MOT as only running in a half-wave double, they don't need to be.
What voltage were you running your MOTs at initially, when they were burning out? Do you think that perhaps running them with an external ballast had more of an effect than removing the shunts (ie, what was the voltage/current at each MOT before and after ballasting)?
It would be nice to nail down the issue of MOT shunts once and for all and determine the best choice when using them in a TC supply. I've got a MOT I'll run some experiments with and publish the data when I am done.
Jon
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