Secondary racing arcs
IamSmooth, Sun Mar 04 2007, 01:20AMIs arcing between windings from the secondary caused by too much coupling between the primary and secondary coil? Would more varnish help? Larger toroid.
I haven't had these problems yet but I want to be prepared after I read on someone's TC site that they fried their secondary coil.
Re: Secondary racing arcs
J. Aaron Holmes, Sun Mar 04 2007, 02:10AM
Probably depends somewhat on the rest of your setup. Coupling is probably the most often-blamed, however too much power (for size of coil), bad tuning, superfast current rise (e.g., in OLTC-ish coils with only a turn or two on the primary), and oversized toploads have also been blamed. These "racing arcs" often leave carbon tracking in hard-to-reach places, or burn right through windings, making some degree of repair/rewind necessary. Coating the secondary generally has more to do with protecting it against moisture, finger oils, and dings gotten from moving it around than it does with preventing racing arcs. In fact, going overboard on the coating is going to make any repair work a lot harder! You could sink your secondary in oil (and I have contemplated such a setup just to see how far coupling can be pushed), but that's a lot of trouble.
I have suffered racing arcs which I believe were of the "bad tuning" variety, however as I was tuning at the time and running at reduced power on purpose, I was able to bring things back down fast enough to avoid damage. When tuning up a big coil, it probably helps to have a few people standing in different places so that you know you have somebody ready to see all the possible bad things (like racing arcs on the side of the coil you're not looking at!)
Regards,
Aaron, N7OE
J. Aaron Holmes, Sun Mar 04 2007, 02:10AM
Probably depends somewhat on the rest of your setup. Coupling is probably the most often-blamed, however too much power (for size of coil), bad tuning, superfast current rise (e.g., in OLTC-ish coils with only a turn or two on the primary), and oversized toploads have also been blamed. These "racing arcs" often leave carbon tracking in hard-to-reach places, or burn right through windings, making some degree of repair/rewind necessary. Coating the secondary generally has more to do with protecting it against moisture, finger oils, and dings gotten from moving it around than it does with preventing racing arcs. In fact, going overboard on the coating is going to make any repair work a lot harder! You could sink your secondary in oil (and I have contemplated such a setup just to see how far coupling can be pushed), but that's a lot of trouble.
I have suffered racing arcs which I believe were of the "bad tuning" variety, however as I was tuning at the time and running at reduced power on purpose, I was able to bring things back down fast enough to avoid damage. When tuning up a big coil, it probably helps to have a few people standing in different places so that you know you have somebody ready to see all the possible bad things (like racing arcs on the side of the coil you're not looking at!)
Regards,
Aaron, N7OE
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