Original poster: "D.C. Cox" <resonance@xxxxxxxxxx> Mike:If you use a 36 inch dia. toroid on a coil similar to my M-150 design, which has 18 inch dia. sec coil, there will not be any toroid to coil strikes.
I didn't have in stock a large enough toroid for the M-200 design that you saw get damaged. We normally use a 60 inch x 20 inch toroid size on this coil and during the Cheesehead event we only used a 48 x 12 inch toroid which didn't offer enough electrostatic shielding for the sec coil.
Good rule of thumb is to use 3-4 x dia. of sec coil for major toroid dia. and then you will not have any problems. A 3:1 major to minor toroid dia. also gives the correct ratio for this toroid design --- either spun or mesh toroid --- makes no difference to the sparks.
Email off-list and I can share a unique design for a chicken wire toroid like we had on the Big Bruiser that can be constructed for under $125 in sizes up to 6 ft. in dia. Big Bruiser uses a 10 ft dia x 24 inch cross section for it's toroid.
Dr. Resonance Subject: Toroid size on Big Coils
Original poster: "MIKE HARDY" <MHARDY@xxxxxxxxxx>From what I see on the profesional coiling sites, in particular KVA effects, and Tesla Technology Research, the toroids seem small for the size of the larger coils. I know the cost of large spun toroids is prohibatively expensive. In the case of the M-13 magnifier, the majority of pics, show the discharges comming off the corona ring and not the toroid. With this coil, and Electrum, many of the arcs seem to be hitting the secondary. At the Cheesehead teslathon this past summer, the M-200 of D.C. Cox had several secondary strikes, one of which severely damaged the sec. He said 'that's what happens with too small of a toroid. How does one avoid this kind of catastrophic damage? I'm planning to make a coil similar to DC's M-150. It uses an 18" form, and I have a 36" spun toroid. I don't want to destroy my secondary.