From: Paul
Date: Mon, 09 Oct 2000 18:27:49 +0100
Subject: [TSSP] Optimum toroid size
Barry (bensonbd@erols.com) wrote: > I have been following the ruminations on toroid size [an ongoing thread on the main tesla list discussing methods of determining the optimum toroid size] > and have a few observations to wonder about. If the toroid were > replaced with a plate with a tiny rim around it, at what point > would the plate size excede the ability for the secondary to > charge it to any given voltage? At what point would the secondary > power dissipation in the RF wire resistance cook it before the > toroid could be made too large? I think I've got this clear... You've fixed a target voltage and you're prepared to feed in as much power as necessary in order to achieve that voltage. Then you want to increase the plate size and you've realised the need to increase the input power further to still reach the target voltage. What's the biggest plate that the coil will cope with? I can only go so far with an answer to this. One thing to note here is that the I^2R loss in the secondary winding is proportional to the peak stored energy in the resonator. For now lets call the constant of proportionality K watts dissipated per joule stored. So the power dissipation in the coil winding is W = BPS * K * 0.5 * (Cplate + Ccoil) * Vtarget^2. You'll have in mind a maximum power dissipation that the coil will tolerate, which you would no doubt determine by running DC through the winding till it approaches your temperature limit. Call that figure Wmax. Then Wmax = BPS * K * 0.5 * (Cplate_max + Ccoil) * Vtarget^2 Now just rearrange that to get Cplate_max in terms of the mysterious factor K and the other stuff. I wouldn't like to try to work out K, but you could measure it. It might not really be a constant either - its quite likely to depend on the resonant frequency and therefore Cplate! If we new that dependency we could factor it out and go further. Sorry I can't do better than that, but maybe you see what you're up against. As usual we're limited by our ability to predict the losses in the resonator. As a consolation I'll just point out that you can always reduce BPS to prevent meltdown and still keep the same peak voltage. > Would it be possible to use a very wide toroid with a small rim > (read cheap to make!) to achieve the same spark length as a fat > toroid (counterintuitive?)?. These questions you raise are all about maximising stored energy, as opposed to optimising the toroid size for maximum output voltage, which is the subject of the other thread. Probably the latter is not the one to go for if you want to put on a performance like the one below! > Richard Hull had a toroid about 6 feet in diameter on top of > a 3" by 12" coil. The sparks were over 10 feet long off the toroid > ( http://www.pilot.infi.net/~rhull/highenergy004.htm ). Cheers, -- Paul Nicholson, Manchester, UK. --
Maintainer Paul Nicholson, paul@abelian.demon.co.uk.