Re: replacing the spark gap with SCRs

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Malcolm Watts" <m.j.watts-at-massey.ac.nz> 

On 28 Oct 2004, at 8:07, Tesla list wrote:

 > Original poster: "eahab el naga" <tesla.dude-at-gmail-dot-com>
 >
 > I finally got two huge SCRs necessary to handle the current needed for
 > the capacitive discharge. I also came up with a schematic that will
 > the fire the SCR's (which are opposing kind running like a triac) at
 > the peaks of the sine wave. I am letting the circuit ring 5 times then
 > wait for the next peak in the sine wave. The SCRs i got are 1800V
 > 1000A puk style and can handle 17000 amps repetative pulse for 10ms
 > each. I really think that i could pull it off..however i am probably
 > going to double the SCR's before i run full power through it
 > (hopefully i'd be able to find a 1kv transformer for several kw)
 > meanwhile i am going to rectify 440volts through a transformer i have
 > and have a capacitor to smooth followed by chokes to the tank
 > capacitor (not sure about my terminology but i'm refering to the one
 > in the LC circuit). I'd like to know how to possibly improve the
 > design and if there are any flaws in this concept. I plan on testing
 > the cuircuit with just 12 volts on it and have a scope monitor it from
 > a few turns of coil placed in the center where the secondary would
 > normally be. If this works i am hopeing to get a dramatic increase in
 > effeciency but i came across a few thoughts: 1) the secondary current
 > would be way too high and instead of getting long streamers i'd get
 > short intense ones because the primary voltage is low (kinda like the
 > effects of a solid state tesla coil) 2) to lower the current rise, I
 > would increase the number of turns of the primary inorder to ease the
 > stress on the SCR's and allow them all to turn on before the high
 > current pulse is sent through them(keeping in mind that i'll be
 > paralling them once i get 4 SCRs),but would that make problem number
 > one more significant. 3) because of the lower primary voltage, can i
 > make the winding closer to the secondary as long as they don't rise
 > too much in order to raise the coupling coeffecient
 >
 > anyways this has a long, long way to go but i plan to have this
 > actually done within 2 weeks.
 >
 > by the way, i also have smaller SCRs that are also puk style that i
 > hope to use on a table top tesla coil one day if this ever works out.
 >
 > thanks a buch,
 > Eahab El Naga
 >
 > my old, old site: http://eahab1.port5-dot-com

Good luck. I've had some Westcode SCRs rated somewhere around 2kV -at-
2.5kA plus diodes to match sitting on a shelf for about eight years.
The reason they're still sitting there is that the coil I'd have to
build in order to use them to full spec and stay within the di/dt
ratings would occupy most of the space in the garage.

Malcolm