Re: replacing the spark gap with SCRs

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

Original poster: "colin heath" <colin.heath4-at-ntlworld-dot-com> 

hi there,
             i think the main prob with using scr as a spark gap is the speed
of switching. its usually way too slow.
thats the main reason igbts weren't used for some time.
i should check the switching speeds are up to it before going too much
further. 5 cycles ringdown will probarbly be too loose coupling for an
efficient coil. but i do hope im totally wrong and your coil rocks.
cheers
colin heath
----- Original Message -----
From: Tesla list <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Thursday, October 28, 2004 3:07 PM
Subject: replacing the spark gap with SCRs


 > 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
 >
 >
 >