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RE: Continuously variable primary

Original poster: Vardan <vardan01@xxxxxxxxxxxxxxxxxxxxxxx>


At 05:54 PM 5/25/2006, you wrote:
Hi Ken:

I'm sure your scheme could be made to work, but it seems very complex.
I think the challenge of building a rotor contact capable of supporting
multi-hundred Amp currents is significant.

I have seen a lot of "poor" or loose contracts for primaries that seem to work just fine! If the spark gap is at say 3 ohms, a 0.1 ohm contact should do very well.

In fact, if the contact is "just close", the HV could just arc over and you would not need "contact" at all. I think the key is to get enough copper and metal in the contact area to carry off any heat and keep it cool. Heat is what burns it up. With a little thought, the contact surface of the coil could be easily cleaned up with a belt sander if ever needed.

One area of concern is if you put say 20000 volts across 2 turns of a 20 turn primary, then the outer unused turn might get up to 200,000 volts and it might arc over. Sort of like variacs do when they are wired wrong (guess how I know that :o)). So, it might be real hard to use in the 1 - 5% area.

Finn wrote:
Armchair coiling is easy indeed, and often includes the imagination of all sorts of difficulties related to not yet tested or constructed equipment. This imagination often stands in the way of endevouring on to construction of such equipment, and worse, discouraging others in doing so.

Oh no!. what you propose there can never work. don`t bother to make it! you`l surely just waste your time, and money.

I guess I have heard "it won't work" more than most :o)) But I always invite those nay sayers incase they might be "right". If I am making some big mistake, I really "do" want to know about it early...

In the OLTC days, Running IGBTs at far above the rated current and far above the rated gate voltage was a real problem for many people. I "knew" it would be ok, but I did not mind the many concerns people had. They did not slow me down in the least. I laugh today when we would never think of running an IGBT "within" specs. :D MMCs had their concerns... Computer modeling was a big sticker too... Richard Hull said it would "Just make you nuts" :o)) I think I "invited" people to laugh at me in one of my first posts where I was going to directly measure top voltage and current :o))

Those things really did break open whole new ground and sort of shattered a lot of old ideas. But I never when into anything "blindly" for the sake of stuburness... They all took a whole lot of careful thought and work... If someone could clue me into a pitfall, that was great!! For my SISG I was pretty excited about using SCRs until Steve Conner mentioned there was a big problem with di/dt. I had never worked with SCRs and did not know this. He was right, and his clue saved me much time and trouble :-)))

So if someone thinks there is a problem, please say so! We might know it is ok or have a work around, but once in a while you really might be right ;-)) And that saves time to get one with things that will work. Sometimes we also have the bandwidth to just do it anyway just to make sure it fails just like it is "supposed" too...

Sometimes it does not go well... Gary Freemyer's MMC blew right up!!!! That is when we discovered the difference between metalized and foil plates... But his problem allowed us to fix things right away!!! He figured out more about MMCs that day than any of the rest of us ever did....

There have been things "I" thought would never work...  Like this odd thing:


It was that "DRSSTC"... "I" blew off Jimmy's DRSSTC at first!! But Jimmy proved me WAY wrong ;-)))


So sometimes we are right, sometimes wrong... But the coils just keep getting better :-))))

BTW - I have not fired up a regular spark gap coil in over a year and a half.... So what do I know ;-)))