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RE: Continuously variable primary
Original poster: Vardan <vardan01@xxxxxxxxxxxxxxxxxxxxxxx>
Hi,
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:
http://www.hot-streamer.com/chunkyboy86/pictures/heatsink.JPG
It was that "DRSSTC"... "I" blew off Jimmy's DRSSTC at first!! But
Jimmy proved me WAY wrong ;-)))
http://www.hot-streamer.com/chunkyboy86/pictures/sparks/spark4.jpg
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 ;-)))
Cheers,
Terry