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Registered Member #87
Joined: Thu Feb 09 2006, 01:36PM
Location: San Jose
Posts: 191
Thos arrester tubes are meant to fire every once in a while, I dunno about them taking continuous currents. I might try it if I come across one this week, my shop has a good ham radio section with all sorts of goodies.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
I've never seen SCRs with a high enough di/dt capability to be any use for firing a Tesla coil. IGBTs work great as a TC spark-gap replacement though. My old OLTC2 coil had two 1.2kV 600A IGBT blocks in parallel as its "spark gap", and a huge tank capacitor (it started as 14uF but I increased it to 30uF later) that was charged to 1kV by a hefty DC power supply. This coil worked OK, at its best I was putting more than 4kW through it and getting sparks over 80".
However, Jimmy Hynes and Steve Ward proved that DRSSTCs give more bang per buck spent on silicon, and longer sparks per watt of power, than OLTCs do, so I kind of gave up on it. In fact I'm converting it to a DRSSTC right now :P
There was recently some discussion on the Pupman tesla coil mailing list about using some old Victoreen gas-filled spark gap tubes (with a 2500v firing voltage) as TC spark gaps. Apparently they worked great on small coils. I think they were originally designed as igniters for arc lamps.
Registered Member #129
Joined: Fri Feb 10 2006, 07:55PM
Location: Austin Texas
Posts: 9
In a commerical TC I got to look at it had a UV triggerd spark gap. I would assume that it was in the 200-150 nm wavelenght to ionize the air. If you happen to have a old or broken mecury vapor lamp around with the quartz discharge tube intact I bet you could use that to ionize the air. But be careful to do it outside as it will produce LOTS of ozone.
Registered Member #139
Joined: Sat Feb 11 2006, 11:01AM
Location: Perth, Western Australia
Posts: 358
Thought about quenching at all? Wouldn't this help reduce spark erosion on the electrodes as well? A nice triggered and quenched "mini" spark gap might make quite a nice project?
Registered Member #87
Joined: Thu Feb 09 2006, 01:36PM
Location: San Jose
Posts: 191
Its closer to cw, and pics will be here later tonight. I don't want to go solid state, but tubes might be a compromise. Tube style gaps and perhaps even a small triode might be tried if I can find them. My tungsten got shipped yesterday, so that success or failure will determine how hard I look for the tubes. As for the tungsten gap, I'll try putting a little fan next to it for quenching, but it's so small I don't think it will be too much of a problem.
Registered Member #341
Joined: Thu Mar 23 2006, 07:41PM
Location: Northern Illinois, USA
Posts: 69
There’s an old saying to the effect that it’s better to be silent and thought a fool than to open one’s mouth and remove all doubt. With that in mind and the knowledge that I’m probably the least qualified on this forum to offer a solution to your problem, I still offer the following.
As others have noted, at this low voltage the balancing act required with a static gap and quenching is problematic, and the tolerances required for a rotary gap (if achieved in the first place) can’t be maintained for any period of time due to erosion. In my simplistic view, the best answer is some sort of brush arrangement, as others noted up-thread.
With that in mind and not having the machines or the skills required to operate them (plus being lazy) I propose obtaining an electric motor with commutator and brushes (field and armature windings removed). Wire the appropriate contacts on the commutator together and drive this motor (now sparkgap) with another motor. Ideally, the sparkgap motor would have a built-in fan.
The bearings, brush holders, contacts, etc. are already in place and aligned. Connecting another motor to the shaft can be as simple as thick walled vinyl tubing or as complex as a belt on opposing cones for a mechanical speed control. My $.02.
Registered Member #87
Joined: Thu Feb 09 2006, 01:36PM
Location: San Jose
Posts: 191
Some pics finally. An overall shot of the coil. I went a bit sharpy crazy on the base while I was laying out where to drill.
And with a bulb on top.
And with Superman drawing an arc.
Once the tungsten comes there will be more. So far though, I'm going to call the 1kv gap a success. It isn't too hard to space well, but did clog after about five minutes run time. Still, the tungsten should keep pretty clean. More pics soon.
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