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Registered Member #7267
Joined: Tue Oct 16 2012, 12:16AM
Location: Detroit, Michigan
Posts: 407
EasternVoltageResearch wrote ...
Check your ground as well. A poorly grounded secondary could cause the secondary voltage to peak at other than the end and explain the arcing you're seeing.
Registered Member #7267
Joined: Tue Oct 16 2012, 12:16AM
Location: Detroit, Michigan
Posts: 407
teravolt wrote ...
another thing I noticed is that your srike rail is to high what do you think
Well I don't know.. but I built it with the exact dimensions as are in Dan's design book (from the top of the supports down to the lowest most turn of the primary is exact dimensions, from the lowest most turn of the primary to the bottom of the support is slightly different because I compensated for coupling) . except the fact that I have the strike rail resting on top of the support zip tied.. so i guess add 1/4" or less to the support height.
Furthermore, My primary has 9 turns when the original design calls for 8. (because my secondary is lower frequency then original design, even though i could have gotten away with 8) So when you think about it, I made my supports slightly shorter as well as added a turn to the primary. So sitting on top of the supports, the strike rail is still at about the same exact distance from the upper most turn of the primary, and about same height as in the original design. It's really not any 'higher' up, maybe 1/4", if that.
Say I get a smaller sized diameter of copper tubing for a new strike rail, or use some extra 1/4" tube, and put that in the original holes that I drilled. Then it will actually be a bit lower then original design.
Whats gonna happen if its that much higher than what the design calls for?
Registered Member #15
Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068
I agree with Teravolt. The strike is much too high. Good catch.
I'll have to doublecheck the dimensions i had in the book - they may have never been updated.
But yes, cut the primary supports to bring the strike rail lower. I'd make the strike rail only about 1/2" higher than the primary coil.
Wow. That coil looks great. That definately brings back some memories. Built that about 10 years ago! Can't believe its been that long. That was a great performer for its time - we had about five (5) of them that we rotated in and out when we used to do school and scouting demos.
Which reminds me, you might need to decrease the coupling a little bit by raising the secondary with respect to the primary coil. (maybe 1/2" to 1"?)
Registered Member #195
Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111
personally I like a tapered primary because of this problem. It has been my experience that .18 to .22 K is a average coupling. Uspring can a tesla be over coupled? should there be room for the tesla to vibrate on it's own as its being excited?
Registered Member #7267
Joined: Tue Oct 16 2012, 12:16AM
Location: Detroit, Michigan
Posts: 407
EasternVoltageResearch wrote ...
I agree with Teravolt. The strike is much too high. Good catch.
I'll have to doublecheck the dimensions i had in the book - they may have never been updated.
But yes, cut the primary supports to bring the strike rail lower. I'd make the strike rail only about 1/2" higher than the primary coil.
Wow. That coil looks great. That definately brings back some memories. Built that about 10 years ago! Can't believe its been that long. That was a great performer for its time - we had about five (5) of them that we rotated in and out when we used to do school and scouting demos.
Which reminds me, you might need to decrease the coupling a little bit by raising the secondary with respect to the primary coil. (maybe 1/2" to 1"?)
Thank you, good sir!!
The height of the primary supports are 7.5". The height of the strike rail support is 1". Distance between the top most turn of the primary to the strike rail is roughly 2.6" or so if I remember correctly, could be higher. But regardless, it sounds like I will have to lower then. If I zip tie it to the bottom of the supports then it will be about 3/4" or less above the primary. Would this be okay?
Regarding the coupling, I just went by values in the book too. 1/2" to 1" would be a coupling of about .2 to .19, correct? When I made the primary supports, I just drilled the holes lower for the entire primary with respect to the secondary so that the coupling is about .18, the secondary sits such that the windings begin about 1" higher than the lowest most turn of the primary.
I guess this all goes to show that I have lots of room for experimentation here...
Registered Member #15
Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068
If you still find you have primary to secondary arcing, then it could be due to too much coupling.
As Teravolt stated, tapered or inverse conical primaries give you the advantage of tight coupling but with more voltage stand-off on the upper turns, but also with a bit more complexity in creating the primary supports - depending on how you make them.
Nowadays, i make almost all my DRSSTC with flat pancake style primaries. Found this works well and its much easier in installing the primary in that you simply press the copper tubing into primary supports as opposed to fishing it through a bunch of holes in vertical primary supports.
Registered Member #7267
Joined: Tue Oct 16 2012, 12:16AM
Location: Detroit, Michigan
Posts: 407
EasternVoltageResearch wrote ...
If you still find you have primary to secondary arcing, then it could be due to too much coupling.
As Teravolt stated, tapered or inverse conical primaries give you the advantage of tight coupling but with more voltage stand-off on the upper turns, but also with a bit more complexity in creating the primary supports - depending on how you make them.
Nowadays, i make almost all my DRSSTC with flat pancake style primaries. Found this works well and its much easier in installing the primary in that you simply press the copper tubing into primary supports as opposed to fishing it through a bunch of holes in vertical primary supports.
Yeah, making a vertical helical primary is definitely not as easy as it may seem, but it sure is sturdy. What about performance of pancakes vs helical? Do you find pancake to be better? I would also think that primary strikes would be more frequent, do you experience more of that or not really?
the mad scientist wrote ...
Are you using a good RF ground? I want to prevent this from happening to me too.
Not at the moment. I am in process of gathering materials to make a good RF ground. It's just that this damn crazy sporadic weather is bringing everything to a stop at the moment.
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Strike rail arcs to secondary. -coupling & tuning-
