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Strike rail arcs to secondary. -coupling & tuning-

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LAN_403

Physics Junkie

Sun Mar 17 2013, 12:23AM

Registered Member #7267 Joined: Tue Oct 16 2012, 12:16AM
Location: Detroit, Michigan
Posts: 407

Hi good peoples. So I did a Low power test of my DRSSTC that I've been working on for months now, finally got everything all put together. By Low power test I mean only 35VAC input from the variac but it is doubled at the DC bridge supply. I slowly crank up the PW on my modulator to see if I get any results, which I did. Just some small sparks off the breakout point. (The reason I didnt go for a full power first light is that we got dumped on with snow last night and I dont have room in the garage or outside at the moment). But I also was getting arcs from the strike rail to the secondary.

Heres some photos of the strike rail, my system and arc to secondary.

1363479478 7267 FT0 Strike Rail To Secondary

So as you can see, the strike rail is not a closed loop, BUT, I used a hack saw to cut it and I never filed/sanded down the edges. If you look close enough there are sharp edges on the end of the strike rail. So what the hell? Even though there are sharp edges, why would there be sparks jumping off it in the first place especially when it is grounded. I dont know any better regarding this, all I know is that the strike rail is supposed to protect the primary from arc's. I understand that poor coupling can cause racing sparks on the secondary. Is this to be considered racing sparks? This is more a direct arc from the edge of the strike rail to resonator.. I appreciate any suggestions.

Edit: Could poor grounding/electrical connection to ground be the main problem. Also, my coupling is about .17 to .18, should I raise the secondary more? I could try smoothing the ends of the strike rail and/or bending them outward..

Feathers

Sun Mar 17 2013, 07:17AM

Registered Member #10052 Joined: Thu Feb 07 2013, 11:31PM
Location: Overland Park, Kansas
Posts: 78

From my experience, it looks like a tuning problem.

I remember being so far off on my first coil, that the largest arcs could be drawn from the middle of the secondary (having the primary tuned to a first or second harmonic of the secondary).

What does the output from your breakout point look like?

Try a smaller topload, and tap more of your primary as you look for resonance.

Just my $.02

- Feathers

Physics Junkie

Sun Mar 17 2013, 07:47AM

Registered Member #7267 Joined: Tue Oct 16 2012, 12:16AM
Location: Detroit, Michigan
Posts: 407

HighVoltageFeathers wrote ...

From my experience, it looks like a tuning problem.

I remember being so far off on my first coil, that the largest arcs could be drawn from the middle of the secondary (having the primary tuned to a first or second harmonic of the secondary).

What does the output from your breakout point look like?

Try a smaller topload, and tap more of your primary as you look for resonance.

Just my $.02

- Feathers

Hi. I read your other post just now, welcome to the site

Thanks for input. I am pretty darn positive it is not tuning. I spent a good two hours going thru several tap points with oscilloscope and function generator and jotting down their respective frequencies and comparing results to the calculated ones using javatc.. I have my primary tuned about 11 kHz lower then my secondary resonant frequency which is 77.64 kHz approx. with topload. primary is tuned to 66.6 kHz. But I will try a few different tap points closer to the 77.64 kHz, since I have only done this one test so far. But the sparks are not being drawn from the secondary, they are coming from the strike rail. Like I said, I am limited to very very low power test at the moment due to bad weather, so the sparks I'm getting at around 35VAC input are your typical bright sparks maybe 5-6 inches or so (low PW too ), pretty much the same as what's coming off the strike rail but a little smaller. I have no other toroid to try

Maurizio Valvo

Sun Mar 17 2013, 09:23AM

Registered Member #3219 Joined: Mon Sept 20 2010, 09:06PM
Location: LeinÃ¬ (Turin), Italy
Posts: 23

Hi, I had the same problem on my DRSSTC during first trials. The sharp edges of the strike rail were indeed one of the main causes (others being probably tuning and coupling). Since I terminated one end of the spark rail with a small brass sphere (unfortunately the spark rail ends are quite close to eachother in my case, so I cannot terminate the other end in the same way because of lack of space) I have never seen secondary to rail sparks again. Filing the edge didn't help. I suggest you terminate both ends with brass spheres if they are quite apart from eachother. I took those normally used to terminate curtain rods.

Physics Junkie

Sun Mar 17 2013, 06:49PM

Registered Member #7267 Joined: Tue Oct 16 2012, 12:16AM
Location: Detroit, Michigan
Posts: 407

Okay I did as suggested, tuned the primary a bit higher, closer to that of resonance with the secondary. I also filed down the ends of the strike rail and then smoothed it with a 320 grit sand paper sponge thingy. I then wrapped a crap load of electrical tape around the edges and bent them downward facing into the strike rail supports. So for the moment this seems to have solved the problem. But when I do higher power testing I will probably have to re-tune it lower again to take into account for larger streamers.

Heres a 12 inch arc to grounded rod at 30-35VAC input, sorry its very bright in the room and can just barely see it.

1363546026 7267 FT152096 12inch Strike 1

And here is what the end of the strike rail looks like

Thanks for suggestions, Austin and Maurizio. Hopefully this solves the problem and I wont have to report back for when I do a full power test

Graham Armitage

Mon Mar 18 2013, 01:10AM

Registered Member #6038 Joined: Mon Aug 06 2012, 11:31AM
Location: Salado, TX
Posts: 248

Looking at the first pic you posted, the strike rail seems to be quite high up the secondary? Obviously the closer it gets to the top f the coil the more of a target it becomes. Any reason it can't sit closer to the primary? Guess what I am saying is that it could just be a proximity problem and not a tuning one.

Physics Junkie

Mon Mar 18 2013, 02:25AM

Registered Member #7267 Joined: Tue Oct 16 2012, 12:16AM
Location: Detroit, Michigan
Posts: 407

Well initally I had drilled holes for the strike rail on the supports that were slightly too small (by my own stupidity) so I just zip tied them to the holes. It hasnt been a problem since I terminated the ends, and now im up to 2 foot arcs in low power tests. Ill just have to wait and see hopefully the snow melts tomorrow

teravolt

Mon Mar 18 2013, 07:32PM

Registered Member #195 Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111

if you have racing sparks up and own the coil it is out of tune. the coil should be a quarter wave length so if the sparks happen in the middle that's where the peak voltage is instead of at the top of the coil.

Physics Junkie

Mon Mar 18 2013, 07:56PM

Registered Member #7267 Joined: Tue Oct 16 2012, 12:16AM
Location: Detroit, Michigan
Posts: 407

teravolt wrote ...

if you have racing sparks up and own the coil it is out of tune. the coil should be a quarter wave length so if the sparks happen in the middle that's where the peak voltage is instead of at the top of the coil.

Not having racing sparks at all. Coil is well in tune I'd say.

]dsc00775.jpg[/file]
]dsc00778.jpg[/file]

Edit: dont know why the images attached like that but w.e. In the second image, that line of sparks on the far right is just my shaky photography

HV Enthusiast

Mon Mar 18 2013, 10:20PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

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.

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