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4hv.org :: Forums :: Tesla Coils
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Strike rail arcs to secondary. -coupling & tuning-

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Physics Junkie
Mon Apr 08 2013, 04:04PM
Physics Junkie Registered Member #7267 Joined: Tue Oct 16 2012, 12:16AM
Location: Detroit, Michigan
Posts: 407
EasternVoltageResearch wrote ...

Physics Junkie,

You say that when you tune lower, you get higher currents and shorter arcs. However, is that only at lower input voltages? Because that is exactly what you want to see initially.

If you are using a variac, if you are tuned considerably lower on the primary, you will initially see higher current and shorter current (or more current required to make the same length arcs as at other tuning points closer to secondary fres). But as the arc grows, it will pull the system more into tune, and the current won't change as much, but the streamer growth will really take off.

Nope. I am doing full variac input now. Really it doesn't matter because anything lower than about 5% detuned I get the same results at high voltage and low voltage input. When tuned lower than about 5%, current quickly exceeds 1000A at +350 volts input (120-140 doubled) and things get explosive.


Uspring wrote ...

Still, low coupling could be a part of the problem. Ward quotes a value of 0.19 for his DRSSTC1 and probably yours is lower than that. It'd be interesting to know Mad Barnkobs DRSSTC1 coupling. Since you can't increase it, you could try reducing your MMC, preferably by lenghtening your strings instead of taking strings off, since that increases the current load on your caps.


I was beginning to think the same thing about the MMC. Might be time to make another adjustment to it.
My coupling is way lower than .19 though that is about where I initially started. If I remember what JavaTC calculated for me last, it was about .14 or .13ish.

Thanks.
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Physics Junkie
Wed Apr 17 2013, 02:50AM
Physics Junkie Registered Member #7267 Joined: Tue Oct 16 2012, 12:16AM
Location: Detroit, Michigan
Posts: 407
I have changed the params quite a bit now:

-New toroid
-New flat pancake Primary
-New DC Bus layout
-New coupling

Other things I am going to change this weekend:

-New MMC
-Increase coupling

The secondary+toroid natural frequency is now 87kHz. The toroid is 4"x18" and completely conductive all the way around.

Primary has 11.5 Turns of 1/4" copper tube with 1/4" spacing. inner radius is roughly 5.5"; outer radius is 11.5". This primary allows for plenty of headroom when changing the secondary frequency and MMC params. One mistake I made was a slight accident when cutting the primary support lengths. Originally I designed the inner most turn to be approximately 1" from the base of the secondary to maintain k= ~.15ish but it turned out to be a bit short with about 2" from the base of the secondary. So K now equals about .12. I'll raise the primary later to compensate for this.

I mounted the DC supply caps directly above the bridge as close as I possibly could, thinking that unwanted inductance could be causing nasty voltage spikes and thus increasing Cpri Irms to unacceptable levels. It does seem to have helped a bit.


45 119

Above: Current signal. Looks fine to me. I did notice a slight decrease in current levels with the same input power and performance as before, which is what my goal was in making all these changes.

06 825

Above: I actually didnt notice this until looking at this picture, maybe it's just an illusion but it appears like the inner most turn is either slightly elliptical or the secondary is offset from the center. Oh well!

43 185

Above: .025mm copper sheet holding the caps above the bridge. This seems to help a bit. Before I had it wired with 10 gauge audio power cable with the caps sitting next to the bridge rectifier seen there.
Below: short 30 sec video of operation with the new setup


Unfortunately, I still dont know what the tuning issue is, or really if there is an issue anymore. I still have to tune the primary to within 2-3% of the secondary natural frequency before performance severely decreases.

Thanks for the help everyone. I will update again when I fix coupling and MMC. I ain't giving up till I get that 60" cheesey
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Graham Armitage
Wed Apr 17 2013, 11:53AM
Graham Armitage Registered Member #6038 Joined: Mon Aug 06 2012, 11:31AM
Location: Salado, TX
Posts: 248
That looks really cool !! Nice job. Seems like the pancake coil is working for you too. I have become a big fan of them. Modifications seem to working. Nice job !
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Physics Junkie
Wed Apr 17 2013, 04:09PM
Physics Junkie Registered Member #7267 Joined: Tue Oct 16 2012, 12:16AM
Location: Detroit, Michigan
Posts: 407
Thank you for your kind words! I do like the pancake coil, very easy to construct and all the extra turns give me room for experimenting (more so I made this primary for another drsstc im beginning to build using two cm400dy smile) . One difference is that I get strikes to the strike rail now whereas i got none with the vertical helical, not really a big deal tho..

P.s. I also ordered one of those new 20m fiber optic cables, the one i sent you a link to from mouser. Anxious to see how it does.
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