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I need some suggestions for maximizing power output

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OiD

Fri Jan 28 2011, 06:03AM

Registered Member #2150 Joined: Tue Jun 02 2009, 08:33PM
Location:
Posts: 29

Hello all!
This is my third and largest SGTC. I am really hoping to get some nice long streamers and I've got to a point where I'm sort of stuck.

Currently I am getting streamers about 30-35cm in lenght, but I should be able to get more according to;
DeepFriedNeon: 63cm
TeslaMap: 70cm
JavaTC: 58cm

My coil consists of;
Secondary:
-9cm Diameter PVC pipe
-901 turns of 0.51mm enameled copper wire
-28cm sphere for the topload

Primary:
-12 turns of 5mm multistrand copper wire (I was using 6 turns of 6mm steel wire before, big improvement)
-0.01uF (10nF) MMC bank (Arcotronics/RS 0.1nF 1500VDC. I'm using one string of 10 capacitors. They stay cold)
-Flat spiral with 14.5cm inner diameter

Power supply:
-NST 10KV 25mA made by F.A.R.T. (Given to me from a repair shop, appears to work well, but I'm starting to think that it might be shorted)
Edit; Turns out one of the windings is shorted. So 5KV 25mA
-Resonant cap size is 8nF and LTR is between 11.9-12.9nF

Spark gap:
-Multigap made from 6 pieces of copper tubbing, total gap size is just under 5mm. More than 5mm and it fires inconsistently.
-Small fan for quenching, but without the fan it quenches pretty much the same.

This is the first picture. The secondary has been cut down and I have removed the extra wire at the top.

f/2.8 ISO 2500 1/2 sec

And here I am using a smaller 12cm sphere with 15-20cm streamers.

First light yielded 5cm sparks to ground and slowly replacing components for better desings I have managed 35cm discharge into the air.

Right now I am using alligator clips on 2.5mm diameter wire, this shall be replaced when I put the coil together in a more definitive form.

I have thought of changing the power supply to a MOT stack and to change the spark gap to a rotary type. Other than that I'm out of ideas.

Thanks in advance for any suggetions/corrections/opinions :)

HV Enthusiast

Fri Jan 28 2011, 01:10PM

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

I would try increasing coupling first by raising primary (or lowering secondary). See if that improves anything. If you get racing sparks, then thats a sign coupling is too high.

And try adjusting spark gap distance too.

Also try experimenting with capacitor size as well as topload size.

But i agree, you should be able to get a lot more output out of the 10kV/25mA than what you are getting.

I get 35cm out of my 4kV/38mA NST for comparisons. You could be able to get twice that from your set-up.

OiD

Fri Jan 28 2011, 04:09PM

Registered Member #2150 Joined: Tue Jun 02 2009, 08:33PM
Location:
Posts: 29

Thanks for the tips, I'll try the coupling a bit more.

I just tested the NST and one of the windings is dead, so I'm getting 5KV at 25mA

I've just got my hands on a few more MOTs and some MOT sized current transformers.

Thanks for the input :)

Edit;

2 MOTs are giving some fierce fat streamers but the static spark gap is quenching terribly. Time to go rotary. I guess the hardest part will be finding a synchronous motor. I hope the caps will cope...

Meatball

Sat Jan 29 2011, 12:42AM

Registered Member #2401 Joined: Mon Sept 28 2009, 04:25PM
Location:
Posts: 74

Here's a start:

OiD

Sat Jan 29 2011, 01:35AM

Registered Member #2150 Joined: Tue Jun 02 2009, 08:33PM
Location:
Posts: 29

Meatball wrote ...

Here's a start:

I've kept eyeing that motor, but it's quite costly and I don't want to know the shipping costs to Spain :(
I'm trying to find some nice information on how to convert a motor to synchronous because I can get plenty of motors from the junkers.

haikara

Sat Jan 29 2011, 02:48PM

Registered Member #3599 Joined: Mon Jan 10 2011, 05:50PM
Location:
Posts: 15

u dont need to be in perfectly sync when using MOT as PSU. am i right? for me, i just want my bps really high.300-500 bps. the output is just one fatty long spark

OiD

Sun Jan 30 2011, 08:33AM

Registered Member #2150 Joined: Tue Jun 02 2009, 08:33PM
Location:
Posts: 29

haikara wrote ...

u dont need to be in perfectly sync when using MOT as PSU. am i right? for me, i just want my bps really high.300-500 bps. the output is just one fatty long spark

Depends if your capacitors can tolerate the overvoltage or not you will need a synchronous gap or not. If your using MOTs and a voltage double you'll have DC so any type of rotary gap will work.

I spent last saturday pulling motors from devices and all of them are universal motors. Any suggestions as what devices use induction motors?
Today I'll start trying to make the disk, I don't have the proper tools for making a nice circular disk thought...

OiD

Wed Feb 02 2011, 04:52PM

Registered Member #2150 Joined: Tue Jun 02 2009, 08:33PM
Location:
Posts: 29

Well, it was the power supply after all. After making a 4MOT stack and modifying the RQ gap a bit It roared to life :)

The caps seem to be holding up without getting warm (considering that its desinged for 15kv DC), the spark gap on the other hand is a mini radiator...

Now to make it look nicer, add the other capacitor banks and a strike rail!

First light and My goal.

If I find the materials I'll make a rotary spark gap aswell.

Thanks for your help

OiD

Thu Feb 03 2011, 05:58PM

Registered Member #2150 Joined: Tue Jun 02 2009, 08:33PM
Location:
Posts: 29

I'm back again!

So my last post I had achieved 70cm streamers, they were nice long "slow" moving thin streamers but suddenly it decreased to about half the lenght and they became fierce and jagged looking with a decent amount of plasma at the breakout point!

Does anyone have a logical explanation for the above? It happened a while after striking a grounded target. I've checked the MOT stack and the capacitor bank value and everything is the same, retuned the coil and played with the spark gap but no change...

I ran the coil long enought for the spark gap to glow red hot and the output stayed the same until the gap shorted some sections out...

Tesla coils are a black art!!

quicksilver

Thu Feb 03 2011, 09:41PM

Registered Member #1408 Joined: Fri Mar 21 2008, 03:49PM
Location: Oracle, AZ
Posts: 679

So at this point you have dumped the faulty NST and created a MOT stack as a PSU. What is your voltage & amperage at this juncture? I had thought that (from what you had previous discussed) that it certainly sounded like a tuning issue and working with a static gap / primary tap is a bit simpler than many other agendas; particularly if you are working with a multiple gap and fan type configuration.
Have you equaled the 5Kv & 25 ma? I would have thought you would have an enormous amount of current running those MOTs.

I have a coil quite similar to yours (in size and build specs) & I have used a 7.5Kv / 30 ma NST with good results. My longest run was perhaps 3 minutes and the simple multiple gap got hot but (I also have a fan and it's got good breathing) never to any extent where it became deeply discolored aside from the contacting surface of the arc.

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