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Neil

Tue Mar 02 2010, 10:38AM

Registered Member #1458 Joined: Wed Apr 30 2008, 09:47AM
Location:
Posts: 51

12 Inch - 7200 Watt Tesla Coil with Synchronous Rotary Spark Gap

I have previously posted some details in the Tesla Coil section as I built this however now I have completed this project and have some nice pictures I wanted to summarise the build and results all together in here.

Here are the main specs of the coil

12 Inch secondary using PVC pipe
AWG18 wire
1200 Turns over 1352mm winding length
The pipe was set up with a pully at one end with a drill driving it, made winding very easy and had it all on in 1 or 2 hours.
Wire was then varnised with about 8 coats and came up looking nice

3/8" Copper pipe primary
12 Turns - Tapped on the 9th for best tune

MMC type capacitor bank
942C20P15K-F caps 14 series x 14 parallel giving 0.15 uF rated for 28,000 Volts
Runs best at 14 series x 8 parallel giving 0.0857 uF. They use autoelectrical connections so its a simple matter of connecting or disconnecting caps as you tune it.

]datasheet_mmc_caps_-_942c20p15k-f.pdf[/file]

The pole transformer is rated 10kVA at 22,000V however have connected it up for 500 volt input which lowers my output to 11,000 Volt which I felt more comfortable designing everything around without stray arcs jumping where I dont want them to such as on my rotary spark gap.

The synchronous rotary spark gap uses a 1470 RPM 1/3 horsepower motor which I have filed 4 flats on the rotor to sync it to 1500 RPM. The wheel is made from lexan and steel, with 4 tungsten electrodes to give 100 discharges per second.

The strike rail has been made using 1/2" copper pipe, each of the supports is insulated from the main ring, which itself is insulated where the join is.

These are a few pics of the build process

Here are some pictures of the coil in action

A video can be found on Youtube HERE

I have been playing around with the tune of it lately and may have got it about as good as I can now, the arcs are the thickest and longest I've got so far and have an almost DC like apearence to them which sounds very nice. I am happy with how the coil has turned out.

RogerInOhio

Tue Mar 02 2010, 01:29PM

Registered Member #1034 Joined: Sat Sept 29 2007, 12:50PM
Location: Chillicothe, Ohio
Posts: 154

Nice coil. You probably know it has the potential for much longer sparks. Just putting on a really big toroid and retuning it should get you out to about 8 to 10 feet. I have a coil about the same size and I use a 14" x 48" toroid on it.

Cheers Roger

StevenCaton

Tue Mar 02 2010, 07:49PM

Registered Member #1845 Joined: Fri Dec 05 2008, 05:38AM
Location: California
Posts: 211

Put a bigger toroid on that thing Neil!

If you have the correct sized toroid, then the thing will hardly make sparks even at 50 percent power, and then all of the sudden the sparks will throw it in tune and the arcs will get huge.

Good luck

brtaman

Tue Mar 02 2010, 11:24PM

Registered Member #2161 Joined: Fri Jun 05 2009, 03:36PM
Location:
Posts: 247

Nice coil, Neil. A mammoth beast.

Like others have said put a much larger torroid on that beast and watch the sparks explode. :) Just don't stand next to it like on the last picture.

As the forecast will be loud and furious with a great chance of ground strikes.

Renesis

Wed Mar 03 2010, 12:10AM

Registered Member #2028 Joined: Mon Mar 16 2009, 08:13PM
Location: Norway
Posts: 319

Nice, this must be communications jamming on a military level.

About your strike rail, is it a full circle? It should have an air gap to prevent eddycurrents draining power from your coil.

Hazmatt_(The Underdog)

Wed Mar 03 2010, 01:18AM

Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735

Definately go with buss bar on your cap bank, but great job!

RogerInOhio

Wed Mar 03 2010, 02:49PM

Registered Member #1034 Joined: Sat Sept 29 2007, 12:50PM
Location: Chillicothe, Ohio
Posts: 154

Neil, I was just curious, do you have a way of adjusting your rotary spark gap to synchronize it ? I was just wondering how that was done. I have never built a SRSGTC before.

Roger

Arcstarter

Wed Mar 03 2010, 08:22PM

Registered Member #1225 Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253

It is an impressive coil :D. Sure is a ton of CDE caps

. As everyone said, more topload, but i am sure you are tired of hearing that!

RogerInOhio wrote ...

Neil, I was just curious, do you have a way of adjusting your rotary spark gap to synchronize it ? I was just wondering how that was done. I have never built a SRSGTC before.

Roger

You and your DC coils

.

I have seen people make some sort of phase shifter, but i am not sure how to do that. Is it something like some passives, or would it have to be something active? That could be worth looking in to, Neil

Neil

Thu Mar 04 2010, 05:46AM

Registered Member #1458 Joined: Wed Apr 30 2008, 09:47AM
Location:
Posts: 51

Thanks for the comments everyone. Since I last posted anything about the build progress in my other thread I have found and added the silver ducting as extra topload after similar comments around its size and I definately did notice a huge improvement. I have been half tempted just to leave it at that with the improvements I have seen already but given the comments to still go bigger by most people who commented it is encouraging for me to spend time on making it larger again, thanks for the advice.

Yeah I have a way to adjust it, the disc has like a boss in the centre of it that goes over the motor shaft and in the back of that, I dont think it can be seen from the pics, there are 2 small bolts at 90 degrees to each other that tighten up and lock it to the shaft. I had considered ways of making this adjustable from the control panel while it was running but by the time I was up to this part I was just dieing to get it finished to see what it could do, so decided on the simpler option. I have ground a grove in the end of the motor shaft so when the disc is loosened all that is needed is a large screwdriver to spin the shaft a little.

It makes a massive difference when this is out even by just a little bit, the gap goes real firey and starts striking the metal part of the disc instead of the electrodes and often the safety gap triggers a lot, with performance of the coil obviously suffering. A real time way of adjusting this as it is running would be really really good.

Neil

Wed Apr 15 2015, 05:39PM

Registered Member #1458 Joined: Wed Apr 30 2008, 09:47AM
Location:
Posts: 51

Hi all its been some time since I posted in here. I have recently made my synchronous spark gap adjustable while the coil is running, to allow easier tuning. I thought I would share pictures.
It has a small 12V 150 watt power supply taking its power from the spark gap motor 240 input. This 12V drives the small electric motor which rotates the arms holding the electrodes. I control this with a switch on the power supply control panel, the relays are used to give forward and reverse control of the motor with a single switch. This control runs through a 3 wire cable.

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