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Small Tesla Coil using disposable camera transformers

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Voltwad

Sun Dec 07 2008, 01:32AM

Registered Member #1829 Joined: Sun Nov 30 2008, 01:06AM
Location: Raleigh N.C.
Posts: 74

This looks awesome. I just got a handful of cameras tonight and I'm gonna start making this tomorrow. I'm wondering what I could do with the flash tubes though. I wonder if they could be used in place of the spark gap with the tickler driven by a 555 or something. My intuition tells me they would be rather inefficient, converting most of the energy into light. Has anyone tried to use a discharge tube as a spark gap for a TC or a marx?

flannelhead

Mon Dec 08 2008, 02:02PM

Registered Member #952 Joined: Mon Aug 13 2007, 11:07AM
Location: Finland
Posts: 388

I've actually tried using the flash tube as a trigger in a coil gun, and that is a very bad idea because most of the power is converted to light. So don't use flash tubes as spark gaps!

Zenador

Mon Dec 08 2008, 02:29PM

Registered Member #1733 Joined: Thu Oct 02 2008, 03:17PM
Location: Hamilton, ON, Canada
Posts: 100

The only good use I have found so far for the 20+ flash tubes I have is lighting them up from the TC. Streamers from the small coil are almost impossible to see in a lit room, arcs from the top load to secondary ground are visible but "weak."

Solder one or two bulbs to a wire, and hold it close to the TC when it running. It acts as a plasma globe. The small coil is also capable of lighting up CFL's.

Voltwad

Thu Dec 11 2008, 06:44AM

Registered Member #1829 Joined: Sun Nov 30 2008, 01:06AM
Location: Raleigh N.C.
Posts: 74

Alright, I've already knocked together a prototype and then taken it apart to try and make it more powerful. I got about a 1cm spark and my mouse and CD drive started freaking out. :) Anyway, I thought I'd share this circuit I worked up. I don't know how others with multiple transformers are connecting their outputs but I figured out I could drive one of the two xfrmers I have backwards and tie the transistor bases together to get two opposite synchronized pulses. Now I can power a fullwave CW generator.

Here's the circuit.

Here's a trace of each HV terminal. The peak of each terminal is between +8 and +10 hundred volts and the ringdown is about -six or -seven hundred.

Here's the voltage between the terminals. Peak is about 14 or 15 hundred volts and ringdown is about 11 hundred.

Zenador

Thu Dec 11 2008, 02:00PM

Registered Member #1733 Joined: Thu Oct 02 2008, 03:17PM
Location: Hamilton, ON, Canada
Posts: 100

The power supply on the schematic looks like it says 1.5V? I drive my 2 xfmr board with 3V (2 AA batteries) to each xfmr, or from a 5-7V bench supply to both xfms, toggled by a 2P2T switch. I'm thinking of building a quad setup, and using higher voltage transistors to run at 12V. 12V to the transistors from the flash boards just blow and start a fire.

How many stages are in your CW?

flannelhead

Thu Dec 11 2008, 02:19PM

Registered Member #952 Joined: Mon Aug 13 2007, 11:07AM
Location: Finland
Posts: 388

Zenador wrote ...

The power supply on the schematic looks like it says 1.5V? I drive my 2 xfmr board with 3V (2 AA batteries) to each xfmr, or from a 5-7V bench supply to both xfms, toggled by a 2P2T switch. I'm thinking of building a quad setup, and using higher voltage transistors to run at 12V. 12V to the transistors from the flash boards just blow and start a fire.

I should note that the insulations of the transformers are not made to stand 12V use, because the secondary voltage will be also significantly higher. But feel free to try, it might work if you're lucky!

Voltwad

Thu Dec 18 2008, 12:14AM

Registered Member #1829 Joined: Sun Nov 30 2008, 01:06AM
Location: Raleigh N.C.
Posts: 74

Awright, my mini camera TC mark II is now finished.

The secondary is 1" dia. x 3.5" h. wound with 30 awg. The topload is blue styrofoam cut and sanded and then covered with aluminum tape. After I put everything in the box, the characteristics of the coil changed so much that I had to add a few more coils to the primary to get it to ring properly. I also added a disc of brass mesh over the topload from which hangs a ground wire to increase the secondary capacitance.

Here's the insides. 2 flash inverters, one positive one negative. A 7 stage fullwave CW generator made with 1KV diodes and 2KV 1 nano caps. A gap made from some small brass nuts and bolts with copper wires soldered on. And the tank cap is two 2.5 nano 10KV CeraMite caps seriesed for 1.25 nano. The battery pack was rewired to parallel the two batteries so I can run it off only one if I want. There's no difference in power throughput using two, only the run time. I could series the batteries but I don't want to overwork the transistor or the transformer secondary. Also the CW is probably being pushed to the limit as it is.

And this is my pathetic attempt at capturing the spark. It's about 15mm spark distance which is probably pretty good for one AA battery yes? My poor digicam just couldn't get a very good still image, let alone video but it looks good running on my desk top.

Arcstarter

Thu Dec 18 2008, 01:16AM

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

If that is metal under the top lid thing, that might be reducing the performance. It acts as a shorted turn, and much of the power would be used in eddy currents in the metal.

Weston

Thu Dec 18 2008, 03:20AM

Registered Member #1316 Joined: Thu Feb 14 2008, 03:35AM
Location: Cambridge, MA
Posts: 365

Voltwad: Cool coil. Is that a bread board? breadboards are not good for high voltage, they can arc over internally.

...

Thu Dec 18 2008, 03:55AM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

I don't think that brass plate will give you too much trouble. For good conductors that act more as a reflector than a shorted turn, although that helical coil is definitely coupling a bit of energy into the plate. If its enough to make a difference is hard to say.

Also, you might want to consider moving the power supply over a piece of protobord instead of a breadbord. You can get pieces with the same pattern so you can make it exactly the same, and then your breadboard will be free

It will also be less likley to short out or go open circuit to boot

BTW my aa powered sparker

get 2.5cm

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