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Stuck on Tesla Coil Project

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skyler

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(go get coffee to wait for the images to load)
Hi everyone,

For the semester, I have been working on a friend on a tesla coil at a club we started at my high school. We seem to get closer and closer, yet more and more problems come up. We are almost totally out of funds, yet everything seems like it is breaking. |O Here is a bunch of photos on our process, and we would appreciate any help or advice on what to do next.

First, the power supply. We have picked up a bunch of Microwave oven transformers. To be exact, we have 6 of them lying around, and another 2 with dead primaries. We were going to first put four in series to get the minimum voltage needed, 8k, but they arced internally, and we have figured out, two is the limit in series.

2j3mskp.jpg


Here is the image of two MOTs together, and following is the rest.

29zrgw8.jpg


With the two MOTS, we realized we would need a voltage doubler, though. We had 5 microwave capacitors, and 4 diodes, and we used 2 of the caps, 2 of the diodes, and another set of 4nf caps to get a 1nf cap across the diode. We used the circuit below:
doubler.gif


We tested the circuit, and had great arcs, and they "looked" like high enough voltage for a power supply. Great! Until..... A capacitor popped. Testing it with all of the other capacitors left, the arcs are very small when we make the doubler, and we made sure the capacitors and diodes worked. Here is a few pics of our capacitors and diodes:

High Voltage diodes
4ic7xi.jpg
2eg4g7m.jpg

1nf Cap bank across the diodes(the blue caps)

Here are the capacitors we have left (we actually might have 3 more microwave capacitors, and 3 diodes at my friends house Note they are all different sizes |O, but all close to 1 microfarad )
2njby9z.jpg


Oh yeah, we forgot to put a safety gap if that is important! We made one since:
zt7pdj.jpg

As shown, we have an electrode for +V,-V,and Gnd from the output of the Doubler.


OK, so on the power supply, what do you suggest? We know we should probably get a NST, but we can't afford one, and for our size of tesla coil, we would atleast need two. (in Parallel)Does anyone know where to get one for a REAlly low price, or maybe someone who would sell one to us for cheap :D

Next is the Primary Capacitor:

Because we are cheap, we created a capacitor using a bucket, beer bottles, motor oil and salt water as shown in this youtube video:

https://www.youtube.com/watch?v=hjqKcRQB3RI

Here is a photo of ours:
260eh42.jpg


We measured the capacitor, and got somewhere around 15 NanoFarads. We are hoping this capacitor will work for the tesla coil, those Cornell Dubilier caps are pretty expensive!

Rotary Spark Gap
I do not have much pictures for this, we are working on this at my friends house, but I think that will be pretty straight forward, we got 5/32 Tungsten rods, and a 3400RPM pool pump motor, which we will attach using non-conductive plastic from instructions on tb3.com>tesla coil>spark gap We know to put a biggg box around this, because the force will be massive flying around on the motor, and the UV will be bad. I did find this picture, though of the tip of the motor, which we will be attaching the tungsten.
2iizdae.jpg


The coil!

The pancake coil on the bottom consists of copper tubing (I think it was quarter inch but it might be bigger). We got 20 feet, thinking that would be enough, but looking at the amount of turns, we may be short. ( I don't know though)

The diameter of the primary coil, which the secondary wraps around is one foot.
6pysl5.jpg


35lxj46.jpg
2u8wfat.jpg


The secondary coil

For the secondary, we took a 4 ft by 1ft diameter Sona tubing, and coiled it with fishing line for spacing, and copper wire. We used almost the whole role of 100 ohms of 24AWG wire, which calculated to about 3500 Feet.

Does the primary and secondary coil "work" for resonance, and will this be adequate? We know the secondary is a bit weird just sitting on the base, and we will be able to raise and lower the coil, we have not glued it down

v5ftpg.jpg


Top of Secondary coil
29wjs7n.jpg


Toroid

We have a few things laying around for the toroid, will these work?
9zwswy.jpg
b9ipm8.jpg

20z4ldf.jpg


Thanks for any help, tips, or advice, We really wanted to get this coil done before the end of the school year, but without any help, we are just stuck.


rkrfj6.jpg

Our work area!
 

In case a simulation will be informative...

Here is a screenshot of the Tesla coil schematic included in Falstad's animated circuit simulator.



The spark consists of several sparks, resulting from resonant action in C1 and transformer #2.

If C1 is large, then it will require more current. You can see a value of 20 nF in the schematic. (Hence 1 uF may be too large.)

You can experiment with this schematic by clicking the link below.

It will open the website www.falstad.com/circuit,
load my schematic into his simulator (assuming you have Java on your computer),
and run it on your computer.

You can observe current direction and intensity, time cycles, voltage levels, etc.

https://tinyurl.com/k328f2g

You can change values by right-clicking on a component, and select 'edit'.

You can modify this simulation so that it runs your own schematic. It should be possible for you to find out what component values are needed to make it work properly.
 

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