DC Power Tesla Coil

[Jeg]

Tnks for the answers guys

Well, I measured it again step by step. The results are:

1. Main MOT unloaded AC Output: 5000V Peak to Peak (Oscilloscope) / 1460V AC RMS (Voltimeter)

2. FWB output without smoothing Cap: 2500V Peak to Peak / 1300V DC RMS

3. FWB output with smoothing Cap: 2120V RMS DC / ~200V p-p Ripple. (low Ripple peak 2000V, high Ripple peak 2200V)

About the diodes.
Tinsel, you are right about the 6 diodes leg of FWB. It handles 6000V 1A per leg.
I thought that the maximum current (shortcut current) of the main MOT secondary HV side, is not more than about 625mA! Is that wrong?

For a start as a spark gap i will use a car spark plug. I opened the tip around 4mm but i will fix it on its final position after getting the right 4,4KV at the output.

I will try today to locate the diodes that you proposed me. I hope that i 'll find them!

Farmhand thanks for the info. I just wonder about your FWB. Each leg will handle not more than about ~700mA/~12KV. Voltage margin is more than enough. But hat about the peak current?   

[TinselKoala]

Thanks Jeg for making the measurments again. It sounds like the basic DC power supply is working without major problems. I would still recommend going to a higher current diode than the 1n4007 though, because of heat dissipation and safety margin. The 6A100 is very common, you should have no problem finding them. But don't stop work while you are waiting, keep going with the "current" bridge, haha.

Next step is to put the de-Qing diode in. That is your MO diode, right?

I really don't think you will be happy using a simple automotive spark plug for your spark gap. I could be wrong, but I think it is likely that you will get a power arc across the gap instead of an interrupting spark. You could try blowing it with compressed air if it turns out that the power arc is a problem.

Here's a photo of a simple multi-element spark gap that might work better than a simple automotive spark plug. I would suggest using 4 tubes to start with, each screwed thru the center as shown, and positioned close together. The resulting gap can then be adjusted by turning the tubes around the screws, so that the tubes are still parallel but closer or further apart.
||||  furthest apart, or //// closer together, get the picture?
So the end tubes are connected to the circuit, the two middle tubes are "passive" and you have three spark regions.

http://www.coe.ufrj.br/~acmq/tesla/mres4gap.jpg

I'll be making one like this to try on my MOT-DC coil fairly soon.

[Jeg]

This is very smart! Do you think that a pipe system doesn't need air blowing? What kind of metal is the best for sparks? I mean is there anything that last for a long time without getting black and carbonized?

And there is something else that i always wonder about. Are Tesla Coil discharges harmful? If a long spark from the top of Tesla coil find your hand will it harm you?

[TinselKoala]

This is very smart! Do you think that a pipe system doesn't need air blowing? What kind of metal is the best for sparks? I mean is there anything that last for a long time without getting black and carbonized?

A good multi-element gap shouldn't need quenching with compressed air, but you still should have some ventilation. The sparks make nitrogen oxides from the air and this isn't good to breathe. Most people use copper pipe because it is cheap, available and easy to work with. You will have to clean the electrodes of any spark gap you build, even if you use tungsten or something like that, but it's easy enough to do.

And there is something else that i always wonder about. Are Tesla Coil discharges harmful? If a long spark from the top of Tesla coil find your hand will it harm you?

A properly running low power Tesla coil's output is a clean sine wave oscillation at a high frequency. This has two effects: First, the nervous system doesn't respond to high frequencies so you won't feel a "shock". Second, the power travels over the skin rather than penetrating deeply. This means that you can take the discharge safely, but NOT DIRECTLY TO THE SKIN because you will get a bad RF burn at the point of contact. However you can hold a wrench or screwdriver firmly in your hand and then let the spark go to the wrench first and then you won't feel it at all. This isn't harmful.... IF the coil is working properly. If there is a short to the primary supply, then DANGEROUS voltages at the low frequency of the mains supply can be mixed with the Tesla discharge and this is VERY dangerous. So for larger coils, for questionable builds or coils that might not be running perfectly... don't do it. I've gotten a couple of bad RF burns. Even small ones are very painful and take a long time to heal.

I used to do a demonstration with my big 2kW class traditional SGTC, with rotary gap and neon sign transformer primary supply. This coil would make a thick ropy arc 18 inches long into a big wrench that I held in one hand. My other hand held one terminal of a small 15-Watt 120V light bulb. I could touch the other terminal of the bulb to another person's skin and the filament would glow brightly.
I was a lot more confident and less careful in those days ! But it was actually fairly safe to do that.

The coil I show in the video below gave me a bad RF burn one day when I reached out and touched the secondary just above the primary winding. There is less than 100 volts DC being switched in the primary!  I thought it would be OK to touch it so low on the secondary but I was wrong. It cooked a pea-sized chunk of meat in my finger, all the way to the bone, took weeks to heal and I still have the scar from it. Even just above the primary winding, the secondary was already making enough voltage to penetrate the insulation on the wire and there was enough power there to cook my finger instantly. I felt that, all right!

http://www.youtube.com/watch?v=UFHNY38GQsI

This is an early demo of a low-power run of a solid-state TC. The boring stuff in the first five minutes can be ignored. I show some power arcs and wood burning to demonstrate that there is power and heat in the discharge, then I let it discharge into a small metal screwdriver that I'm holding.
I am not confident enough to try this with full power in my blown MOT-DC coil but I've done it with the SassyClassE SSTC.

And I would not recommend trying it on a MOT-powered coil, or ANY coil, unless you are absolutely sure of two things: It must be _impossible_ for any of the primary tank supply to be directly connected to the secondary output discharge in any way. You have to be very careful about this because the primary can spark to the secondary down low where you might not be able to see it and this can mix primary tank current into the secondary discharge. Second, make sure the coil's output is "clean", a sinusoidal oscillation at the resonant frequency with not much distortion or noise.

I don't recommend this at all, actually. If you do decide to take a Tesla Coil discharge into your body, even from a small coil, you are RISKING YOUR LIFE if something goes wrong, and MOT powered coils are especially dangerous because the MOT does not  limit current in the same way that a NST does.

[Farmhand]

I agree a SG TC with a damped wave is nasty only a continuous wave transformer at HF is actually "really" safe.
You might see people do it on video and walk away but the long term effects they likely won't admit to.

It is a very good idea to start with low power solid state transformers.

Here is a clip of a 12 volt solid state continuous wave transformer, it burned holes in glass and fingers no problem with only about 600 volts on the terminal.
I originally kept this video private for a friend so I am relaxed and off guard. I show the voltage gradient, put a small hole in a neon which usually works better
than it did and qt 6:15 near the end I get a HF arc burn halfway up the extra coil..  It burned right through the tough skin on the end of my finger in about 0.5 of a second, it left a small crater so the skin was vaporized. I didn't see any smoke. 

http://www.youtube.com/watch?v=4b4qzdBQgWg

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