DC Power Tesla Coil

[Jeg]

Nice work guys and cool videos! HV is dangerous but so fascinating! 

Well, i tried almost everything to double the voltage but nothing. The only thing i didn't try is to disconnect the input pcb which was taken from a microwave oven. It suppose to be just a line filter and an inrush current limiter! How can this affect the output? Anyway. I am thinking to built Farmhand's circuit for 8000V. Two mots input, middle ground output, and charging coil after rectification.

If i use copper for spark gap then what the color of the spark would be?     

[Jeg]

Well, i built Farmhand's circuit but again the same problem! L2 and L3 don't double the 5KV output of the two antiparallel input mots. I start to believe that the problem is the input pcb! Tomorrow i ll disconnect it and measure again.

Farmhand did you use mots for L2 and L3?

Tnks

[Farmhand]

Hi Jeg, L2 and L3 are just extra coils they aren't really necessary, L4 is the main charging inductor, it's the MOT secondary and the frame will be "hot" because it's in an active line. I just put the L2 and L3  coils there of a millihenry or few every bit helps I guess, as long as it's thick wire, that is because being less inductance they will not increase too much the voltage so mustn't waste power either. I think even MOT primaries would be too much, I don't even think my coils are 1 mH.  Good job getting two in anti parallel anyway.

Now with the MOT for the charging coil, you can set it up on something that is a good insulator so it does not arc into the table and back to the supply/circuit ground, I had mine on a wood base that also had the power MOT's screwed onto it and the charging MOT arced into the wood which drained my power a lot. I had it screwed in to the base as well so I didn't see it until I tested it.

I wouldn't think the line filter would limit anything. Unless it's damaged maybe. Is it fused ? Try a different fuse maybe if it is.

Can you show a picture or a drawing of your circuit now ? Even the two MOT's in parallel should work a gap Ok but you'll want some restriction of current I agree.

One other thing is that with a charging circuit to get it going on a static gap it might be necessary to halve the spark gap distance because no doubling will occur until after the first cycle is finished maybe two cycles.

Tesla used a static spark gap with one electrode one electrode that was movable so he could tap an insulated extension of the electrode to "narrow the gap to start the process. With the rotary gap I can have a very small gap and it makes it work, I adjust it so that when the electrodes heat up the almost start to touch and sometimes do.
The less the gap the less the resistance of the gap. Another reason rotary gaps are good. But a static will work if the process is started somehow. If the gap is too narrow to start with and fixed so it works straight away the extra voltage would maybe cause power arcing in the gap

With a well setup air blown gap the gap can be small and blown after starting to prevent power arcs in the spark gap.

I hope we can help you sort this out. 

..

[Jeg]

Hi Farmhand

Arcing through wood??? Almost unbelievable! I will try a pcb under the mot. I hope this will give a good isolation.

About the drawing, it's the same with yours but with my input pcb which i will disconnect i hope today. I will change the topology again, and i will stick on one mot input and charging coil for 5KV. This is enough for me as i want to use it for gray's tube also.

After some tries to locate capacitors for the tank cap, i finally bought MKP caps (blue and yellow) 1600V each. I don't know if they are robust enough to handle all this charge/discharge thing, but it's a start. What type of caps do you use for that job?

Well, the filter line has a fuse but i didn't test it because power comes in and goes out from pcb, and i had guessed that was ok! I will do some tries today and i'll post again the results. Thanks for sharing your experience.