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1st timer with Tesla Coils (coil kicks ass)

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Kizmo

Tue Jul 31 2007, 04:17PM

Registered Member #599 Joined: Thu Mar 22 2007, 07:40PM
Location: Northern Finland, Rovaniemi
Posts: 624

Hi!

Im 1st timer with RSG tesla coils and im planning to build my own. I did some drawings

and now i need word from experts if there is design flaws or something that need to be changed before i build anything. There will be powerful fan for RSG and RSG electrodes will be TIG welder wolfram electrodes.

UPDATE 30.4.2012

This coil is kicking ass!

Spec:
200x740mm secondary, about 1300 turns
10 turn primary
74.5nF 45kV "MMC" made out of 6 General atomics pulse capacitors
ARSG
Huge 3-ring topload
DC Resonant charging topology, 14.2kV charge voltage
Rectified 3 phase pole transformer as power source

Secondary, one topload ring and base are still same original stuff i had when this coil first fired almost 5 year ago. It has been very interesting experience so far. Last night i burned out 3ph rectifier (24kV 700mA). I think common mode overvoltage caused this. More protection is needed and new 50kV 6A rectifier is under work ;)

Wonder if i can push it even harder.. :p

Sulaiman

Tue Jul 31 2007, 08:43PM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

If you could convert the MOT output to dc and use resonant charging I think you'd get better results.

Kizmo

Tue Jul 31 2007, 08:47PM

Registered Member #599 Joined: Thu Mar 22 2007, 07:40PM
Location: Northern Finland, Rovaniemi
Posts: 624

That is one of my future plans but i think its better to start with AC coil. I got idea about coil like this from tesladownunders web page

Pretty amazing how long sparks is possible to get from coil like that.

Hazmatt_(The Underdog)

Wed Aug 01 2007, 12:28AM

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

You're going to need to take some special precautions for the current involved with your setup, its a lot of current!

Look at the destruction from my 60mA setup:

These were the old electrodes, broken circuit board drills. They have a Tungsten core, but still disintegrated

It's hard to see, but the arc causes basically a weld pool to form on the set screw, destroying it after a while. You might want to use a heavy brass stud or something for this part.

Going through the rebuild process and adding 1/8" 98% Tungsten stationary electrodes.
Your safety gap is going to have a lot of problems with power arcing if the motor isn't synchronized properly, and that's a huge problem with these little sewing machine motors. They don't stay at one speed no matter if you use a solid state control or variac. To regulate one of these motors you would need a closed loop control with PID.
This one 'gets the job done' but not the best way. If you have the opportunity, go for a motor that is a fixed speed or 90VDC motor with controller.

Kizmo

Wed Aug 01 2007, 08:11AM

Registered Member #599 Joined: Thu Mar 22 2007, 07:40PM
Location: Northern Finland, Rovaniemi
Posts: 624

Hazmatt_(The Underdog) wrote ...

Your safety gap is going to have a lot of problems with power arcing if the motor isn't synchronized properly, and that's a huge problem with these little sewing machine motors. They don't stay at one speed no matter if you use a solid state control or variac. To regulate one of these motors you would need a closed loop control with PID.
This one 'gets the job done' but not the best way. If you have the opportunity, go for a motor that is a fixed speed or 90VDC motor with controller.

What would be the cheapest way to get around this problem? Maybe i just don't put any safety gaps for MOTstack because MOTs are almost indestructible and if one dies in time, i can get new from junkyard for free (actually i already got about 20 MOTs here). How about jakob's ladder style safety cap, it will at least shut the arc off?

sparky

Wed Aug 01 2007, 05:25PM

Registered Member #530 Joined: Sat Feb 17 2007, 07:56AM
Location: Victoria BC, Canada
Posts: 178

I have been using thickest Zirconium Tugsten electrodes avaliable on the welding market. They survived everything I threw at them --- I've run quad pack MOt supplies at 400mA 10kV. Yet again I do run these electrodes at 10,000 rpm using an el'cheapo angle grinder.

Hazmatt_(The Underdog)

Thu Aug 02 2007, 12:55AM

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

What you could do is run your system at 3600 RPM. I designed mine for 1800 RPM, but because I'm trying to limit the stress on the NST, the gaps still fire over. When I speed up to 3600 the safety gap stops firing because I'm no longer firing at the peak of each half cycle, I'm firing twice each half cycle and the output is roughly the same. So if you set the gaps to fire at the peak you're going to have to trigger your discharge sooner to eliminate the safety gap breakdown.

You could set the gap wider but I would be cautious when doing it since you're already stressing the mots insulation.

Steve Conner

Thu Aug 02 2007, 11:13AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

The cheapest way to get around the problem is probably to just increase the speed of the thing, like Hazmatt suggested. If it's going fast enough that the electrodes always present several times per half cycle, and the power supply has plenty of current to charge the tank capacitor quickly, it doesn't really matter whether it's synchronous or asynchronous, the coil will work pretty well regardless.

Kizmo

Mon Aug 06 2007, 02:41PM

Registered Member #599 Joined: Thu Mar 22 2007, 07:40PM
Location: Northern Finland, Rovaniemi
Posts: 624

I have one question left: I know that with PVC pipes they use carbon based substance to get black color. And that makes the pipe conductive -> useless. But how about black Polypropylene (PP) pipes? I just found source for great looking 160mm (6") Polypropylene pipe but it is black. I tried to measure pipes resistance with multimeter @ 40Mohm range and even when i pushed probes against the pipe wall so that they were only 1mm from each other, i didn't get any sort of reading.

Is this pipe safe to use?

Steve Conner

Mon Aug 06 2007, 03:54PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

I don't know about PP, but I've made many Tesla coil parts out of black polyethylene, like primary supports and what not. I've never had any trouble.

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