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Making my first coil, SGTC need help with powersupply.

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Estragon

Mon Jul 14 2008, 01:02PM

Registered Member #1391 Joined: Fri Mar 14 2008, 04:49PM
Location:
Posts: 40

Hello! Coilers!
I am currently building my first Tesla Coil (the simples kind of SGTC, nothing out of the ordenary)
I have tried some diffrent power supplies, first a compact flourscent lightbulb powering a modern flyback from a TV, but that had manny faults; the flyback had a LOW amperage output, but maybe 30KV+ voltage. And it was DC, that would complicate things. I failed to remove the diod of serval flybaks (it is just to burried).

Then I made a 260 Ohm, 27 Omh, NPN transistor thingy (don't know the name) driver for the flyback this gave it higher amperage, but lower volt, the spark jumped about half the lenght of when i ran it whit the CFL-bulb wich is about 0.7-1.5 cm compared to 2cm +.
But when i mounted this settup on an OLD flyback who did give AC output, it made a very weak spark (less that one mm, coud then be pulled out to about 0.6 cm) , the old flyback made a much better output with the CLF-bulb (0.4-0.8 cm sparks)

Any way the CLF-bulb is no good sulution because it gives so little power (11W, i might find a better one though) and i failed to wire it so i always "push" electricity, when it dident have anny conection betwen the HV-out and the zero-volt it just started to light the lightbulb instead. (kinda like a safty feature) If I removed the glasstube from the buld and added capacitors to mimmic the fillaments it woud work, but it cought fire and destroyed itself if i ever did not allow the flyback to "putout" electicity.

With all the abbow things I never had a problem with any of the part becomming even slightly hot, amazingly! (except the transistor, but it was mounted on a large heatsink so it could handle it)

Okay here comes the problem; I don't know if even a flyback could give enogh output for my coil to work, it is medium sized. 8cm diameter of the primary (kinda sloppy woud, some over lapping turns, wil this be a problem? I got enough wire to make a new one), 54cm length, that means an 1:7 (ew!) ratio. I may make a new one.
But the deal is i got 13! Microwave oven transformators (one rated for 3KV!) and 14 microwave oven capacitors (one with 2ÂµF and one for 3KV). Any thing usefull i can make of these? Like a TC powesupply (i also got 14 HV diodes).
I am thinging about putting them in series with ballas and then sink them in oil (just 4 of them), or is there a better sullution i can make when i got som manny?

I also got manny flybacks of diffrent sizes but just two (smal) old ones without the internal diode.

As capacitors i was planning on either using glass-bottle or self-rolled onece, Any suggesstion here? Like how manny for what kind of powesupply? Also should i just go for a simple spark gap made of two round electrodes or make a rotarty with tungsten electrodes?
I am aiming for the longest streamers possible. I haven't got my hands on coppertubing, so I'll have to use thik wire for secoundary, (eew hard to tune).

Anny help would make me greatly thankfull, I live in Norway (parts and stuff is hard to get, NST impossible (?), but dumpsers are never guarded) so please have my english excused :P I kinda have been lurking on this forum for a while, and i love it.

Estragon

Mon Jul 14 2008, 07:40PM

Registered Member #1391 Joined: Fri Mar 14 2008, 04:49PM
Location:
Posts: 40

This was a bit unclear, what i mean is;
What kind of capacitor should i go for salt water or rolled?
What kind of powersupply should i go for MOT's or Flyback? And how should i wire it?
And any other kind of help/hints/sollutions :)

Arcstarter

Mon Jul 14 2008, 08:20PM

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

I would recommend a more simple approach than mot's, like a neon sign transformer.. I do see that you cannot get one though. If you would like i will sell you a 6kv 30ma nst for 20 bucks and shipping. If you can get some money try to buy some of these :

I would suggest 9 in series for about 16nf and 14kv. They would last quite a long time and they have great performance. I am currently using CDE capacitor and i get 2 foot sparks with a 12kv nst. I got about 1 foot arcs to ground with my 6kv nst and i had a very bad primary and secondary. I had too thin wire for both. I am sure you could get 2 foot sparks with this nst if you do all of the necessary work.

Do not use microwave caps as tank caps, as they are rated for dc, not ac and not pulsed duty. But if you want a very powerful supply like rogerinohio :

You just series two mots and have a series/parallel arrangement of moc's so that it adds up too 1uf at 4kv and put in in a doubler arrangement. The schematic is shown of his video.

UPDATE: I forgot to say, you do not want to try to use an ac flyback for a tesla coil. It would take a very small capacitor and it would not get good sparks, and it would have to charge and then discharge the capacitor at whatever frequency you are running the flyback, so it would not quench properly so it would not run properly.

Estragon

Mon Jul 14 2008, 10:39PM

Registered Member #1391 Joined: Fri Mar 14 2008, 04:49PM
Location:
Posts: 40

Okay, thank you for that nice offer, but I'll have to consider it.
That rules flybacks out :P
But, what is limmiting the capacitors from working well, even in series, the problem is not breakdown? Is it inductance?(long rolled strips inside) I also noticed 1ÂµF is a very high value for the tank capacitor. (How many farad would it be if it was like 8 in series with one of them only being 0.7 ÂµF?)
Eeew, good comercial capacitors are hard to find (cheaply, kinda working on a low budget coil :) )
If i could get MOT's working it would be a good easy sulution. Hmm.
But this charging chocke in the DC tesla coil, what is it? Coud it be a modifyed MOT with an airgap, or?

Arcstarter

Tue Jul 15 2008, 03:06AM

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

Estragon wrote ...

Okay, thank you for that nice offer, but I'll have to consider it.
That rules flybacks out :P
But, what is limmiting the capacitors from working well, even in series, the problem is not breakdown? Is it inductance?(long rolled strips inside) I also noticed 1ÂµF is a very high value for the tank capacitor. (How many farad would it be if it was like 8 in series with one of them only being 0.7 ÂµF?)
Eeew, good comercial capacitors are hard to find (cheaply, kinda working on a low budget coil :) )
If i could get MOT's working it would be a good easy sulution. Hmm.
But this charging chocke in the DC tesla coil, what is it? Coud it be a modifyed MOT with an airgap, or?

Well im sure that would work but you need more mots to handle the voltage. I would just use 4 mots in series, it would be a good value of inductance and it would handle the voltage good because it would be using them at there rated voltage. I dont really think there is an easy cheap way to make a good enough capacitor for an mot supply. It would take 40 nf at like 15kv for good safety margin. You should just make some money and put it to the side and buy a good commercial capacitor.

Estragon

Sat Aug 02 2008, 06:40PM

Registered Member #1391 Joined: Fri Mar 14 2008, 04:49PM
Location:
Posts: 40

Still the same coil, but i think i am going for a higher power AC settup istead :( I'm lame.

Now i have been doing some rolling :) !

You guys think the coil got any chance of working with 38 (where aiming for 40) nF (increase/decrease?) rolled capacitors for bank, with 3(can I use three i always see either 2 or 4, but at 4 the MOT start to break down, and at 2 they are a bit to to low, voltage vise)
So, can i use three MOT'sin series with one more as ballast for HV supply? Should I maybe also use a lightbulb to for both resistive/inductive current limmiting? That would make "enough" voltage for a spark gap to work, i think.

As sparkgap i have made two round metal doorknobs mouted on plexi-glass with easly adjustable distance betwen them, and a fan blowing on them for quenching, may that work?

For primary what kind of shape would be best? I do not got acces to copper tubing, so I would have to use thik, stranded wire (eew). With many cuts in the insulation for tuning,. I got a big plastic pipe who would fitt nicly around the primary for cylindrical shaped coil around the secoundary coil (twice the diameter of the secoundary) But, i have only seen this in solid state coils so i guess there is a good reason for that. The plastic of the pipe is 1cm thik so i think it would isolate, though.
I also got some nice plastic cutting board I could cut so it made a conical shape.
Or just make a flat pancake coil? I think it looks kinda boring though :P
The coil is for low MOT voltage, so what is important then?

Grounding for the secoundary coil is also a problem, could i use mains ground for this, or should i make smothing, would 10, 35cm, thin iron spikes in the earth work? The deal is, it would be cool to use it inside and move it around and that settup would not be portable or "inside friendly". I can remmember somthink about an EMI (?) filter what is that?

And with the current limmiting, how many amps would the transformators draw?

Please still have my spelling excused, I have never been good at languages :P I am starting physics next year so i hope i can gain a deeper understanding of... yeah, those matematic formulas and.. well, and all those words i never had hear before I got interested in coils.

Arcstarter

Sun Aug 03 2008, 12:26AM

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

Well i was wrong... for 4 mot's you will need about 80nf. you could use two mot's and a simple doubler using microwave capacitors and diodes from either microwave or use a bunch of smaller diodes. That would be called a dc resonant charging coil. That would take about 40 nf. You can use 1 mot and a tripler or quadrupler and a small tank cap and rotary spark gap for a nice small but powerful coil.

1 mot with tripler and about 11.55nf tank cap and rsg(required):

1 mot and quadrupler and a rsg(required):

2 mot and doubler and 40nf tank capacitance with i think 7 foot spark(no rsg needed but suggested):

2 mot tesla coil without voltage multiplier(no rsg needed):

Estragon

Sun Aug 03 2008, 12:04PM

Registered Member #1391 Joined: Fri Mar 14 2008, 04:49PM
Location:
Posts: 40

Thanks for those links an all the help :)

BTW, i tested my rolled caps today, they are insanely sturdy! (kinda)
I used a flyback who is powered with a compact fluorescent bulb, so it gets a kickstart who makes an at least 4cm spark, but after startup it won't sparck more than 1.7cm, but allow me to pull it out to 2-4cm. The capacitors where ablo to hold the 4cm spark... nice!

I have drawn two schematics for the two settups i think i may do. They are kinda ugly, sorry made them in paint.

This is the first, a really simple, boring one who I am sure the MOT's will die fast with. But, its simple.

This is the more complex DC one: I kinda just copied it from cfavreau's video that you linked :)
But, made a drawing to make sure I got it, did I ?

Wich of these should i chose? (I think i am gonna go for the DC on, so much more fun)

Well, I am sure my capacitor bank values are a bit off so please correct me here.
Is the current limmiting neccesary, the resistive one I nearly never see.
Is the fan a usable motor for RTSG?
What kind of RF ground should i go for?
If anything is wrong/uneccesary/weird please tell me.
Should i use more charging chokes?

I hope you may point me in the right directions here :D !
Kinda unsure here :S

Estragon

Sun Aug 03 2008, 12:04PM

Registered Member #1391 Joined: Fri Mar 14 2008, 04:49PM
Location:
Posts: 40

Hmm, how to delete double.. excuse this, please.
Well anyway, you think the voltage tripler settup would pull low amper?

Arcstarter

Mon Aug 04 2008, 01:47AM

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

That second schematic is the one you should go with. The top one is very high power and harder to perfect and all that good stuff. But things i noticed on the second on which you should consider changing...

1. The tank capacitor should be about 10nf (of course a rsg would be needed with this circuit.)

2. The primary does not need to be ballasted, as it is only one mot and it has two mot's as chokes which will limit current.

You should use a variable speed asynchronous rotary spark gap for this circuit if possible, so that way you can can vary the bps and the overall power, low bps and you are using less power because the supply is going to keep the capacitor charged, so that will not change, and lower bps means it has to charge the capacitor less. Higher bps, and you will see the same spark length but more sparks per second and high power input. That being the case, will lower your power input even further, thus not needing a ballast, unless you have only a very small circuit breaker. I am sure that you will only pull about 5 amps from 240 volts, because that is around half of the current of most shorted mot's that i have used. I use 120 volts and i pull 20 amps short circuit from mot so just divide that by 2. But, if you need to use a ballast, just use the shorted mot in series with the supply mot, and no heating element.

What i did to make a simple variable speed arsg using a wood circular cutout saw attachment for a drill for the disk and an electric scooter motor for the motor. I just cut out the disk with the biggest hole saw i had, and screwed it onto a scooter motor with the hole in the middle. I then just put 8 screws evenly spaced on the disk and connected all of them with some wire. It would be best to use some flashing or strapping for this so it has lower resistance and higher current capabilities. I mount the motor on a piece of plywood and made two stationary electrodes with screws and pieces of 1 1/2 x 1 hardwood. I have used it with a 20nf capacitor charged to 12kv and got great results.

That was my motor, you could just buy one you like. This motor is good for 286 bps at full speed and you can change the speed with a pwm controller which you can find here:

That took me forever and a day to type

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