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First Tesla Coil

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Ryan Parle

Wed Apr 08 2009, 12:16PM

Registered Member #2038 Joined: Fri Mar 20 2009, 03:39PM
Location: Bristol Uk
Posts: 60

I guess i could make a basic safety gap with materials i've already got, and i suppose it will be better than nothing. My problem is that i dont like things to look cheap and dirty.

I'll have a look around and see what i can find.

i suppose i could actually use my current spark gap as the safety gap and add a centeral electrode for earth, although i have used all the M6 threaded bar, i might be able to find a suitibly long M6 screw instead.
I've got some 22mm copper tube that i could use to replace the existing spark gap.

Plasma Lover

Wed Apr 08 2009, 07:18PM

Registered Member #1911 Joined: Mon Jan 05 2009, 06:30PM
Location: Salem, Oregon, USA
Posts: 165

Your coil looks very nice. I'll bet you're proud.

You're getting fairly good output at 7 inches(?). What are the dimensions of the secondary coil?

For some reason, the burn on top in the photo that was shown looks like it contains the letters 'P, E, N, E, X, I, S' in that order. A bit off topic,but it's just one of those funny things that sometimes happen.

When it comes to the safety gap, I agree that making a new spark gap would be best, because you can adjust it and you're not depending on an electrode that goes to earth that is placed further from the arc than is natural. You definitely need a new gap so that you can adjust it separately from the other gap and can fine-tune it so that it will barely not be able to arc over to Earth when the NST is running without capacitors. The reason you do it without capacitors is so that your gap fires at a voltage that's safe for your transformer.

As for your comment about not wanting to make it out of things you just have lying around, I will remind everyone of a certain someone's signature - "The speed is the enemy of the perfection."

Let us know your progress.
=)

Ryan Parle

Thu Apr 09 2009, 03:06PM

Registered Member #2038 Joined: Fri Mar 20 2009, 03:39PM
Location: Bristol Uk
Posts: 60

Yes i am quite proud of my work, there are a few more things i intend to do in order to improve the apearence, during the beginning when all i had was a a length of copper tube, a length of plastic tube, some magent wire and a few bits of wood i took lots of time making all parts as nice as possible. Once i had the capacitors and NST i wanted to get the thing working, so i built it all up without taking time to sand down all the wooden parts. I'm going to strip it all down soon and finish sanding the wooden parts that make up the lower base and support legs for the upper base, then give it all a good coat of polyeurethane varnish.

The final basic specs of my coil are:
Secondary: 15"x 2.9" with 28AWG wire.
Top load: 4.6" dia plastic sphere(oid) covered in aluminium tape
Primary: 0.32" tube, inner diameter 4.9" with a coil spacing of 0.32"
Tank Capacitor: 30nf (3 strings of 10x .1uf 1500v)
NST: 10kv/50mA

I can give more detail if needed.

My current spark gap is easily adjusted and there will be ample room in the middle for the ground electrode should i decide to use it as the safety gap, which i think will definitely happen soon. I'll then make a new spark gap, i'm not quite sure what design to use yet, but what ever one i chose will have some kind of air feed to aid quenching.

yesterday afternoon i started making a new toroidial top load from a couple of cheap cake tins, and some aluminium coregated tube, all was going well until the seam broke and the tube began to un-coil luckly i had just enough spare to cut the tube in to two pieces and butt them together. i started to cover the assembly with aluminium tape i got about 1/3 round and ran out of tape, i've just ordered some more from ebay (local prices are way to expensive) so as soon as that arrives i'll finish the top load. dispite it being incomplete i decided to give it a try and found it to perform pretty much the same as the original top load. although the corona was much more defined (probably the fact that at the moment there are more sharp edges than before) I also noticed that when the grounded rod was just out of striking range there was a nice purple stream of plasma around a few very fine sparks, it looked pretty nice.

this morning it was suggested that my tank capacitor was too big, so i'm going to try using just the two strings next time.

Ryan Parle

Tue Apr 14 2009, 01:58PM

Registered Member #2038 Joined: Fri Mar 20 2009, 03:39PM
Location: Bristol Uk
Posts: 60

Well i had chance to try out my new toroid today, although it is not quite finished i figured that it would be "safer" compared with the small sphere, the only reason it is not finished is because i ran out of aluminium foil tape about 1/3 of the way round, its not the most attractive toroid by a long shot, but it works.

after a quick retune i found that the spark length had increased by about another inch, but i was having big problems with my spark gap not quenching so i could only get the occasional strike at 9" for a few seconds after startup.

i then decided to remove a string of capacitors from my MMC to reduce the tank capacitors value to 20nf, WOW. at 8" the spark was much brighter and louder than i had seen before, there were also plenty of fairly bright corona streamers just shooting in to the air, i then moved the earthed rod out to about 12" and the spark was still nice and solid, at 14" there was a faint field of plasma with thin dim streamers and the occasional big loud spark.

At this point i got a bit cocky and decided to move the earthed rod out a little further whilst the coil was running, now if i had thought about this a little more i would have stayed clear, my earthed rod was atached to a meter of plastic electrical trunking, the trunking was taped to an aluminium garden chair. Anyway as i started to move the earth point away, i watched a big fat streamer shoot from the toriod and hit me straight in the hand! Fortunately it was only a very short duration shock i felt a slight tingle in my hand but dont see or feel any signs of damage. i dropped the chair and switched off the power. then got a tape measure and measured the distance between my hand and the point where the spark left the toroid to be about 30" WOW!!

i moved the earth point out to about 20" and was getting occasional strikes, before noticing my secondary sparking at the same point as i noticed the other day. so i stopped experimenting for the day, but i'm very impressed with the improvement, and now have decided that i really need a safety gap and strike rail.

Plasma Lover

Tue Apr 14 2009, 02:59PM

Registered Member #1911 Joined: Mon Jan 05 2009, 06:30PM
Location: Salem, Oregon, USA
Posts: 165

Congrats. I'll bet that that strike made you pretty happy, even if it scared you a little bit. ;)

Have you not been bitten by a transformer, like an NST, yet? I don't see how somebody could make a complete, functioning Tesla coil for their first time and NOT get zapped at least once. Everybody has that first bite.

So do we get any more pictures of the setup? Did you take it all apart and make it pretty like you said you would?

Ryan Parle

Tue Apr 14 2009, 04:08PM

Registered Member #2038 Joined: Fri Mar 20 2009, 03:39PM
Location: Bristol Uk
Posts: 60

yeah, i was quite happy with the big spark that jumped to me!

This was the first bite i have had from any of the tesla coil project at all, not even any static from the secondary assembly during adjustment. i'm not sure how similar the voltage and currents are to a high frequency TIG welder, but i've had a few zaps from those in the past... and they hurt. But it taught me a few important things about working with high voltage, and i now try to keep my distance, only ever use 1 hand for the initial touch, i also tend to wipe all bare terminals with a grounded rod to make sure there is no residual charges.

I've not got round to making it more pretty yet, i expect i will strip it down and do it all tomorrow since it is forecast to rain most of the day. i just found another electrode that i can use in making my first safety gap. so i'll be working on that too.

I'll post some more pics ASAP.

Steve Conner

Tue Apr 14 2009, 05:34PM

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

"Getting bitten by a transformer" stands a chance of killing you, so it's absolutely to be avoided. The Tesla coil streamers are quite harmless in comparison.

When you say "Everybody has that first bite", you probably heard that off some old grandpa who serviced tube radios in the 60s. The voltages and currents from NSTs and MOTs are far higher and more dangerous than the few hundred volts in an old radio, and that "first bite" could possibly also be the last.

Ryan Parle

Tue Apr 14 2009, 06:06PM

Registered Member #2038 Joined: Fri Mar 20 2009, 03:39PM
Location: Bristol Uk
Posts: 60

Yes i'm with you on this one Steve, although i've never been bitten by any of my own HV experiments (with the exeption of my little tingle this morning) i'm generally very cautious around HV.
I certainly wouldnt dream of deliberatly touching any of the components when the coil is in operation and after todays "tingle" i will be even more carefull of how close i get to the running coil.

in the past i have had my fair share of electric shocks. when i was about 18 i was asked by my supervisor to switch two phases of a 3 phase motor which was running backwards, there was a single strand of copper that had escaped the bootlace terminal sticking out, and a fault in the wiring of the breakers leaving this 1 phase live, when i put my hand in to remove the wire i brushed the loose strand. i bounced accross the room to the nearest filing cabinet knocking myself out on the way! it turned out the guy who wired the breakers was an alchoholic and was drunk on the job (he was dismissed the following day)... i consider myself rather lucky as most 3 phase shocks are much worse than what i encountered.

my other bad experience was when my idiot ex boss left a live 40A 240v feed for a shower right by the entrance to a loft hatch, i put my hands down to lower myself out of the loft, my right hand landed on the bare wires under my full body weight, i fell through the hatch, got tangled in the ladder and nearly went over the banister and down the stairs.

There have been plenty other zaps I have had but I dont really want this thread to turn in to storys of electrocution so i'll stop there

Renesis

Tue Apr 14 2009, 06:42PM

Registered Member #2028 Joined: Mon Mar 16 2009, 08:13PM
Location: Norway
Posts: 319

i just found another electrode that i can use in making my first safety gap. so i'll be working on that too.

How about those tungsten TIG-electrodes?

Ryan Parle

Tue Apr 14 2009, 06:51PM

Registered Member #2038 Joined: Fri Mar 20 2009, 03:39PM
Location: Bristol Uk
Posts: 60

Renesis wrote ...

i just found another electrode that i can use in making my first safety gap. so i'll be working on that too.

How about those tungsten TIG-electrodes?

Tungsten is a bit OTT for a safety gap isnt it...

I have a few old ball bearings from my mini's CV joint, i've drilled them before and once you get through the hardened outer layer they are actually pretty soft.

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