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My First Tesla coil. SGTC

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porkcake

Tue Aug 24 2010, 06:31PM

Registered Member #3138 Joined: Tue Aug 24 2010, 05:20PM
Location: Herefordshire
Posts: 7

Hi, this is my first posting on here, so please be patient!

I have just constructed my first proper Tesla coil, after collecting various parts over the last few years and actually getting around to putting it together.

It still needs some refining and a toroid, i will be making a better SSG with tungsten electrodes and quenching. Now I know it works, it has given me loads more inspiration.

Here's a component breakdown:

Tunewell 230v/ 5kV 36mA nst 50Hz (ebay)

18 1000vdc polypropelyne capacitors 0.1uF in series, 4 sets of these in parallel, giving about 22nF (RS 114-604) (rescued from a factory clearence!)

10 Mohm bleed resistors accross caps

Primary coil - 14 turns of 8mm copper tube, tapped about 4.5 turns.

SSG, currently two brass knobs

secondary coil, 0.3mm (ish) copper transformer wire, approx 1224 turns on 70mm drain pipe, coil height 355mm

All put together on the wifes LDPE chopping boards.

calculations done by hand and using teslamap. I've had 4" streamers on a rough set up with no toriod so far, and have just got some alu duct tape to make one up.

I was well chuffed on my trial run! i have a video on youtube here's the link:

and will get some pictures up soon.

Many thanks fellow coilers, great site too!

porkcake

PS any comments or pointers are most welcome,

quicksilver

Wed Aug 25 2010, 06:17PM

Registered Member #1408 Joined: Fri Mar 21 2008, 03:49PM
Location: Oracle, AZ
Posts: 679

Congratulations on getting her up and running and on getting solid 4" streamers from a 5K NST! With a well thought out top-load you may be pretty surprised - if you're getting 4" from a naked coil. - Good stuff.

If you haven't tried plugging the stats into JAVATC:

Try it and see if there are suggestions that may tune it further.

If you do take pics, please include a picture of what caps you used. I am always interested when someone uses "rescued caps" & they work out. This can help various folks who do know where some are or get a good deal, etc.

porkcake

Wed Aug 25 2010, 07:54PM

Registered Member #3138 Joined: Tue Aug 24 2010, 05:20PM
Location: Herefordshire
Posts: 7

Many thanks Quicksilver,

I had a play on that JavaTC last night and have just finished making an 11inch (O/D) toroid from some 4" aluminium ducting and have just coated the lot in alu duct tape! this should give me the 12pF top load that i need. Hopefully i'll fire her up tomorrow evening and get some pics, as its lashing it down here at present!

I also aquired some nylon M8 bolts and nuts today to fix it onto my secondary. Any suggestions for getting the best contact between coil wire and top load? i was intending to wrap it around the bolt a few times and sandwich it upto the aluminium.

The caps have been sat in my garage for about 4 years, they came from a job lot of stuff an ex-boss bought, i thought "tesla" when i saw them, so kept them to one side!

thanks

quicksilver

Wed Aug 25 2010, 11:21PM

Registered Member #1408 Joined: Fri Mar 21 2008, 03:49PM
Location: Oracle, AZ
Posts: 679

Disclaimer: I am very new to this , I am not an engineer; I'm just a hobbyist & I've only made a few SGTC & 1 SSTC.

RE your question. At the toroid-secondary junction you're are not getting much current at your connection to the top-load, therefore a clean & short connection is your best bet: no need for monster wiring at that connection. Strip the secondary's wire very clean (scape gently with knife blade to assure it's clean contact) for a few inches and when it's under the tape allow for a few solid inches of contact with "finger tight compression". Aside from that; keep it short. Also, use your multi-meter and test for any shorts in the completed toroid. Sometimes (rarely) there can be a place where the "glue" has kept contact from completing, etc.
Issues to consider are the physical make-up of the top-load: you have aluminum tape which may have incomplete conductivity due to adhesive (or debris from the ducting...) & it takes a really well thought out taping job to get it smooth. But that simply provides a break-out point. Unless you don't like that effect visually and like the smooth "swirl of streamers". However soldering a Al to Cu is not too easy. But it may be unnecessary if your contact is solid & unmovable (make sure everything is REALLY clean if you're going to rely on simple compression connection)..... Avoid having excess secondary wire floating around the inside of your coil form: keep connections short all around.

Watch the coil in the DARK. Look for corona effects; especially near the top toward the toroid or racing sparks at the junction (between) the primary and secondary. OFTEN a coil can preform well and these things are unnoticed in all but the darkest room. Tune further, till your rid yourself of them & you may get even better performance! On the other hand, with some coils the arcing can be bad enough to burn a secondary's wire (occasionally....just builds & "pop").

With a sizable toroid, it IS possible to get a strike to your primary (consider a strike rail if you see that possibility). The dangerous potion of the coil will be in that primary & putting something up to catch an arc from the toroid is a very simple insurance step. If I read your description correctly, your primary is a 14 turn pan-cake (flat type) and you're using only 4.5 turns of it, yes? So that primary extends outward (looking down from atop the toroid (once it's there).
I'd put in a strike rail just in case. It's not a big deal to make.
You may also want to get creative with your spark gap. A single tungsten SC is nice because it's easy to adjust but it also get really hot. The real reason I stopped using those is because they are SO DAMN LOUD!
The 5-gap style is not easy to adjust or to get "perfect" becasue it's not a walk in the park to construct; but it is much cooler and (much) quieter.

I am quite sure that many other, more experienced than I can add helpful suggestions, but it sounds like you're off to a great start. Creativity has always been my friend as has reading about this stuff. It's the few times that I have actually used algebra (so I can look back & be grateful).

HV Enthusiast

Thu Aug 26 2010, 11:29AM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

Congratulations on your Tesla coil. Looks good. Only comment is that your MMC is way overkill for that NST.

You could have gotten by with using maybe a few (like 4-6) panasonic polypro caps.

porkcake

Thu Aug 26 2010, 06:03PM

Registered Member #3138 Joined: Tue Aug 24 2010, 05:20PM
Location: Herefordshire
Posts: 7

thanks for the info quicksilver, its taken on board especially about the corona, i was using a brass bolt in the top of the coil and seeing arcs off the top of the secondary winding. the inside of the pipe also reaked of ozone. I wound the coil a year ago, then read that a black pvc pipe contains carbon. i'm not sure how much difference this will make, but we'll see.

i will reduce the amount of turns on the primary and make a strike rail, although i just got some 4 or 5 mm copper tube and may make a new primary from that.

its like winter here, so no run tonight. bloody English weather!

as for the caps
my original design was utilising a 15/40 oil burner ignitor but this turned out to be no good, i managed to get a second hand nst from ebay, really hard to get them here. i didnt want to pay Â£160 for a new 15/40!

so i had to mod the cap bank from 32 0.1uF's in series, running 2 in parallel to its current set up. a pain but worth it now.

i also have my eye on a 10/40 nst on ebay, and a long piece of 7" MDPE gas pipe for a future project, i'll finish this one first though!

the site is very interesting Eastern Voltage Research, some nice looking gear!

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