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Re: [TCML] Burnt Joint (Cap Bank)

Thanks again for all the advice, really appreciate it. I've had another
crack this weekend and I'm happy to report partial success! I have a number
of questions too...

To respond to earlier messages, I firstly cut my strike rail down a bit so
there's a decent (~2 inch) gap between the two ends, thanks for pointing
that one out. With regard to the wood framework I've used for most of it,
I'm going to order a load of Perspex sheeting to re-design the framework
altogether. Does anyone have any recommendations for this? I'm in the UK
and will probably just order some 15mm thick acrylic sheets from an online
vendor, unless advised otherwise. To answer Phil, my NST is a 10kV 50mA
unit and I actually need to re-wind a new secondary anyway (current one was
damaged earlier). So would be a good opportunity to make this one slightly
larger in radius and slightly taller. What sort of dimensions would be
suitable? The one I'm using at the moment is 5.6cm in diameter and approx
27cm tall.

I have put a breakout point onto the toroid and introduced a breakout
target, in the form of a grounded wire suspended close to it. This seems to
have done the trick, as the toroid is now sparking nicely, albeit only to
the grounded wire target! In daylight I have achieved consistent spark
lengths of approx 12cm, I can go longer but they become quite irregular and
inconsistent. How fine does everyone tune their coils? I've identified the
best position for mine is between 3.5 and 3.75 turns - should I try to be
more accurate with this?

Right now I'm waiting for darkness before I get back to it. I will try
the florescent lamp, just to see it in action. I will then try it without
the grounded target and if that works I will try without the breakout point
on the toroid. I'm skeptical though, something tells me it's not going to
spark without the grounded target. When I was testing/tuning it earlier, I
was moving the target back and forth and at distances greater than 12/13cm
the coil struggled and sometimes didn't spark at all. Could I improve
performance by increasing the secondary radius and/or height? With more and
wider turns, the secondary would surely develop greater voltages?

I've been running the coil outside, and it's fairly windy. When I first
fired it up, it fried the spark gap fan I had in place (it was just a
computer case fan running on batteries). The arcing between the main spark
gap, presumably because it's windy outside, moves around a lot and actually
sometimes develops a circular path from one electrode to the other, i.e.
not directly across the gap. I probably had the fan too close and fried the
motor or something. So how important is the spark gap fan, considering I'm
using it outside? And on that note, would it be worth moving the coil
inside temporarily to do some further fine-tuning in still conditions (i.e.
no wind!)?

Having properly set-up both the safety gaps and the main gap, the safety
gaps would still fire intermittently during operation. The main gap would
be firing all the time, but every few seconds or so the safety gap would
fire, either a short series of small sparks or one very loud spark. Is this
normal...? I'm not sure if it makes any difference but the safety gaps are
what looks like aluminium (drawer knobs) and the main gap looks to be
bronze (coat hangers). Should I use the same material/apparatus for both
gaps so that their behavior is more similar? The bronze coat hangers are
looking really quite burnt out at the tips...! The aluminium is definitely
marked but not so disfigured.

Anyway I'm happy to have it working(ish), but clearly have plenty of
improvements to be made!

Thanks again,


On 8 May 2013 22:22, Yurtle Turtle <yurtle_t@xxxxxxxxx> wrote:

> In addition to a breakout point, place an RF grounded wire "target" near
> the breakout point. Start really close if you have to. Then try moving it
> out a bit and retune. Repeat. Eventually you should get breakout without
> the target.
> ----- Original Message -----
> From: Phil Tuck <phil@xxxxxxxxxxx>
> To: 'Tesla Coil Mailing List' <tesla@xxxxxxxxxx>
> Cc:
> Sent: Tuesday, May 7, 2013 4:14 PM
> Subject: RE: [TCML] Burnt Joint (Cap Bank)
> Michael,
> You have correctly followed through with a logical test sequence, and it
> should work, so I am wondering if your problem may lay with having a toroid
> that has a minor diameter that is too big for the output voltage you are
> producing. The bigger the diameter, the more top volts are needed to
> achieve
> breakout, and the secondary geometry looks a bit small for the toroid size
> chosen.
> The fact that the spark gap alters both its appearance and sound when
> everything is in circuit, points to the fact that the tank circuit (the cap
> & primary inductance) are all present.
> You don't say, or I missed it, what the output voltage of your neon tranny
> is, so that may be insufficient for that toroid size. Or it could be the
> tuning is way out, or a combination.
> Try putting a breakpoint (BP) on the toroid and seeing if you get anything
> then. A BP will allow the toroid to breakout at a lower voltage.
> Also either download JAVATC or use the webpage version (
> http://www.classictesla.com/java/javatc/javatc.html  ) and enter all your
> data into that and then see what it gives for optimal tuning, or the tap
> position.
> The strike rail, as already commented, needs a 2 inch gap in it somewhere,
> although while it will cause a loss of power as it is, it won't be enough
> to
> cause the current trouble 99% of the time.
> Also have you checked the secondary to make sure there are no shorted turns
> at all from bad winding? Javatc will give you the DC resistance of the
> secondary, and you could check this with an ohmmeter to see if you get the
> same (or near).
> As it's a new build, and your first coil, (don't shout at the PC screen
> now....but....) you have checked the top secondary winding is actually
> electrically connected to the toroid?
> Good luck and hope this helps. Others more knowledgeable may chip in as
> well, so hopefully you'll get it running in the end.
> PS: I notice you have used wood for one of the gaps to be mounted on. This
> is not a good idea, as wood will conduct unless very dry.
> May pay you to power it up (working or not) in the dark, and look for any
> tracking on the MMC board or the wood.
> Regards
> Phil Tuck
> www.hvtesla.com
> -----Original Message-----
> From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On Behalf
> Of Michael Gray
> Sent: 06 May 2013 12:35
> To: Tesla Coil Mailing List
> Subject: Re: [TCML] Burnt Joint (Cap Bank)
> Okay, I resoldered the cap bank board last night, and had another crack at
> running the TC this morning. Still doesn't work...!
> Just a quick run through of what I did: first I connected the safety spark
> gap directly across NST and adjusted so it was just wider than the NST
> could arc across. I then did the same for the main spark gap, except this
> time a tiny bit narrower than max. Then checked all connections with
> continuity tester and checked the wiring was correct. Here's a pic of my
> circuit diagram:
> http://imageshack.us/photo/my-images/211/20130504191918.jpg/
> Then I fired it up (variac was connected but I just had it on 100%), and
> the main spark gap was going, very bright with a loud crackling sound which
> I presume is about right. But the toroid wasn't doing anything. I left it
> running like that for about 10 - 20 seconds and still nothing, so I
> switched it off to investigate.
> Disconnected everything and re-tuned the spark gaps as described above.
> Then connected the NST across the Terry filter, with the other end of the
> Terry filter left open, and powered up - no sparks on safety gap (as
> expected). Moved on to connect Terry filter up to the main spark gap,
> powered up and the spark gap was arcing much quieter and continuously (as
> expected). Then connected one end of the spark gap to one end of the
> capacitor bank, with other end of cap bank left open, powered up and spark
> gap continued to arc the same as before (as expected). Then connected the
> other end of the spark gap to the base (inside most) tap point of the
> primary, powered up and spark gap continued arcing as before (as expected).
> Just to be thorough, I then disconnected the spark gap from the primary and
> instead connected the other end of the capacitor bank to the outer tap
> point on the primary, powered up and spark gap again arced as before (as
> expected). So up until now everything seemed okay, until I completed the
> circuit by connecting the spark gap to the primary again. On powering up,
> the spark gap this time was arcing as I described earlier, i.e. much
> brighter with a very loud crackling noise (as expected), but the toroid
> wasn't up to much, in fact nothing whatsoever. I was quite disappointed to
> be honest...!
> Anyway I've taken a load of pictures of it (below), does anyone have any
> ideas?
> http://imageshack.us/photo/my-images/51/20130506121432.jpg/
> http://imageshack.us/photo/my-images/138/20130506113409.jpg/
> http://imageshack.us/photo/my-images/194/20130506113502.jpg/
> http://imageshack.us/photo/my-images/199/20130506113443.jpg/
> http://imageshack.us/photo/my-images/545/20130506113418.jpg/
> http://imageshack.us/photo/my-images/405/20130506113427.jpg/
> http://imageshack.us/photo/my-images/12/20130506113343.jpg/
> On 5 May 2013 21:56, Michael Gray <graymp89@xxxxxxxxx> wrote:
> > Thanks for the advice everyone. I must have forgotten to include the
> > bleeder resistors. This board is the second iteration of my cap bank; the
> > first had bleeder resistors on it so I must have forgotten to include
> them
> > on this one. So I'm resoldering it completely, removing the red wiring
> > between each cap and replacing with the legs of the resistors as they are
> > long enough to adjoin each cap too. Good point about the trailing leads -
> > I've now tied each trailing lead to the board with some magnet wire,
> > through the board holes and twisted taught.
> >
> > When I first turned on the coil I did here what sounded like arcing as I
> > was turning up the variac (before spark gap had fired), but I wasn't sure
> > what it was as I couldn't see the cap bank from where I was standing, and
> > of course it was my first go so I didn't know what to expect. So that was
> > probably the dry solder joint as has been suggested. I'll hopefully have
> > the board resoldered tonight, and will have another crack at it in the
> > morning. Hopefully it works, very excited, thanks everyone!
> >
> >
> > On 5 May 2013 08:54, Phil Tuck <phil@xxxxxxxxxxx> wrote:
> >
> >> Michael,
> >> You need to physically anchor all of those 12 red 'trailing leads' to
> the
> >> board. Either by wrapping some wire around the lead itself and then
> >> through
> >> the board's holes, close to the edge of the board, or a spot of 'Hot
> Glue'
> >> to tack them to the board. Otherwise they are relying on the soldered
> >> connections everytime the leads move or flex.
> >> The original trouble, as the others say, was a 'dry joint' (solder not
> >> properly melting onto the wire, or only being held there by the resin in
> >> the
> >> solder)
> >> I have used that board to mount a string of diodes once, to rectify
> 10kV,
> >> and the board ending up tracking. I had to put it under oil to allow it
> to
> >> work (it was just a temporay test setup anyway).
> >>
> >> Regards
> >> Phil Tuck
> >>
> >> www.hvtesla.com
> >>
> >> -----Original Message-----
> >> From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On
> >> Behalf
> >> Of Michael Gray
> >> Sent: 04 May 2013 22:05
> >> To: Tesla Coil Mailing List
> >> Subject: [TCML] Burnt Joint (Cap Bank)
> >>
> >> I fired up my (first) TC for the first time today, after months of
> putting
> >> everything together. Needless to say, it didn't work! I was slowly
> turning
> >> up the variac, the spark gap fired up, and then I saw some smoke coming
> >> from the cap bank. So I powered down and investigated - turns out one of
> >> the soldered joints had smoked. I kinda regret buying the caps I did,
> the
> >> legs on them are tiny and this makes it difficult to string them
> together.
> >> The caps are mounted on some Vector prototyping board, and because the
> >> legs
> >> are so small I've had to solder a very small length of high voltage wire
> >> between each cap. I'm looking for some advice really on my cap bank - is
> >> soldering prone to burning out like this? What's the best way to make
> the
> >> connection? Should I try to solder the legs directly together instead of
> >> using an adjoining length of wire? Should I invest in different caps?
> >>
> >> The caps are rated at 0.047uF at 2kV:
> >>
> >>
> http://uk.mouser.com/ProductDetail/Kemet/PHE450SD5470JR06L2/?qs=s4t14sB06yQT
> >> V0lacTv0rw==
> >>
> >> In 6 strings of 10 their total capacitance should be in the region of
> >> 28.2nF.
> >>
> >> Here are a couple of pictures of it, you can see the burnt out joint on
> >> the
> >> right:
> >>
> >> http://imageshack.us/photo/my-images/841/20130504212930.jpg/
> >> http://imageshack.us/photo/my-images/713/20130504212952.jpg/
> >> _______________________________________________
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> >> Tesla@xxxxxxxxxx
> >> http://www.pupman.com/mailman/listinfo/tesla
> >>
> >> _______________________________________________
> >> Tesla mailing list
> >> Tesla@xxxxxxxxxx
> >> http://www.pupman.com/mailman/listinfo/tesla
> >>
> >
> >
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