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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:


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


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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