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Re: [TCML] Burnt Joint (Cap Bank)

Hi Michael!

Another possible problem I noticed. It looks in the pictures like your main gap is mounted on an adjustable wooden platform. Above 5-10 KV wood is nicely conductive. You may have a carbon track through the inside of the wood which, as you ramp up the voltage will take more and more of the power through the wood instead of across the gap.

Matt D.

-----Original Message-----
From: Michael Gray <graymp89@xxxxxxxxx>
To: Tesla Coil Mailing List <tesla@xxxxxxxxxx>
Sent: Sun, May 5, 2013 5:25 pm
Subject: Re: [TCML] Burnt Joint (Cap Bank)

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!

> -----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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