Re: [TCML] Spark gap fan smoked

[Bert Hickman <bert.hickman@xxxxxxxxxx>]

Hi Dennis,

In a SGTC, the RF ground typically has high amplitude (many 100's to 
over 1000 volts) RF spikes. When you connect your fan motor chassis to 
this, you're stressing and overvolting the insulation system between the 
motor windings and the fan motor stator. Eventually, the insulation 
fails and you end up with a partial or total short circuit between the 
winding and the RF ground, cooking or opening the winding.

Either let the fan chassis float or, better yet, connect it to the mains 
earth/ground instead. Note that the NST case SHOULD remain tied to your 
RF ground. While this does stress the NST primary-core insulation 
system, it is the safer mode of operation especially if you are seeing 
significant TC secondary-to-ground power arcing.

Bert
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otmaskin5@xxxxxxx wrote:
> Hi, happy holidays everyone.  For the first time in the 4 years since
> I built my first coil (15/60), I finally seem to have it running
> great without problems.  Strikes to ground targets are reaching out
> into the low 50"s at a conservative 0.18" spark gap setting & variac
> driving it at no more than 120v (problem with the sweeper & it won't
> quite get to 120v).  So I'm fairly pleased with the performance given
> I'm not pushing the coil too hard to do what it's doing.  Best of
> all, I finally reached the point where I seem to have eliminated all
> the other issues like racing sparks & incessant safety gap firing.
> So that's the good part.
>
> Then, yesterday I was just enjoying playing with the coil & watching
> the sparks when smoke started pouring out of the segmented spark gap.
> Looks like I burned up the 340 cfm 5" muffin fan for the spark
> gap...which brings me to my question.  When wiring in the fan, I had
> only the hot & neutral wires going back to the mains, not the 3d
> prong ground.  I had the chassis of the fan grounded to the NST case
> which is connected to the RF ground and a pipe driven into the ground
> outside of the garage.  This is the second fan that I smoked and both
> were wired in the same fashion.  I'm wondering whether I got it wrong
> relative to grounding the fan to the RF ground. - I thought this was
> a best practice, but maybe not.  I'd welcome any suggestions.
> Thanks, Dennis Hopkinton MA 
> _______________________________________________ Tesla mailing list 
> Tesla@xxxxxxxxxx http://www.pupman.com/mailman/listinfo/tesla


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