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RE: [TCML] Never Work With Children, Chemicals or Tesla Coils
For my sins I provided the coil and Jacob's ladder were mine. I've known Pete (the lecturer) for 25+ years and when he wanted lightning he knew I'd be pleased to help.
The coil is a Maggie. 3KVA (cont.) 10KV RMS tranny, 94nF 26KV MMC, 200bps SRSG, oil immersed driver unit with 11 turn 5" primary / 150 turn 4.5" secondary, flying wire up to the suspended tertiary with ~950turns of 0.5mm wire on a 5" former and a 24"x10" a/c duct topload. While not the most elegant, the latter was selected to keep the flying weight under 5Kg.
The real problem was earthing/counterpoise/return paths. The RI lecture theatre is on the 1st floor, almost 200 years old, with a wooden floor (Faraday's first lecture was in 1825). When I did the initial sizing up in August and the first test runs in December this wasn't too much of a problem, with nice solid external grounds available and a dedicated 500A power board with supposedly was only going to be used by me.
I've done quite a number of public demos in the past, including some filmed with Phantom 1000fps cameras without problems, however I was well aware that the raised wooden floor and large loop area in the return path had the potential to cause issues.
When I arrived for the full rehearsals on the Monday there were suddenly 8 very expensive broadcast cameras all connected via umbilicals to a "gallery" room in the basement, plus 3 networked cameras for showing the audience less than 8' from the topload. Unsurprisingly they formed lovely antenna picking up lots of interference. A counterpoise under the rubber mat flooring helped, but the close seating meant it couldn't extend far enough out to really kill interference.
During testing I also managed to set off the building fire alarm twice (RF units which lost contact when the coil was running) and I fried a custom DMX to legacy lighting controller which sat under the floor and controlled the house lights in the ceiling!
I'd previously tested to coil out to about 7'-8' arcs, but had to limit it to around 4' for the demo with arcs to the ground stick most of the time to limit E fields.
Pete's take on the affair can be found here http://www.huffingtonpost.co.uk/dr-peter-wothers/never-work-with-children-_b_2352036.html
Colin.
-----Original Message-----
From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On Behalf Of Harold Weiss
Sent: 26 December 2012 04:11
To: Tesla Coil Mailing List
Subject: Re: [TCML] Never Work With Children, Chemicals or Tesla Coils
I've had the fun disco lights with ETC dimming systems. Likes to play havoc with the SIMM module. My thought was that it was getting into the dimmers through the leads haning down from the raceway boxes on the overhead electrics pipes. But I didn't have much choice for ground. It had to be power ground, as I would have needed to run 200+ feet of cable to get out of the building to a ground stake.
I've had no problems in theatres with variac dimmers!
David Weiss
> OOps!
>
> I haven't been with KVa for quite some time now, and I DO know that
> great pains are taken for safety. Sounds to me like there was
> inadequate or missing grounding for the structure. (One reason why I
> carry a bunch of grounding clips...)
>
> Just goes to show that even though you THINK everything is OK, it
> might just not. Triple-check and then check it again with another person...
>
> - brent
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