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Re: [TCML] Repairing a Coil - Please Help
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Brian Kelly wrote:
Hail to the great TCML geniuses, I am in need of help.
The National Center for Atmospheric Research is hosting a Super Science Saturday this weekend and has previously done a lightning demonstration with a Tesla coil. However, it is not working well today and I have been asked to help because of my limited coil experience from high school. Any suggestions to get it working again for the kids would be most appreciated.
My understanding is that the transformer went bad and was replaced. I was told the coil needs a 60KV, 120mA transformer but that it currently had "only" a 60KV, 60mA installed. We later discovered that the installed transformer was actually 15KV and 60mA. I suspect the original transformer was 15KV and 120mA but I am not certain.
A 60KV 120mA transformer would be rather largish ( avg size about the
same as one of those Milk crates that hold 4 gallons of milk) a 15KV
120 or 60mA transformer would be about the size of a shoe box if not a
tad bit smaller.
The coil itself is modest. The secondary is about six inches in diameter and three feet tall. The primary is about seven turns of .25 inch tubing. The capacitor is an array of 16 high voltage DC caps with a total capacitance of 19.2 nF. Two nice inductors (about 500 turns around 2 inch plastic pipe) protect both poles of the transformer. The spark gap is enclosed in square metal plates sandwiched together in a way that made me originally mistake the whole unit for another capacitor. 4 long nylon screws hold the whole thing together so I wonder if the gap is adjustable.
sounds like it is adjustable, take a look to see if there is some dust
bunnies or foriegn objects between the plates, could be artificially
reducing the gap width and lowering the firing voltage which will
produce smaller fuzzy output.
Fuzz ... normally know as corona. The coil is putting out a voltage off
of the top load but not nearly as much as it should be.
Right now, when the coil is turned on, the spark gap fires and the secondary coil gets a bit of charge, I would describe it as fuzz when you get a ground wire close. It is nothing like the 6 foot sparks I understand it is normally able to produce. I suspect the coil is well tuned as the clip location for the primary is very well marked, although again, I could be mistaken.
Changing the transformer from one amperage capacity to one of a lower
value ( in your case by 50%) it would increase the cap charge time
considerably ( 2-3X factor).
My main question - is it possible that switching out the transformer with one with half the amperage could make the difference between fuzz and 6 foot sparks? Would the voltage have to change or would there need to be another problem?
Without seeing/hearing the coil running, it would be somewhat difficult
to tell you how to do that. Things I would check on ( process of
elimination) would be
And my followup - does anyone have any suggestions that might make this coil function for the kids, even if at a lower capacity?
1. check spark gap for dirt etc between plates. ( avg total gap width
should be around 5/8" to 1/2")
2. consider the multi cap system having one or more caps not functioning
properly ( dried out, shorted internally)
3. see if the transformer is putting out the proper voltage on both
4. look carefully at the primary for previous marks as to where the lead
5. see if the safety gap is firing too often when running ( more than
once per several seconds is a minimum)
6. MAKE SURE that the secondary coil base wire is attached to a solid
earth grounded item ( preferably its own ground rod)
7. Stand facing N.E. on one foot while holding your left hand palm up to
the East while chanting some monosylabic verse 5 times when you turn it
My thanks in advance,
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