Bride of Frankenstein
Photo from Richie Burnett
This coil - with a lot of help from my friends managed a 10 foot arc (measured distance from toriod to strike pole) at the Corby Teslathon on 27th May 2000 - biggest arc in the UK that we know of.
The bride of Frankenstein coil was wound to be an exact replica of Mike Tucknott's Frankenstein coil. These are intended to be a matched pair and coupled together. The specs are given at the end
Frankenstein (right) with Bride of Frankenstien (left) at Amberly where we discovered the dificulties of coiling outdoors - still one day these two will be joined in an unnatural union and then the world will be ours.......
night at amberly - poor ground and breeze limited us to about 4 foot arcs.
I am very grateful to Mike for a piece of PVC pipe and help with obtaining wire for the secondary. I also very grateful to Richie Burnett who loaned a variac, ballast chokes, and caps and to Bob Golding who helped with an extra radar transformer, ballast, and variac, operating the coil required the three of us to bring up our power levels on the variacs simultaneously. My MMC cap didn't even get warm despite consist of just 9 caps rated for 1500v DC in series, 20 strings about 0.104uF this was supplemented with Richie's MMC's to bring us up to 0.19uF.
The first distance attempted was 92 inches - just to beat the 91 inches that Mike and Brian set at Cambridge. Then we kept pushing out, till we got to 120 inches - 10 feet. (3.04m). There will be a rematch soon no doubt - "Revenge of Frankenstein" as Mike and Brian will be tooling up.
The primary is shown above.
I use a strike rail which I mounted on a plywood ring - but with the big toriod the strike rail didn't seem to be doing any business. I decided not to have plywood across the gap in the strike rail.
The Rotary Gap
The rotary gap was built around a new grinder purchased from B and Q for the sum of nineteen quid (pounds sterling= $30), which is what you could pay for a second hand motor. Of course you can use the other end to for occasional grinding. If it ever gets zapped then its under 1 years guarantee. B and Q also do a small grinder for 15 quid which has also been used as the basis for a rotary.
A grinder is already prepared for spinning discs, I removed the grinding wheel and used the existing bosses. It was difficult to shim the disc so that it ran true, in the end I had to make a slight compensation with the electrode lengths. The disc is 1cm thick tufnol, 8" diameter, with four M8 brass screws into which are drilled to take the tungsten electrodes a second hole is drilled into the side of the head of the nut and tapped to take an M2.5 grub screw which holds the electrodes in place. The electrodes are one inch lengths of tungsten (zirconium) welding rods about 1/8" diameter. Its impossible to saw these - grind a grove and strike with a hammer to break to length, an aluminium ring connects the four screws on the rotary.
I used two sets of stationary electrodes offset by 45 degrees, it is equivalent to having one pair of stationary electrodes and 8 spinning electrodes - only it is easier to do and the power is shared between two sets of stationary electrodes. There is also a pair of M10 brass bolts acting as a safety gap. I used lock nuts on the bolts. 2950 rpm motor, gives a break rate of 395 BPS, this is on 50Hz UK mains. It is also possible to remove one of the stationary electrodes to run at 197 BPS I tried this at 2 KW - no increase in spark length but it was really surging. I am running this asynchronous - though someone in the UK has successfully modified one for sync use.
There was no breakout from the lower toriod which is shielded by the big one.
I thought a bigger toriod would help a little. I obtained some 8" ducting material from RS (they also have 12") unfortunately, though its aluminium laminate, it is outside in - there is a plastic spiral running round the outside which gives it strength. So I had to coat it with a couple of rolls of Aluminium tape. I used two 24 inch diameter plywood discs to form a drum and wrapped the ducting around this. I also attached a couple of handles to the drum for carrying.
Ducting and drum
photo from Richie Burnett
Form 9.25" X 50", Wind length 45", H/D ratio 4.86:1
Wire 1mm/18AWG, Turns/inch 23.5, No turns 1057
Wire length 2491.80 ft, Wire weight 5.51 kg
Inductance 46.07 mH, Self C 18.43 pF
Frequency 172.72 KHz
Inside dia 11", Conductor dia 0.312"
Space between turns 0.25", Number of turns 13
Total inductance 0.0919 mH
D1 34", D2 8", Capacitance 42pF
Secondary frequency with toroid 95kHz
Power supply 3*8kV 250mA trans (total output 750mA)
input power was probably 6 - 8 kW
Cap size 0.19uF MMC
Tap point 5 on primary