final prep of coil
Subject: final prep of coil
Date: Sat, 07 Jun 1997 12:57:40 -0400
From: Michael Bauer <mbauer-at-execpc-dot-com>
That last couple weeks I have made much progess on my latest coil. I
done rough tuning but need to finish my grounding system and disconnect
few ham radio antennas. My yard is really limited in size here in town,
only low power settings will be used until I transport it up to my
north". Part of the fun in this project was building a good power
cabinet. I loaded a full height 19" rack cabinet with a TEK scope,
relays and time delay relays, electronic sampling of voltage and current
nodes, SCR DC motor control for the RSG, variac panel with cooling fan,
In the tuning tests I found out the I get resonance just at the end of
primary coil. I may need to add another turn or two of tubing if I
to a larger toroid. Here are my coil specs, and if anyone has questions,
feel free to ask.
primary coil: 6 3/4 turns of 1/2" copper tubing, spaced 1.375", with 22
Primary cap: (two) 0.2 uf/20 kvdc caps in series for 0.1 uf/40 kvdc (I
need to upgrade voltage rating here)
RSG: 3600 RPM DC motor, 3/4 Hp, belt drive to spindle mounted 12" disk
12 studs on 10" circle. Studs are 5/6" brass, fixed electrodes are 3/8"
stainless. DC motor SCR speed controller is 0 - 90 vdc with reversing
relays and start/stop input. Speed is controlled by a pot for any speed
between 0 and 3600 RPM.
Secondary coil: 20" OD by 40" tall, wound on wooden form. Three plywood
disks support 1/2" X 1" slats open spaced around perimeter. Slats are
and doweled to disks. About a third of the wire is supported by slats,
rest of the perimeter is air spaced. 17 turns per inch, or about 675
Final tune with toroid is 66 Khz.
Toroid: 6" by 30" aluminum ducting covered in aluminum tape. Center is
covered plywood. Ends of duct were first hot melt glued together before
Transformer: 10 Kva pole pig, 2 insulating electrodes on secondary.
Kv/25.3 Kv depending on internal HV connections. I made a safety gap
assembly that mounts to the output studs that allow easy setup for Jacob
Ballast: 140 amp welder with manual taps for low volt current side.
variac: 240 vac/16 amp. Not nearly big enough but I am fan cooling it
a large squirrel cage fan until it blows or I find a cheap replacement.
Conrol panel: Low voltge relays, start/stop buttons, and indicators for
power up sequencing. I added time delay lockouts between powering the
and pig power to give the motor time to spinup (10 sec). Main contactor
100 amp rated.
Instrument panel: Volt and current measurements of many points
simultaneously, each sensing circuit feeding a BNC connector. Current
sensing done with hall effect current loops feeding op amp circuitry.
Variac voltage and current displayed on panel meters.