Re: final prep of coil

Subject:     Re: final prep of coil
      Date:  Sat, 07 Jun 1997 20:34:16 -0500
      From:  Chuck Curran <ccurran-at-execpc-dot-com>
        To:  Tesla List <tesla-at-pupman-dot-com>
References:  1

Tesla List wrote:
> Subject:  final prep of coil
>   Date:   Sat, 07 Jun 1997 12:57:40 -0400
>   From:   Michael Bauer <mbauer-at-execpc-dot-com>
>     To:  tesla-at-pupman-dot-com
> That last couple weeks I have made much progess on my latest coil.  I
> have
> done rough tuning but need to finish my grounding system and disconnect
> a
> few ham radio antennas.  My yard is really limited in size here in town,
> so
> only low power settings will be used until I transport it up to my
> "cabin up
> north".  Part of the fun in this project was building a good power
> control
> cabinet.  I loaded a full height 19" rack cabinet with a TEK scope,
> control
> relays and time delay relays, electronic sampling of voltage and current
> nodes, SCR DC motor control for the RSG, variac panel with cooling fan,
> etc.
> In the tuning tests I found out the I get resonance just at the end of
> my
> primary coil.  I may need to add another turn or two of tubing if I
> change
> 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
> " ID.
> Primary cap: (two) 0.2 uf/20 kvdc caps in series for 0.1 uf/40 kvdc (I
> may
> need to upgrade voltage rating here)
> RSG: 3600 RPM DC motor, 3/4 Hp, belt drive to spindle mounted 12" disk
> with
> 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
> glued
> and doweled to  disks.  About a third of the wire is supported by slats,
> the
> rest of the perimeter is air spaced.  17 turns per inch, or about 675
> turns.
> Final tune with toroid is 66 Khz.
> Toroid: 6" by 30" aluminum ducting covered in aluminum tape.  Center is
> tape
> covered plywood.  Ends of duct were first hot melt glued together before
> taping.
> Transformer:  10 Kva pole pig, 2 insulating electrodes on secondary.
> 14.4
> 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
> ladder demo's.
> 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
> with
> 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
> is
> 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.


You sure have made a lot of progress since your last update.  I'd really
like to see your coil before you haul it up north--any chance?  I am
interested in how the wooden secondary form is going to work out.  I
believe that others have used Stitka Spruce, (probably spelled that
wrong) for forms but I am not aware of exactly how they are sealed, if
at all.  Keep us posted.  You also mentioned your op amp metering
circuit--Um, I blew up two digital meters in about 2 minutes last year,
so just a forwarning, hope you excel at shielding that circuit. I would
suggest adding about two more primary turns for tuning activities, hope
your structure will allow for that.  Have fun!

Chuck Curran