[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: First coil- need help

Original poster: "Malcolm Watts by way of Terry Fritz <twftesla-at-qwest-dot-net>" <m.j.watts-at-massey.ac.nz>

Hi Jolyon,
           You can build a far better secondary on the same tube by 
using 0.2mm or smaller magnet wire, closewound. That'll pull your 
operating frequency down and allow the use of somewhat more primary 
capacitance (with hopefully a bit more energy in the primary). I've 
obtained sparks over 3" long and 5-6" thin streamers using a similar 
setup. It was a great ozone producer BTW.


On 7 May 2002, at 12:37, Tesla list wrote:

> Original poster: "Jolyon Vater Cox by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <jolyon-at-vatercox.freeserve.co.uk>
> First TC -need help.
> Last year I built my first tesla coil -a mini-coil- the performance of which
> has not been totally satisfactory. I am writing from England as a newcomer to
> this activity and while I have gleaned quite a bit of information from
> sources I do not presume to have all the answers; it would however be
> interested to know as to what improvements could be made to the coil design.
> The statistics are as follows:-
> The primary consists of a flat spiral 11.75 turns of 24 SWG Tinned CopperWire
> (wire diameter 0.022") which is supported by four 15-way terminal blocks
> mounted at 90degrees around the centre of a 12" square plywood base (which is
> not treated in any way). When the primary was tapped for max. spark
length (at
> 7.75 turns) the Inductance was calculated to be 9.1936275uH.
> The secondary consists of 130 turns of PVC insulated hookup wire (1 amp?)
> on a plastic tube (industrial cotton bobbin) measuring 2.8946305"
diameter, the
> winding extending to 7.25" along the tube.
> Inductance of the secondary was calculated at 413.91928uH.
> The primary cap was measured at 350 pF; it is composed of sixteen capacitors
> divided into eight strings of 2 caps -each cap is a plastic film can filled
> with saline wallpaper paste gel on the inside and covered with foil on the
> outside. 
> The Tesla coil is powered by an auto ignition coil via transistor ignition
> driver (Velleman KD2543) driven by a 555 oscillator - spark length form the
> ignition coil alone is about 1 inch long. 
> Unfortunately the maximum spark length from the toroid to an ungrounded
> is little over 1" with about 0.25"of primary spark; it it appears to be EVEN
> LESS to a grounded object, although in subdued light I have observed
> thin filamentary discharges of up to 2" from the toroid to a sharp point
> -although it is doubtful as to whether these could be accurately described as
> either sparks or arcs. Performance is worse without the toroid but
worsens when
> the topload capacitance is further increased; form which I presume the toroid
> size is near optimal. 
> I have also noticed that the tone of the primary spark gap changes whenever
> discharges from the toroid are drawn- is this normal or does it suggest a
> problem?
> The Medhurst capacitance of the secondary was calculated at 3.7838601pF.
> Primary resonant frequency was calculated at 2.846.6706 Mhz which means that
> the balance of the capacitance needed to match the secondary to the
primary (a
> total of 8.437785 pF) would have to be provided by a toroid with
capacitance of
> 4.650918361
> pF. I have not yet calculated the capacitance of the toroid yet -I have seen
> formulae which claim to do this however I believe the distance above the
> plane also affects the capacitance and I am not sure how this is
calculated -am
> I incorrect on this latter point?
> Why is performance so poor and why is spark length increased to ungrounded
> objects as opposed to grounded objects. Is the problem likely to be found
> the primary cap or or primary wire diameter, or frequency-splitting, or what