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Re: First coil- need help
Original poster: "colin.heath4 by way of Terry Fritz <twftesla-at-qwest-dot-net>" <colin.heath4-at-ntlworld-dot-com>
im also fromthe uk if you are looking for better performance than you
are getting at the moment i would redesign the whole coil i would make a
secondary with between 700-1200 turns with a primay of 18swg wire a small
mmc which will cost a few pounds and a better transformer perhaps small nst
if you want detail give me a shout off list and i will send specs of my
small coil which puts out 8" max
----- Original Message -----
From: Tesla list <tesla-at-pupman-dot-com>
Sent: Tuesday, May 07, 2002 7:37 PM
Subject: First coil- need help
> Original poster: "Jolyon Vater Cox by way of Terry Fritz
> First TC -need help.
> Last year I built my first tesla coil -a mini-coil- the performance of
> has not been totally satisfactory. I am writing from England as a newcomer
> 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
> The statistics are as follows:-
> The primary consists of a flat spiral 11.75 turns of 24 SWG Tinned
> (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
> not treated in any way). When the primary was tapped for max. spark length
> 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"
> 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
> divided into eight strings of 2 caps -each cap is a plastic film can
> with saline wallpaper paste gel on the inside and covered with foil on the
> The Tesla coil is powered by an auto ignition coil via transistor ignition
> driver (Velleman KD2543) driven by a 555 oscillator - spark length form
> 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
> 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
> either sparks or arcs. Performance is worse without the toroid but worsens
> the topload capacitance is further increased; form which I presume the
> size is near optimal.
> I have also noticed that the tone of the primary spark gap changes
> discharges from the toroid are drawn- is this normal or does it suggest a
> The Medhurst capacitance of the secondary was calculated at 3.7838601pF.
> Primary resonant frequency was calculated at 2.846.6706 Mhz which means
> the balance of the capacitance needed to match the secondary to the
> total of 8.437785 pF) would have to be provided by a toroid with
> pF. I have not yet calculated the capacitance of the toroid yet -I have
> 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
> 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