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Nick: Your new coil

Hi Nick,

I just visited your site last night. I noticed you are using 0.6
mm wire to wind your new secondary coil, so I decided to
fool around with a calculator and I think you might be running
into some trouble with this setup.

Coil Specs:
--------------
                    Diameter: 325 mm
                    Height: 1400 mm
                    Wire: 0.6 mm
                    L: 366 mH
                    H/D ratio: 4.3:1

What I was suspicious of, was the resulting DC resistance. Let�s
have a look at this.

I will assume 0.6 mm is bare wire diameter, so with enamel this
would be around 0.635 mm in diameter. (0.6 mm ~~AWG 23). I
will also 1st assume that you wound only 1300 mm of the tube
(is 1400 mm the total length or the actual winding length?).

Length per turn: PI*d or ~1.021 meters per turn.
# of turns: 1300 mm/0.635 mm  ~2050 turns
Length of wire: 2050t*1.021mpt= 2093 meters of wire

AWG 23/0.635 mm wire roughly has 0.067925 ohms per meter, so
your coil has a DC resistance of ~142 ohms. This is quite high and
I could imagine your 10kV power source might have a hard time,
driving this (with 4J of input power) coil. Of course, you WILL get
sparks, but I think you will be loosing quite a bit of efficiency in
your secondary.

Now my question to you: Why did you go this route of using such
thin wire? For a ~13" secondary I would have used at least AWG
18, maybe even bigger. From my experience, there is no need for
an ultra high secondary inductance (My 8" has ~36 mH and 17 ohms
DC-R). In fact, a high impedance might even give you some further
headaches, when it comes to driving the toroid�s capacitance. I
would definitely stay well below ~60-70 ohms DC-R, when it comes
to the secondary coil construction.

I back calculated the inductance values with my HBTCP (homebrew
TC program) and the 366 mH seems high. With the 1300 mm
winding length used above, I get 301 mH and with the full 1400 mm
length (which would further increase DC-R) I get 325 mH. For my
coil the program was very accurate. I calculated 35.67 mH and
measured a true 36 mH (LCR meter) for my coil. Also, your
unloaded FRes is ~60 kHz. With a 6x40" toroid this will drop your
FRes (loaded) to around 36 kHz. This will require a VERY large
primary inductance (as your cap is kind of small for this sort of
FRes) in order to tune properly. This further means your primary
current won�t be very high and your setup will (probably) need a
pretty high coupling factor. I would suggest you reduce your BPS
(simply don�t use all 12 electrodes) and go for quite a bit bigger
primary capacitor.


No offenses meant. I just thought I would mention it. Of course, I
will be awaiting your (spark) results in suspense.

Coiler greets from Germany,
Reinhard